# Fileset

[BCSJ-2024-0242_Author.pdf](https://mdr.nims.go.jp/filesets/4e45e502-0dac-40c0-83c4-6ae4fa408759/download)

## Creator

Nadiia Velychkivska, Anna Golunova, Viktoria Oleksa, Jiří Brus, Pragati A Shinde, Abin Sebastian, [Renzhi Ma](https://orcid.org/0000-0001-7126-2006), Katsuhiko Ariga, Yusuke Yamauchi, [Jonathan P Hill](https://orcid.org/0000-0002-4229-5842), [Jan Labuta](https://orcid.org/0000-0002-8329-0634), [Lok Kumar Shrestha](https://orcid.org/0000-0003-2680-6291)

## Rights

This is a pre-copyedited, author-produced version of an article accepted for publication in Bulletin of the Chemical Society of Japan following peer review. The version of record Nadiia Velychkivska, Anna Golunova, Viktoria Oleksa, Jiří Brus, Pragati A Shinde, Abin Sebastian, Renzhi Ma, Katsuhiko Ariga, Yusuke Yamauchi, Jonathan P Hill, Jan Labuta, Lok Kumar Shrestha, Nanoarchitectonics of hydrogel-derived ultrahigh surface area nanoporous carbon materials with enhanced supercapacitance performance, Bulletin of the Chemical Society of Japan, Volume 98, Issue 3, March 2025, uoaf011 is available online at: https://doi.org/10.1093/bulcsj/uoaf011.[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

## Other metadata

[Nanoarchitectonics of hydrogel-derived ultrahigh surface area nanoporous carbon materials with enhanced supercapacitance performance](https://mdr.nims.go.jp/datasets/057287a7-eca6-4a85-80e1-5bcb48002e7f)

## Fulltext

For Peer Review1 Nadiia Velychkivska,1,2,* Anna Golunova,2 Viktoria Oleksa,1,2 Jiří Brus,2 Pragati A. Shinde,1 Abin Sebastian,1 Renzhi Ma,1 Katsuhiko Ariga,1,3 Yusuke Yamauchi,4,5,6 Jonathan P. Hill,1,* Jan Labuta,1,* and Lok Kumar Shrestha1,7,* 1Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan2Institute of Macromolecular Chemistry, AS CR, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic3Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa277-8561, Chiba, Japan4Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Queensland 4072, Australia5Department of Materials Process Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Aichi 464-8603, Japan6Department of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, South Korea7Department of Materials Science, Institute of Pure and Applied Sciences, University of Tsukuba 1-1-1, Tennodai, Tsukuba 305-8573, Ibaraki,Japan*Corresponding author: Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. Email:SHRESTHA.Lokkumar@nims.go.jp1. Introduction 1 In the era of a climate-neutral society, sustainable 2 development pathways are in high demand to deliver 3 advanced large-scale energy storage and energy 4 conversion solutions.1 In this regard, supercapacitors 5 can provide an opportunity for enhancement of storage 6 Nanoarchitectonics of Hydrogel-derived Ultrahigh Surface Area Nanoporous Carbon Materials with Enhanced Supercapacitance Performance Abstract In the era of the decarbonization economy, supercapacitors offer a realistic solution to the energy storage problem due to their rapidly chargeable electrical double layers. Here we present the energy performance of ultrahigh surface area nanoporous carbon materials having abundant hierarchical micro/mesopores obtained by in situ potassium carbonate (K2CO3) activation of polyacrylamide (PAM) hydrogel. The resulting nanoporous carbon materials obtained by the carbonization of the hydrogel in the temperature range 600 to 900 °C possess high BET surface areas up to ca. 3038 m2 g-1 for the material prepared at 800 °C (PAM4-K800). Electron microscopy analyses revealed the formation of micro/mesoporous amorphous carbon structures. Surface composition and nitrogen and oxygen doping of the carbon matrix were verified by X-ray photoelectron spectroscopy (XPS). The electrochemical supercapacitance performance was tested using a three-electrode system in an aqueous electrolyte (1M H2SO4). The optimal sample (PAM4-K800) achieved the largest value of specific capacitance of 313.3 F g-1 at a current density of 1 A g-1, with excellent capacitance retention of 97.5% after 10,000 charge/discharge cycles. Furthermore, a symmetric supercapacitor device prepared using the optimum material delivered a high energy density of 12.3 Wh kg-1 at a high power density of 309.4 W kg-1 and an outstanding cycle life of 95.9% after 10,000 cycles. The outstanding electrochemical performance of PAM hydrogel-derived carbon materials makes them promising candidates for high-performance supercapacitor applications. Keywords: Polyacrylamide (PAM) hydrogel, hierarchically porous carbon, supercapacitor Graphical abstract Lok Kumar Shrestha Lok Kumar Shrestha received a Ph.D. Degree from Yokohama National University in 2008. He joined the National Institute for Materials Science (NIMS) as an ICYS-MANA researcher in 2010. Currently he is a Principal Researcher at the Research Centre for Materials Nanoarchitectonics (MANA), NIMS. He has also been appointed as Associate Professor at the University of Tsukuba. For Peer Review2 capacities due to their superior power density, rapid 1 charging, stable/long cycle life performances, and 2 almost instantaneous release of large quantities of 3 energy .2–4 Supercapacitors store charge by physical ion 4 adsorption/desorption processes at the 5 electrode/electrolyte interface (in the case of 6 electrochemical double-layer capacitors (EDLCs)), and 7 through non-diffusion limited, fast faradaic redox 8 reactions (in the case of pseudocapacitive materials).5–7 9 Supercapacitors are used extensively for storage 10 purposes in renewable applications such as solar and 11 wind energy generation, in electric vehicles, and for 12 management of building energy consumption.8–10 To 13 meet the rising requirement for effective energy 14 storage supercapacitors, the selection and design of 15 materials used as electrodes in these devices is critical. 16 Carbonaceous materials are commonly chosen as 17 supercapacitor electrode materials due to their 18 excellent cost-effectiveness, high surface areas with 19 hierarchically evolved micro/meso porosity, high 20 thermal stabilities and electrical conductivity, stable 21 charge-discharge cycling performances, and excellent 22 cyclic durabilities. They include activated carbons,11–14 23 from both natural and synthetic sources, carbon 24 aerogels and graphene,15–18 carbon foams,19,20 carbide-25 derived carbons,21,22 and carbon nanotubes.23,24 The 26 specific capacitance (Cs) value, together with energy 27 and power densities, strongly depends on the surface 28 area, pore-size distribution, and pore availability for the 29 electrolyte ions. Consequently, to enhance the 30 capacitive performance of the supercapacitor, materials 31 having high surface areas with suitable pore size 32 distributions, which would allow fast mass and ion 33 transport through the porous network, are required.  34 There are several methods to modify the texture and 35 surface of carbon materials using chemical, physical, or 36 hydrothermal carbonization methods.25 Chemical 37 activation, in contrast to the other methods, leads to 38 the formation of carbon materials with high or ultrahigh 39 surface areas and hierarchically layered porous 40 structures. In this process, chemical activators 41 including alkaline or alkali metal hydroxides and salts 42 KOH, K2CO3, NaOH, ZnCl2, KHCO3, and mixtures of 43 salts ZnCl2-KCl, K2CO3-Na2CO3, LiCl-KCl are commonly 44 used.25–29 K2CO3 is an attractive chemical activator due 45 to its low cost, low toxicity, and environmental 46 friendliness.30–32 In this case, a complex carbon 47 architecture is formed by the following mechanism. 48 When potassium carbonate reacts with the carbon 49 precursor under an inert atmosphere, the following 50 reactions occur (Equations 1-3): 51 K2CO3 + 2C → 2K + 3CO↑ (1) 52 K2CO3 → K2O + CO2↑ (2) 53 K2O + C → 2K + CO↑ (3) 54 After reduction of potassium carbonate. metallic 55 potassium intercalates and expands the carbon 56 network while gaseous carbon monoxide exfoliates the 57 carbon sheets, creating a porous carbon architecture 58 (Equation 1). Potassium oxide is obtained as an 59 intermediate (Equation 2), which is later also reduced to 60 potassium and carbon monoxide (Equation 3). The 61 residual potassium byproducts in the carbon structures 62 are then eliminated by thorough washing using water, 63 which further enhances the porosity. 64 Porous carbonaceous electrode materials for 65 supercapacitors can also be prepared using natural 66 carbon sources, such as biomass, wood, and coal.33–35 67 For instance, Zhao et al. prepared rodlike KOH-activated 68 - carbon material derived from tobacco, which exhibited 69 a specific capacitance of 286.6 F g-1 at  current density 70 0.5 A g-1 measured in 6M KOH electrolyte in a three-71 electrode setup.36 In other work, an acacia wood-based 72 electrode activated with KOH exhibitrd a specific 73 capacitance of 224.92 F g-1 at 0.5 A g-1 measured in 2M 74 KOH in a three-electrode system.37 However, the 75 composition of carbon materials from different natural 76 sources varies depending on the origin of the material, 77 making it difficult to reproduce specific capacitances of 78 the resulting electrodes.  79 In order to overcome this obstacle, synthetic carbon 80 materials can be used since they offer a high degree of 81 control over morphological properties, are easy to 82 prepare, and can be cost-effective. In this respect, 83 hydrogel-derived carbon materials appear to be 84 especially suitable candidates for energy storage 85 applications due to their tunable textural parameters.38 86 Of the available materials, polyacrylamide (PAM) 87 hydrogels are particularly interesting due to their 88 chemical structure consisting of (-CH2-CH-CO-NH2-) 89 units, which presents a source of self-doping by oxygen 90 and nitrogen functionalities in the 3D network.39–44 For 91 example, the hierarchically porous carbon electrode 92 prepared from the KOH-activated 93 resorcinol/formaldehyde-polyacrylamide 94 interpenetrating polymer network showed a high 95 specific surface area of 2544 m2 g-1 and specific 96 capacitance of 261 F g-1 at 1.0 A g-1 measured in 6M 97 KOH.45 Moreover, Gao et al. obtained carbon materials 98 from ZnCl2-activated PAM hydrogel (Free-PC) and 99 polypyrrole-PAM (PPC) hydrogels with surface areas of 100 1363 m2 g-1 and 1797 m2 g-1, respectively. In a three-101 electrode system, these self-oxygen/nitrogen-doped 102 carbon materials exhibited high specific capacitance 103 values of 262 F g-1 and 398 F g-1 at a current density of 104 0.5 A g-1 for Free-PC and PPC, respectively.46 The 105 presence of N,O dopants contributes favorably to the 106 electrode surface wettability and induces 107 pseudocapacitance that leads to high specific 108 capacitance. Similarly, carbon materials prepared from 109 MgAl-layered double hydroxides and polyacrylamide 110 showed promising electrochemical performance values 111 (356 F g-1 at 0.5 A g-1) and a good durabilities.47 Since 112 PAM-hydrogel carbons are still emerging electrode 113 materials for supercapacitor applications, there remains 114 a gap in the knowledge of their textural and 115 electrochemical properties. 116 For Peer Review3 In this work, we present the preparation, 1 characterization, and electrochemical performance of 2 intrinsically N,O doped polyacrylamide hydrogel-derived 3 carbon materials with ultra-high surface areas, and well-4 developed micro and meso pores for supercapacitor 5 applications. The hydrogels were prepared from 6 acrylamide and N,N-methylenebisacrylamide (MBA), 7 then freeze-dried and annealed at high temperatures 8 (600–900 °C). Hierarchical micro and mesoporous 9 architectures of the carbon materials obtained were 10 adjusted by in situ introduction of a chemical activating 11 agent K2CO3 with a subsequent annealing process 12 (Scheme 1). Of the carbon materials obtained, the 13 sample annealed at 800 °C (PAM4-K800) showed the 14 highest BET surface area of 3038.4 m2 g-1 with the 15 largest pore volume of 1.852 cm3 g-1. The presence of 16 nitrogen and oxygen functionalities on the synthesized 17 carbon surfaces was confirmed by XPS analysis. 18 According to the physicochemical characterization, 19 three-electrode electrochemical measurements 20 revealed otstanding performances of the carbon 21 materials as supercapacitor electrode materials. Of the 22 materials, PAM4-K800 demonstrated a superior specific 23 capacitance of 313.3 F g-1 at a current density of 1 A g-1 24 in an aqueous 1M H2SO4electrolyte. The electrode 25 material is stable even after 10000 cycles with a cycling 26 performance of 97.5%. Based on the electrochemical 27 data, polyacrylamide hydrogel-derived hierarchically 28 porous carbon materials have strong potential in high-29 performance supercapacitor applications. 30  31 2. Experimental 32 2.1 Materials 33 Acrylamide (AM), sodium sulfite (Na2SO3), and 34 potassium persulfate (K2S2O8) were purchased from 35 Wako Pure Chemical Industries, Tokyo, Japan. N,N′-36 methylenebisacrylamide (MBA) was purchased from 37 TCI, Tokyo, Japan. Potassium carbonate (K2CO3) was 38 purchased from Nacalai Tesque, Kyoto, Japan. 39 Deionized (DI) water (H2O) was obtained using a Direct 40 Q 3UV water purification system, Merck Millipore, 41 Darmstadt, Germany; Resistivity ≥ 18 MΩ cm at 25 °C). 42 The hydrogels were prepared in DI water, and the 43 resulting carbon materials were also washed using DI 44 water. 45  46 2.2 Preparation of porous carbon materials from PAM 47 hydrogels 48 PAM hydrogels were synthesized as described in our 49 previous research.48 Briefly, AM (360 mg), MBA (40 mg), 50 and K2CO3 (500 mg) were loaded into a 30 mL glass vial 51 and dissolved in DI water (8 g). Then, the mixture was 52 degassed, and 1 mL of Na2SO3 (10 mg) and 1 mL of 53 K2S2O8 (20 mg) were injected into the deoxygenated 54 reaction mixture to initiate the free radical 55 (co)polymerization reaction. After gelation was 56 complete, the hydrogels were freeze-dried, annealed at 57 various temperatures, and thoroughly washed with DI 58 water. The samples are referred to according to their 59 compositions as follows: PAM4-KX, where subscript 60 index 4 is the concentration of PAM hydrogel (4 wt%), 61 X is the annealing temperature (600, 700, 800, 900 °C), 62 and K indicates the presence of the chemical activation 63 agent (K2CO3). 64  65 2.3 Materials characterization 66 PAM hydrogel-derived carbon materials were studied 67 by thermogravimetric analysis (TGA) using STA 2500 68 (Regulus, Netzsch, Wittelsbacherstraße, SELB, 69 Germany) under an inert atmosphere of nitrogen at a 70 heating rate of 10 °C per minute. Raman scattering 71 spectroscopy at a neon laser excitation wavelength of 72 532.09 nm (NRS-3100, JASCO, Tokyo, Japan) was 73 applied to characterize graphitic and disordered states 74 of PAM hydrogel-derived carbons. The amorphous 75 structure of PAM hydrogel-derived carbons was 76 confirmed by powder X-ray diffraction (XRD) (Rigaku X-77 ray diffractometer, RINT, Tokyo, Japan) with the 78 following measurement conditions: the scan range of 79 2θ = 15 – 50°; V = 40 kV; I = 40 mA; Cu-Kα radiation 80 source; 25 °C. X-ray photoelectron spectroscopy (XPS) 81 (Quantera SXM instrument, ULVAC-PHI, Chanhassen, 82 Scheme 1. Schematic representation of the synthetic route for PAM hydrogel-derived carbon materials For Peer Review4 MN, USA) was used to study the surface composition 1 of PAM hydrogel-derived carbon materials. Fourier-2 transform infrared (FTIR) spectroscopy NICOLET iS20 3 (Thermo-Fisher Scientific, Waltham, MA, USA) proved 4 the presence of nitrogen and oxygen-containing 5 functional groups in PAM hydrogel and corresponding 6 carbon samples. Scanning electron microscopy (SEM) 7 (S-4800, Hitachi Co., Ltd., Japan, V = 10 kV) and 8 transmission electron microscopy (TEM) (JEM2100F 9 instrument, JEOL, Tokyo, Japan, V = 200 kV) were 10 used for examination of the surface morphologies of 11 PAM hydrogel-derived carbon materials. To reduce 12 charging effects during SEM imaging, the samples 13 were coated with platinum (∼2 nm) using a Hitachi S-14 2030 ion coater. Brunauer−Emmett−Teller (BET) 15 specific surface area and porosity method was used to 16 study the textural properties of PAM hydrogel-derived 17 carbons. N2 adsorption/desorption measurements 18 were made under high vacuum at 77 K using 19 (Quantachrome Autosorb-iQ2 instrument, Boynton 20 Beach, FL, USA). Before the BET measurements, 21 carbon samples were degassed under low pressure at 22 120 °C for 24 h. The density functional theory (DFT) and 23 Barrett−Joyner−Halenda (BJH) methods were used to 24 calculate the pore dimensions and pore volumes of the 25 studied carbon samples. 26  27 2.4 Electrochemical measurements 28 The electrochemical performance was evaluated using 29 galvanostatic charge−discharge (GCD), cyclic 30 voltammetry (CV), and electrochemical impedance 31 spectroscopy (EIS) measurements. GCD, CV, and EIS 32 measurements were executed in a three-electrode 33 setup in 1M H2SO4 electrolyte at 25 °C using an ALS 34 CHI 660E workstation (CH Instruments, Inc. Austin, TX, 35 USA). The working electrode was coated with the 36 electrode material (1 cm × 1 cm) on graphite paper 37 which had previously been etched in ethanol. Electrode 38 material was prepared by grinding a mixture of active 39 PAM hydrogel-derived carbon material, carbon black, 40 and polyvinylidene fluoride (mass fraction: 80%: 10%: 41 10%) in N-methyl-2-pyrrolidone (NMP). The 42 homogenous slurry was applied onto the electrode, 43 which was then dried in air overnight at 80 °C. The 44 mass of the active material on the prepared electrodes 45 was 2.0-2.5 mg. A platinum wire was used as a counter-46 electrode, and Ag/AgCl was used as a reference 47 electrode. EIS measurements were performed at open 48 circuit potential conditions in the frequency range of 49 0.01 Hz−100 kHz at an amplitude of 5 mV. GCD data 50 were used for the estimation of specific capacitance 51 values (Cs, F g-1) using Equation 4: 52 𝐶𝑠 =𝐼 ∙ 𝑡𝑑𝑚 ∙ ∆𝑉   (4) 53 where I is the discharge current (in A), td is the 54 discharge time (in s), m is the active mass of the carbon 55 material loaded on the working electrode (in g), and ∆V 56 is the potential window (1.1 V). 57 The charge storage behavior of PAM4-K800 was 58 precisely evaluated by the power law using the 59 following Equation 5: 60 𝑖 = 𝑎𝑣𝑏    (5) 61 where i (A g-1) is the sum of surface-controlled 62 (capacitive) and diffusion-controlled current 63 contributions, v is the applied scan rate (mV s-1) a and b 64 are variable parameters. If the b value is ~1, then a 65 surface-controlled charge storage mechanism 66 dominates. If the b value is ~0.5, then a diffusion-67 controlled energy storage process prevails.Surface-68 controlled and diffusion-controlled contributions can be 69 obtained quantitatively from Equation 6: 70 𝑖(𝑉) = 𝑘1𝑣 + 𝑘2𝑣1/2  (6)71 where i, v, k1, and k2 indicate the current, scan rate, and 72 two constant parameters, respectively. 73 A symmetric supercapacitor cell was assembled with a 74 similar mass loading of 1.2 mg using 1 M H2SO4 75 electrolyte. Galvanostatic charge−discharge tests 76 (current density of 0.5−20 Ag−1) and cyclic voltammetry 77 measurements (scanning rate of 5−100 mV s−1) were 78 conducted using a BioLogic station VSP-3e (Grenoble, 79 France). 80 The energy density and power density of the 81 symmetric supercapacitor device were calculated using 82 the following Equations 7 and 8 83 𝐸 =0.5 ∙𝐶𝑠(∆𝑉2)3.6(7) 84 𝑃 =3600∙𝐸𝑡𝑑(8) 85 where E is energy density (Wh kg-1) and P is power 86 density (W kg-1). 87  88 3. Results and discussion 89 Thermogravimetric analysis (TGA) was used to study 90 the thermal stability of synthesized K2CO3-activated 91 PAM hydrogel (Figure 1a). Below 200 °C, material 92 weight loss occurs due to the evaporation of residual 93 moisture from the hydrogel structure. Between 200 °C 94 For Peer Review5 and 500 °C, the collapse of the hydrogel network takes 1 place, which is associated with the formation of imides 2 and further random decomposition accompanied by the 3 release of volatile gases, including ammonia, carbon 4 dioxide, and water.49 Above 500 °C, the carbon material 5 is fully developed, so that the following carbonization 6 temperatures were selected for further examination: 7 600 °C, 700 °C, 800 °C, and 900 °C. K2CO3-activated 8 PAM hydrogel was further characterized by using FTIR 9 spectroscopy (Figure 1b). The FTIR spectrum contains 10 the following bands due to PAM at 3336 cm-1, 2964 cm-11 1, 1657 cm-1, 1442 cm-1, which are N-H, C-H, C=O 12 (carbonyl), and C-N stretching vibrations, 13 respectively.50,51 Moreover, FTIR analysis reveals that 14 the higher the carbonization temperature, the lower the 15 content of oxygen-containing (band at 1657 cm-1) and 16 nitrogen-containing (band at 1442 cm-1) functional 17 groups in the carbon structure (Figure S1).  18  19 To estimate the surface area of the PAM hydrogel-20 derived carbon materials, N2 adsorption/desorption 21 experiments were carried out, the results of which are 22 shown in Figure 2a. PAM4-800, which is a reference 23 sample directly carbonized at 800 °C but not activated 24 using potassium carbonate (Figure 2a, black curve), 25 shows a Type III isotherm with BET surface area of only 26 245,3 m2 g-1.52 The presence of K2CO3 as an activation 27 agent has an significant effect on the textural properties 28 Figure 1. (a) TGA. Red arrows on the TGA graph show the carbonization temperatures used. (b) FTIR spectrum of K2CO3-activated PAM hydrogel. 200 400 600 800 10000204060801004000 3500 3000 2500 2000 1500 1000Weight (%)Temperature (°C)Wavenumber (cm-1)1657333614422964Intensity (a.u)a)b)135811148477041060Figure 2. Textural properties obtained by nitrogen sorption measurements. (a) Nitrogen adsorption/desorption isotherms at 77 K of PAM4-800, PAM4-K600, PAM4-K700, PAM4-K800, PAM4-K900 samples; (b) pore-size-distribution profiles from the density functional theory (DFT) method; and (c) pore-size-distribution profiles obtained from the Barrett–Joyner–Halenda (BJH) model. 0.0 0.2 0.4 0.6 0.8 1.0020040060080010004 6 8 10 12 14 16 18 200.5 1.0 1.5 2.0Volume @ STP (cc/g)P/P0PAM4-800PAM4-K600PAM4-K700PAM4-K900PAM4-K800a) b) c)dV(r) (cc/nm/g)Pore diameter (nm)PAM4-K900PAM4-K800PAM4-K700PAM4-K600PAM4-800Half pore width (nm)dV(r) (cc/nm/g)PAM4-K700PAM4-K800PAM4-K900PAM4-K600PAM4-800For Peer Review6 of the carbon materials obtained substantially 1 increasing their surface areas. The mechanism of 2 K2CO3 activation has already been discussed.48 In the 3 case of K2CO3-activated PAM hydrogel-derived carbons, 4 a temperature increase from 600 to 800 °C leads to an 5 increase in the formation of high surface area 6 microporous carbons. PAM4-K600, PAM4-K700, and 7 PAM4-K800 show typical Type I isotherms with high 8 nitrogen uptake in the low relative pressure region (P/P0 9 < 0.1), which confirms the presence of a significant 10 quantity of micropores (Figure 2a).  11  12 Carbonization at 900 °C (PAM4-K900) stimulates 13 coalescence of the micropores with further 14 arrangement as mesopores. The characteristic 15 mesoporous capillary condensation behavior is 16 represented by mixed Type I/Type IV isotherms with a 17 hysteresis loop in the middle of the relative pressure 18 region (0.4< P/P0 < 0.6). DFT (Figure 2b) and BJH 19 (Figure 2c) models provide information about pore-size-20 distribution profiles of the carbon materials obtained 21 and further confirmed their hierarchical 22 micro/mesoporous nature. The well-developed 23 micro/mesoporosity of carbon materials is a 24 predominant factor in effective electrolyte diffusion 25 onto the surface of a supercapacitor electrode.  26 The textural properties of PAM hierarchically 27 interconnected micro-mesoporous carbon materials are 28 shown in Table 1 and indicate the evident dependency 29 of structural parameters on carbonization temperature, 30 i.e. higher temperature induces an increase in specific 31 surface area. However, at 900 °C, the formation of 32 mesopores due to the coalescence of micropores 33 commences, resulting in a decrease in microporous 34 surface area. As a result, the optimal sample among 35 these carbon materials is PAM4-K800 (BET surface 36 area: 3038.4 m2 g-1, pore volume: 1.852 cm3 g-1), with 37 the highest degree of microporosity and sufficient total 38 pore volume suggesting excellent energy storage 39 capabilities for this material. 40 In order to gain insight into the inner structure of carbon 41 materials the morphology was studied. Figure 3 shows 42 electron micrographs (SEM: Figure 3a,b; TEM: Figure 43 3c,d) of the K2CO3-activated sample with the optimal 44 surface textural properties, PAM4-K800. Additional 45 SEM images (Figure S2) and TEM images (Figure S3) 46 are supplied in the Supplementary Information. At the 47 macroscale, the sample morphology of the carbonized 48 sample has a honeycomb-like irregular structure (Figure 49 3a). High-resolution SEM (Figure 3b and Figure S2) and 50 TEM images (Figure 3c,d and Figure S3) show well-51 developed micro/mesoporous amorphous carbon 52 structures due to K2CO3 activation. Directly carbonized 53 reference sample, PAM4-800 does not exhibit porous 54 surface structure (Figure S4). However, K2CO3-55 activated carbon materaisl obtained at different 56 carbonization temperatures shows similar hierarchical 57 micro/mesopores architectures to that of the optimal 58 sample, well-defined pore size distribution, large pore 59 volume, and high specific surface area (Figure S5: SEM 60 images of PAM4-K600, Figure S6: SEM images of 61 PAM4-K700, Figure S7: SEM images of PAM4-K900, 62 Figure 3. (a) Electron microscopy observations of PAM4-K800 carbon material. (a, b) SEM images; (c) TEM image; and (d) HR-TEM image. Table 1. Textural properties of PAM hydrogel-derived carbon materials1. Sample SBET (m2 g−1) Smicro (m2 g−1) Smeso (m2 g−1) Vp (cm3 g−1) Vmicro (cm3 g−1) Vmeso (cm3 g−1) Wp (nm) Dp (nm) PAM4-800 245.3 212.8 142.4 0.435 0.242 0.193 2.594 3.90 PAM4-K600 1014.1 1122.9 93.3 0.640 0.501 0.139 0.287 3.10 PAM4-K700 2526.9 2511.0 143.3 1.362 1.162 0.200 0.273 2.97 PAM4-K800 3038.4 2669.9 209.1 1.852 1.567 0.278 0.610 3.12 PAM4-K900 2567.8 2326.2 342.7 1.898 1.487 0.411 0.610 3.31 1SBET = BET surface area, Smicro = micropore surface area, Smeso = mesopore surface area, Vp = total pore volume, Vmicro = pore volume from micropores, Vmeso = pore volume from mesopores, Wp = average half pore width, Dp = average mesopore diameter. theory (DFT) method; and (c) pore-size-distribution profiles obtained from the Barrett–Joyner–Halenda (BJH) model.For Peer Review7 and Figure S8: TEM and HR-TEM images of PAM4-1 K900,). 2 3 To support the SEM observations, XRD analysis was 4 performed. X-ray diffraction patterns of PAM4-800, 5 PAM4-K600, PAM4-K700, PAM4-K800, and PAM4-K900 6 samples are shown in Figure 4a. Two broad diffraction 7 peaks located at around 2θ = ~24° and ~43.5° are 8 related to the disordered structure of the amorphous 9 carbon from (002) and (100) planes, respectively.53 10 Activation with K2CO3 promotes abundant pores and 11 defect site formation in the carbon lattice, which is 12 further confirmed by the highly attenuated (002) peak. 13 These carbon materials have many defects in their 14 amorphous structure, low crystallinity, and good 15 electric conductivity, which is important for 16 supercapacitor applications. Raman spectroscopy 17 measurements were performed to gain more 18 information about the structural defects of the carbon 19 materials.54 Raman spectra show two bands located at 20 around ~1350 and ~1600 cm-1, which were 21 deconvoluted using five Lorentzian line shapes for the 22 D1 (~1360 cm-1), D2 (~1620 cm-1), D3 (~1520 cm-1), D4 23 (~1270 cm-1), and G (~1590 cm-1) bands (Figure 4b).36,55 24 The G band corresponds to the graphite-type lattice 25 vibrations. D1 band is assigned to graphene layer edges, 26 the D2 band is due to  vibrations at the surfaces of 27 graphitic layers, the D3 band is characteristic of 28 amorphous carbon and N,O-doped carbon, and the D4 29 band vibration is related to polyenes and ionic 30 impurities, for example, potassium from potassium 31 carbonate. The ratio of peak intensities of G and D 32 bands (ID1/IG) is called the degree of graphitization (e.g., 33 crystallinity) and can be used to evaluate the presence 34 of defects in the carbon structure. While carbonation 35 temperature increases ID1/IG ratio decreases suggesting 36 the decrease of significant structural defects or 37 enhancement in the degree of graphitization (Figure 4b). 38  39 Figure 4. (a) XRD patterns and (b) Deconvoluted Raman spectra of PAM4-800, PAM4-K600, PAM4-K700, PAM4-K800, PAM4-K900 samples.  15 20 25 30 35 40 45 50 1000 1200 1400 1600 1800 20002q (degree) (002) PAM4-K900(100)PAM4-K800PAM4-K700PAM4-K600PAM4-800b)Raman shift (cm-1)ID1/IG = 3.44a)Intensity (a.u)Intensity (a.u)PAM4-K900PAM4-K800PAM4-K700PAM4-K600PAM4-800ID1/IG = 3.73ID1/IG = 4.44ID1/IG = 5.18ID1/IG = 3.69D4D1D3GD2Figure 5. XPS spectra of PAM-hydrogel-derived carbons. (a) XPS survey spectra of PAM4-800, PAM4-K600, PAM4-K700, PAM4-K800, PAM4-K900; (b) XPS C 1s core level spectra with the deconvoluted peaks; (c) XPS N 1s core level spectra with the deconvoluted peaks; (d) XPS O 1s core level spectra with the deconvoluted peaks. 800 600 400 200 0 294 292 290 288 286 284 282 408 406 404 402 400 398 396 394 536 534 532 530 528Binding energy (eV)O 1sN 1sC 1sC = 85.83 %N = 2.83 % O = 11.35 %C = 90.67 %N = 1.56 % O = 7.77 %C = 83.91 %N = 4.14 % O = 11.95 %C = 79.48 %N = 8.89 % O = 11.63 %PAM4-800PAM4-K600PAM4-K700PAM4-K800PAM4-K900Intensity (a.u)C = 84.28 %N = 8.21 % O = 7.53 %Binding energy (eV)284.5285.4290.0 Intensity (a.u)PAM4-K700PAM4-K600PAM4-800PAM4-K800PAM4-K900 C 1sBinding energy (eV)a) b) c) d) Intensity (a.u)PAM4-K700PAM4-K600PAM4-800PAM4-K800PAM4-K900 N1 s398.0400.0402.5Binding energy (eV)Intensity (a.u)532.7530.9534.5PAM4-800PAM4-K600PAM4-K700PAM4-K800PAM4-K900 O 1sFor Peer Review8 The XPS technique was applied to study surface 1 composition and functional groups present in the PAM-2 hydrogel-derived carbon materials (Figure 5). The 3 survey XPS spectra show C 1s, N 1s, and O 1s 4 components  with peaks at about ~284, 400, and 532 5 eV, respectively (Figure 5a). The intensity of nitrogen 6 and oxygen peaks in XPS survey spectra decreases 7 with increasing carbonization temperature from 600 to 8 900 °C (Figure 5a), indicating lower contents of 9 hydrophilic N and O functionalities in the carbon 10 framework. Deconvolution of the C 1s spectra reveals 11 three peaks with centers at ~284.5, 285.4, and 290.0 12 eV attributed to C=C (sp2), C–C/C–N (sp3), and O-C=O 13 bonding states, respectively (Figure 5b). Deconvolution 14 of N 1s spectra indicates the presence of three types 15 of nitrogen at the surfaces of the samples (Figure 5c). 16 The signal at ~398.0 eV belongs to the pyridinic 17 nitrogen (N-6), that at ~400.0 eV is attributed to the 18 pyrrolic nitrogen (N-5), and the peak at ~402.5 eV is 19 assigned to N-oxide (N-X).56 O 1s spectra deconvolution 20 reveals the presence of three peaks at around ~530.9 21 eV, 532.7 eV, and 534.5 eV, which are attributed to 22 carbonyl (C=O), ester (C–O–C), and carboxylic 23 (O−C=O) groups, respectively, with C=O and C–O–C 24 groups being the most abundant (Figure 5d). Carbonyl 25 and ester groups enrich electrode capacitance through 26 reversible redox reactions, whereas carboxylic groups 27 promote charge transfer resistance, decreasing the 28 electrode's electrochemical performance.57 The 29 presence of nitrogen and oxygen functionalities is 30 favorable for fast electron transfer, but also improves 31 the wettability of the hydrophobic carbon 32 nanoarchitecture promoting redox reactions, which 33 effectively contributes to the energy storage capacity. 34 Since the textural properties, morphology, and surface 35 composition of these carbon materials are favorable, 36 we decided to study their electrochemical 37 supercapacitance properties by using CV, GCD, and EIS 38 measurements for the three-electrode setup in an 39 aqueous electrolyte (1M H2SO4). CV curves of PAM4-40 800, PAM4-K700, PAM4-K800, and PAM4-K900 samples 41 at a scan rate of 5 mV s-1 and a potential window of -42 0.1−1V are shown in Figure 6a. The voltammograms 43 have quasi-rectangular shapes, which is characteristic 44 of an EDLC energy storage mechanism. Weak 45 oxidation and reduction peaks at ~0.5 V and ~0.4 V, 46 respectively, confirm the presence of nitrogen and 47 oxygen functionalities in the carbon structure. 48 Voltammograms for the PAM4-K800 sample at sweep-49 rates of 5, 10, 20, and 40 mV s-1 have quasi-rectangular 50 shape, and at higher potential sweep 60, 80, 100 mV s-51 1, a deviation from the quasi-rectangular shape and 52 abatement of redox peaks is observed. This behavior 53 could be related to limitations caused by the diffusion 54 Figure 6. (a) Comparison of the CV profiles of PAM carbon-derived materials at 5 mV s-1; (b) CV profile of PAM4-K800 at different scan rates (5−100 mV s-1); (c) GCD profiles of PAM4-800, PAM4-K700, PAM4-K800, PAM4-K900 measured at current density of 1 A g-1; (d) GCD profiles at different current densities (1 to 20 A g-1) for PAM4-K800; (e) calculated specific capacitance Cs vs. current density; (f) Nyquist plots for PAM4-800, PAM4-K700, PAM4-K800, PAM4-K900; (g) logarithm relationship of oxidation peak current versus scan rate; (h) Capacitive or Surface-controlled (Qs) and diffusion-controlled (Qd) current contribution of the PAM4-K800 electrode analyzed at various scan rates. -0.2 0.0 0.2 0.4 0.6 0.8 1.0-2.5-2.0-1.5-1.0-0.50.00.51.01.52.02.5-0.2 0.0 0.2 0.4 0.6 0.8 1.0-15-10-50510150 200 400 6000.00.20.40.60.81.00 200 400 6000.00.20.40.60.81.00 5 10 15 20501001502002503000 5 10 15 20 25051015202561%69% 75% 81%39%31% 25% 19%Current density (A g-1)Potential (V vs. Ag/AgCl)PAM4-K800PAM4-K900PAM4-K700PAM4-800@ 5 mV s-1Current density (A g-1)Potential (V vs. Ag/AgCl)PAM4-K800100 mV s-15Potential (V)Time (s)@1 A g-1PAM4-K800PAM4-K700PAM4-K900PAM4-800Potential (V)Time (s) 1 A g-1 2 A g-1 3 A g-1 4 A g-1 5 A g-1 6 A g-1 7 A g-1 8 A g-1 9 A g-1 10 A g-1 12 A g-1 14 A g-1 16 A g-1 18 A g-1 20 A g-1PAM4-K8001.0 A g-120Cs (F g-1) Current density (A g-1)PAM4-800PAM4-K700PAM4-K900PAM4-K800a) b) c) d)e) f) g) h)-Z² (ohm)Z¢ (ohm)PAM4-K800PAM4-K900PAM4-K700PAM4-8000.6 0.8 1.0 1.2 1.4 1.6 1.8 2.00.00.20.40.60.81.0Log (peak current) (A)Log (scan rate) (mV s-1)  Linear fit Oxidative peak currentb = 0.87R2 = 0.99972PAM4-K800 PAM4-K8005 10 20 40 60020406080100120Current contribution (%)Scan rate (mV s-1) Qd QsFor Peer Review9 process at the higher scan rates (Figure 6b). The GCD 1 profiles of PAM4-800 and K2CO3-activated PAM-2 hydrogel-derived carbons at the current density of 1 A 3 g-1 within the potential window of -0.1 to 1.0 V are 4 represented in Figure 6c. The GCD curves exhibit a 5 quasi-triangular shape, thus indicating that ion storage 6 occurs due to an EDLC mechanism. The GCD profile of 7 the PAM4-K800 sample exhibits the longest discharge 8 time, which coincides that sample having the largest 9 BET surface area. With increase of the current density 10 from 1 to 20 A g-1 the shape of GCD curves remains 11 quasi-triangular, manifesting efficient electrolyte ion 12 transfer to the surface of the PAM4-K800 electrode 13 (Figure 6d, Figure S9). Data obtained from GCD 14 measurements were used to calculate the specific 15 capacitance Cs values applying Equation 4 and are 16 shown in Figure 6e. PAM4-K800 has the highest 17 specific capacitance value of ~313.3 F g-1 at a current 18 density of 1 A g-1 with a capacitance retention of ~64% 19 at a high current density of 20 A g-1 (Figure S10). The 20 obtained value of the specific capacitance is higher than 21 the values of several other porous carbon materials 22 derived from various carbon sources (Table S1). The 23 data shows that 97.5% of the capacitance retention 24 measured at 15 A g-1 for the PAM4-K800 system is 25 retained after 10000 cycles (Figure S11). Specific 26 capacitances at a current density of 1 A g-1 for the other 27 materials are as follows: ~257.6 F g-1 (PAM4-K700), 28 ~260.4 F g-1 (PAM4-K900), ~97.3 F g-1 (PAM4-800). 29 Electrochemical kinetics characterization was then 30 performed for PAM4-K700, PAM4-K800, PAM4-K900, 31 and PAM4-800 materials using electrochemical 32 impedance spectroscopy (Figure 6f). The Nyquist plots 33 obtained consist of a semicircle in the high-frequency 34 region and a vertical line in the low-frequency region for 35 all samples. The values of the equivalent series 36 resistance (ESR), the first intersection point on the real 37 axis, for synthesized carbons, are as follows: 4.20 Ω 38 (PAM4-K700), 3.60 Ω (PAM4-K800), 1.52 Ω (PAM4-K900), 39 7.13 Ω (PAM4-800) indicating favorable electrical 40 conductivity. Additionally, the charge storage 41 mechanism for the PAM4-K800 sample was calculated 42 in terms of capacitance contributions from the electrical 43 double layer and the pseudocapacitance. As a result, 44 the diffusion-controlled (Qd) and surface-controlled (Qs) 45 or capacitive component current components were 46 evaluated. The value of b was evaluated using Equation 47 5 and is 0.87 (Figure 6g), referring to the predominance 48 of the surface-controlled or capacitive component over 49 the diffusion-controlled mechanism, which increases 50 with increasing scan rate (Equation 6, Figure 6h). 51 According to the electrochemical measurements, 52 K2CO3-activated PAM hydrogel-derived carbons, 53 especially PAM4-K800, show high specific capacitance 54 values, excellent capacitance retention at high current 55 density, and long cycle lives, rendering the materials as 56 promising supercapacitor electrodes. 57 A symmetric cell device was constructed using PAM4-58 K800 material. Its CV performance was tested in the 59 potential window of 1.1 V at different scan rates from 60 Figure 7. (a) CV profiles of PAM4-K800 supercapacitor device at different scan rates (5−100 mV s-1); (b) GCD curves at different current densities (0.5 to 20 A g-1) in the voltage window of 0−1.1 V; (c) calculated specific capacitance Cs vs. current density; (d) Nyquist plot for the device; (e) Cycle life and Coulombic efficiency at a current density of10 A g-1; (f) Ragone plot with energy density comparison with the literature. 0.0 0.2 0.4 0.6 0.8 1.0 1.2-30-20-1001020300 50 100 150 200 250 300 3500.00.20.40.60.81.00 5 10 15 200102030405060700 5 10 15 2005101520101 102 103 104100101Current density (A g-1)Potential (V vs. Ag/AgCl)5100 mV s-1Potential (V)Time (s) 0.5 A g-1 1 A g-1 2 A g-1 4 A g-1 6 A g-1 8 A g-1 10 A g-1 12 A g-1 14 A g-1 16 A g-1 18 A g-1 20 A g-10.5 A/g20 c)d) e) f)b)a)Cs (F g-1) Current density (A g-1)-Z² (ohm)Z¢ (ohm)0.0 0.5 1.0 1.5 2.0 2.50.00.51.01.52.02.5-Z² (ohm)Z¢ (ohm)0 2000 4000 6000 8000 10000020406080100020406080100Cs retention (%)Cycle number Capacitance retention Coulombic efficiency95.9%Coulombic efficiency (%)99.4%[61]Energy density (Wh kg-1)Power density (W kg-1) This work[59][58][60][62][63][64][65]For Peer Review10 5 to 100 mV s-1 (Figure 7a). CV profiles have a quasi-1 rectangular shape at low and high scan rates indicating 2 typical electrical double-layer capacitor behavior. Figure 3 7b shows the charge-discharge curves of the 4 supercapacitor device measured at various current 5 densities (0.5 – 20 A g-1). GCD profiles are essentially 6 triangular supporting an EDLC supercapacitor energy 7 storage mechanism. GCD data were used to calculate 8 the gravimetric specific capacitance, which is highest 9 at 64.8 F g-1 at 0.5 A g-1(Figure 7c). EIS measurement 10 was performed on the device cell prior to stability 11 measurements in order to study the ions diffusion 12 process at the electrode-electrolyte interface (Figure 13 7d). The Nyquist plot contains a semicircle in the high-14 frequency region and Warburg impedance in the low-15 frequency region. The value of ESR is ∼0.36 Ω and a 16 vertical line in the low-frequency region indicates 17 dominant capacitive behavior with rapid diffusion of 18 electrolyte ions. The supercapacitor cell was tested for 19 its long-term cycling stability at a current density of 10 20 A g-1 during 10000 cycles (Figure 7e). The cell 21 demonstrated outstanding cycle life (95.9%) and 22 coulombic efficiency (99.4%), indicating that the 23 excellent electrochemical stability of the electrode 24 material is maintained. The energy and power densities 25 of the assembled supercapacitor device were 26 calculated and are represented in the Ragone plot 27 (Figure 7f). The device exhibited an energy density as 28 high as 12.3 Wh kg-1 at a power density of 309.4 W kg-29 1 at a current density of 0.5 A g-1. The energy 30 performance of the device is comparable or better to 31 earlier published literature on porous carbon and other 32 composite materials, including walnut shell-derived 33 carbon on silver nanowires,58 date seeds-derived 34 carbon,59 tamarind seeds-derived carbon,60 hemp stem-35 derived carbon,61 corn stalk-derived porous carbon,62 36 spiral algae and bamboo-derived carbon,63 graphene 37 sheets (GNSs)–cotton cloth (CC) composite fabric,64 38 PANI/N-CNT@CNT Fiber.65 The K2CO3-activated PAM 39 hydrogel-derived hierarchically porous carbons have 40 ultra-high surface areas and are heteroatom self-doped. 41 As a result of their textural properties, these materials 42 are suitable candidates for supercapacitor applications 43 with acceptable energy and power density values, and 44 excellent cycling stability. 45  46 4. Conclusion 47 To summarize, we have synthesized highly porous 48 carbon materials by carbonization (600 – 900 °C) of 49 K2CO3-activated polyacrylamide (PAM) hydrogels. 50 Modulation of the critical parameter of porosity in the 51 carbon materials was accomplished by including an 52 activating agent and by variation of carbonization 53 temperature. The materials were analyzed using 54 various techniques, namely TGA, FTIR, RAMAN, XRD, 55 XPS, BET, SEM, and TEM. Surface compositions 56 confirmed the presence of nitrogen and oxygen 57 dopants in the carbon framework, which promote the 58 capacitance of electrode materials. The most important 59 samples were subjected to electrochemical testing 60 using GCD, CV, and EIS measurements. The optimum 61 sample was obtained by K2CO3 activation with 62 carbonization at 800 °C, having an ultrahigh BET surface 63 area of 3038.4 m2 g-1. In a three-electrode system, this 64 sample showed excellent specific capacitance of 313.3 65 F g-1 at a current density of 1 A g-1 in an aqueous 66 electrolyte (1M H2SO4) with capacitance retention after 67 10000 cycles being 97.5%. Furthermore, a symmetric 68 supercapacitor device prepared using the optimum 69 material delivered a high energy density of 12.3 Wh kg-70 1 at a power density of 309.4 W kg-1 demonstrating that 71 polyacrylamide hydrogel-derived hierarchically porous 72 carbon materials are very promising candidates as 73 electrode materials for supercapacitor applications. 74  75 Supplementary data 76 Supplementary material is available at the Bulletin of 77 the Chemical Society of Japan. 78  79 Funding 80 This work was supported by the Japan Society for the 81 Promotion of Science (JSPS) for a JSPS postdoctoral 82 fellowship (P21764) supported by JSPS KAKENHI Grant 83 Number JP22KF0385. The authors are also grateful to 84 JST-ERATO Yamauchi Materials Space-Tectonics 85 Project (JPMJER2003) and the Queensland Node of the 86 Australian National Fabrication Facility (ANFF-Q). 87  88 Conflict of interest statement. None declared. 89  90 References 91 (1) X. He, X. Zhang, J. Energy Storage 2022, 56, 106023.92 https://doi.org/10.1016/j.est.2022.106023.93 (2) Y. Shao, M. F. El-Kady, J. Sun, Y. Li, Q. Zhang, M. Zhu,94 H. Wang, B. Dunn, R. B. Kaner, Chem. Rev. 2018, 118,95 9233–9280.96 https://doi.org/10.1021/acs.chemrev.8b00252.97 (3) F. Wang, X. Wu, X. Yuan, Z. Liu, Y. Zhang, L. Fu, Y. Zhu,98 Q. Zhou, Y. Wu, W. Huang, Chem. Soc. Rev. 2017, 46,99 6816–6854. https://doi.org/10.1039/C7CS00205J.100 (4) N. Wu, X. Bai, D. Pan, B. Dong, R. Wei, N. Naik, R. R.101 Patil, Z. Guo, Adv. Mater. Interfaces 2021, 8, 1–17.102 https://doi.org/10.1002/admi.202001710.103 (5) H. Shao, Y.-C. Wu, Z. Lin, P.-L. Taberna, P. Simon, Chem. 104 Soc. Rev. 2020, 49, 3005–3039.105 https://doi.org/10.1039/D0CS00059K.106 (6) S. Najib, E. Erdem, Nanoscale Adv. 2019, 1, 2817–2827.107 https://doi.org/10.1039/C9NA00345B.108 (7) R. G. Shrestha, S. Maji, L. K. Shrestha, K. Ariga,109 Nanomaterials 2020, 10, 1–27.110 https://doi.org/10.3390/nano10040639.111 (8) J. Zhang, M. Gu, X. Chen, Micro Nano Eng. 2023, 21,112 100229. https://doi.org/10.1016/j.mne.2023.100229.113 (9) J. Libich, J. Máca, J. Vondrák, O. Čech, M. Sedlaříková,114 J. Energy Storage 2018, 17, 224–227. 115 https://doi.org/10.1016/j.est.2018.03.012. 116 (10) J. Zhao, A. Burke, J. Energy Chem. 2020, 59, 276-291.117 https://doi.org/10.1016/j.jechem.2020.11.013.118 (11) W. Ao, J. Fu, X. Mao, Q. Kang, C. Ran, Y. Liu, H. Zhang,119 For Peer Review11 Z. Gao, J. Li, G. Liu, J. Dai, Renew. Sustain. Energy Rev. 1 2018, 92, 958–979. 2 https://doi.org/10.1016/j.rser.2018.04.051. 3 (12) T. Tsubota, M. Morita, S. Kamimura, T. Ohno, J. Porous 4 Mater. 2016, 23, 349–355.5 https://doi.org/10.1007/s10934-015-0087-6.6 (13) F. Ma, S. Ding, H. Ren, Y. Liu, RSC Adv. 2019, 9, 2474–7 2483. https://doi.org/10.1039/C8RA09685F.8 (14) P. Forouzandeh, V. Kumaravel, S. C. Pillai, Electrode9 Materials for Supercapacitors: A Review of Recent10 Advances. Catalysts 2020, 10, 969.11 https://doi.org/10.3390/catal10090969.12 (15) J. Sun, W. Li, L. E, Z. Xu, C. Ma, Z. Wu, S. Liu, J. Power 13 Sources 2019, 438, 227030.14 https://doi.org/10.1016/j.jpowsour.2019.227030.15 (16) Z.-S. Wu, A. Winter, L. Chen, Y. Sun, A. Turchanin, X.16 Feng, K. Müllen, Adv. Mater. 2012, 24, 5130–5135.17 https://doi.org/10.1002/adma.201201948.18 (17) P. Hao, Z. Zhao, J. Tian, H. Li, Y. Sang, G. Yu, H. Cai, H.19 Liu, C. P. Wong, A. Umar, Nanoscale 2014, 6, 12120–20 12129. https://doi.org/10.1039/C4NR03574G.21 (18) R. R. Salunkhe, Y.-H. Lee, K.-H. Chang, J.-M. Li, P. Simon,22 J. Tang, L. N. Torad, C.-C. Hu, Y. Yamauchi, Chem. Eur. 23 J. 2014, 20, 13838–13852. 24 https://doi.org/10.1002/chem.201403649.25 (19) J. Chen, J. Xu, S. Zhou, N. Zhao, C.-P. Wong, Nano 26 Energy 2016, 25, 193–202.27 https://doi.org/10.1016/j.nanoen.2016.04.037.28 (20) Y. Wang, Y. Liu, D. Wang, C. Wang, L. Guo, T. Yi, Appl. 29 Surf. Sci. 2020, 506, 145014.30 https://doi.org/10.1016/j.apsusc.2019.145014.31 (21) M. Alhabeb, M. Beidaghi, K. L. Van Aken, B. Dyatkin, Y.32 Gogotsi, Carbon 2017, 118, 642–649.33 https://doi.org/10.1016/j.carbon.2017.03.094.34 (22) B. Dyatkin, O. Gogotsi, B. Malinovskiy, Y. Zozulya, P.35 Simon, Y. Gogotsi, J. Power Sources 2016, 306, 32–41.36 https://doi.org/10.1016/j.jpowsour.2015.11.099.37 (23) Q.-L. Chen, K.-H. Xue, W. Shen, F.-F. Tao, S.-Y. Yin, W.38 Xu, Electrochim. Acta 2004, 49, 4157–4161.39 https://doi.org/10.1016/j.electacta.2004.04.010.40 (24) G.-M. Weng, J. Li, M. Alhabeb, C. Karpovich, H. Wang,41 J. Lipton, K. Maleski, J. Kong, E. Shaulsky, M. Elimelech,42 Y. Gogotsi, A. D. Taylor, Adv. Funct. Mater. 2018, 28,43 1803360. https://doi.org/10.1002/adfm.201803360.44 (25) Z. Gao, Y. Zhang, N. Song, X. Li, Mater. Res. Lett. 2017, 45 5, 69–88.46 https://doi.org/10.1080/21663831.2016.1250834.47 (26) H. Zhang, Y. Zhang, L. Bai, Y. Zhang, L. Sun, J. Mater. 48 Chem. A 2021, 9, 12521–12552.49 https://doi.org/10.1039/D1TA00790D.50 (27) A. M. Abioye, F. N. Ani, Renew. Sustain. Energy Rev. 51 2015, 52, 1282–1293.52 https://doi.org/10.1016/j.rser.2015.07.129.53 (28) C. L. Gnawali, L. K. Shrestha, J. P. Hill, R. Ma, K. Ariga,54 M. P. Adhikari, R. Rajbhandari, B. P. Pokharel, C Journal 55 of Carbon Research 2023, 9, 109.56 https://doi.org/10.3390/c9040109.57 (29) R. L. Shrestha, R. Chaudhary, T. Shrestha, B. M.58 Tamrakar, R. G. Shrestha, S. Maji, J. P. Hill, K. Ariga, L.59 K. Shrestha, Materials 2020, 13, 5434. 60 https://doi.org/10.3390/ma13235434. 61 (30) G.-G. Song, J. Yang, K.-X. Liu, Z. Qin, X.-C. Zheng, Diam. 62 Relat. Mater. 2021, 111, 108162. 63 https://doi.org/10.1016/j.diamond.2020.108162. 64 (31) D. R. Lobato-Peralta, A. Ayala-Cortés, A. Longoria, D. E.65 Pacheco-Catalán, P. U. Okoye, H. I. Villafán-Vidales, C. A. 66 Arancibia-Bulnes, A. K. Cuentas-Gallegos, J. Energy 67 Storage 2022, 52, 104888. 68 https://doi.org/10.1016/j.est.2022.104888. 69 (32) M.-J. Kim, S. W. Choi, H. Kim, S. Mun, K. B. Lee, Chem. 70 Eng. J. 2020, 397, 125404. 71 https://doi.org/10.1016/j.cej.2020.125404. 72 (33) S. Maji, R. Chaudhary, R. G. Shrestha, R. L. Shrestha, B.73 Demir, D. J. Searles, J. P. Hill, Y. Yamauchi, K. Ariga, L.74 K. Shrestha, ACS Appl. Energy Mater. 2021, 4, 12257–75 12266. https://doi.org/10.1021/acsaem.1c02051.76 (34) L. K. Shrestha, R. G. Shrestha, R. Chaudhary, R. R.77 Pradhananga, B. M. Tamrakar, T. Shrestha, S. Maji, R. L.78 Shrestha, K. Ariga, Nanomaterials 2021, 11, 1–16.79 https://doi.org/10.3390/nano11123175.80 (35) M. Kim, H. Lim, X. Xu, M. S. A. Hossain, J. Na, N. N.81 Awaludin, J. Shah, L. K. Shrestha, K. Ariga, A. K.82 Nanjundan, D. J. Martin, J. G. Shapter, Y. Yamauchi,83 Microporous Mesoporous Mater. 2021, 312, 110757.84 https://doi.org/10.1016/j.micromeso.2020.110757.85 (36) Y.-Q. Zhao, M. Lu, P.-Y. Tao, Y.-J. Zhang, X.-T. Gong, Z.86 G.-Q. Yang, Li, H. Zhang, J. Power Sources 2016, 307,87 391–400.88 https://doi.org/10.1016/j.jpowsour.2016.01.020.89 (37) H. A. Hamouda, H. I. Abdu, Q. Hu, M. A. Abubaker, H.90 Lei, S. Cui, A. I. Alduma, H. Peng, G. Ma, Z. Lei, Front. 91 Chem. 2022, 10, 1–14.92 https://doi.org/10.3389/fchem.2022.1024047.93 (38) Y. Guo, J. Bae, Z. Fang, P. Li, F. Zhao, G.Yu, Chem. Rev. 94 2020, 120, 7642-7707.95 https://doi.org/10.1021/acs.chemrev.0c00345.96 (39) X. Meng, J. Zhang, Q. Chen, L. Hou, C. Yuan, New J. 97 Chem. 2020, 44, 21279–21287.98 https://doi.org/10.1039/D0NJ04942E.99 (40) A. Pourjavadi, H. Abdolmaleki, M. Doroudian, S. H.100 Hosseini, J. Alloys Compd. 2020, 827, 154116.101 https://doi.org/10.1016/j.jallcom.2020.154116.102 (41) Q. Du, Y. Zhao, K. Zhuo, Y. Chen, L. Yang, C. Wang, J.103 Wang, Nanoscale 2021, 13, 13285–13293.104 https://doi.org/10.1039/D1NR01848E.105 (42) Y. Wang, B. Ding, D. Guo, X. Wu, A Microporous 106 Mesoporous Mater. 2019, 282, 114–120.107 https://doi.org/10.1016/j.micromeso.2019.03.031.108 (43) Y. Yang, D. Chen, W. Han, Y. Cheng, B. Sun, C. Hou, G.109 Zhao, D. Liu, G. Chen, J. Han, X. Zhang, Carbon 2023, 110 205, 1–9. https://doi.org/10.1016/j.carbon.2023.01.013.111 (44) F. Zhang, H. Liu, Z. Wu, J. Zhang, E. Cui, L. Yue, G. Hou,112 ACS Appl. Energy Mater. 2021, 4, 6719–6729.113 https://doi.org/10.1021/acsaem.1c00777.114 (45) L. Miao, X. Qian, D. Zhu, T. Chen, G. Ping, Y. Lv, W.115 Xiong, Y. Liu, L. Gan, M. Liu, Chinese Chem. Lett. 2019,116 30, 1445–1449.117 https://doi.org/10.1016/j.cclet.2019.03.010.118 (46) H. Gao, D. Zhang, H. Zhou, J. Wu, G. Xu, Z. Huang, M.119 Liu, J. Yang, D. Chen, Appl. Surf. Sci. 2020, 534, 147613.120 https://doi.org/10.1016/j.apsusc.2020.147613.121 (47) C. Fan, Y. Tian, S. Bai, C. Zhang, X. Wu, J. Energy 122 Storage 2021, 44, 103492.123 https://doi.org/10.1016/j.est.2021.103492.124 (48) N. Velychkivska, A. Golunova, A. Panda, P. A. Shinde, R.125 Ma, K. Ariga, Y. Yamauchi, J. P. Hill, J. Labuta, L. K.126 Shrestha, ACS Appl. Energy Mater. 2024, 7, 2906–2917.127 https://doi.org/10.1021/acsaem.4c00141.128 (49) X. Zhang, M. Han, A. Fuseni, A. M. Alsofi, J. Pet. Sci. Eng. 129 2019, 180, 518–525.130 For Peer Review12 https://doi.org/10.1016/j.petrol.2019.04.092.1 (50) L. H. Gaabour, Results Phys. 2017, 7, 2153–2158.2 https://doi.org/10.1016/j.rinp.2017.06.027.3 (51) A. M. Dumitrescu, G. Lisa, A. R. Iordan, F. Tudorache, I.4 Petrila, A. I. Borhan, M. N. Palamaru, C. Mihailescu, L.5 Leontie, C. Munteanu, Mater. Chem. Phys. 2015, 156,6 170–179.7 https://doi.org/10.1016/j.matchemphys.2015.02.044.8 (52) L. K. Shrestha, Z. Wei, G. Subramaniam, R. G. Shrestha,9 R. Singh, M. Sathish, R. Ma, J. P. Hill, J. Nakamura, K.10 Ariga, Nanomaterials 2023, 13, 1–17.11 https://doi.org/10.3390/nano13050946.12 (53) Z.-W. Ma, H.-Q. Liu, Q.-F. Lü, J. Energy Storage 2021, 13 40, 102773. https://doi.org/10.1016/j.est.2021.102773.14 (54) J. H. Khan, J. Lin, C. Young, B. M. Matsagar, K. C. W.15 Wu, P. L. Dhepe, M. T. Islam, M. M. Rahman, L. K.16 Shrestha, S. M. Alshehri, T. Ahamad, R. R. Salunkhe, N.17 A. Kumar, D. J. Martin, Y. Yamauchi, M. S. A. Hossain,18 Mater. Chem. Phys. 2018, 216, 491–495.19 https://doi.org/10.1016/j.matchemphys.2018.05.082.20 (55) A. Sadezky, H. Muckenhuber, H. Grothe, R. Niessner, U.21 Pöschl, Carbon 2005, 43, 1731–1742.22 https://doi.org/10.1016/j.carbon.2005.02.018.23 (56) A. J. R. Rennie, P. J. Hall, Phys. Chem. Chem. Phys. 24 2013, 15, 16774. https://doi.org/10.1039/c3cp52233d.25 (57) Y.-R. Zhao, C.-C. Liu, Q.-Q. Lu, O. Ahmad, X.-J. Pan, M.26 Daria, New Carbon Mater. 2022, 37, 875–897.27 https://doi.org/10.1016/S1872-5805(22)60637-1.28 (58) Q. Bai, G. Zhang, X. Bai, Y. Liu, Y. Wang, C. Li, Y. Shen,29 H. Uyama, Applied Surface Science 2024, 678, 161140.30 https://doi.org/10.1016/j.apsusc.2024.161140.31 (59) R. Farma, A. Indriani, and I. Apriyan, J Mater Sci: Mater 32 Electron 2023, 34, 81. https://doi.org/10.1007/s10854-33 022-09446-5.34 (60) M. Raja, B. Sadhasivam, R. J. Naik, R. Dhamodharan and35 K. Ramanujam, Sustainable Energy Fuels, 2019, 3, 760-36 773. https://doi.org/10.1039/c8se00530c.37 (61) D. Qiu, C. Kang, A. Gao, Z. Xie, Y. Li, M. Li, F. Wang, and38 R. Yang, ACS Sustainable Chem. Eng. 2019, 7,39 14629−14638.40 https://doi.org/10.1021/acssuschemeng.9b02.41 (62) Y. Zhang, Y. Cai, T. Li, M. Wang, X. Chen, and Y. Xu, J 42 Mater Sci: Mater Electron, 2024 35, 116.43 https://doi.org/10.1007/s10854-024-11944-7.44 (63) W. Yue, Z. Yu, X. Zhang, H. Liu, T. He, Journal of 45 Analytical and Applied Pyrolysis, 2024, 178, 106409.46 https://doi.org/10.1016/j.jaap.2024.106409.47 (64) W. W. Liu, X. B. Yan, J. W. Lang, C. Peng and Q. J. Xue,48 J. Mater. Chem., 2012, 22, 17245-17253. 49 https://doi.org/10.1039/C2JM32659K. 50 (65) J. Tian, N. Cui, P. Chen, K. Guo and X. Chen, J. Mater. 51 Chem. A, 2021, 9, 20635–20644.52 https://doi.org/10.1039/D1TA03663G.53 54