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Yuki Sano, Daichi Nakajima, [Biplab Manna](https://orcid.org/0000-0002-7619-7765), [Koki Chida](https://orcid.org/0000-0003-1197-8592), [Ryojun Toyoda](https://orcid.org/0000-0002-0168-0533), [Shinya Takaishi](https://orcid.org/0000-0002-6739-8119), [Kazuyuki Iwase](https://orcid.org/0000-0002-5196-741X), [Koji Harano](https://orcid.org/0000-0001-6800-8023), [Yuta Nishina](https://orcid.org/0000-0002-4958-1753), [Takeharu Yoshii](https://orcid.org/0000-0002-1869-6021), [Ryota Sakamoto](https://orcid.org/0000-0002-8702-1378)

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[Thermally polymerizable phthalocyanine realizes a metal–nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO<sub>2</sub>RR activity](https://mdr.nims.go.jp/datasets/c1f48bce-64f6-4d58-808a-d851e5ee5799)

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Thermally polymerizable phthalocyanine realizes a metal–nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO2RR activityJournal ofMaterials Chemistry ACOMMUNICATIONOpen Access Article. Published on 26 August 2025. Downloaded on 9/9/2025 10:40:02 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineView Journal  | View IssueThermally polymaDepartment of Chemistry, Graduate SchAramaki Aza-Aoba, Aoba-ku, Sendai 980-8tohoku.ac.jp; ryota.sakamoto.e3@tohoku.acbCenter for Basic Research on Materials, NaNamiki, Tsukuba, Ibaraki 305-0044, JapancInstitute of Multidisciplinary Research for A1-1 Katahira, Aoba-ku, Sendai, Miyagi, 980-tohoku.ac.jpdResearch Center for Autonomous Systems MResearch, Institute of Science Tokyo, 4259Kanagawa 226-8501, JapaneGraduate School of Natural Science andTsushimanaka, Kita-ku, Okayama 700-8530fResearch Institute for InterdisciplinaryTsushimanaka, Kita-ku, Okayama 700-8530gDivision for the Establishment of FrontierStudies at Tohoku University, 2-1-1 KatahirCite this: J. Mater. Chem. A, 2025, 13,28887Received 6th April 2025Accepted 13th August 2025DOI: 10.1039/d5ta02720arsc.li/materials-aThis journal is © The Royal Society oerizable phthalocyanine realizesa metal–nitrogen-doped carbon material featuringa defined single-atom catalyst motif with CO2RRactivityYuki Sano,a Daichi Nakajima,a Biplab Manna, b Koki Chida, c Ryojun Toyoda, *aShinya Takaishi, a Kazuyuki Iwase, *c Koji Harano, bd Yuta Nishina, efTakeharu Yoshii c and Ryota Sakamoto *agMetal–nitrogen-doped carbon materials (MNCs) exhibit good electro-catalytic performance owing to the intrinsic advantages of carbon-basedmaterials and the presence of isolated and stabilized metal atomscoordinated by nitrogen sites. However, conventional high-temperaturepyrolysis of precursor molecules make it difficult to control the coor-dination structure precisely. To address this issue, here we report a newsynthesis strategy for MNCs. Specifically, we design and synthesize Ni-phthalocyanine functionalized with ethynyl groups as solid-statethermal polymerization points. After depositing the Ni-phthalocyanineprecursor on a carbon support and performing a thermal treatment,the resultant carbon composite material features a Ni–N4 coordinationstructure derived from the precursor, and enhanced porosity. Thismaterial demonstrates high catalytic activity for the CO2 reductionreaction (CO2RR). Our synthetic approach is applicable to variousprecursormolecules and carbon supports, paving theway for the furtherdevelopment of MNC-based electrode catalysts.IntroductionIn recent years, extensive research and development efforts havebeen devoted to various energy conversion technologies, suchas water electrolysis,1–3 fuel cells,4,5 metal–air batteries,6,7 CO2ool of Science, Tohoku University, 6-3578, Japan. E-mail: ryojun.toyoda.a8@.jptional Institute for Materials Science, 1-1dvanced Materials, Tohoku University, 2-8577, Japan. E-mail: kazuyuki.iwase.a6@aterialogy (ASMat), Institute of IntegratedNagatsuda-cho, Midori-ku, Yokohama,Technology, Okayama University, 3-1-1, JapanScience, Okayama University, 3-1-1, JapanSciences of Organization for Advanceda, Aoba-ku, Sendai 980-8577, Japanf Chemistry 2025reduction reactions,8,9 and N2 reduction reactions,10,11 toaddress the pressing issues of the energy crisis and globalwarming. Noble metal-based catalysts, including Pt, Au, and Ag,are known to function as electrocatalysts in these technologies,demonstrating exceptional performance.12–17 However, theirhigh cost and limited availability impose signicant constraintson large-scale commercialization.18 Consequently, there isa growing demand for the development of alternative catalystmaterials that can serve as viable substitutes.19Single-atom catalyst (SAC), in which metal atoms aredispersed in an isolated atomic state, has earned signicantattention as a novel catalyst material.20 Due to its inherentelectronic structure, SAC exhibits high catalytic activity andselectivity. Moreover, maximizing atomic utilization efficiencyenables a substantial reduction in the consumption of catalyticmetals, making it a promising candidate for sustainable catalystdevelopment.21SAC requires a support substrate to immobilize metal atoms,and various materials, including metal oxides22,23 and metal–organic frameworks24,25 (MOFs), have been investigated. Amongthem, metal–nitrogen-doped carbon materials (MNCs), whichfeature metal atoms coordinated to doped nitrogen sites,exhibit excellent performance as SAC due to its isolated andstabilized metal atoms at nitrogen sites, as well as its superiorproperties derived from carbon materials such as mechanicalproperties, specic surface area, electronic conductivity, struc-tural exibility, low cost, and chemical stability.26–29MNCs have been applied in various catalytic reactions suchas oxygen reduction reaction27–29 (ORR), hydrogen evolutionreaction30,31 (HER), oxygen evolution reaction32 (OER), andcarbon dioxide reduction reaction33,34 (CO2RR). In particular,CO2RR, which electrochemically reduces CO2 to produce morevaluable compounds, is regarded as one of the essential tech-nologies for achieving carbon neutrality and has beenresearched actively.35 For example, Su et al. reported thesynthesis of an MNC with Ni–N coordination sites throughthermal treatment of an organometallic complex containing Ni–N bonds and its application as a CO2RR electrocatalyst,J. Mater. Chem. A, 2025, 13, 28887–28895 | 28887http://crossmark.crossref.org/dialog/?doi=10.1039/d5ta02720a&domain=pdf&date_stamp=2025-09-06http://orcid.org/0000-0002-7619-7765http://orcid.org/0000-0003-1197-8592http://orcid.org/0000-0002-0168-0533http://orcid.org/0000-0002-6739-8119http://orcid.org/0000-0002-5196-741Xhttp://orcid.org/0000-0001-6800-8023http://orcid.org/0000-0002-4958-1753http://orcid.org/0000-0002-1869-6021http://orcid.org/0000-0002-8702-1378http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d5ta02720ahttps://pubs.rsc.org/en/journals/journal/TAhttps://pubs.rsc.org/en/journals/journal/TA?issueid=TA013035Fig. 1 Strategy of this study for the creation of metal–nitrogen-dopedcarbon materials.Journal of Materials Chemistry A CommunicationOpen Access Article. Published on 26 August 2025. Downloaded on 9/9/2025 10:40:02 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinedemonstrating Faraday efficiency for CO production (FECO)exceeding 90%.36 Similarly, Pan et al. demonstrated that anMNC with atomically dispersed Co–N5 sites achieved FECOabove 90% and sustained both current density and FECO for 10hours of continuous operation.37 These ndings highlight thehigh reaction selectivity and excellent stability of MNCs, andnumerous reports of MNCs with outstanding CO2RR electro-catalytic performance have since followed.38–47MNCs intended for SAC applications are typically synthe-sized through high-temperature pyrolysis of selected precursorsunder a controlled atmosphere, such as inert gases (N2, Ar) ornitrogen sources48 (e.g. NH3). Mixtures of carbon matrix,nitrogen precursors, and metal sources,49,50 or MOFs51,52 aretypically used as precursors, and it is considered that bymodifying the composition and structure of precursors, thebinding energy and the form of bonding between the catalystand reactant molecules can be efficiently adjusted, therebymodulating catalytic activity.53,54 However, in practice, due tocomplex pyrolysis reactions during thermal treatment, activesites formed by metal centers coordinated to nitrogen atomspossess diverse coordination structures, making it difficult toprecisely control their structure.55 As a result, the coordinationstructures of MNCs remain unclear, which means it is difficultto conduct detailed studies of reaction mechanisms using DFTcalculations.55 Furthermore, the electronic properties of themetal atoms and their corresponding catalytic reactions aregreatly inuenced by the coordination environment, whichmakes controlling catalytic reactions challenging due to thecomplicated coordination structures.56 Therefore, to addressthese challenges and further enhance the practicality of MNCs,the development of new synthetic methods that can achieveboth precisely controlled coordination structures and superiorperformance is necessary.In this study, we propose a novel strategy for synthesizingMNCs by embedding well-dened chemical structures intocarbon frameworks using precursor molecules bearing ther-mally polymerizable groups. In this approach, the nano-crystallized precursor molecules are rst supported on carbonmaterials, which play a crucial role in their uniform distributionand stabilization as active centers.57,58 Subsequent thermaltreatment facilitates the formation of a composite in which theprecursor structure is embedded within the carbon matrix.Furthermore, the introduction of thermally polymerizablegroups enables polymerization and carbonization to occur attemperatures lower than the decomposition point of theprecursors, thereby allowing the chemical structure of theprecursor to be precisely retained.59 Specically, we design andsynthesize a nickel phthalocyanine molecule (Ni-OEPPc) witheight ethynyl groups as thermally polymerizable functionalgroups, which is supported on a carbon substrate, and thenthermally polymerized and carbonized (Fig. 1). The combina-tion of this synthesis method using thermal polymerization andcarbon supporting of precursors is expected to enable thesynthesis of carbon materials that simultaneously achieve thedesired chemical structure and pore structure and maximizethe potential of the introduced chemical structure. In this28888 | J. Mater. Chem. A, 2025, 13, 28887–28895paper, we also demonstrate that the resultant MNC has SACcenters and evaluate its CO2RR ability.Results and discussionTo demonstrate the strategy for MNCs creation, we designedand synthesized a new compound, [2,3,9,10,16,17,23,24-octa-kis(4-ethynylphenyl)phthalocyaninato]nickel(II) (Ni-OEPPc,Fig. 1), which is a nickel phthalocyanine derivative with thermalpolymerization groups, as the precursor and aimed to introducethe Ni–N4 coordination structure into carbon materials (Fig. 1).Phthalocyanines possess high thermal and chemical stability,as well as robust redox activity.60 Due to these characteristics,their metal centers are known to exhibit high performance asactive sites for various electrocatalytic reactions.61–68 Speci-cally, unsubstituted nickel phthalocyanine (Ni-Pc) has been re-ported to show high CO selectivity (FE > 90%) as an active sitefor CO2RR.69–73 However, a molecular material generally has lowelectrical conductivity, and its durability at high current densityis a concern.74–76 Therefore, in this study, we attempted tosynthesize carbon materials that precisely maintain the Ni–N4coordination structure, analyzed their structure, and theninvestigated the CO2RR electrocatalytic performance of theresulting materials. The synthesis of Ni-OEPPc was carried outaccording to the synthetic route shown in Fig. S1. Thesuccessful synthesis of compounds 2, 3, and 4 was conrmed byNMR and mass spectrometry (Fig. S2–S11). Ni-OEPPc was ob-tained from 4 as a solid product via in situ deprotection andprecipitation.77 An excess amount of tetrabutylammoniumuoride was added dropwise to a solution of 4 in anhydroustetrahydrofuran under a nitrogen atmosphere. The obtainedgreen solid precipitate of Ni-OEPPc was isolated by ltration.The success of the synthesis was conrmed by infrared spec-troscopy and mass spectrometry (Fig. S12 and S13). Hereaer,aNi-OEPPc sample subjected to thermal treatment is referred toas Ni-OEPPc_x (x denotes the calcination temperature), whilethat on a carbon support (CNovel 010-00®)78 is referred to as Ni-This journal is © The Royal Society of Chemistry 2025http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d5ta02720aCommunication Journal of Materials Chemistry AOpen Access Article. Published on 26 August 2025. Downloaded on 9/9/2025 10:40:02 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineOEPPc/C. A Ni-OEPPc sample which was calcined aer beingsupported on the carbon support is expressed as Ni-OEPPc/C_x.To gain a deeper understanding of the structure of Ni-OEPPcaer thermal treatment, Ni-OEPPc was subjected to thermaltreatment alone, and its structure aer thermal treatment wasanalyzed. Thermal treatments of Ni-OEPPc were carried outunder an Ar atmosphere at different calcination temperatures ata heating rate of 10 °C min−1. The thermal behavior of Ni-OEPPc was investigated by thermogravimetry-differentialthermal analysis (TG-DTA) and compared with unsubstitutedNi-Pc. Fig. 2 shows the weight changes measured by TG and theDTA curves for Ni-OEPPc and Ni-Pc. DTA measurementsrevealed an exothermic peak observed only for Ni-OEPPcaround 215 °C, which is considered to be associated withthermal polymerization.79 The progress of the polymerizationreaction of the ethynyl groups was also conrmed by othermeasurements. In IR spectra, two peaks attributed to thevibrations of the ethynyl group were observed before thermaltreatment at 3273 cm−1 (C–H) and 2099 cm−1 (C^C).80However, these absorption peaks disappeared aer thermaltreatment at 250 °C (Ni-OEPPc_250), suggesting that the ethynylgroups were converted during thermal treatment (Fig. S14).Furthermore, in solid-state 13C NMR measurements of Ni-OEPPc andNi-OEPPc_250, the spectra before thermal treatmentexhibited multiple peaks in the 100–150 ppm range derivedfrom aromatic carbon, along with peaks around 70–80 ppmattributed to sp bonding. In contrast, aer thermal treatment,a reduction in the sp bonding and broadening of the aromaticcarbon-derived peaks were observed, indicating that the poly-merization reaction proceeded during thermal treatment(Fig. S15). TG measurements revealed that Ni-OEPPc exhibitedonly a 6% weight loss at 700 °C, demonstrating excellentthermal stability. To investigate the thermal stability durabilityof polymerized Ni-OEPPc at higher temperatures above 700 °C,TG-DSC for Ni-OEPPc was conducted up to 1600 °C (Fig. S16),disclosing that 80% of the initial weight was retained with theformation of a graphitic structure (Fig. S17). In contrast, Ni-PcFig. 2 TG-DTA curves of Ni-OEPPc and Ni-Pc. Dark and light colorscorrespond to those of Ni-OEPPc and Ni-Pc, respectively.This journal is © The Royal Society of Chemistry 2025showed a 37% weight loss at the same temperature. From theseresults, it is considered that thermal polymerization of theethynyl groups and subsequent carbonization suppressesdecomposition of the phthalocyanine macrocycle. Additionally,thermogravimetry–differential scanning calorimetry–massspectroscopy (TG-DSC-MS) was used to analyze the volatilecomponents during thermal treatment. The detected chemicalspecies were derived from partial structures other than thephthalocyanine ring (Fig. S18).Ni-OEPPc aer thermal treatment was structurally charac-terized by Raman spectroscopy, infrared (IR) spectroscopy,electrical conductivity test, X-ray photoelectron spectroscopy(XPS), X-ray absorption ne structure (XAFS) analysis, X-raydiffraction (XRD), and nitrogen adsorption measurement.Raman spectroscopy was performed at different thermal treat-ment temperatures, and up to 700 °C, a series of Raman peaksderived from the phthalocyanine macrocycle were observed atapproximately 650 cm−1–750 cm−1 and 1100 cm−1–1600 cm−1,suggesting that the coordination structure was retained at thistemperature (Fig. S19). In contrast, the metal phthalocyanine-derived peaks disappeared in Ni-OEPPc_800, and broad peakswere observed at 1336 cm−1 and 1592 cm−1 (Fig. S19), corre-sponding to the D and G bands, respectively. Given the high ID/IG ratio, these features indicate the formation of a defect-richcarbonaceous framework.81,82 Similarly, The IR spectraconrmed that absorption peaks in the ngerprint region weremaintained aer thermal treatment up to 700 °C (Fig. S20).Electrical conductivity measurements revealed that Ni-OEPPcwas initially insulating (2 × 10−8 S m−1), but its conductivitysignicantly increased with higher thermal treatment temper-atures. Notably, Ni-OEPPc_700 exhibited excellent electricalconductivity of 1.2 × 10−1 S m−1, indicating the progression ofcarbonization as the temperature increased (Table S1). Thisenhanced electrical conductivity is likely governed by multiplemechanisms, including hopping conduction and tunnelingconduction between sp2 domains, as well as charge transportthrough partially graphitized sp2 carbon structures, all of whichare intricately involved.83,84 XPS measurements and analysis ofthe N 1s and Ni 2p spectra showed that the overall spectralfeatures of Ni-OEPPc were consistent with previously reportedXPS spectra of Ni-Pc.85 The Ni 2p3/2 spectrum of Ni-OEPPc_700exhibited slight broadening, which may be attributed to thepresence of a small amount of oxidized Ni species, carbides, ormetallic Ni.86 In addition, the N 1s spectrum of Ni-OEPPc_700revealed additional components attributed to graphitic N andpyrrolic N, which are likely due to the thermal transformation ofcertain nitrogen-containing structures within Ni-OEPPc duringthe carbonization process (Fig. S21). In the X-ray absorptionnear edge structure (XANES) spectrum of Ni-OEPPc (Fig. 3a),a shoulder peak was observed around 8335 eV (1s / 4pz tran-sition), which is characteristic of square-planar congurationwith high metal–N4 (M–N4) symmetry.87 Additionally, in thewhite line region, peaks derived from the convolution of the 1s/ 4px,y transitions and multiple scattering processes wereobserved.87 In previous studies, it has been reported that MNCsderived from Ni-Pc exhibit XANES spectra different from thoseof Ni-Pc,88,89 and this difference has been attributed to the lossJ. Mater. Chem. A, 2025, 13, 28887–28895 | 28889http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d5ta02720aFig. 3 (a) XANES spectra of Ni-OEPPc and Ni-OEPPc_700. (b) EXAFSspectra of Ni-OEPPc and Ni-OEPPc_700, together with those of Ni-Pc, Ni foil, and NiO as references. (c) XRD patterns of Ni-OEPPc andNi-OEPPc_700. (d) Nitrogen adsorption and desorption isotherms at77 K for Ni-OEPPc and Ni-OEPPc_700.Journal of Materials Chemistry A CommunicationOpen Access Article. Published on 26 August 2025. Downloaded on 9/9/2025 10:40:02 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlineof Ni–N fragments around Ni atoms during thermal treatment,leaving the unsaturated M–Nx moieties.90 Meanwhile, Ni-OEPPc_700 exhibited a similar XANES spectrum, which meansthe Ni–N4 coordination structure was strictly preserved aerthermal treatment. Moreover, the EXAFS spectra of both Ni-OEPPc and Ni-OEPPc_700 were nearly identical, and no Ni–Nipeak (2.18 Å) was detected91 (Fig. 3b). This suggests that metalaggregation did not occur during thermal treatment, which isconsistent with the XPS measurement and the XRD measure-ment results discussed later. Furthermore, the EXAFS spectrumof Ni-OEPPc_700 was tted (Fig. S22b and Table S2). As a result,the experimental spectra are reproduced with a tetra-coordination structure, indicating that the Ni–N4 coordinationstructure of mother Ni-OEPPc is maintained. XRD measure-ments were conducted to analyze the structural periodicity ofNi-OEPPc before and aer thermal treatment (Fig. 3c). Beforeheating, multiple peaks originating from the crystalline struc-ture of Ni-OEPPc were observed, with the sharpest peakappearing at 4.12° (20.93 Å). This peak was also present in Ni-OEPPc_700, which implies that the precursor-derived orderedstructure was partially retained even aer thermal treatment at700 °C.92,93 The porosity and pore structure were evaluatedthrough nitrogen adsorption measurements at 77 K (Fig. 3d).The adsorption–desorption isotherm of Ni-OEPPc exhibiteda rapid gas uptake up to a low relative pressure (P/P0), con-rming the presence of micropores. The specic surface area ofNi-OEPPc, determined by Brunauer–Emmett–Teller (BET)method, was 144 m2 g−1. Aer thermal treatment, the shape ofthe isotherm changed, and Ni-OEPPc_700 displayed a Type Iisotherm. BET specic surface area of Ni-OEPPc_700 increasedto 184 m2 g−1, indicating enhanced porosity. Pore size analysisusing nonlocal density functional theory (NLDFT) furtherrevealed the distribution of a large number of pores smallerthan 1 nm (Fig. S23).Next, introduction of the Ni–N4 structure into the carbonmaterial was carried out through the loading of Ni-OEPPc onto28890 | J. Mater. Chem. A, 2025, 13, 28887–28895the carbon support and subsequent thermal treatment. Thedispersibility of insoluble Ni-OEPPc was investigated usingdynamic light scattering (DLS), which indicated that the particlesize of Ni-OEPPc dispersed in tetrahydrofuran (THF) wasapproximately 20 nm to 40 nm (Fig. S24b). Additionally, TEMimages ofNi-OEPPc indicated good agreement with the result ofDLS measurements (Fig. S25). Based on the above ndings andthe XRD results, Ni-OEPPc is considered to exist as highlycrystalline particles on the nanoscale in THF. The loading of Ni-OEPPc onto the carbon support was carried out using theimpregnation method. Dehydrated THF was added to Ni-OEPPcand the carbon support, and the mixture was subjected toultrasonic treatment. The solvent was then removed, yieldingthe supported Ni-OEPPc sample, Ni-OEPPc/C. The morphologyof Ni-OEPPc/C was observed using scanning transmissionelectron microscopy (STEM). The corresponding elementalmaps obtained from energy-dispersive X-ray (EDX) analysisconrmed that N atoms and Ni atoms were uniformly dispersedon carbon, suggesting that Ni-OEPPc is uniformly supported onthe carbon support (Fig. S26). In addition, a comparison of theXPS spectra of Ni-OEPPc and Ni-OEPPc/C revealed no signi-cant differences in the position or shape of the Ni 2p3/2 peaks,suggesting that the oxidation state of Ni remained unchangedupon supporting. In the N 1s spectra, components corre-sponding to graphitic N and pyrrolic N were observed, which areconsidered to originate from nitrogen species inherentlypresent in the carbon support (Fig. S27). Then, thermal treat-ment of Ni-OEPPc/C was performed. Considering the results ofthe thermal treatment of Ni-OEPPc alone, the temperature wasraised to 700 °C, which was deemed appropriate for bothmaintaining the Ni–N4 coordination structure and promotingcarbonization. The process was conducted under an Ar atmo-sphere at a heating rate of 10 °C min−1, yielding the supportedand thermal-treated sample, Ni-OEPPc/C_700. The metalcontent of Ni-OEPPc/C_700 was analyzed using inductivelycoupled plasma (ICP) analysis, revealing that the Ni wt% wasapproximately 1.2%, almost equal to the loading (1.07 wt%).The structure of Ni-OEPPc/C_700 aer thermal treatmentwas investigated by XPS, XAFS, XRD, STEM, and nitrogenadsorption tests. XPS measurements of Ni-OEPPc/C and Ni-OEPPc/C_700 showed similar spectral changes to thoseobserved in thermally treated Ni-OEPPc alone (Ni-OEPPc_700).Specically, a slight broadening of the Ni 2p3/2 peak and anincrease in the components corresponding to graphitic N andpyrrolic N in the N1s spectrum were observed (Fig. S24). In XAFSmeasurements, an unsubstituted Ni-Pc-used composite (Ni-Pc/C_700) was synthesized for comparison (Fig. 4a and S28). TheXANES spectra of Ni-OEPPc/C and Ni-OEPPc/C_700 closelyresembled that of Ni-OEPPc, implying that the Ni–N4 coordi-nation structure remained intact (Fig. 4a and S29). In contrast,a signicant change in the shape of spectra was observed for Ni-Pc/C_700, indicating that the Ni–N4 coordination structure wasaltered due to thermal decomposition (Fig. 4a). The EXAFSspectra of Ni-OEPPc/C and Ni-OEPPc/C_700 were nearly iden-tical, and no Ni–Ni peak (2.18 Å) was detected,91 suggesting thatmetal aggregation did not occur during thermal treatment(Fig. S30). Ni–N4 coordination structure of Ni-OEPPc isThis journal is © The Royal Society of Chemistry 2025http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d5ta02720aFig. 4 (a) XANES spectra of Ni-OEPPc/C, Ni-OEPPc/C_700, Ni-Pc/C,and Ni-Pc/C_700. (b) Nitrogen adsorption and desorption isothermsat 77 K forNi-OEPPc/C,Ni-OEPPc/C_700, and the carbon support. (c)Representative TEM image of Ni-OEPPc/C_700. (d-h) HAADF-STEMimage of Ni-OEPPc/C_700 and corresponding EDX maps of C/Nioverlay, C, N, and Ni, respectively.Communication Journal of Materials Chemistry AOpen Access Article. Published on 26 August 2025. Downloaded on 9/9/2025 10:40:02 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinemaintained when Ni-OEPPc was heat-treated aer it was loadedon carbon support (Fig. S22c and Table S2). The porosity of Ni-OEPPc/C and Ni-OEPPc/C_700 was investigated using nitrogenadsorption measurements at 77 K. The results revealed thatboth Ni-OEPPc/C and Ni-OEPPc/C_700 exhibited adsorption–desorption isotherms and pore size distributions using NLDFTsimilar to those of the carbon support (Fig. 4b and S31). Thisindicates that the pore structure derived from the carbonsupport was preserved. Fig. 4c and S32 show the representativeTEM images of Ni-OEPPc/C_700, and Fig. 4d–h presents theHAADF-STEM image and the corresponding elemental mapsobtained by EDX analysis. The elemental maps indicate that Nand Ni atoms are uniformly distributed on carbon. Consideringthe results of the XAFS measurements, this suggests that in Ni-OEPPc/C_700, the Ni–N4 structure is dispersed on carbon.To investigate the CO2RR activity of Ni-OEPPc/C_700, cyclicvoltammetry (CV) measurements were conducted using a CO2-saturated KHCO3 solution and an Ar-saturated phosphatebuffer solution. The increase in current under CO2 conditionsconrmed that Ni-OEPPc/C_700 functions as a CO2RR catalyst(Fig. S33). To further analyze the CO2 reduction productsFig. 5 (a) FECO and FEH2 forNi-OEPPc/C_700 at current densities of 10, 5OEPPc/C_700 for 4 h at 50 mA cm−2.This journal is © The Royal Society of Chemistry 2025generated by Ni-OEPPc/C_700, electrolysis was performedunder static conditions for 30 min using a gas diffusion elec-trode (GDE) loaded with Ni-OEPPc/C_700. The gaseous CO2reduction products were then quantitatively analysed by gaschromatography. The dependence of FEH2 and FECO on currentdensity is presented in Fig. 5a. At 10 mA cm−2, Ni-OEPPc/C_700exhibited FECO of 84% at −0.56 V vs. reversible hydrogen elec-trode (RHE), demonstrating high activity for CO production.The reaction mechanism for CO2 reduction is considered to besimilar to that reported for SACs with M–N4 coordinationstructures in previous studies21,94–96 (Fig. S34). Furthermore, itmaintained a FECO value of above 90% up to a current density of150 mA cm−2 with TOF of 2.6 s−1 (9360 h−1), which is relativelyhigh or comparable to those of reported Ni-SACs (Tables S4–S6).A comparison of catalytic performance at 150 mA cm−2 amongNi-OEPPc/C_700, Ni-Pc/C_700, and Ni-OEPPc/C demonstratedthat Ni-OEPPc/C_700 exhibited the lowest overpotential and thehighest FECO. These results indicate that both carbonizationand the stabilization of the coordination structure enabled bythe introduction of the ethynyl groups contribute to theenhancement of the catalytic performance (Fig. S35). In addi-tion, measurements of the electrochemical surface area (ECSA)revealed a decrease in ECSA for Ni-OEPPc/C_700 compared toNi-OEPPc/C. Nevertheless, Ni-OEPPc/C_700 exhibited higherspecic activity at both 10 mA cm−2 and 150 mA cm−2. Theseresults further support that the enhanced performance of Ni-OEPPc/C_700 is not attributed to an increase in ECSA, butrather to other factors, such as carbonization and the stabili-zation of the Ni–N4 coordination structure induced by thermaltreatment (Fig. S36 and Table S7). Furthermore, the FECO of Ni-OEPPc_700 and Ni-OEPPc_700/C (Ni-OEPPc was calcined at700 °C, and then deposited on the carbon substrate) weremerely 10% and 23% at 10 mA cm−2 (Table S8), underscoringthe importance of the deposition of Ni-OEPPc_700 on thecarbon support before calcination for enhancing the accessi-bility of the active metal sites. To quantify liquid products otherthan the main products (CO and H2), the electrolyte aer thereaction was analyzed using NMR spectroscopy. The results0, 100, 150, and 200mA cm−2. (b) Long-term test curves and FE of Ni-J. Mater. Chem. A, 2025, 13, 28887–28895 | 28891http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d5ta02720aJournal of Materials Chemistry A CommunicationOpen Access Article. Published on 26 August 2025. Downloaded on 9/9/2025 10:40:02 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinerevealed the presence of a very small amount of formic acid(approx. 0.1% at 10–150 mA cm−2) (Table S9). Finally, thedurability of Ni-OEPPc/C_700 was analyzed under a constantcurrent of 50 mA cm−2 (Fig. 5b and Table S10). Gas productswere characterized every 30 min by gas chromatography, andthe change in FECO was negligible for 4 h. In addition, XAFSmeasurements for Ni-OEPPc/C_700 suggested that the valenceand coordination structure of the nickel center remainedunchanged before and aer the CO2 electrolysis (Fig. S37).Furthermore, the morphology of Ni-OEPPc/C_700 waspreserved before and aer the CO2RR operation (Fig. S38 andS39). These ndings demonstrate that Ni-OEPPc/C_700 retainsits coordination structure under high current densities andprolonged electrolysis, thereby enabling sustained and efficientCO2-to-CO conversion. To further evaluate the durability, long-term electrolysis was performed using a GDE with enhancedhydrophobicity achieved through PTFE treatment, as reportedin a previous study,97 with the electrolyte replaced every 2.5 h. Asa result, Ni-OEPPc/C_700 exhibited stable CO production at 50mA cm−2 even aer 10 h of operation (Fig. S40 and S41).ConclusionIn this study, we aimed to develop carbon materials with well-dened chemical structures by exploring a novel approach tomodifying the structure of carbon materials using moleculeswith thermally polymerizable groups and attempted to intro-duce the metal phthalocyanine structure into carbon materials.First, an analysis of the thermal properties ofNi-OEPPc revealedthat polymerization proceeded at approximately 210–215 °C,and the chemical structure was retained even aer thermaltreatment at 700 °C. The preservation of the coordinationstructure was attributed to the strong Ni–N4 coordinationenvironment and the thermal polymerization induced by theethynyl groups. Subsequently, Ni-OEPPc was supported on thecarbon support and subjected to thermal treatment at 700 °C tomodify the carbon material. The resulting Ni-OEPPc/C_700successfully maintained both the Ni–N4 coordination structureand the pore structure derived from the carbon support. Resultsof XAFS analysis and Electron microscopy observations sug-gested that the Ni–N4 coordination structure was uniformlydistributed on the carbon support, indicating the successfulsynthesis of an MNC with a well-dened chemical structure.Furthermore, Ni-OEPPc/C_700 exhibited high performance asa CO2RR electrode catalyst, demonstrating efficient COproduction at a high current density of 150 mA cm−2, high-lighting its excellent potential as a SAC. Although introducingthermally polymerizable groups into precursor molecules is notalways facile, this method can be applied to other precursormolecules as well, enabling the modication of carbon mate-rials with diverse coordination structures by selecting appro-priate precursors. Additionally, by choosing suitable supportmaterials based on the desired properties, it becomes possibleto synthesize carbon materials that simultaneously achievespecic chemical structures and pore morphologies. Thus, thisstudy is expected to contribute to the further advancement ofMNCs development.28892 | J. Mater. Chem. A, 2025, 13, 28887–28895Author contributionsYuki Sano: conceptualization, data curation, investigation,formal analysis, writing original manuscripts, review, andediting. Daichi Nakajima: investigation. Biplab Manna: inves-tigation, formal analysis. Koki Chida: investigation. RyojunToyoda: funding acquisition, methodology, resource, writingoriginal manuscripts, review, and editing. Shinya Takaishi:methodology, resource. Kazuyuki Iwase: formal analysis, fund-ing acquisition, investigation, methodology, resource, writingreview, and editing. Koji Harano: formal analysis, fundingacquisition, investigation, resource, writing review, and editing.Yuta Nishina: formal analysis, funding acquisition, investiga-tion, resource, writing review, and editing. Takeharu Yoshii:investigation, funding acquisition. Ryota Sakamoto: conceptu-alization, formal analysis, funding acquisition, methodology,project administration, resource, supervision, writing originalmanuscripts, review, and editing.Conflicts of interestThere are no conicts to declare.Data availabilityThe data supporting this article have been included as part ofthe SI.Experimental details; Synthetic scheme of Ni-OEPPc; Char-acterization data for the small molecules; IR and solid-state 13CNMR spectra for Ni-OEPPc and Ni-OEPPc_250; TG-DSC for Ni-OEPPc up to 1600 °C; XRD for Ni-OEPPc, Ni-OEPPc_700, Ni-OEPPc_1600; TG-DSC-MS for Ni-OEPPc; Raman and IR spectra,XPS of Ni-OEPPc before and aer calcination; EXAFS ttingcurves of Ni foil, Ni-OEPPc_700, Ni-OEPPc/C_700; Pore sizedistributions using NLDFT method for Ni-OEPPc_700; Photo-graph and particle size distribution for Ni-OEPPc suspension;Bright-eld TEM image of Ni-OEPPc; HAADF-STEM image andEDX mapping for of Ni-OEPPc/C; XPS of Ni-OEPPc, Ni-OEPPc/C,and Ni-OEPPc/C_700; EXAFS for Ni-OEPPc/C_700, Ni-OEPPc/C,Ni-Pc/C_700, and Ni-Pc/C; XANES and EXAFS for Ni-OEPPc, Ni-OEPPc/C, Ni-OEPPc/C_700, Ni-Pc, Ni foil, and NiO; Pore sizedistributions for Ni-OEPPc/C, Ni-OEPPc/C_700, and the carbonsupport; TEM images of Ni-OEPPc/C_700; Cyclic voltammo-grams of Ni-OEPPc/C_700 in CO2 saturated 1 M KHCO3;Proposed reaction pathway of CO2 reduction to CO on Ni SAC;FE and potential betweenNi-OEPPc/C_700,Ni-OEPPc/C, andNi-Pc/C_700; Cyclic voltammograms of Ni-OEPPc/C_700 and Ni-OEPPc/C; XANES and EXAFS spectra of Ni-OEPPc/C_700 aerelectrolysis; SEM images of Ni-OEPPc/C_700 aer electrolysis;Further long-term measurement of Ni-OEPPc/C_700; Electricalconductivity; EXAFS tting parameters; Actual measured valuesof electrolysis; Summary of reported Ni-SAC; Faraday efficiencyfor Ni-OEPPc_700 and Ni-OEPPc_700/C; ECSA and specicactivity of Ni-OEPPc/C_700 and Ni-OEPPc/C; Faraday efficiencyof formic acid for Ni-OEPPc/C_700. See DOI: https://doi.org/10.1039/d5ta02720a.This journal is © The Royal Society of Chemistry 2025https://doi.org/10.1039/d5ta02720ahttps://doi.org/10.1039/d5ta02720ahttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d5ta02720aCommunication Journal of Materials Chemistry AOpen Access Article. Published on 26 August 2025. Downloaded on 9/9/2025 10:40:02 PM.  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineAcknowledgementsThe present work was supported chiey by JST-CREST(JPMJCR24S6 to Y. N., T. Y., and R. S.). This work was partiallysupported by JST-FOREST (JPMJFR203F to R. S.) and JST-PRESTO (JPMJPR2371 to K. I.; JPMJPR23QA to T. Y.;JPMJPR22Q5 to R. T.). JSPS KAKENHI (Grant No. JP25H01644,JP25H01999, JP24K01494, JP24H01690, JP23H04874) supportspartly the present work. The Asahi Glass Foundation supportspartly the resent work (to R. S.). 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A, 2025, 13, 28887–28895 | 28895http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d5ta02720a Thermally polymerizable phthalocyanine realizes a metaltnqh_x2013nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO2RR activity Thermally polymerizable phthalocyanine realizes a metaltnqh_x2013nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO2RR activity Thermally polymerizable phthalocyanine realizes a metaltnqh_x2013nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO2RR activity Thermally polymerizable phthalocyanine realizes a metaltnqh_x2013nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO2RR activity Thermally polymerizable phthalocyanine realizes a metaltnqh_x2013nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO2RR activity Thermally polymerizable phthalocyanine realizes a metaltnqh_x2013nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO2RR activity Thermally polymerizable phthalocyanine realizes a metaltnqh_x2013nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO2RR activity Thermally polymerizable phthalocyanine realizes a metaltnqh_x2013nitrogen-doped carbon material featuring a defined single-atom catalyst motif with CO2RR activity