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Qingqing Yang, Hao Wan, Ying Zhang, Songtao Zhang, Xiaohe Liu, [Renzhi Ma](https://orcid.org/0000-0001-7126-2006), Hairong Xue

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[Metal organic frameworks-derived hollow functional materials: Synthetic strategies and electrocatalytic applications](https://mdr.nims.go.jp/datasets/afe62614-c7df-41c0-a8c5-20851540306d)

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Review Article Metal  organic  frameworks-derived  hollow  functional  materials:Synthetic strategies and electrocatalytic applicationsQingqing Yang1,2,§, Hao Wan1,2,3,4,§, Ying Zhang1,2,3,4,§, Songtao Zhang5, Xiaohe Liu1,2,3,4, Renzhi Ma6, andHairong Xue1,2,3,4 ( )1 Zhongyuan Critical Metals Laboratory, Zhengzhou University, Zhengzhou 450001, China2 School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China3 Zhongyuan Critical Metals Laboratory, Zhengzhou 450001, China4 State Key Laboratory of Critical Metals Beneficiation, Metallurgy and Purification, Zhengzhou 450001, China5 Testing Center, Yangzhou University, Yangzhou 225009, China6 Research Center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan§ Qingqing Yang, Hao Wan, and Ying Zhang contributed equally to this work. Received: 13 October 2025 / Revised: 21 November 2025 / Accepted: 3 December 2025 / Published date: 8 January 2026ABSTRACTHollow  nanostructure  materials  derived  from  metal-organic  frameworks  (MOFs)  have  many  promising  applications  inelectrochemical  energy  storage  and  conversion,  benefiting  from  their  large  specific  surface  area  and  void  space,accelerating  electron  and  mass  transport.  Significant  efforts  have  been  devoted  to  designing  and  fabricating  hollowmaterials  with  manipulated  geometric  morphology,  optimized  electronic  structure,  and  diverse  composition.  This  reviewsummarizes the current research progress of MOF-derived hollow materials for electrocatalysis. Here, we commence withthe  synthesis  strategies  for  MOF-derived  hollow  functional  materials,  providing  a  comprehensive  overview  of  designapproaches for  hollow structures.  These encompass acid etching,  ion exchange,  templating methods,  and autocatalyticpyrolysis,  demonstrating  the  rich  possibilities  and  advantages  in  designing  and  synthesising  MOF-derived  hollowmaterials. Subsequently, we focus on representative advances in the application of MOF-derived hollow materials withinthe  field  of  small-molecule  conversion,  including  hydrogen  evolution  reactions,  oxygen  evolution  reactions,  and  oxygenreduction  reactions.  Finally,  synthesis  optimization  and  application  prospects  of  MOF-derived  hollow  materials  areprovided.KEYWORDSmetal-organic framework, hollow structure, nanomaterials, controllable synthesis, electrochemical applications  1    IntroductionThe  increasing  global  consumption  of  conventional  fossil  fuels,escalating  energy  demands,  and  worsening  environmental  issueshave  propelled  rapid  advancements  in  renewable  energytechnologies [1]. Central to this transition is the growing need foradvanced  energy  conversion/storage  devices,  including  fuel  cells[2–5], water electrolyzers [6–8], and rechargeable batteries [9–11].However,  the  performance  of  electrode  materials,  as  criticalcomponents  in  these  devices,  remains  suboptimal.  To  date,significant efforts have been devoted to designing and developingcost-effective,  durable  electrode  materials  with  enhancedfunctionality [12–15].Metal-organic  frameworks  (MOFs)  have  emerged  as  a  rapidlyexpanding  research  frontier  due  to  their  structural  designability,diverse  building  units,  and  tunable  architectures  [16, 17].Benefiting  from  uniform  pore  structures,  adjustable  porosity,atomic-level  uniformity,  and  vast  compositional  diversity,  MOFshave been extensively explored for energy conversion and storageapplications  since  their  discovery  [18–22].  Compared  to  pristineMOFs,  their  derivatives  inherit  porous  characteristics  whileexhibiting  superior  stability,  electrical  conductivity,  andelectrochemical  properties,  making  them  highly  attractive  forelectrocatalysis  [23–25].  Electrocatalytic  reactions  are  inherentlycomplex  processes  involving  multiple  steps  and  intermediates[26, 27].  The  activity  and  selectivity  of  these  reactions  arepredominantly  governed  by  the  adsorption/desorption  energeticsof  intermediates  on  catalyst  surfaces  [28–30],  with  charge  statemodulations  significantly  influencing  intermediate  bindingdynamics  [29, 31].  Consequently,  both  the  density  of  active  sitesand  their  intrinsic  activity  are  critical  determinants  ofelectrocatalytic  performance  [32–34].  Rational  engineering  ofgeometric  configurations  and  electronic  structures  offers  a ISSN 2791-0091 (print); 2790-8119 (online)https://doi.org/10.26599/NRE.2025.9120214  © The Author(s) 2026. Published by Tsinghua University Press. The articles published in this open access journal are distributed under the terms of theCreative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction inany medium, provided the original work is properly cited.Address correspondence to Hairong Xue, xuehairong@zzu.edu.cnhttps://doi.org/10.26599/NRE.2025.9120214http://creativecommons.org/licenses/by/4.0/promising  approach  to  achieve  electrocatalysts  with  exceptionalactivity and selectivity.The  physical  and  chemical  properties  of  materials  are  jointlydetermined  by  their  structural  and  compositional  characteristics.In the case of  MOFs,  their  synthesis  dictates their  unique porousarchitectures  and  tunable  chemical  compositions.  MOFs  exhibitdistinct  advantages  as  precursors  for  constructing  functionalmaterials.  Their  morphologies  are  well-preserved  during  thermaltransformation  processes,  wherein  controlled  growth  of  MOFprecursors  enables  the  fabrication  of  diverse  carbon-basedmaterials,  including  one-dimensional  (1D)  nanorods,  two-dimensional  (2D)  nanobelts,  and  three-dimensional  (3D)hierarchical  porous  architectures  [35, 36].  Furthermore,  theunique  benefits  of  MOF  precursors  are  fully  manifested  in  thesynthesis  of  hollow  structures.  These  hollow  architectures,characterized by high surface areas and open frameworks, provideabundant  active  edges  and  exposed  catalytic  sites,  therebyenhancing their electrochemical performance [37–41].In this review, we systematically summarize synthesis strategiesfor MOF-derived hollow structures, with a focus on acid etching,ion  exchange,  templating  approaches,  and  self-catalytic  pyrolysis(Fig. 1).  We  subsequently  discuss  their  applications  as  advancedelectrode materials  in key electrocatalytic processes,  including theoxygen  evolution  reaction  (OER),  hydrogen  evolution  reaction(HER), and oxygen reduction reaction (ORR). Finally, we presentcritical  perspectives  on  existing  challenges  and  future  directionsfor the rational design of MOF-derived hollow architectures. 2    Synthesis  methods  for  MOF-derived  hollowstructures 2.1    Synthesis  strategies  for  MOF-derived  hollowstructuresThe  properties  of  materials  are  determined  by  their  internalmicrostructure.  While  different  types  of  materials  inherentlypossess  distinct  properties,  even  the  same  material  can  exhibitvarying  properties  when  subjected  to  different  processingtechniques  that  result  in  distinct  microstructures.  The  distinctiveconfiguration  of  hollow  materials  confers  a  multitude  ofadvantageous  properties,  including  enhanced  surface-to-volumeratio,  diminished  density,  micro-reactor  environments,  higherloading  capacity,  and  diminished  mass  and  charge  transportlengths. Consequently, hollow materials have garnered significantattention  for  future  technological  applications.  The  fabrication  ofhollow structural materials remains a prominent research domain.Initial  methodologies  were  confined  to  controlled  synthesis  andregulation at  macro- and micro-scales  via methods such as spraydrying and purging [42]. In 1998, Caruso pioneered the synthesisof hollow silica and silica-polymer hybrid spheres using micelles astemplates  [43],  thereby  establishing  templating  as  a  universalparadigm for  hollow material  synthesis.  In  recent  years,  a  varietyof  synthetic  strategies  for  hollow  structural  materials  have  beeninvestigated, with concise overviews of the formation mechanismsof  each  approach  (Fig. 2).  These  processes  primarily  includetemplate-mediated  assembly,  stepwise  dissolution-re-growth  viaOswald ripening, and selective chemical etching. Notwithstandingsubstantial  accomplishments,  the  controlled  synthesis  ofporous/hollow  materials  with  meticulously  engineered  structures(particularly complex ones) and precise compositions continues topose significant challenges.MOFs represent a class of materials formed by the coordinationof  organic  ligands  with  metal  ions  or  metal  clusters  throughcoordination  bonds.  The  resulting  materials  show  manyadvantages, such as open lattice structure, high porosity, structuralflexibility, and tunability [44, 45]. However, MOFs also show someinherent limitations. Their chemical stability is relatively poor, andtheir  electrical  conductivity  is  limited.  These  constraints  restricttheir  application  in  electrocatalysis  as  well  as  energy  conversionand storage [46].  The inherent structural  characteristics of MOFsmake them ideal precursors or templates for obtaining derivativeswith  different  morphologies  or  compositions  by  compositionmodification or transformation control during thermal treatment[47]. Three main morphological control strategies for MOFs havebeen  identified:  (i)  Control  of  the  crystallization  process  orincorporation of templates to inherit the morphological features ofMOF  precursors;  (ii)  Introduction  of  reducing  gases  into  thesystem  during  thermal  decomposition  or  placement  ofcomponents that can generate reducing gases upstream, as well ascontrol  of  morphological  changes  by  gas  release  from  MOFsduring  thermal  decomposition  [48];  (iii)  Rigorous  treatments,such as  chemical  modification and thermal activation,  on carbonmaterials  obtained after  thermal  decomposition [49].  The uniqueadvantages  of  MOFs  as  precursors  are  fully  demonstrated  in  thesynthesis  of  hollow  materials.  Due  to  their  distinctive  porousstructures  and  tunable  chemical  compositions,  MOFs  enable  thecontrolled  preparation  of  hollow  nanostructures.  In  recent  years,efforts  have  been  dedicated  to  the  development  of  multipleinnovative synthesis methodologies for constructing hollow MOFswith  heterostructures  [50].  Notably,  both  solid-liquid  reactionsand thermal treatments are often employed in tandem. The solid-liquid reaction method is a widely used technique for constructinghollow structures, including etching, ion exchange, and template-assisted methods. 2.2    Acid etchingThe  acid  etching  technique  is  recognized  as  an  importantsynthetic  strategy  for  fabricating  hollow-structured  materials,capitalizing on the inherent differential chemical stability betweeninternal  and  exterior  domains  within  MOFs  crystals  [51].  The Figure 1    Illustration  of  the  synthesis  strategies,  and  applications  of  MOF-derived hollow structures.    2 Nano Research Energy  2026, 5: e9120214  structural  heterogeneity  of  MOFs  crystals  originates  fromanisotropic distributions of metal-ligand bond densities and defectpopulations  along  distinct  crystallographic  orientations  duringcrystal  growth [52].  This structural non-uniformity,  coupled withthe  labile  nature  of  metal-ligand coordination  bonds,  enables  theacid-induced structural  decomposition of  MOFs crystals  throughaccelerated hydrolysis of coordination bonds in acidic media [53].The  derivatives  of  MOFs  into  hollow  metal  organic  frameworks(HMOFs) with high surface areas and active sites show promisingpotential  for  enhancing  the  rates  of  ORR,  HER,  and  OER.Moreover,  non-precious  metal-based  catalysts  exhibit  excellentactivity and stability, making them ideal candidates for improvingcatalytic performances for ORR, HER, and OER [46].Phosphate-based  ligands,  such  as  phytic  acid  (C6H6(H2PO4)6),possess  strong  chelating  abilities,  which  can  act  as  both  aphosphorus  source  and  an  etching  agent.  Their  interaction  withMOFs  can  produce  hollow  transition  metal  phosphide.  Forexample, our group had reported a novel hollow leaf-like Co2P/N-doped  porous  carbon  (Co2P-NC)  composite,  synthesized  usingpolydopamine  (PDA)-coated  Co-doped  zeolitic  imidazolateframework  nanoleaf  (Co-ZIF-L)  as  precursors  and  phytic  acid(PA)  as  both  an  etching  agent  and  phosphorus  source(Figs. 3(a)‒3(c)) [54]. The hollow architecture was formed througha  one-step  pyrolysis  process  (Fig. 3(d)),  driven  by  etching  andcoordination reactions between PA and the leaf-like Co-ZIF-L. Inthe  as-prepared  transition  metal  phosphide  (TMPs)/carboncomposite,  Co2P  nanoparticles  are  encapsulated  and  uniformlydispersed within the 2D hollow leaf-like  N-doped porous carbonmatrix. Owing to its structural and compositional advantages, theCo2P-NC  catalyst  exhibits  remarkable  catalytic  activity  anddurability  for  both  the  HER  and  OER,  as  well  as  overall  watersplitting  (OWS)  in  alkaline  media.  The  authors  emphasize  that,compared  to  conventional  gas–solid  reaction  methods  for  TMPssynthesis,  this  strategy  offers  a  safer  and  more  straightforwardapproach,  demonstrating  significant  feasibility  for  designinghollow  TMPs/porous  carbon  composites.  Similarly,  Li  et  al.employed ZIF-67 as a precursor to fabricate hollow dodecahedralstructures  through  phytic  acid  treatment,  which  was  furtherpyrolyzed  to  obtain  hollow  HCoP/C  composite  (Fig. 3(e))  [55].The  dodecahedral  ZIF-67  (as  shown  in Fig. 3(f))  was  firstsynthesized,  followed  by  the  gradual  addition  of  a  mixed  phyticacid/ethanol  solution  (Vphytic  acid: Vethanol =  1:40)  into  an  ethanolsolution  containing  ZIF-67  and  polyvinylpyrrolidone  (PVP)(Fig. 3(g)).  This  process  effectively  preserved  the  morphology  ofmaterial while inducing hollow structure, as illustrated in Fig. 3(h).During  thermal  treatment,  the  cleavage  of  P-O  bonds  in  thephosphate groups of phytic acid released phosphorus ions, whichreacted with Co ions to form CoP. In the etching process, protonsreleased  by  phytic  acid  diffused  into  the  ZIF-67  core,  graduallyforming  a  core-shell  structure.  The  surface-functionalized  PVPeffectively  inhibited  the  penetration  of  phytic  acid  ions  into  theZIF-67 framework, thus preventing structural collapse of the ZIF-67  dodecahedrons.  In  addition,  Lou  et  al.  utilized  MIL-88A  as  aprecursor  through  phytic  acid  treatment,  demonstrating  highactivity and exceptional stability for water electrolysis across a fullpH  range  (Fig. 3(i))  [56].  The  Fe-based  MIL-88A  hexagonalnanorods  were  first  synthesized  and  the  effect  of  Ni  doping  ontheir  morphology was subsequently  investigated.  With increasing Figure 2    An overview of the synthetic approaches and their corresponding reaction mechanisms. Reproduced with permission from Ref. [48], © 2019 WILEY-VCHVerlag GmbH & Co. KGaA, Weinheim.    Nano Research Energy  2026, 5: e9120214 3  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nreNi doping  contents,  the  average  length  of  the  material  decreasedfrom 3.2 to 1.6 μm, while the average width increased from 400 to600 nm, as  shown in Figs.  3(j)–3(m).  Furthermore,  the influenceof  etching temperature  (30 °C,  60  °C,  90  °C,  and 120 °C)  on themorphology  was  explored.  As  the  temperature  increased,  thenanorods  gradually  transformed  into  well-dispersed  hollowparticles with core-shell/yolk-shell structures or aggregates of smallhollow  nanoparticles,  as  illustrated  in Figs.  3(n)–3(q).  Aftertreatment with 0.1 M PA at 90 °C, both MIL-88A and Ni-dopedMIL-88A samples underwent coordination and etching processes,where the solid inner layers were etched away to form hollow rod-like nanostructures. While the overall morphology was preserved,the  aspect  ratio  of  the  nanorods  changed,  as  depicted  inFigs. 3(r)–3(u).Tannic acid (TA) is also commonly used as etching agents, notonly  increasing  the  number  of  surface  activity  sites  but  alsoprotecting metal ions and enhancing the performance of catalysts[57].  Additionally,  TA  possesses  a  large  number  of  phenolichydroxyl  groups,  which  can  significantly  improve  the  stability  ofMOFs  [58].  As  exemplified  by  Lv  et  al.,  ZIF-67  nanocubeprecursor  was  subjected  to  etching  with  tannic  acid,  resulting  inthe  formation  of  ZIF-67  nanoboxes  structure,  as  shown  inFig. 4(a) [59]. More specifically,  ZIF-67 nanocubes were preparedby  using  tetradecyltriamethylbromochalkoform  (CTAB)  as  acapping  agent.  Due  to  etching  and  coordination  of  tannic  acid,ZIF-67 hollow nanoboxes were obtained, as illustrated in Figs. 4(c)and 4(d).  Subsequently,  ion  exchange  between  ZIF-67  hollownanoboxes  and  2,3,6,7,10,11-hexaiminotriphenylene  (HTP)ligands was employed to assemble Co-MOF nanoboxes, as shownin Figs.  4(e) and 4(f).  The  strong  chelating  ability  of  the  HTPligand  caused  the  aggregation  of  numerous  Co-MOFnanoparticles  into  well-organized  nanobox  structures,  facilitatingthe  exposure  of  active  sites  and  enhancing  liquid  mass  transfer,thus  significantly  improving  the  electrocatalytic  performance[60, 61].  Moreover,  density  functional  theory  (DFT)  calculationsrevealed  that  the  Co-N4 center  in  a  low-spin  state  with  atomdispersion acts as the catalytic active site [59]. Li et al. developed aunique  etching  functionalization  strategy  to  construct  single-flavonoid functionalized MOFs with a  distinctive  combination ofhollow walls and 3D ordered macroporous (H-3DOM) structures,as  illustrated  in Figs.  4(g)‒4(k) [62]  .  These  MOFs,  using  single-flavonoids  as  precursors,  were  further  used  to  synthesize  Co-loaded  carbon  materials  with  H-3DOM  structures  and  ahydrophilic  surface  by  high-temperature  pyrolysis.  Single-flavonoids,  characterized  by  their  rich  oxygen-containingfunctional  groups  and  appropriate  acidity,  serve  as  effectiveetching agents. They not only selectively etch the inner walls of themacro  pores  to  create  hollow  structures  but  also  introduceabundant  oxygen-containing  functional  groups  on  the  samplesurface,  thereby  forming  a  hydrophilic  surface  and  enhancingliquid  mass  transfer  efficiency.  Utilizing  tetradecylthiosulfate(TAA) to etch MOF precursors provides a direct route to hollowmetal sulfide materials.It  has  been  demonstrated  that  using  TAA  as  an  etchant  is  aneffective  method  for  creating  central  pores  and  depositing  metalsulfides [63–65].  Yang et  al.  utilized a cobalt-based metal-organicframework  (Co-MOF)  as  both  a  precursor  and  a  self-sacrificialtemplate,  successfully  synthesizing  highly  hierarchical  MoS2/CoS2nanotube  arrays  through  TAA-based  selective  etching  (Fig. 5(a))[66].  The  process  begins  with  the  growth  of  1D  Co-MOF Figure 3    (a) Schematic illustration of the preparation of Co2P-NC composite. (b)‒(d) Transmission electron microscopy (TEM) images of Co-ZIF-L@PDA, Co-ZIF-L@PDA-PA and Co2P-NC samples. (a‒d) Reproduced with permission from Ref. [54], © 2024 Published by Elsevier B.V. (e) Schematic illustration of the HCoP/Ccatalyst fabrication process. (f) Scanning electron microscopy (SEM) image of pristine ZIF-67 crystals, (g) SEM and (h) TEM images of acid-etched ZIF-67 derivatives.(e‒h) Reproduced with permission from Ref. [55], © 2024 Elsevier Ltd. (i) Synthetic schematic of Ni-doped FeP/C hollow nanorods. TEM images depict: (j) pristineMIL-88A  and  (r)  its  phosphoric  acid-treated  counterpart  (90  °C);  (k‒m)  Ni-doped  MIL-88A  nanorods  with  Ni/Fe  atomic  ratios  of  1:3,  2:2,  and  3:1,  respectively,alongside their phosphoric acid-treated derivatives (s-u, 90 °C); (n‒q) temperature-dependent morphological evolution (30 °C, 60 °C, 90 °C, 120 °C) of Ni-doped MIL-88A under phosphoric acid treatment. (i‒u) Reproduced with permission from Ref. [56], © 2019 Lu, X. F. et al.    4 Nano Research Energy  2026, 5: e9120214  nanotube arrays on carbon paper using 2-merimidium and cobaltnitrate  hexahydrate  (Co(NO3)2·6H2O).  Subsequently,  the  simplehydrothermal  reactions  were  employed  to  deposit  ultra-thin  2DMoS2 nanosheets  on  the  Co-MOF  surfaces  in  an  ammoniumtetramolybdate  ((NH4)2MoS4)  solution.  Co-MOF  can  provideabundant  surface  anchoring  sites  for  the  MoS2 nucleationoccurred  on  the  Co-MOF  surface.  Simultaneously,  Co3+ ionsderived  from  the  Co-MOF  can  serve  as in-situ catalysts,  whichlead  to  the  transformation  of  Co-MOF  into  CoS2 on  the  carbonpaper,  forming  MoS2/CoS2 solid  nanowires.  Finally,  selectiveetching  with  TAA  solutions  was  performed  on  the  MoS2/CoS2solid  nanowires,  resulting  in  nanotube  arrays  assembled  withMoS2 nanosheets with hollow structure, as depicted in Figs. 5(b)‒5(g). Generally, TAA hydrolyzes to produce hydrogen sulfide andacid, which act as dual etching agents. The produced acid not onlyinduces Co3+ ions to transform into Co2+ ions, forming CoS2 on thecarbon paper but also promotes the in suit deposition of CoS2 viareaction  with  hydrogen  sulfide.  The  hierarchical  MoS2/CoS2nanotube arrays exhibit good HER performance across the full pHrange.  DFT  calculations  reveal  that  the  strong  interfaceinteractions  at  the  heterogeneity  interface  play  a  pivotal  role  inenhancing HER performance by increasing the electronic states atS-S edges.  This  increase in electronic  states  lowers  the Gibbs freeenergy of H2 adsorption and reduces the activation energy barrierfor  water  splitting,  thereby  improving  the  overall  catalyticefficiency of the nanotube arrays. Similarly, Zhang et al. employedTAA  as  both  an  etching  agent  and  sulfur  source  to  synthesizeMOF-derived  hollow  Zn-Co-Ni  sulfide  (ZCNS)  nano-swordarrays, with the experimental workflow illustrated in Fig. 5(h) [67].Initially, 1D ZnCo MOF solid nano-sword arrays were grown onnickel  foam  (NF)  via  a  hydrothermal  reaction.  Subsequently,  asecondary  hydrothermal  treatment  using  TAA  as  the  dual-functional etchant/sulfur precursor yielded the ZCNS nano-swordarrays, as depicted in Figs. 5(i)‒5(n). Notably, TAA simultaneouslyetched  the  NF  substrate  to  generate  nickel  sulfide  phases.Throughout  the  sulfidation-etching  process,  progressive  S2–substitution  within  the  organic  framework  of  ZnCo  MOFfacilitated  the  formation  of  hollow  ZCNS  architectures.  Theresultant  hollow  ZCNS  nano-sword  arrays  exhibited  exceptionalelectrocatalytic  activity  and  stability  for  both  the  HER  and  OER.The coexistence of (i) Co9S8(111)@Ni3S2(101) heterointerfaces and(ii)  ZnS(111)  crystallographic  facets  within  the  ZCNS  matrixpromotedlocalized  charge  redistribution,  thereby  enhancinginterfacial  charge transfer kinetics.  DFT calculations revealed thatthe  heterostructure  synergistically  modulates  the  electronic  statesof  Co9S8 and  Ni3S2,  significantly  lowering  the  energy  barriers  forrate-determining steps in both HER and OER pathways.In  previous  reports,  triply  bonded  thiouracil  acid  (TTCA)  has Figure 4    (a) Schematic illustration of the formation process of Co-MOF NBs. (b) HAADF-STEM and corresponding elemental mapping images of Co-MOF NBs;(c) SEM and (d) TEM images of TA-Co NBs. (e) SEM and (f) TEM images of Co-MOF NBs. (a‒f) Reproduced with permission from Ref. [59], © 2024 Elsevier B.V.(g) Fabrication process of hierarchically porous 3D-ordered macroporous Co/N-doped carbon (H-3DOM-Co/ONC). (h) SEM and (i) TEM images of 3DOM-ZnCo-ZIF precursor. (j) SEM and (k) TEM images of H-3DOM-ZnCoZIF/ZnCo TA hybrid. (g‒k) Reproduced with permission from Ref. [62], © 2023 Wiley-VCH GmbH.    Nano Research Energy  2026, 5: e9120214 5  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nrebeen widely  used as  both a  sulfur  source  and a  carbon source  tosynthesize  cobalt-based catalysts  such as  Co9S8 [68].  However,  itsapplication  as  an  etchant  and  its  potential  for  forming  porousstructures  directly  through  interaction  with  MOFs  has  not  beenreported.  For  the  first  time,  Wang  et  al.  successfully  synthesizednitrogen  and  sulfur-doped  porous  CoP  carbon  nanocages  byemploying  TTCA  not  only  as  an  etchant  but  also  as  a  sulfursource  [69].  TTCA  exhibits  strong  chelating  abilities  with  metalions, enabling direct interaction with the MOF framework. Duringthe  etching  process,  Co  ions  bind  to  TTCA  and  form  Co-KYcomplexes on the ZIF-67 surface, resulting in a shell structure. Asthe etching proceeds inwardly, metal ions migrate outward while Sions migrate inward, leading to differences in their diffusion rates.This  causes  progressive  shell  breakdown  within  the  ZIF-67framework,  ultimately  forming  a  porous  shell  structure.  Byadjusting  the  etching  time  and  calcination  temperature,  optimalHER performance under alkaline conditions can be achieved. Themechanism reveals that sulfur doping and calcination significantlyenhance  HER  activity.  This  improvement  is  attributed  to  thesynergistic  effects  between the metal  elements  Co and non-metalelements  S,  which collectively  enhance  the  catalytic  performance,while also exhibiting excellent cyclic stability.Through etching strategies, not only heteroatoms such as P andS  can  be  introduced,  but  also  single  metal  atoms.  For  instance,Huang et al. employed a selenic acid etching-assisted approach toobtain  isolated  metal-semimetal  diatomic  catalysts  (DACs)  [70].First,  the  ZIF-8  precursor  was  etched  with  SeO2,  followed  bycalcination.  During  calcination,  evaporated  Se  species  werereduced  and  doped  into  the  nitrogen-doped  carbon  (NC)substrate,  forming  an  atomically  dispersed  Se  catalyst  (Se-NC)with a hierarchical hollow nanostructure. Subsequently,  Fe atomswere adsorbed and anchored onto the Se-NC framework, yieldinghighly  dispersed  Fe-Se  DAC  materials  via  thermal  activation.Mechanism studies indicate that the synergistic effect of Fe-N4 andSe-C2 atomic configurations endows Fe-Se DAC with outstandingCO2 reduction  reaction  (CO2RR)  activity.  Concurrently,  theelectronic  configuration  at  Fe-Se  hybrid  sites  promotes  CO2activation and optimises the binding strength of key intermediatesat active sites, thereby enhancing CO2 conversion rates.The acid etching strategy remains a prevalent methodology forsynthesizing  hollow-structured  materials.  Contemporaryimplementations  predominantly  employ  organic  acidscharacterized  by  high  molecular  weights  and  inherent  structuralconfigurations that confer strong chelating capacity toward metalions.  During etching processes,  these macromolecular acids formprotective  layers  on  MOF  surfaces  through  coordinate  bonding,effectively  mitigating  over-etching  phenomena.  Besides,  beyondtheir  primary etching function,  such organic  acids  concomitantlyintroduce  heteroatoms  (e.g.,  P,  S  and  Se)  into  the  materialmatrix,  thereby  streamlining  synthesis  protocols  throughmultifunctional  reagent  utilization.  However,  current  research onacid  etching  mechanisms  remains  insufficiently  explored,  withparticularly  limited  investigations  into  etching  conditionoptimization.  Systematic  studies  are  urgently  required  toestablish  a  comprehensive  theoretical  framework  governingetching  thermodynamics/kinetics  and  structure-propertycorrelations.  Moreover,  introducing  gas-releasing  substancesduring  pyrolysis  can  also  achieve  acid  etching  effects,  enabling Figure 5    (a)  Schematic  illustration  of  the  synthesis  route  for  2D/1D  MoS2/CoS2 heterostructured  catalysts  grown  on  carbon  paper.  (b,  e)  SEM  and  (c,  f)  low-magnification  TEM  images  of  MoS2/CoS2 NTs.  (d)  Enlarged  TEM  view  of  the  marked  region  in  (f),  revealing  vertically  aligned  MoS2 nanosheets  with  layeredmorphology. (g) High-resolution TEM (HRTEM) image confirming the coexistence of crystalline CoS2 phases. (a‒g) Reproduced with permission from Ref. [66], ©2019  The  Royal  Society  of  Chemistry.  (h)  Synthesis  pathway  for  MOF-derived  hollow  Zn-Co-Ni  sulfide  (ZCNS)  nanosword  arrays  (NSAs).  (i,  l)  SEM  images  atvarying magnifications, and (j, k) cross-sectional versus (m, n) top-view TEM images of individual ZCNS units. (h‒n) Reproduced with permission from Ref. [67], ©2021 Institute of Process Engineering, Chinese Academy of Sciences.    6 Nano Research Energy  2026, 5: e9120214  relatively  straightforward  synthesis  of  hollow  functionalmaterials.  For  instance,  Zhu  et  al.  employed  a  gas  diffusionstrategy  to  synthesise  bowl-shaped  porous  nano-Pb  single-atomcatalysts  (Pb  SAC)  featuring  a  highly  asymmetric  coordinationmicroenvironment [71]. 2.3    Ion exchange strategyThe  solid-state  MOFs  precursor  reacts  with  suitable  chemicalagents in solution to form a rigid shell at the solid-liquid interface,while  simultaneously  transforming  or  etching  the  core  to  createhollow  structures.  This  strategy  has  been  widely  employed  forconverting solid MOFs into hollow multifunctional materials. Theformation  of  hollow  architectures  can  be  achieved  via  anion-exchange  reactions  between  anionic  ligands  in  MOFs  precursorsand  solution-phase  reactants,  which  drive  the  chemicaltransformation  of  MOFs  into  structurally  engineered  hollowconfigurations.For  example,  Kim  et  al.  synthesized  NiFe-PBA  hollownanorods  (NiFe-PBA  HNRs)  using  a  Ni-based  MOF  as  bothprecursor  and  self-sacrificing  template  through  an  ion-exchangestrategy  (Fig. 6(a))  [72].  The  authors  first  synthesized  Ni-MOFnanorods via ultrasonic synthesis and used them as self-sacrificialtemplates to homogeneously mix them with K3[Fe(CN)6] solutionfor  ion  exchange  reaction.  The  Ni2+ cations  from  the  Ni-MOFinterior diffused outward to react with the [Fe(CN)6]3– anion, andin  the  process,  the  internal  Ni-MOF  was  completely  convertedinto PBA, resulting in hollow architecture, as depicted in Figs. 6(b)and 6(c).  Finally,  a  distinctive  hollow  carbon  materialincorporating  Ni-Fe  mixed  metal  phosphides  and  amorphouscarbon  was  successfully  synthesized  via  high-temperaturecalcination  and  phosphidation  under  an  argon  atmosphere,  asillustrated  in Figs.  6(d) and 6(e).  Notably,  the  shell  composed  ofnumerous  Ni2P  and  Fe2P  nanoparticles  displayed  porouscharacteristics,  exposing  more  active  sites  and  facilitatingelectrolyte  diffusion.  Metal  species  incorporated  through  ion-exchange processes not only generate monometallic nanoparticlesbut  also form alloy phases  with host  metal  species  within MOFs,demonstrating  a  versatile  synthetic  strategy  for  hybridnanocomposites.  Zhang  et  al.  reported  the  synthesis  of  CoRualloy/N-doped  carbon  hollow  nanomaterials  (CoRu@NCHNs)(Fig. 6(f))  [73].  Using  ZIF-67  as  precursor,  they  introduced  Ru3+cations through ion exchange while simultaneously incorporatingnitrogen  atoms  via  dopamine  (DA)  addition.  The  strongcoordination between DA and Co ions induced ZIF-67 structuraldecomposition,  releasing  alkaline  2-methylimidazole.  Underalkaline  conditions,  DA  underwent  self-polymerization  to  formPDA  shells  encapsulating  ZIF-67,  while  Ru3+ was  simultaneouslyincorporated  into  the  PDA  shell  through  strong  synergisticinteractions, resulting in CoRu/PDA HNS hollow nanostructures,as  shown  in Figs.  6(g)‒6(i) [74].  Subsequent  pyrolysis  producedCoRu@NCHNs with well-preserved morphology.  It's  noteworthythat  the  CoRu/PDA  HNS  exhibited  rough  surfaces  due  to  finePDA  particulates.  During  pyrolysis,  organic  ligands  underwentreductive decomposition at elevated temperatures, reducing metalions  to  metallic  species  and  nanoparticles,  thereby  enhancingmaterial conductivity.The  traditional  hollow  frameworks  show  well-defined  internalspaces  and  large  surface  areas,  which  have  been  extensivelystudied.  However,  these  frameworks  exhibit  high  transmissionresistance and limited accessibility of internal space owing to theirrigid structure.  Following this  approach,  Shi  et  al.  utilized the in-situ self-sacrificial template strategy of MOFs, synthesize Co/CoOheterojunction  (Co/CoO@HNC)  fixed  on  spinel-like  hollownitride-doped carbon (the synthesis  process  illustrated in Fig. 6(j)[75].  By  employing  MIL-88A  as  the  self-sacrificial  template(Figs. 6(k) and 6(o)), pyrole and (NH4)2S2O8 were introduced intothe  system.  The  positively  charged  pyrole  was  attracted  andadsorbed  onto  the  negatively  charged  MIL-88A  surface,  while(NH4)2S2O8 served  as  the  initiator  to  promote  poly-pyroleformation.  During  the  polymerization of  pyrole,  the  free  H+ ions Figure 6    (a) Schematic illustration of the synthesis of (Ni, Fe)2P/C hollow nanorods (HNRs). (b) SEM and (c) TEM images of NiFe-PBA HNRs; (d) SEM and (e)TEM  images  of  (Ni,  Fe)2P/C  HNRs.  (a‒e)  Reproduced  with  permission  from  Ref.  [72],  ©  2022  The  Royal  Society  of  Chemistry.  (f)  Schematic  illustration  of  thesynthesis of CoRu@NCHNSs. (g) and (h) TEM images of ZIF-67 and CoRu/PDA hollow nanospheres (HNSs), and (i) HR-TEM image of CoRu/PDA HNSs. (f‒i)Reproduced with permission from Ref. [73], © 2024 The Royal Society of Chemistry. (j) Schematic illustration of the synthesis process of Co/CoO@HNC. (k) SEM and(o) TEM images of MIL-88A; (l) SEM and (p) TEM images of HPPy nanocages; (m) SEM and (q) TEM images of Co-LDH@HPPy; (n) SEM and (r) TEM images ofCo/CoO@HNC. (j‒r) Reproduced with permission from Ref. [75], © 2022 Elsevier B.V.    Nano Research Energy  2026, 5: e9120214 7  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nrefacilitated  the  coordination  of  the  organic  ligand,  leading  to  thecleavage  of  Fe-O bonds  in  MIL-88A through ion exchange.  Thisprocess resulted in the complete dissolution of MIL-88A (Figs. 6(l)and 6(p)).  Subsequently,  under  simple  hydrothermal  conditions,Co2+ underwent  hydrolysis  to  generate  a  cobalt-based  layereddouble hydroxide (Co-LDH) on the hollow poly-pyrole nanocageframework,  as  illustrated  in Figs.  6(m) and 6(q).  Finally,  the  Co-LDH underwent thermal decomposition to yield Co/CoO@HNCin  an  N2 atmosphere  at  700  °C.  The  external  framework  ofCo/CoO@HNC is assembled from interconnected nitrogen-dopedcarbon  spheres  (Figs.  6(n) and 6(r)),  effectively  preserving  theorthogonal  spinel-like  hollow  structure  of  Co-LDH@HPPy,  asshown  in Fig. 6(q).  The  incorporation  of  Co/CoO@HNCsignificantly modifies the local electronic environment, enhancingthe  electron  transfer  capability  and  improving  the  catalyticperformances of oxygen reduction and oxidation reactions.In addition, Wang et al. developed binder-free NiCo2O4 hollownano-wall  arrays  through  a  sequential  ion-exchange/etchingstrategy  (Fig. 7(a))  [76].  The  synthesis  was  initiated  with  theepitaxial  growth  of  2D  cobalt-metal  organic  framework  (2D  Co-MOF)  nanosheet  arrays  on  conductive  carbon  cloth  via  acoordination-driven precipitation process (Figs.  7(b) and 7(c)).  Asubsequent  anion-exchange-etching  treatment  using  Ni(NO3)2solution  induced  structural  evolution  from  dense  MOF  walls  toporous NiCo2O4 hollow configurations, as depicted in Figs.  7(d)‒7(g). Mechanistic analysis reveals that the hydrolysis of Ni2+ cations(Ni2+ + H2O → Ni(OH)+ + H+) generates acidic microenvironmentsthat  simultaneously:  (1)  etch  the  organic  framework  throughproton-assisted ligand dissolution, and (2) drive the interfacial co-precipitation  of  Ni-Co  layered  double  hydroxide  (LDH)precursors.  This  dual-function  mechanism  preserves  the  nano-wall  morphology  while  creating  hierarchical  porosity  spanningmeso-/macropores.  The  interconnected  hollow  architecturefacilitates  rapid  electrolyte  diffusion  and  exposes  abundantelectroactive  sites,  synergistically  enhancing  OER  kinetics.Significantly, the monolithic electrode design eliminates polymericbinders,  minimizing  interfacial  charge  transfer  resistance.Complementing  this  work,  Luo  et  al.  proposed  a  controlled  ionexchange  method  to  construct  amorphous  Zn/Co-Fe  hollownano-walls  on  carbon  cloth  (Figs.  7(h) and 7(i))  [77].  Theirmethodology  involved  first  synthesizing  crystalline  bimetallicZn/Co-MOF  nanoarrays  through  controlled  coprecipitation, Figure 7    (a) Schematic illustration of the formation of hollow nickel-cobalt oxide nanostructures from 2D Co-MOF solid nanowalls. (b) SEM and (c) TEM images of2D Co-MOF nanowalls; (d) SEM and (e) TEM images of Ni–Co LDH hollow nanostructures; (f) SEM and (g) TEM images of NiCo2O4 hollow nanostructures. (a‒g)Reproduced  with  permission  from  Ref.  [76],  ©  2017  WILEY-VCH  Verlag  GmbH  &  Co.  KGaA,  Weinheim.  (h)  Synthesis  process  for  bimetallic-MOF-derivedamorphous  Zn/Co–Fe  HNAs  on  carbon  cloth.  (i)  Schematic  illustration  of  the  construction  of  bimetallic-MOF-derived  amorphous  Zn/Co–Fe  HNAs  by  an  ion-exchange and etching strategy. (j) and (k) SEM images of bimetallic Zn/Co MOF-derived amorphous Zn/Co–Fe HNAs at different magnifications; (l) and (m) TEMand HRTEM images  of  a  single  Zn/Co bimetallic  amorphous MOF-derived Zn/Co–Fe hollow nanowalls  and its  element  mapping of  Zn,  Co,  Fe,  O as  well  as  theselected area electron diffraction pattern in the inset. (h‒m) Reproduced with permission from Ref. [77], © 2021 Wiley-VCH GmbH.    8 Nano Research Energy  2026, 5: e9120214  followed  by  Fe2+-mediated  structural  reconstruction.  During  theion-exchange  phase,  Fe2+ hydrolysis  (Fe2+ +  2H2O  →  Fe(OH)2 +2H+)  induces  proton-driven  ligand  dissociation,  disrupting  theoriginal  Zn/Co-MOF  coordination  network.  The  released  Zn2+and  Co2+ ions  subsequently  react  with  ferric  hydroxide  to  formamorphous  Zn/Co-Fe  hollow  nano-wall  arrays,  as  depicted  inFigs. 7(j)‒7(m).The  ion-exchange  strategy  represents  another  prevalentapproach  for  synthesizing  hollow-structured  materials,fundamentally operating through solid-liquid interfacial reactions.The  ionic  substitution  pathways  are  governed  by  the  chemicalnature  of  reactant  species  in  the  liquid  phase,  thereby  enablingcontrolled  introduction  of  foreign  metal  ions-either  singular  ormultiple-into the framework. This mechanism serves as a versatileplatform  for  fabricating  bimetallic  or  multimetallic  MOFs  withtailored compositional complexity. 2.4    Template-assisted methodsThe  template-directed  approach  has  emerged  as  a  fundamentalstrategy  for  fabricating  porous  materials  through  controlledsacrificial  templating  mechanisms.  This  methodology  enablesprecise  construction  of  porous  architectures  via  a  sequentialfabrication  process:  initially  forming  core-shell  compositeprecursors  through  surface  templating,  followed  by  structuralconsolidation  and  subsequent  template  elimination  whilepreserving  morphological  integrity.  The  paramount  advantage  ofthis  technique  stems  from  the  inherent  replicability  of  templategeometries, allowing systematic regulation of pore dimensions andmaterial  morphology  through  judicious  template  selection  andoptimized  coating  parameters.  Current  template  classificationsystems  typically  differentiate  three  principal  categories  based  ontemplate  characteristics  and  interaction  mechanisms:  self-templating processes, hard-template replication, and soft-templateapproaches. 2.4.1    Self-template methodRecent  advancements  have  demonstrated  that  hollow  MOFnanostructures  can  be  engineered  through  dissolution-regrowthmechanisms, with Ostwald ripening and metastable core-directedsecondary  growth  processes  emerging  as  prominent  pathways[78]. These template-free strategies streamline synthetic workflowsby  eliminating  the  need  for  exogenous  templates,  therebyenhancing process efficiency and reducing manufacturing costs.Ostwald  ripening  has  been  established  as  an  efficient  self-templating  strategy  for  fabricating  hollow  architectures,  withwidespread  applications  in  nanomaterial  synthesis.  Thisthermodynamically  driven  process  involves  the  dissolution  ofsmaller  crystals/colloidal  particles  and subsequent redeposition ofdissolved  species  onto  larger  particles,  governed  by  the  Gibbs-Thomson  principle  [79].  Due  to  their  higher  surface  energy,smaller  crystallites  undergo  preferential  dissolution  andrecrystallization,  as  their  elevated  Gibbs  free  energy  significantlyenhances  solubility  compared  to  larger  counterparts.  Theformation of hollow structures via this mechanism arises from theinward-to-outward  diffusion  of  dissolved  species  from  smallerinternal  aggregates  to  larger  external  crystals.  A  representativedemonstration  by  Kim  et  al.  utilized  Ostwald  ripening  tosynthesize  Se-doped  CoS2 hollow  nanospheres  (Fig. 8(a))  [80].Template-free  ZIF-67  precursors  were  initially  prepared  throughcoordination-driven  crystallization  in  methanol  containingCoSO4·7H2O  and  2-methylimidazole,  as  depicted  in Fig. 8(b).Methanol's low dielectric constant (ε=32.7) reduces critical nucleusradius,  elevating  solution  supersaturation  to  enable  rapidhomogeneous  nucleation  of  spherical  particles.  The  strongcoordination  capability  of  SO42– anions  facilitated  extensivedecomposition  of  Co2+-2-methylimidazole  complexes  in  ZIF-67,triggering  an  inside-out  ripening  mechanism.  This  processfeatured  mass  transfer  from  small-grained  core  regions  to  large-grained  shell  domains  through  dissolution-recrystallization Figure 8    (a)  Synthetic  process  for  preparing Se-doped MOF CoS2 hollow spheres.  (b)  SEM images of  ZIF-67 hollow spheres;  (c)  and (d) SEM images at  differentmagnifications, (f) and (g) TEM images, and (h) HRTEM image of Se-doped MOF CoS2 hollow spheres at different magnifications; (e) and (i) EDX and HR-EDXmapping of Co, S, Se, C, N, and O of the Se doped MOF CoS2 hollow spheres. (a‒i) Reproduced with permission from Ref. [80], © 2023 Elsevier B.V.    Nano Research Energy  2026, 5: e9120214 9  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nrekinetics.  Subsequent  sulfuration/selenization  in  a  tubular  furnaceyielded  Se-doped  CoS2 hollow  spheres,  as  depicted  in Figs.  8(c),8(d), 8(f)‒8(h). The elemental mapping demonstrated that the Co,S,  Se,  C,  N,  and  O  constituents  are  distributed  uniformlythroughout  the  product,  as  illustrated  in Figs.  8(e) and 8(i).  Theproduct  exhibited  exceptional  bifunctional  OER/ORR  catalyticactivity  in  alkaline  media.  DFT  calculations  revealed  that  Se-doping  optimizes  the  Gibbs  free  energy  of  oxygen  intermediateadsorption  on  Co  active  sites,  thereby  enhancing  intrinsic  OERactivity. 2.4.2    Hard template methodCovalently  bonded  rigid  templates-including  polymericarchitectures  with  diverse  spatial  configurations,  anodizedaluminum oxide (AAO) membranes,  porous silicon frameworks,metallic templates, natural biopolymers, zeolites, colloidal crystals,and  carbon  nanotubes-exhibit  superior  structural  stability  andprecise  nanoconfinement  effects,  enabling  stringent  control  overnanoparticle  dimensions  and  morphologies.  Commonly  usedmaterials  include  polystyrene  (PS)  spheres  and  silica  (SiO2).  Thisstrategy  primarily  utilizes  the  coordination  interaction  betweensurface functional groups and metal nodes to coat a layer of MOFnuclei  on  the  template  surface.  For  example,  Xue  et  al.  preparedhollow  mesoporous  carbon  spheres  (HMCSs)  and  MOF-derivedcarbons (NC(M)/HMCSs and NC(M)@HMCSs) using SiO2@SiO2-PDA  core-shell  spheres  as  dual-functional  templates  [81],  thespecific  synthesis  process  is  shown  in Fig. 9(a).  The  interfacialcoating strategy involved epitaxial growth of ZIF(M) nanocrystalson  SiO2@SiO2-PDA  surfaces,  followed  by  carbonization  andtemplate etching to yield NC(M)/HMCSs composites. In contrast,the  spatial  encapsulation  approach  first  generated  HMCSs  viasequential  pyrolysis  and  etching,  then  confined  ZIF(M)  growthwithin  HMCSs  cavities  to  construct  ZIF(M)@HMCSsheterostructures.  By modulating metal precursors (Mn/Co/Ni/Cunitrates)  and  Zn-to-metal  molar  ratios,  a  library  of  HMCSs/ZIFshybrids  was  synthesized,  as  demonstrated  in Figs.  9(b)‒9(k).During  pyrolysis,  volatile  Zn  species  were  selectively  removed,while  trace  transition metals  remained anchored on HMCSs andNC(M)  matrices.  The  incorporation  of  a  secondary  MOFprecursor  as  a  co-precursor  within  the  MOF-coated  shelltemplated on a substrate enables the pyrolysis-driven formation ofultrafine  alloy  nanoparticles,  a  structural  outcome  unattainablethrough  thermal  decomposition  of  individual  MOF  precursorsalone.  For  instance,  Lou  et  al.  devised  a  dual-MOF-assistedpyrolysis protocol to fabricate Co-Fe alloy/N-doped carbon hollowspheres  using polystyrene (PS)  colloidal  templates  (Fig. 9(l))  [82].MIL-101  nanoparticles  (50  nm),  Co(NO3)2·6H2O,  and  2-methylimidazole  were  sequentially  introduced  into  PSsuspensions,  enabling  the  hierarchical  assembly  of  MIL-101/ZIF-67  nanoshells  on  PS  surfaces,  as  depicted  in Fig. 9(m).  Thermal Figure 9    (a) Schematic illustration of the synthesis processes for NC(M)/HMCSs and NC(M)@HMCSs. Hollow mesoporous carbon spheres (HMCSs) synthesizedvia interfacial coating method: (b‒f) TEM images of NC(Zn)/HMCSs, NC(Zn, Mn)/HMCSs, NC(Zn, Co)/HMCSs, NC(Zn, Ni)/HMCSs, and NC(Zn, Cu)/HMCSs,respectively. HMCSs synthesized via spatial encapsulation method: (g‒k) TEM images of ZIF(Zn)@HMCSs, ZIF(Zn, Mn)@HMCSs, ZIF(Zn, Co)@HMCSs, ZIF(Zn,Ni)@HMCSs,  and ZIF(Zn,  Cu)@HMCSs,  respectively.  (a‒k)  Reproduced with  permission from Ref.  [81].  © 2024 Tang,  Y.  J.  et  al.  (l)  Formation process  of  Co-Fealloy/N-doped carbon hollow spheres. (m) and (n) TEM images of PS@MIL-101/ZIF-67 core-shell composite and Co-Fe/NC hollow spheres, respectively. (o) and (p)HRTEM image and SAED pattern of Co-Fe/NC, respectively. (l‒p) Reproduced with permission from Ref. [82], © 2019 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim.  (q)  Schematic  illustration  of  the  synthesis  process  of  Fe-ZIF@PAA-SPB  using  templates  with  different  PAA-SPB  chain  lengths.  (r‒t)  HAADF-STEMimages of s-Fe-HNC, m-Fe-HNC, and l-Fe-HNC, respectively. (q‒t) Reproduced with permission from Ref. [83], © 2023 The Royal Society of Chemistry.    10 Nano Research Energy  2026, 5: e9120214  annealing  simultaneously  decomposed  PS  templates,  obtaininghollow spheres (as shown in Figs. 9(n)‒9(p)), and reduced MOF-encapsulated  Fe3+/Co2+ to  homogenized  Co-Fe  nanoalloys.  TheMIL-101  co-precursor  facilitated  confined  pyrolysis  within  theMOF  matrix,  suppressing  nanoparticle  coalescence.  By  tuningCo2+ concentrations  and  2-methylimidazole  ratios,  MIL-101loading  densities  in  MOF  shells  were  precisely  controlled.  Theoptimized  catalyst  demonstrated  exceptional  ORR  activity  anddurability,  attributed to  synergistic  effects  between metallic  activesites and N-doped conductive frameworks.Beyond  conventional  approaches  involving  direct  MOF  corecoating  on  template  surfaces,  materials  derived  from  secondarysurface-engineered  templates  through  re-growth  of  MOF  nucleidemonstrate  substantially  enhanced  performance  characteristics.Dai  et  al.  developed  an  electrostatic  confinement  strategy  usinganionically charged spherical polyacrylic acid brushes (PAA-SPBs)as  adaptive  templates  to  synthesize  ZIF-8-derived  SACs  withtunable  hollow  carbon  nanostructures  (Fig. 9(q))  [83].  Themethodology commenced with the synthesis of monodisperse PScores (~69 nm in diameter) via emulsion polymerization, followedby  UV-initiated  grafting  of  polyacrylic  acid  (PAA)  chains  withprecisely  controlled lengths onto PS surfaces.  The resulting high-density  anionic  brush  layer  exhibited  strong  electrostatic  bindingcapacities  for  cationic  metal  precursors  (Zn2+/Fe2+),  effectivelyrestricting  ion  migration  through  Donnan  equilibrium  effects.Sequential  infusion  of  Zn2+/Fe2+ and  2-methylimidazole  triggeredconfined  coordination  polymerization,  forming  Fe-doped  ZIF-8nanocrystals  (Fe-ZIF@PAA-SPB)  spatially  constrained within  thebrush  layer.  Crucially,  PAA  chain  length  dictated  finalarchitectures.  For  short-chain  PAA,  partial  protonation  of -COOH  groups  reduced  electrostatic  screening,  enabling  internalZIF nucleation within swollen brushes. This produced small ZIF-8crystallites and post-pyrolysis spherical hollow N-doped carbons (s-Fe-HNC),  as  demonstrated  in Fig. 9(r).  The  PAA  chains  inducechain  collapse  due  to  the  strong  adsorption  of  highly  negativelycharged carboxylate ions (-COO-) toward Zn2+ and Fe2+ ions. Thisphenomenon concomitantly drives the formation of large-grainedZIF-8 crystallites on the PAA-SPB template surface. Consequently,the  subsequent  pyrolysis  process  yields  disordered  hollowarchitectures  in  both  mesoporous  Fe-doped  hollow  N-dopedcarbon  (m-Fe-HNC)  and  its  layered  counterpart  (l-Fe-HNC),  asevidenced in Figs. 9(s) and 9(t). Controlled pyrolysis (900 °C, N2)simultaneously  carbonized  ZIF-8  and  decomposed  PAA-SPBtemplates,  retaining  Fe  as  isolated  single  atoms  without  metallicclustering.  This  chain-length-dependent  templating  mechanismenables  programmable  design  of  SAC  architectures,demonstrating structure-performance correlations in ORR. 2.4.3    Soft template methodSoft  templates,  predominantly  comprising  self-assembledsurfactant  aggregates,  constitute  a  class  of  amphiphilicarchitectures including lyotropic liquid crystalline phases, vesicularbilayers,  micellar  assemblies,  microemulsion  droplets,  Langmuir-Blodgett films, and biomimetic supramolecular frameworks. Thesesystems leverage competing hydrophobic-hydrophilic interactionsto  establish  spatially  organized  nanoreactors,  enabling  precisecontrol over nucleation and crystallization dynamics.Shahrokhian  et  al.  developed  an  emulsion-directed  interfacialassembly  technique  to  architect  ultrafine  Ru/RuO2 nanoclusters(<3  nm)  within  CuCo  nitride-embedded  N-doped  carbonmatrices  (Ru/RuO2/CuCoN@NC)  (Fig. 10(a))  [84].  Thehierarchical  synthesis  comprised  three  synergistic  stages:  (1)Aqueous  nanodroplets  containing  Cu2+/Co2+ and  steric  stabilizerPVP  were  homogenized  in  1-octanol  via  high-shearemulsification.  PVP's  amphiphilic  character  generated  steric-electronic  stabilization,  suppressing  droplet  coalescence.  (2)Controlled infusion of 1,3,5-benzenetricarboxylate (BTC) from theorganic  phase  induced  interfacial  supersaturation,  driving  rapidcoordination polymerization at the liquid-liquid boundary. BTC'strifunctional  carboxyl  groups  facilitated  pH-modulatedheterometallic  coordination,  yielding  epitaxial  CuCo-BTC  MOFshells  through  entropy-driven  supramolecular  assembly,  and  themorphology structure as illustrated in Figs.  10(b)‒10(e).  (3) Post-synthetic Ru3+ ion-exchange preceded gradient thermal processing:primary  carbonization  (700  °C,  N2,  2  h)  induced  metal  nitrideformation  (CuCoN),  followed  by  oxidative  activation  (300  °C,O2/N2=1:4)  to  engineer  Ru/RuO2 heterojunctions.  The  molecularsieving  effect  of  MOF  shell  imposed  ionic  diffusion  constraints,effectively inhibiting Oswald ripening and ensuring monodisperseshell architectures.The  template  method  is  a  commonly  employed  technique  forpreparing hollow structural functional materials, yet its significantdrawbacks  limit  widespread  application.  Hard-template  methodsdemand  stringent  conditions  for  template  removal,  such  asemploying  strong  acids  or  alkalis  for  silica  and  polystyrenetemplates.  Moreover,  hard-template  structures  exhibit  limited Figure 10    (a) Synthesis processes of Cu-Co/MOF-HS and Ru-RuO2/CuCoN@NC-HS. (b) and (c) SEM images and (d) and (e) TEM images of Cu-Co/MOF-HS atdifferent magnifications. (a‒e) Reproduced with permission from Ref. [84], © 2022 Elsevier Inc.    Nano Research Energy  2026, 5: e9120214 11  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nrediversity,  yielding  hollow  structures  with  minimal  morphologicalvariation.  Soft  templates,  whilst  offering  greater  morphologicalflexibility  and  simpler  removal,  suffer  from  poor  structuralstability  and  low  synthesis  efficiency.  Consequently,  there  is  apressing need to broaden the range of materials suitable for use astemplates. 2.5    Self-catalytic pyrolysis methodHollow  nanoporous  carbon  structures  (HNCs)  hold  significantapplication  potential,  yet  their  straightforward  and  efficientsynthesis  remains  a  challenge.  The  aforementioned  strategies  forsynthesizing  hollow-structured  materials  all  involve  multi-stepreaction processes characterized by inherent complexity, requiringmeticulous control over multiple interdependent variables.Recently,  Zhou  et  al.  addressed  this  by  modulating  crystalgrowth kinetics to synthesize MOF precursors with heterogeneouscrystallinity  and  diverse  morphologies,  which  were  directlyconverted into HNCs through a single-step pyrolysis process [85],and  the  synthesis  process  is  shown  in Fig. 11(a).  This  workrepresents the first  demonstration of facile  and versatile  synthesisof  functional  HNCs  from  single-component  MOF  crystals.  Theprotocol involved the following steps: Zn-MOF particles (denotedas STU-1) were synthesized by dissolving Zn(NO3)2 and 1,2-bis(5-imidazol-4-yl)methylene  hydrazine  in  N,  N-dimethylformamide(DMF).  By  tuning  crystal  growth  parameters-includingligand/metal  ion  ratios,  solvent  composition,  and  temperature-STU-1  particles  with  varying  morphologies  were  obtained,  asillustrated in Figs. 11(b), 11(f), 11(h) and 11(j). A visual diagnosticmethod  was  developed  to  evaluate  intracrystalline  uniformity.Treatment  with  6  M  acetic  acid  selectively  etched  the  core  ofcrystallographically  heterogeneous  MOFs  while  leaving  the  outershell  intact  (as  evidenced  in Fig. 11(c),  whereas  homogeneouscrystals  remained  unaffected.  For  example,  STU-1a  (synthesizedvia  solvothermal  methods)  yielded  solid  carbon  spheres  afterpyrolysis.  Acid  etching  confirmed  its  crystallographichomogeneity,  as  no  core  dissolution  occurred.  STU-1  particleswith  engineered  crystallinity  gradients,  produced  by  adjustinggrowth  kinetics  in  solution-phase  reactions,  underwentspontaneous  cavity  formation  during  pyrolysis.  This  processgenerated  diverse  HNC  architectures,  including  yolk-shellpolyhedrons,  mesoporous frameworks,  hollow microspheres,  andhierarchical  superstructures,  as  depicted  in Figs.  11(d), 11(e),11(g), 11(i) and 11(k).  Mechanistic  studies  revealed  that  the  self-driven  hollowing  arises  from  differential  thermal  contractionbetween  the  heterogeneous  core  and  shell  components  of  theMOF  precursors  during  carbonization.  This  work  establishes  ageneralizable  strategy  for  tailoring  HNC  morphologies  byleveraging crystallinity gradients in MOF templates. 3    Application of MOF-derived hollow materialsfor electrocatalysisWater  splitting  and  energy  conversion  technologies,  including Figure 11    (a) Schematic illustration of the facile synthesis of HNCs (hollow nanocarbons) via crystalline uneven MOFs. (b, f, h, j) TEM images of as-synthesized STU-1b, STU-1c, STU-1d, and STU-1e solid microparticles. (d, g, i, k) TEM images of STU-1b, STU-1c, STU-1d, and STU-1e microparticles after pyrolysis. (c) TEM imageof STU-1b microparticles after selective etching of a small amount of crystalline nucleus by dilute CH3COOH aqueous solution (6 mM). (e) SEM image of the focusedion beam (FIB)-section after the pyrolysis of STU-1b at 900 °C. Scale bars: 1 μm. (a‒k) Reproduced with permission from Ref. [85], © 2024 Wiley-VCH GmbH.    12 Nano Research Energy  2026, 5: e9120214  metal-air  batteries  and fuel  cells,  are  crucial  for  addressing futureresource  and  environmental  challenges.  The  HER  and  OER  aretwo  critical  half-reactions  involved  in  the  water-splitting  process.Additionally,  the  OER  and  the  ORR  are  of  great  importance  inmetal-air batteries. The four-electron ORR is also one of the mostfundamental  electrochemical  reactions  in  fuel  cells.  Thenanostructures  of  electrocatalytic  materials  can  significantly  altertheir physical and chemical properties, making the rational designof  the  structures  and  compositions  of  MOF-derived  materialsbeneficial to enhance their electrocatalytic performance [86, 87]. Inrecent  years,  significant  efforts  have  been  devoted  to  developingMOF-derived  materials  with  superior  HER,  OER,  ORR,  andsimultaneous  bifunctional  and  trifunctional  electrocatalyticactivities.  Hollow  nanomaterials  have  gained  increased  attentiondue  to  their  benefits  in  offering  abundant  active  sites,  a  highelectrode-electrolyte contact area, and enhanced charge transfer. 3.1    Hydrogen evolution reactionThe rapid depletion of fossil fuels is poised to trigger energy crisesand  exacerbate  environmental  problems.  Hydrogen,  as  a  cleanenergy  source,  is  expected  to  replace  traditional  fossil  fuels  [88].Hydrogen  production  driven  from  electrolyzed  water  is  anefficient,  environmentally  friendly,  and highly  promising  methodto  produce  hydrogen.  Pt  and  Pt-based  catalysts  are  recentlyregarded  as  the  most  efficient  HER  catalysts  due  to  theirexceptional intrinsic activity and rapid reaction kinetics. However,their  scarcity  hinders  large-scale  commercial  availability,prompting the development of non-precious metal materials withoutstanding  activity  and  stability  [60, 89, 90].  Among  the  widelyreported  non-precious  metal-based  hollow  electrocatalyticmaterials  are  metal  oxides,  alloys,  transition  metals,  and  theirderivatives,  such  as  metal  nitrides,  metal  phosphides,  and  metalsulfides. 3.1.1    MOF-derived non-precious metal hollow electrocatalystsConductive metal-organic frameworks are effective electrocatalysts.Lou  et  al.  successfully  prepared  Cu-MOF  hollow  structuressupported on Fe(OH)x nanoboxes, specifically Fe(OH)x@Cu-MOFNBs,  through  solvothermal  reaction  and  selective  redox  etchingusing Cu2O nanocubes as precursors (Figs. 12(a) and 12(b)) [91].Characterization and theoretical analysis revealed that this uniquestructure  features  highly  exposed  ligand-unsaturated  Cu1-O2centers  (Fig. 12(e)),  which  notably  accelerate  the  efficientformation of the intermediate *H and enhance HER kinetics. Thehighly  exposed  active  centers,  enhanced  charge  transfer,  androbust  hollow  nanostructures  endow  Fe(OH)x@Cu-MOF  NBswith  excellent  HER  electrocatalysts.  The  prepared  samplesdemonstrated an overpotential of 112 mV at a current density of10  mA·cm–2 and  a  Tafel  slope  of  76  mV·dec–1,  as  illustrated  inFigs.  12(c) and 12(d).  As  previously  demonstrated,  Zhang  et  al.reported  a  one-step  synthesis  of  CoRu@N-doped  hollownanostructured  carbon  (CoRu@NCHNS)  materials  using  ZIF-67as a precursor (Figs. 12(f) and 12(g)) [73]. This was accomplishedthrough  a  simple  liquid  phase  diffusion  method  and  ionexchange strategy. The synergistic effect of CoRu alloy, the uniquehollow  structure,  and  N-doped  contribute  to  the  materialexhibiting outstanding HER performance with an overpotential of13  mV  at  a  current  density  of  10  mA·cm–2 and  a  Tafel  slope  of69.4 mV·dec–1, as demonstrated in Figs. 12(h) and 12(i). 3.1.2    MOFs-derived  transition  metal-derived  hollowelectrocatalystsAmong  transition  metal  elements,  cobalt-based  electrocatalysts,including their  nitrides,  phosphides,  oxides,  sulfides,  and metalliccobalt, demonstrate exceptional HER properties, highlighting theirpromising  potential  for  development.  MOFs,  especially  cobalt-based zeolitic imidazolium frameworks (ZIF-67), serve as excellentprecursors  or  templates  for  the  preparation  of  non-noble  metalelectrocatalysts.  Jeon  et  al.  successfully  prepared  N-doped  hollownanocages  composed  of  metallic  cobalt/cobalt  sulfideheterostructures  (Co/CoxSy@NC-750)  through  a  one-steppyrolysis  method,  assisted  by  H2 reduction  and  sulfur  powdersulfurization  (Figs.  13(a) and 13(b))  [92].  The  precise  control  ofthe pyrolysis temperature and its composition play a crucial role inmaterials  engineering.  The  resulting  materials  exhibitedremarkable  HER  activity  with  overpotentials  and  Tafel  slopes  of130  mV  (current  density  of  10  mA·cm–2)  and  82  mV·dec–1 in  anacidic  (0.5  M  H2SO4)  medium  and  330  mV  (current  density  of10  mA·cm–2)  and  160  mV·dec–1 in  basic  (1.0  M  KOH)  medium,respectively,  as  shown  in Figs.  13(c) and 13(d).  In  addition,  theunique  structure  of  the  cobalt  metal  core/cobalt  sulfide  shell  isconducive  to  maintaining  long-term  durability  for  over  30  h  in Figure 12    (a)  and  (b)  TEM  images  of  Fe(OH)x@Cu-MOF  hollow  nanoboxes  at  different  magnifications.  (c)  LSV  curves  and  (d)  corresponding  Tafel  slopes  ofFe(OH)x@Cu-MOF and other control materials. (e) Calculated free energy changes for *H adsorption on Cu sites of Cu1-O4 and Cu1-O2 centers. (a‒e) Reproducedwith permission from Ref. [91], © 2021 Cheng, W. R. et al. (f) and (g) TEM image of CoRu/PDA HNSs and HRTEM image of CoRu@NCHNSs; (h) LSV curves and(i) corresponding Tafel slopes of CoRu@NCHNSs. (f‒i) Reproduced with permission from Ref. [73], © 2024 The Royal Society of Chemistry.    Nano Research Energy  2026, 5: e9120214 13  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nreacid  conditions  and  40  h  in  alkaline  conditions.  Yang  et  al.reported  the  preparation  of  a  novel  braided  hollow  nanowallarrays with three-dimensional (3D) self-branched ultrasmall cobaltphosphide  (CoP)  nanoparticles  embedded  in  N,  P  co-dopedcarbon  nanotubes  (CoP@NPCNTs)  via  a  simple  two-steppyrolysis synthesis strategy (Figs. 13(f)‒13(i)) [93]. The Kirkendalleffect  induced the formation of  irregular  hollow nanowall  arrays.The braided hollow nanowall  arrays of N, P co-doped CNTs notonly provide conductive support but also exhibit protective effectsfor the embedded CoP NPs. Meanwhile, the embedded CoP NPsprovide  abundant  exposure  active  sites  and  short  ion/electrondiffusion  pathways,  enhancing  the  overall  catalytic  performance.The  introduction  of  heteroatoms  (N,  P)  can  modulate  theelectronic  structure  of  the  catalyst  surface,  create  more  activedefects  and  boost  the  catalytic  activity.  The  material  exhibitedexcellent  HER  performance  in  acidic  and  basic  electrolytes.  Inacidic  conditions  (0.5  M H2SO4),  it  exhibited  an  overpotential  of53.1 mV at  a  current density of  10 mA·cm–2 and a Tafel  slope of40.8  mV·dec–1,  as  illustrated  in Figs.  13(j) and 13(k).  In  basicconditions  (1.0  M KOH),  the  overpotential  was  101.9  mV at  thesame  current  density  and  a  Tafel  slope  of  65.4  mV·dec–1,  asdepicted  in Figs.  13(l) and 13(m).  Moreover,  theoreticalcalculations  revealed  that  electron  transfer  occurred  between  theCNTs  and  the  CoP  NPs.  Moreover,  the  CoP  NPs  not  onlyenhanced  the  electronic  states  near  the  Fermi  energy  level  of  theCo  d-orbitals  but  also  increased  the  hydrogen  bonding  strength,resulting  in  improved  electrocatalytic  performance. Table  1summarizes  the  applications  of  MOF-derived  hollow  functionalmaterials  synthesized  in  recent  years  in  the  electrocatalytichydrogen  evolution  reaction,  demonstrating  their  potentialapplications in water splitting. 3.2    Oxygen evolution reactionAs one of the half-reactions in water splitting, the OER involves acomplex  4e– transfer  process,  and  its  slow kinetics  greatly  hinderthe  efficiency  of  hydrogen  production  via  water  splitting.Therefore, developing effective OER electrocatalysts to reduce theenergy  barrier  of  the  OER  reaction  is  crucial  to  improving  theefficiency  of  overall  water  splitting.  Currently,  RuO2 is  thebenchmark for OER electrocatalysts, but its high price and scarcitylimit its large-scale application. Therefore, there is an urgent needto  explore  non-noble  metal-based  electrocatalysts  with  highactivity,  stability,  and  selectivity.  MOF-derived  catalysts  withunique hollow structures involve more exposure to surface-activeregions  and  high  mechanical  stability.  Meanwhile,  the  structureand  component  tunability  of  MOFs  enables  them  to  exhibitsynergistic  physical  or  chemical  properties,  which  has  attractedconsiderable attention. Currently, more studied non-noble metal-based hollow electrocatalytic materials are metals/metal oxides andother metallizations (sulfides, nitrides, phosphides, etc.). 3.2.1    Metals/metal oxidesQian  et  al.  reported  the  synthesis  of  hollow  structures  fromprecursors  via  a  simple  ion  exchange  strategy  (Figs.  14(a) and14(b))  [94].  Then,  the  synthesis  of  hollow  binary  zeoliteimidazolium  salt  frameworks  and  Prussian  blue  analog  (PBA)heterostructures (ZIF-67@PBA) through a MOF-on-MOF hybridapproach uses ligand induction. After carbonization at 850 °C, theresulting material,  CoxFe-ZP, not only provided more active sitesto  improve  the  electrocatalytic  OER  performance  but  alsoencapsulated CoxFe nanoparticles in carbon nanotubes to improvethe  material  stability.  The  catalyst  exhibited  excellent  OERperformance with an overpotential of 302 mV at a current density Figure 13    (a, b) TEM images of Co/CoxSy@NC. (c, d) LSV curves of Co/CoxSy@NC materials prepared at different temperatures in 0.5 M H2SO4 and 1.0 M KOHsolutions.  (e)  Performance  diagram  comparing  HER  catalysts  based  on  overpotential,  Tafel  plots,  acid/alkali  stability,  and  capacitance.  (a‒e)  Reproduced  withpermission from Ref. [92], © 2024 The Royal Society of Chemistry. (f, g) SEM images, (h) TEM image, and (i) HRTEM image of CoP@NPCNTs. (j, k) LSV curves andcorresponding Tafel slopes of CoP@NPCNTs in 0.5 M H2SO4, and (l, m) in 1.0 M KOH solutions. (f‒m) Reproduced with permission from Ref. [93], © 2024 Wiley-VCH GmbH.    14 Nano Research Energy  2026, 5: e9120214   Table 1    Summary of the performance of MOF-derived hollow materials for HERMOF-derived hollowstructures MOF Precursors Performance Reference electrode Ref.Ni-doped FeP/C hollownanorods MIF-88A nanorodsη10 mA·cm−2η10 mA·cm−2η10 mA·cm−20.5 M H2SO4:  = 72 mV; Tafel slope = 54 mV·decade–1;1.0 M PBS (phosphate buffered saline): = 117 mV; Tafel slope = 70 mV·decade–1;1.0 M KOH:  = 95 mV; Tafel slope = 72 mV·decade–1;Ag/AgCl (KCl-saturated) [56]Hierarchical MoS2/CoS2nanotube arraysCo-MOF nanorodarraysη10 mA·cm−2η10 mA·cm−2η10 mA·cm−20.5 M H2SO4:  = 90 mV; Tafel slope = 30 mV·decade–1;1.0 M PBS:  = 150 mV; Tafel slope = 66.1 mV·decade–1;1.0 M KOH:  = 84 mV; Tafel slope = 34 mV·decade–1;0.5 M H2SO4: saturatedcalomel electrode (SCE)1.0 M PBS and 1.0 MKOH: Hg/HgO(1M KOH)[66]Hollow ZnS@Co9S8@Ni3S2nanosword arraysZnCo MOFsnanosword arraysη10 mA·cm−21.0 M KOH:  = 97 mV;Tafel slope = 42.24 mV·decade–1;Ag/AgCl (KCl-saturated) [67]N-doped carbon hollownanostructure loaded with theCoRu alloyZIF-67 dodecahedron ηmA·cm−21.0 M KOH:  = 13 mV;Tafel slope = 69.4 mV·decade–1; Hg/HgO [73]MOF-derived ultra-smallRu/RuO2 nanoparticles dopedin copper/cobalt nitride(CuCoN) encapsulated innitrogen-doped nanoporouscarbon frameworkBimetallic Cu-Co/MOFhollow nanospheresη10 mA·cm−21.0 M KOH:  = 41 mV;Tafel slope = 45 mV·decade–1; Ag/AgCl (3 M KCl) [84]Hollow Fe(OH)x@Cu-MOFnanoboxes Cu2O nanocube η10 mA·cm−21.0 M KOH:  = 112 mV;Tafel slope = 76 mV·decade–1 Hg/HgO [91]Co/CoxSy nanoparticleswithin N-doped graphiticcarbonZIF-67 dodecahedron η10 mA·cm−2η10 mA·cm−20.5 M H2SO4:  = 130 mV; Tafel slope = 82 mV·decade–11.0 M KOH:  = 330 mV; Tafel slope = 160 mV·decade–10.5 M H2SO4: SCE1.0 M KOH: Hg/HgO [92]N, P-codoped carbonnanotubes knitted hollownanowall arraysCo-MOF carbontextilesηmA·cm−2η10 mA·cm−20.5 M H2SO4:  = 53.1 mV; Tafel slope = 40.8 mV·decade–11.0 M KOH:  = 101.9 mV; Tafel slope = 65.4 mV·decade–1 SCE [93] Figure 14    (a, b) HR-TEM images of CoxFe-ZP. (c) LSV curve, (d) comparison of η10 values (representing the average of three repeated tests for the same sample), and(e) Tafel slope of CoxFe-ZP in 1.0 M KOH solution. (a‒e) Reproduced with permission from Ref. [94], © 2024 Elsevier Inc. (f) TEM image and (g) HR-TEM image ofS-NiCo2O4 hollow cubic nanosheets. (h) iR-compensated LSV curve and (i) Tafel slope of the sample in 1.0 M KOH solution. (f‒i) Reproduced with permission fromRef. [95], © 2023 Elsevier Inc. (j) and (k) TEM and HR-TEM images of CoVOx/Ag. (l) LSV curve and (m) Tafel slope of CoVOx/Ag in 1.0 M KOH solution. (j‒m)Reproduced with permission from Ref. [96], © 2024 Elsevier Inc.    Nano Research Energy  2026, 5: e9120214 15  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nreof 10 mA·cm–2 and a Tafel slope of 60.0 mV·dec–1 in 1.0 M KOH,as  illustrated  in Figs.  14(c)‒14(e).  The  authors  attributed  theexcellent  OER  performance  as  a  result  of  the  combination  ofmorphology  and  composition  through  activation  energy  studies.Zhang et al. successfully synthesized sulfur-doped NiCo2O4 hollowcubic  nanocages  through  a  sophisticated  ion-exchangemethodology  (Figs.  14(f) and 14(g))  [95].  The  synthetic  protocolcommenced  with  the  controlled  growth  of  c-NiCo  ZIF-67nanocubes, where CTAB served as a facet-selective capping agentto  regulate  anisotropic  crystal  development.  Subsequentintroduction of sodium sulfide (Na2S) initiated ligand-directed ionexchange,  simultaneously  inducing  the  liberation  ofundercoordinated  Ni2+ and  Co3+ cations.  These  metallic  speciessubsequently underwent anion-mediated co-precipitation, yieldingsulfur-doped  NiCo-layered  double  hydroxide  (S-NiCo-LDH)nanosheets  preferentially  aligned  along  the  nanocube  edges.Remarkably,  this  structural  evolution  occurred  withoutcompromising  the  parent  ZIF-67’s  cubic  framework.  Theobserved  bulk  MOF/surface  hydroxide  coexistence  stems  fromcomparable  ionic  mobility  between  the  constituent  species:  Theminimal radius differential between Ni2+/Co3+ and hydroxyl anionsestablishes  a  quasi-equilibrium  in  interdiffusion  kinetics.Subsequent  thermal  treatment  under  aerobic  conditions  inducedoxidative  decomposition  of  organic  linkers  (liberated  as  CO2),ultimately  generating  the  distinctive  hollow  architecture.  Thisstudy  demonstrates  that  strategic  sulfur  doping  coupled  withoptimized  calcination  parameters  enables  precise  engineering  ofhollow  nanostructures  with  preserved  morphological  fidelity  andenhanced  structural  uniformity.  Controlled  S2– coordinationcoupled  with  air  annealing  facilitates  the  formation  of  uniformhollow architectures,  while  simultaneous  sulfur  doping  optimizessurface  charge  distribution,  significantly  enhancing  oxygenevolution  reaction  (OER)  activity.  Under  alkaline  conditions(1.0 M KOH), the material exhibits an overpotential of 262 mV at10 mA·cm–2 current density with a Tafel slope of 83.36 mV·dec–1,as demonstrated in Figs. 14(h) and 14(i).Li  et  al.  synthesized  CoVOx/Ag  with  hollow  nano-prismaticstructure  via  a  simple  solvothermal  and  liquid  phase  stirringmethod  using  an  ion-exchange  strategy  (Figs.  14(j) and 14(k))[96].  The  interaction  of  CoVOx and  Ag  nanoparticles  optimizedthe electronic structure of the material, while the hollow structureprovided more active sites, resulting in a significant enhancementof the OER performance. The overpotential is 247 mV at a currentdensity of 10 mA·cm–2 and a Tafel slope of 61.15 mV·dec–1 underalkaline conditions (1.0 M KOH), as evidenced in Figs.  14(l) and14(m).  In  addition,  the  material  exhibited  better  stability,highlighting its potential to be used in hydrolysis. 3.2.2    Other metallized materialsBaeck et al. used an ion-exchange strategy and a two-step pyrolysismethod  to  synthesize  Fe  and  F  double-doped  hollow  CoS2nanospheres  (Fe-CoS2-F)  (Figs.  15(a) and 15(b))  [97].  Thehomogeneous  hollow porous  structure  of  Fe-CoS2-F  significantlyincreased  the  specific  surface  area  and  the  number  of  exposedactive  sites.  Moreover,  the  synergistic  effect  of  Fe  and  F  doubledoping  optimized  the  electronic  structure  of  the  material,facilitating  the  adsorption/desorption  of  oxygen-containingreaction intermediates on the active sites during the OER processunder  alkaline  conditions  (1.0  M  KOH).  Theoretical  calculationsfurther demonstrated that  the change of  Gibbs free energy at  therate-determining step of the OER process (ΔGRDS) was superior tothat  of  the  undoped  material.  Fe-CoS2-F  exhibits  excellent  OERactivity, achieving an overpotential of 298 mV at a current densityof 10 mA·cm–2 and a Tafel slope of 46.0 mV·dec–1, as evidenced inFigs.  15(c) and 15(d).  In  a  separate  study,  Lou  et  al.  preparedtrimetallic  MOFs  supported  on  S/N-doped  macroporous  carbonfibers  by  a  cation  exchange  strategy  (S/N-CMF@FexCoyNi1–x–y-MOF)  (Figs.  15(e) and 15(f))  [98].  Taking  advantage  of  theinherent catalytic activity of the trimetallic and the increased activesites  exposed  on  the  hollow  S/N-CMF  matrix,  S/N-CMF@FexCoyNi1–x–y-MOF  exhibits  excellent  basic  OER  activity  andstability. The overpotential was 296 mV at a current density of 10mA·cm–2 and  a  Tafel  slope  of  53.5  mV·dec–1 in  1.0  M  KOH,  asdepicted  in Figs.  15(g) and 15(h).  The  authors  demonstratedthrough  characterization  and  theoretical  calculations  that  theformation  of  Fe/Co-doped  γ-NiOOH  after  OER  operation  isresponsible  for  its  superior  OER  properties. Table  2 summarizesthe  applications  of  MOF-derived  hollow  functional  materials Figure 15    (a,  b)  TEM and HR-TEM images  of  Fe-CoS2-F.  (c) iR-compensated (85%) LSV curve  and (d)  Tafel  slope  of  Fe-CoS2-F  in  1.0  M KOH solution.  (a‒d)Reproduced with permission from Ref. [97], © 2024 Elsevier Inc. (e, f) HAADF-STEM and TEM images of S/N-CMF@Ni-MOF. (g) LSV curve and (h) Tafel slope ofS/N-CMF@Ni-MOF in 1.0 M KOH solution. (e‒h) Reproduced with permission from Ref. [98], © 2023 Wiley-VCH GmbH.    16 Nano Research Energy  2026, 5: e9120214  synthesized in recent years in the electrocatalytic oxygen evolutionreaction,  demonstrating  their  potential  applications  in  watersplitting. 3.3    Oxygen reduction reactionThe  ORR  process  involves  multi-step  adsorption  of  oxygen-containing  intermediates,  making  the  ORR  activity  of  theelectrocatalysts depend largely on the adsorption energy of oxygen-containing  intermediates  at  catalysts’ active  sites.  The  adsorptionenergy is related to the electronic structure of the active site, whichcan be tuned through the structural  and compositional  design ofthe electrocatalyst. 3.3.1    MOFs-derived hollow materials for 4e– ORRConducting  hollow  cobalt  organic  framework  nanoboxes  (Co-MOF  NBs)  (Figs.  16(a) and 16(b))  synthesized  by  Wang  et  al.using TA etching and a ligand exchange strategy as mentioned inthe  previous  paper,  which  had  excellent  catalytic  performanceapplied as electrocatalysts for 4e– ORR. The resulting catalyst had amore  positive  half-wave  potential  of  0.88  V  and  a  smaller  Tafelslope  of  35.4  mV·dec–1 in  an  alkaline  solution,  as  illustrated  inFigs. 16(c) and 16(d). Based on the cathode catalysts of Co-MOFNBs, the assembled zinc-air battery had an open circuit voltage of1.46  V  and  a  peak  power  density  of  230  mW·cm–2.  Le  et  al.synthesized  a  heterogeneous  zinc-air  battery  consisting  ofFe2NiO4/FeNiS2 nanosheet-assembled  hollow  microtubule(Fe2NiO4/FeNiS2 MTs)  structures  through  a  sequentialhydrothermal and calcination process (Figs. 16(e)‒16(g)) [99]. Thestrong  interactions  between  Fe2NiO4/FeNiS2 nanosheets  withFe2NiO4 and  FeNiS2 at  the  heterogeneous  interfaces  tuned  theelectronic  structure  of  the  materials,  leading  to  an  increase  incatalytic  activity.  The  hollow  structure  effectively  reduces  thecharge/mass  transfer  resistance  and  increases  the  surface  area  ofthe  materials.  The  onset  and  half-wave  potentials  were  0.97  and0.87 V, respectively, under alkaline conditions, and the assembledcathode  material  for  zinc-air  batteries  exhibited  outstandingcycling performance with a power density of 144.22 mW·cm–2 andmore  than  1500  cycles  (40  min  each)  at  a  current  density  of2.0  mA·cm–2,  as  depicted  in Figs.  16(h)‒16(j).  Peng  et  al.constructed a novel catalytic material with the construction of N-bridged  Cu-Zn  diatomic  hollow  carbon  N-doped  materials  (Cu-Zn DA/HNC) via  TA etching and the Kirkendall  effect-pyrolysisstrategy  (Figs.  16(k) and 16(l))  [100].  The  N  atoms  bridgedbetween  Cu  and  Zn  atoms  favor  the  enhancement  of  theirsynergistic  effect,  demonstrating  a  correspondingly  enhanced  O*binding  capacity.  Furthermore,  the  N-doped  hollow  structurefavors  mass  transfer  and  exposure  of  more  active  sites.  Theresulting  Cu-Zn  DA/HNC  exhibits  excellent  ORR  activity  inalkaline  electrolytes  (0.1  M  KOH)  with  a  half-wave  potential  of0.82  V  and  a  Tafel  slope  of  44  mV·dec–1,  as  demonstrated  inFigs.  16(m) and 16(n).  As  a  cathode  material  applied  to  Zn-airelectrodes,  it  has a long cycle life  of  up to 910 h and strong low-temperature (–40 °C) adaptability. 3.3.2    MOFs-derived hollow materials for 2e– ORRCurrently, the industrial production of hydrogen peroxide (H2O2)relies  on  the  anthraquinone  method,  which  suffers  fromsignificant  drawbacks  such  as  large  infrastructure  requirements,complex operation,  and high storage and transportation costs.  Incontrast,  electrochemical  synthesis  has  emerged  as  a  promisingalternative  for  direct  on-site  synthesis  of  H2O2 due  to  its  safety,operational  simplicity,  and  environmental  friendliness.  In  recentyears, the electrochemical two-electron oxygen reduction reaction(2e– ORR)  has  attracted  increasing  attention  as  one  of  the  mostpromising pathways for H2O2 production. However, this reactioncompetes  with  the  four-electron  ORR,  which  leads  to  theproduction  of  H2O.  Consequently,  significant  efforts  have  beendevoted  to  the  development  of  task-tailored  electrocatalysts  forselective  O2 to  H2O2 reduction.  MOF-derived  hollow  materialshave  been widely  explored in  electrocatalysis  due  to  their  uniquestructural  features,  but  their  application  to  the  electrocatalyticproduction of H2O2 has been less studied. In recent years, porous Table 2    Summary of the performance of MOF-derived hollow materials for OERMOF-derived hollow structures MOF Precursors Performance Reference electrode Ref.Hollow ZnS@Co9S8@Ni3S2 nanosword arrays ZnCo MOFs nanoswordarraysη20 mA·cm−21.0 M KOH:  = 233 mV;Tafel slope = 100.69 mV·decade–1; Ag/AgCl (KCl-saturated) [67](Ni,Fe)2P/C hollow nanorods Ni-MOF nanorods η10 mA·cm−21.0 M KOH:  = 258 mV;Tafel slope = 45.5 mV·decade–1Ag/AgCl (saturated KClsolution) [72]N-doped carbon hollow nanostructure loadedwith the CoRu alloy ZIF-67 dodecahedron η10 mA·cm−21.0 M KOH:  = 238 mV;Tafel slope = 240.71 mV·decade–1; Hg/HgO (1 M KOH) [73]Selenium-doped MOF CoS2 hollow spheres ZIF-67 hollow spheres η10 mA·cm−21.0 M KOH:  = 290 mV;Tafel slope = 50.8 mV·decade–1;Ag/AgCl (saturated KClsolution) [80]MOF-derived ultra-small Ru/RuO2nanoparticles doped in copper/cobalt nitride(CuCoN) encapsulated in nitrogen-dopednanoporous carbon frameworkBimetallic Cu-Co/MOFhollow nanospheresη10 mA·cm−21.0 M KOH:  = 231 mV;Tafel slope = 81 mV·decade–1; Ag/AgCl (3 M KCl) [84]Hollow MOF-on-MOF derived Fe-dopedcobalt-carbon nanomaterials CoxZnyZIF-67 dodecahedron η10 mA·cm−21.0 M KOH:  = 302 mV;Tafel slope = 60 mV·decade–1 SCE [94]S-doped NiCo2O4 hollow cubic nanocage NiCo ZIF-67 nanocubes η10 mA·cm−21.0 M KOH:  = 262 mV;Tafel slope = 83.36 mV·decade–1 Ag/AgCl [95]Hollow CoVOx/Ag Co precursors η10 mA·cm−21.0 M KOH:  = 247 mV;Tafel slope = 61.15 mV·decade–1 Ag/AgCl (KCl saturated) [96]Fe and F dual-doped CoS2 hollow sphere Co-glycerate nanosphere η10 mA·cm−21.0 M KOH:  = 298 mV;Tafel slope = 46.0 mV·decade–1 Hg/HgO [97]FexCoyNi1–x–y-MOF supported over S/N-doped carbon macroporous fibers 1D solid CdS@PAN fibers η10 mA·cm−21.0 M KOH:  = 296 mV;Tafel slope = 53.5 mV·decade–1 Hg/HgO [98]    Nano Research Energy  2026, 5: e9120214 17  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nreconducting MOFs have been widely used in electrocatalysis due totheir  dispersed  planar  metal  nodes  and  2D  π-conjugatedstructures.  In  addition,  recent  studies  have  shown  that  low-coordinated  metal  sites  are  beneficial  in  improving  the  catalyticperformance  and  selectivity  of  catalysts.  Lou  et  al.  designed  andsynthesized  a  low-coordinated,  2D  conducting  Zn/Cu  metal-organic  framework  supported  on  hollow  nanocubes  (Figs.  17(a)and 17(b))  [101].  The  authors  used  zinc  and  copper  molecularsieve imidazole framework (ZIF) nanocubic structures (ZnCu-ZIFNCs)  as  precursors,  formed  hollow  nanocubic  structures  (PA-ZnCu HNCs) through etching with phytic acid (PA). Finally, theysynthesized  electrically  conductive  hollow  MOFs  by  ligandreplacement  using  2,3,6,7,10,11-hexahydroxytriphenylene(HHTP).  The  prepared  ZnCu-MOF  (H)  catalysts  demonstratedexcellent  performance  and  selectivity  in  basic  (0.1  M  KOH)  andneutral  (0.1  M K2SO4)  electrolytes,  achieving  exhibiting  good  2e–ORR  performance  and  selectivity  up  to  exceeding  90%  andFaraday  efficiency  of  over  95%  at  a  current  density  of  25.0mA·cm–2,  as  illustrated  in Figs.  17(c)‒17(f).  Furthermore,  ZnCu-MOF (H) also exhibits excellent stability over 80 h with negligibleloss  of  Faraday  efficiency  and  no  structural  degradation.Theoretical  calculations  indicate  that  ZnCu-MOF  (H)  with  lowcoordination  metal  sites  optimizes  the  adsorption/desorptioncapacity and energy barrier of the oxygen intermediates, as shownin Figs.  17(g) and 17(h). Table  3 summarizes  the  applications  ofMOF-derived  hollow  functional  materials  synthesized  in  recentyears in oxygen reduction reactions, demonstrating their potentialfor  use  in  fuel  cells  and  on-site  production  of  low-concentrationhydrogen peroxide. 3.4    Others 3.4.1    CO2 reduction reactionCO2 conversion and utilisation represent an effective measure forachieving  carbon  neutrality  objectives,  enabling  thetransformation  of  CO2 into  high-value-added  products  throughelectrochemical reactions [102].  CO2 reduction reaction (CO2RR)processes  typically  involve  multiple  electron  and  proton  transfer Figure 16    (a, b) SEM and TEM images of Co-MOF nanobelts (NBs). (c) LSV curve and (d) Tafel slope of Co-MOF NBs in 0.1 M KOH solution. (a‒d) Reproducedwith permission from Ref.  [59],  © 2024 Elsevier B.V. (e–g) TEM and HR-TEM images of  Fe2NiO4/FeNiS2 nanotubes (NTs).  (h) LSV curve,  (i)  Tafel  slope,  and (j)cycling stability of Fe2NiO4/FeNiS2 NTs during galvanostatic discharge/charge cycles at 2 mA·cm–2 in 0.1 M KOH solution (inset: cycling performance within 3.5 h peroperation at  initial,  intermediate,  and final  cycles).  (e–j)  Reproduced with permission from Ref.  [99],  © 2024 Elsevier B.V. (k) and (l)  TEM images of  Cu-Zn dual-alloy/hollow nanocarbon (Cu-Zn DA/HNC). (m) LSV curve and (n) Tafel slope of Cu-Zn DA/HNC in 0.1 M KOH solution. (k‒n) Reproduced with permission fromRef. [100], © 2024 Elsevier B.V.    18 Nano Research Energy  2026, 5: e9120214  steps,  yielding  diverse  C1 to  C3 carbon-based  products.  Amongthese,  CO  stands  as  the  core  feedstock  for  basic  chemicalindustries  and holds the greatest  economic value [103].  The CO2molecule  possesses  a  highly  symmetrical  structure  and  a  stableC=O  bond.  Consequently,  achieving  highly  selective  conversionfrom  CO2 to  CO  within  a  broad  potential  window  whilemaintaining  stability  remains  a  key  research  focus.  Chen  et  al.employed  a  melamine-assisted  pyrolysis  method  to  prepare  self-supporting carbon hollow fibre electrodes (Ni-N2-CHF) modifiedwith an unsaturated Ni-N2 coordination structure [104]. Throughcombined DFT calculations and experimental studies, the authorsdemonstrated  that  the  unsaturated  Ni-N2 coordination  structurereduces  the  energy  barrier  for  forming  the  key  reactionintermediate COOH* compared to the saturated Ni-N4 structure,significantly  enhancing  the  electrocatalytic  activity  for  CO2reduction  reactions.  The  Ni-N2-CHF  achieved  over  90%  COFaraday efficiency and a partial  current density of 61 mA·cm–2 in0.5  M KHCO3 solution,  maintaining  this  high  performance  withexcellent  durability  exceeding  100  hours.  Gong  et  al.  synthesisedhollow  carbon  spheres  (Ag@C)  using  SiO2 spheres  as  templatesthrough  a  series  of  processes:  Ag  nanoparticle  loading,  Stöbercoating,  high-temperature  calcination,  and  chemical  etching  toremove  the  template  [105].  These  Ag@C  structures  exhibitedhighly  efficient  CO2RR  activity  in  strongly  acidic  electrolytes Figure 17    (a, b) SEM and TEM images of ZnCu-MOF(H). LSV curves and calculated selectivity of ZnCu-MOF(H) in (c, d) 0.1 M KOH solution and (e, f) 0.1 MK2SO4 solution. (g) Activity volcano plot and (h) free energy diagram for different sites (including Cu1-O3 and Zn1-O3 in ZnCu-MOF(H), and Zn1-O4 and Cu1-O4 inZnCu-MOF) at *U* = 0.7 V. (a‒h) Reproduced with permission from Ref. [101], © 2024 Pei, Z. H. et al. Table 3    Summary of the performance of MOF-derived hollow materials for ORRMOF-derived hollow structures MOF Precursors Performance Referenceelectrode Ref.Hollow conductive Co-MOF nanoboxes ZIF-67 nanocubes 0.1 M KOH: E1/2 = 0.88 V vs. RHE; Tafel slope =35.4 mV·decade–1; n = 3.81 SCE [59]Nitrogen-Co-doped carbon composites withhollow-wall and 3D-ordered macroporousstructures and hydrophilic surfaces3D-orderedmacroporous structuresZnCo-ZIF0.1 M KOH: E1/2 = 0.841 V vs. RHE; Tafel slope =69 mV·decade–1; n = 3.90Ag/AgCl(saturated KClsolution)[62]Co/CoO heterojunction stitched in mulberry-like hollow N-doped carbon MIF-88A nanorods 0.1 M KOH: E1/2 = 0.83 V vs. RHE; Tafel slope =96.8 mV·decade–1Ag/AgCl(saturated KClsolution)[75]Selenium-doped MOF CoS2 hollow spheres ZIF-67 hollow spheres 0.1 M KOH: Eonset = 0.952 V vs. RHE; E1/2 = 0.88 V vs. RHE;Tafel slope = 49.8 mV·decade–1Ag/AgCl(saturated KClsolution)[80]Fe single-atom catalysts (s-Fe-HNC) with ahollow structure and ultrathin carbon shellFe-ZIF@PAA-SPB(sphericalpoly(acrylic acid)brush)0.1 M KOH: E1/2 = 0.83 V vs. RHE; Tafel slope =42 mV·decade–1; n = 3.90Ag/AgCl(3 M KCl) [83]Fe2NiO4/FeNiS2 hollow-structuredmicrotubesFe-based MOFsmicrorods0.1 M KOH: Eonset = 0.97 V vs. RHE; E1/2 = 0.87 V vs. RHE;Tafel slope = 67.55 mV·decade–1; n = 3.94 SCE [99]N-bridged Cu-Zn dual-atom supported onhollow N-doped carbonCu-Zn bimetallic MOFdodecahedron0.1 M KOH: E1/2 = 0.82 V vs. RHE; Tafel slope =44 mV·decade–1; n = 3.84‒3.94 Ag/AgCl [100]2D conductive ZnCu MOFs hollownanocubes ZnCu-ZIF nanocubes0.1 M K2SO4: H2O2 selectivity: over 90%; FE: 95%(25 mA·cm–2); Tafel slope = 93 mV·decade–1; n: close to 20.1 M KOH: Eonset = 0.74 V vs. RHE; H2O2 selectivity: over90%; FE: 98% (25 mA·cm–2); Tafel slope = 65 mV·decade–1n: close to 2Ag/AgCl(3 M KCl) [101]Note: The discrepancies in performance evaluation criteria primarily stem from variations in the data presented within the literature.    Nano Research Energy  2026, 5: e9120214 19  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nre(0.05  M  H2SO4 and  0.5  M  K2SO4,  pH  1.1).  Faraday  efficiencyexceeded  95%  at  a  current  density  of  300  mA·cm–2,  with  single-pass  carbon efficiency (SPCE) reaching 46.2% at  a  CO2 flow rateof  2  cm3·min–1.  Stability  was  enhanced  compared  to  alkalineconditions.  Theoretical  calculations  revealed  that  the  uniquestructure  of  Ag@C  modulates  OH– and  H+ diffusion  processes,confining  the  local  reaction  environment  at  high  pH  values  topromote activity. 3.4.2    N2 reduction reactionAgainst  the  backdrop  of  the  global  energy  crisis  andenvironmental  pollution,  adjusting  the  production  methods  forindustrial chemicals and energy represents an effective measure toalleviate  this  situation.  As  one  of  the  world’s  most  widely  usedinorganic chemicals, NH3 is primarily employed in the productionof inorganic fertilisers,  explosives,  nitric  acid,  and pharmaceuticalintermediates  [106].  The  conventional  Haber-Bosch  processnecessitates  operation  under  elevated  temperatures  (350‒550  °C)and pressures (150‒350 Pa), consuming substantial electricity andgenerating  significant  CO2 emissions  [107, 108].  Electrochemicalconversion  of  N2 to  NH3 at  ambient  temperature  and  pressurerepresents  a  promising  alternative  approach.  The  primarychallenge lies in activating inert nitrogen gas while suppressing thecompeting  HER,  necessitating  the  development  of  highly  active,cost-effective electrocatalysts [109]. Huo et al. synthesised a hollowamorphous  CrO2/carbon  hybrid  amorphous  metal  catalyst(HCrOx/C-550)  featuring  a  multi-level  porous  structure  throughselective  etching  and  controlled  pyrolysis  [110].  HCrOx/C-550exhibits outstanding electrocatalytic N2 reduction reaction (N2RR)performance at ambient temperature and pressure, demonstratinga yield of 19.10 μg·h–1·mgcat–1 at –0.7 V vs.  RHE in 0.1 M Na2SO4electrolyte,  with  a  Faradaic  efficiency  of  1.4%,  alongside  excellentstructural  and  cycling  stability.  Notably,  the  amorphous  metaloxide  obtained  via  controlled  pyrolysis  possesses  abundantunsaturated catalytic sites and optimised conductivity, attributableto  the  controllable  metal-oxygen  bond  rearrangement  and  thedoping effect of carbon materials from organic ligands. 4    Summary and outlookThe  unique  porosity  and  tunable  chemical  composition  ofmorphological offering frameworks (MOFs) make them excellentprecursors  for  constructing  porous  structures.  Morphologicallyengineered hollow structures inherit the morphological features oftheir  precursors  while  exhibiting  highly  exposed  active  sites  andshorter  charge  and  mass  transfer  paths.  These  advantageousproperties  accelerate  the  rate  of  charge  transfer  duringelectrocatalytic  reactions,  thereby  enhancing  the  electrocatalyticperformance.  As  a  result,  MOFs-based  materials  are  particularlysuitable  as  electrically  charged  electrodes  in  electrochemicalapplications.  This  review  synthesizes  recent  advancements  in  theresearch of functional materials derived from MOFs as precursorsfor  creating  hollow  structures,  with  a  brief  overview  of  theirapplications  in  electrocatalysis.  Based  on  the  characteristics  ofMOFs precursors, the commonly used synthesis strategies includeacid  etching  strategies,  ion  exchange  strategies,  template-basedmethods,  and  self-catalytic  thermal  decomposition.  Despitesignificant  efforts  dedicated  to  this  field  and  notable  progressachieved,  challenges  remain  in  the  synthesis  and  application  ofhollow  structure  functional  materials  derived  from  MOFsprecursors.Firstly,  the  precise  control  of  the  structural  and  compositionalcomplexity  in  hollow  structures  derived  from  multi-componentMOFs  precursors  presents  notable  challenges.  Although  anincreasing  number  of  reports  have  been  published  on  functionalmaterials derived from MOFs hollow structures, there is a lack ofuniversal  theoretical  guidance  for  the  precise  regulation  of  poredimensions, shell thickness, and pore distribution. Additionally, inthe context of acid etching strategies, the solubility and pH of thesolvent  play  critical  roles  in  determining  the  etching  results.  Toachieve  more  generalized  conditions,  further  investigation  isrequired.  Moreover,  it  is  imperative  to  consider  environmentalimpacts  and  explore  greener  synthesis  pathways,  such  as  thedevelopment of  low-temperature solvent  methods and the use ofionic liquids to minimize the reliance on organic reagents.Secondly,  the  synergistic  interactions  among  differentcomponents,  including  diverse  atoms  (e.g.,  N,  S,  P)  and  metal-based  species  (e.g.,  metal  carbides,  nitrides,  phosphides),  arecrucial  for  enhancing  electrocatalytic  performance.  In  multi-component hybrid materials, each component contributes uniquefunctionalities  to  address  the  limitations  of  individualcomponents,  thereby  producing  synergistic  effects.  However,conventional  synthesis  approaches  for  MOFs  hollow  materialspredominantly  utilize  single-metal  or  dual/third-metal  MOFsprecursors.  Future  research  should  focus  on  the  exploration  ofMOFs  precursors  containing  multiple  metal  centers,  aiming  toexploit new opportunities arising from such materials.Thirdly,  the  mechanistic  understanding  of  the  relationshipbetween  the  structural  features  of  MOFs  hollow  materials  andtheir  enhanced  electrocatalytic  performance  remains  incomplete.While  structural  and  compositional  correlations  are  oftenattributed  to  the  synergistic  effects  of  architecture  andcomposition,  a  more  detailed  and  accurate  mechanisticexplanation is still lacking. With advances in computer technologyand  theoretical  computation,  theoretical  simulation  calculationshave provided an effective means for gaining deeper insights intocatalytic  reaction  mechanisms  and  determining  structure-activityrelationships.  However,  the  multifactorial  nature  ofelectrochemical  processes  means  theoretical  computationalmodels  alone  are  insufficient  to  fully  elucidate  the  influence  ofheterogeneous  interfaces  and  synergistic  effects  on  catalyticreactions.  In  such  circumstances,  integrating  theoreticalcalculations  with  advanced in-situ characterisation  techniques,such  as  synchrotron  X-ray  diffraction  (XRD),  X-ray  absorptionspectroscopy  (XAS),  and in-situ TEM,  will  facilitate  theinvestigation  of  relationships  between  structure  andelectrocatalytic performance.Finally, the scaling up of MOFs hollow materials synthesis is ofcritical  importance.  Currently,  many  methods  for  constructinghollow structures are limited to laboratory-scale applications, withrelatively  low  yields,  rendering  them  unsuitable  for  industrialproduction.  To meet  the  demands  of  industrial  applications,  it  isessential  to  develop  synthesis  strategies  that  are  compatible  withindustrial  needs.  Moreover,  expanding  the  application  scope  ofMOFs hollow materials from small-molecule conversions to large-molecule conversions is crucial to satisfy future energy demands.In conclusion, the rapid development of MOFs-derived hollowstructures  has  provided  numerous  new  opportunities  andchallenges  in  the  field  of  electrocatalysis.  The  pursuit  of  simplerand  more  customizable  methods  to  synthesize  desired  structuresand  compositions  for  electrocatalytic  materials  andelectrochemical  materials  will  significantly  advance  energyconversion  and  storage  technologies.  We  anticipate  that,  in  thenear  future,  MOFs-derived  hollow  materials  will  be  better    20 Nano Research Energy  2026, 5: e9120214  equipped to meet practical application demands. AcknowledgementsThe  authors  express  their  appreciations  for  the  financial  supportfrom  the  project  of  Zhongyuan  Critical  Metals  Laboratory(GJJSGFYQ202422,  GJJSGFYQ202315  and  GJJSGFYQ202336).H.  R.  Xue acknowledges  support  from Zhongyuan Youth TalentCultivation Project for Scientific and Technological Innovation. Declaration of conflicting interestsThe authors declare no conflicting interests regarding the contentof this article. Data availabilityAll  data  needed  to  support  the  conclusions  in  the  paper  arepresented in the manuscript and/or the Supplementary Materials.Additional  data  related  to  this  paper  may  be  requested  from  thecorresponding author upon request.References  Xue,  Z.  Q.;  Liu,  K.;  Liu,  Q.  L.;  Li,  Y.  L.;  Li,  M.  R.;  Su,  C.  Y.;Ogiwara, N.; Kobayashi, H.; Kitagawa, H.; Liu, M. et al. Missing-linker  metal-organic  frameworks  for  oxygen  evolution  reaction.Nat. Commun. 2019, 10, 5048.[1] Beltrán,  D.  E.;  Ding,  S.;  Xu,  H.;  Wu,  G.;  Litster,  S.  Aircontamination of platinum-group metal-free fuel cell cathodes withatomically  dispersed  iron  active  sites.  Appl.  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Her  research  interests  include  carbon  materials,  MOF-derived  materials,  andtheir applications in electrocatalysis and fuel cells.  Hao Wan is an assistant professor of the Zhongyuan Critical Metals Laboratory at Zhengzhou University. He received hisBSs (2013)  and PhD (2019) from Central  South University.  From September 2016 to September 2018,  he studied as anexchange student at the National Institute for Materials Science (NIMS) in Japan. His recent research interests include thedesign and synthesis of advanced nanostructures for electrochemical energy storage and conversion.    24 Nano Research Energy  2026, 5: e9120214  https://doi.org/10.1002/smll.202310012https://doi.org/10.1016/j.jcis.2024.05.168https://doi.org/10.1016/j.jcis.2023.11.094https://doi.org/10.1016/j.jcis.2024.01.073https://doi.org/10.1016/j.jcis.2024.01.073https://doi.org/10.1016/j.jcis.2024.03.201https://doi.org/10.1002/adma.202207888https://doi.org/10.1016/j.cej.2024.151210https://doi.org/10.1016/j.apcatb.2024.124288https://doi.org/10.1016/j.apcatb.2024.124288https://doi.org/10.1002/smll.202403808?af=Rhttps://doi.org/10.1002/anie.202414506https://doi.org/10.1021/acs.chemrev.4c00664https://doi.org/10.1002/advs.202502947https://doi.org/10.1039/D3SC01040Fhttps://doi.org/10.1126/science.345.6197.610https://doi.org/10.1016/j.cep.2015.02.004https://doi.org/10.1021/acssuschemeng.0c01206https://doi.org/10.1021/jacs.2c10637https://doi.org/10.1021/acsami.2c00018https://doi.org/10.1021/acsami.2c00018  Ying  Zhang is  an  assistant  professor  of  the  Zhongyuan  Critical  Metals  Laboratory,  School  of  Chemical  Engineering  atZhengzhou University. He received his B.E. (2009) and PhD (2019) from the Central South University (China). He studied asa visiting researcher from 2017 to 2019 at  the University of  California San Diego (United States).  Currently,  his  researchfocuses on natural resource derived nanostructures for energy storage and environmental applications.  Hairong  Xue received  his  B.S.  (2009),  M.S.  (2012)  and  PhD  degree  (2016)  at  the  College  of  Material  Science  andTechnology,  Nanjing  University  of  Aeronautics  and  Astronautics  (NUAA,  China).  He  worked  as  a  lecturer  at  College  ofChemical  Engineering,  Zhejiang  University  of  Technology  (ZJUT,  China)  after  graduation.  During  2018–2022,  he  hasworked  at  National  Institute  for  Materials  Science  (NIMS,  Japan)  as  a  Postdoctoral  Fellow.  Since  2023,  he  has  been  aProfessor  at  Zhongyuan  Critical  Metals  Laboratory,  Zhengzhou  University.  His  research  interest  centers  on  developingfunctional materials for energy storage and conversion.    Nano Research Energy  2026, 5: e9120214 25  https://www.sciopen.com | https://mc03.manuscriptcentral.com/nre | Nano Research Energyhttps://www.sciopen.comhttps://mc03.manuscriptcentral.com/nre 1 Introduction 2 Synthesis methods for MOF-derived hollow structures 2.1 Synthesis strategies for MOF-derived hollow structures 2.2 Acid etching 2.3 Ion exchange strategy 2.4 Template-assisted methods 2.4.1 Self-template method 2.4.2 Hard template method 2.4.3 Soft template method 2.5 Self-catalytic pyrolysis method 3 Application of MOF-derived hollow materials for electrocatalysis 3.1 Hydrogen evolution reaction 3.1.1 MOF-derived non-precious metal hollow electrocatalysts 3.1.2 MOFs-derived transition metal-derived hollow electrocatalysts 3.2 Oxygen evolution reaction 3.2.1 Metals/metal oxides 3.2.2 Other metallized materials 3.3 Oxygen reduction reaction 3.3.1 MOFs-derived hollow materials for 4e– ORR 3.3.2 MOFs-derived hollow materials for 2e– ORR 3.4 Others 3.4.1 CO2 reduction reaction 3.4.2 N2 reduction reaction 4 Summary and outlook Acknowledgements Declaration of conflicting interests Data availability References