氮掺杂多孔碳包覆铁纳米粒子催化剂用于高效碱性介质中氧还原反应

doi:10.13208/j.electrochem.2210241

摘要/Abstract

摘要：

合理设计和合成非贵金属催化剂对提高氧还原反应的催化活性和稳定性具有重要意义，但仍然存在重大挑战。本工作采用功能化金属有机框架材料为前驱体，合成了氮掺杂多孔碳包覆Fe纳米粒子催化剂（Fe@N-C）。Fe纳米颗粒的嵌入提高了催化剂的石墨化程度和石墨化氮的比例，同时促进了中孔的形成。Fe@N-C-30催化剂在碱性溶液中表现出良好的氧还原反应活性（E₀ = 0.97 V vs. RHE，E_1/2 = 0.89 V vs. RHE）。此外，与商用Pt/C相比，Fe@N-C-30催化剂具有更好的耐甲醇性和循环稳定性。其优异的电催化活性归因于高的电化学表面积、相对高比例的石墨化氮、独特的孔结构以及包覆的Fe颗粒与碳层之间的协同效应。本工作为利用金属有机框架材料制备高效非贵金属ORR催化剂提供了一种有前景的方法。

关键词: 金属有机框架, 多孔结构, 铁纳米粒子

Abstract:

Rational design and synthesis of non-precious-metal catalyst plays an important role in improving the activity and stability for oxygen reduction reaction (ORR) but remains a major challenge. In this work, we used a facile approach to synthesize iron nanoparticles encapsulated in nitrogen-doped porous carbon materials (Fe@N-C) from functionalized metal-organic frameworks (MOFs, MET-6). Embedding Fe nanoparticles into the carbon skeleton increases the graphitization degree and the proportion of graphitic N as well as promotes the formation of mesopores in the catalyst. The Fe@N-C-30 catalyst showed the excellent ORR activity in alkaline solutions (E₀ = 0.97 V vs. RHE, E_1/2 = 0.89 V vs. RHE). Moreover, the Fe@N-C-30 catalyst exhibited better methanol resistance and long-term stability when compared to commercial Pt/C. The superior ORR performance could be attributed to the combination of high electrochemical surface area, relative high portion of graphitic-N, unique porous structures and the synergistic effect between the encapsulated Fe particles and the N-doped carbon layer. This work provides a promising method to construct efficient non-precious-metal ORR catalyst through MOFs.

Key words: Metal-organic frameworks, Porous structures, Fe nanoparticles

李春艳, 张蕊, 巴笑杰, 姜晓乐, 阳耀月. 氮掺杂多孔碳包覆铁纳米粒子催化剂用于高效碱性介质中氧还原反应[J]. 电化学（中英文）, 2023, 29(5): 2210241.

Chun-Yan Li, Rui Zhang, Xiao-Jie Ba, Xiao-Le Jiang, Yao-Yue Yang. Fe Nanoparticles Encapsulated in N-Doped Porous Carbon for Efficient Oxygen Reduction in Alkaline Media[J]. Journal of Electrochemistry, 2023, 29(5): 2210241.

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链接本文: https://electrochem.xmu.edu.cn/CN/10.13208/j.electrochem.2210241

https://electrochem.xmu.edu.cn/CN/Y2023/V29/I5/2210241

图/表 11

参考文献 61

[1]	Hu J, Zhang C X, Sun M Z, Qi Q L, Luo S X, Song H C, Xiao J Y, Huang B L, Leung M K H, Zhang Y J. Ultrastable bimetallic Fe₂Mo for efficient oxygen reduction reaction in pH-universal applications[J]. Nano Res., 2022, 15(6): 4950-4957. doi: 10.1007/s12274-022-4112-1
[2]	Liu M M, Zhang R Z, Chen W. Graphene-supported nanoelectrocatalysts for fuel cells: synthesis, properties, and applications[J]. Chem. Rew., 2014, 114(10): 5117-5160. doi: 10.1021/cr400523y URL
[3]	Xu L Y, Yu M Z, Yang P J, Wang Z Y, Qiu J S. Caging porous Co-N-C nanocomposites in 3D graphene as active and aggregation-resistant electrocatalyst for oxygen reduction reaction[J]. J. Electrochem., 2018, 24(6): 715-725.
[4]	Ye L, Chai G L, Wen Z H. Zn-MOF-74 derived N-doped mesoporous carbon as pH-universal electrocatalyst for oxygen reduction reaction[J]. Adv. Funct. Mater., 2017, 27(14): 8.
[5]	Zaman S, Huang L, Douka A I, Yang H, You B, Xia B Y. Oxygen reduction electrocatalysts toward practical fuel cells: Progress and perspectives[J]. Angew. Chem. Int. Ed., 2021, 60(33): 17832-17852. doi: 10.1002/anie.202016977 pmid: 33533165
[6]	Zhang X R, Lyu D D, Mollamahale Y B, Yu F, Qing M, Yin S B, Zhang X Y, Tian Z Q, Shen P K. Critical role of iron carbide nanodots on 3D graphene based nonprecious metal catalysts for enhancing oxygen reduction reaction[J]. Electrochim. Acta, 2018, 281: 502-509. doi: 10.1016/j.electacta.2018.05.206 URL
[7]	Liu X, Park M, Kim M G, Gupta S, Wang X J, Wu G, Cho J. High-performance non-spinel cobalt-manganese mixed oxide-based bifunctional electrocatalysts for rechargeable zinc-air batteries[J]. Nano Energy, 2016, 20: 315-325. doi: 10.1016/j.nanoen.2015.11.030 URL
[8]	Sui S, Wang X Y, Zhou X T, Su Y H, Riffat S, Liu C J. A comprehensive review of Pt electrocatalysts for the oxygen reduction reaction: Nanostructure, activity, mechanism and carbon support in PEM fuel cells[J]. J. Mater. Chem. A, 2017, 5(5): 1808-1825. doi: 10.1039/C6TA08580F URL
[9]	Li T, Zhao H X, Wang R L, Wang S Y. Carbon-based, metal-free electrocatalysts for renewable energy technologies[J]. Prog. Mater. Sci., 2021, (116): 313-334.
[10]	Prati L, Chan-Thaw C E, Campisi S, Villa A. N-modified carbon-based materials: Nanoscience for catalysis[J], Chem. Rec., 2016, 16(5): 2187-2197. doi: 10.1002/tcr.v16.5 URL
[11]	Jaleh B, Nasrollahzadeh M, Eslamipanah M, Nasri A, Shabanlou E, Manwar N R, Zboril R, Fornasiero P, Gawande M B. The role of carbon-based materials for fuel cells performance[J]. Carbon, 2022, 198: 301-352. doi: 10.1016/j.carbon.2022.07.023 URL
[12]	Zhang J, Zhang J J, He F, Chen Y J, Zhu J W, Wang D L, Mu S C, Yang H Y. Defect and doping Co-engineered non-metal nanocarbon ORR electrocatalyst[J]. Nanomicro Lett., 2021, 13(1): 65.
[13]	Wang Y C, Lai Y J, Song L, Zhou. Z Y, Liu J G, Wang Q, Yang X D, Chen C, Shi W, Zheng Y P, Rauf M, Sun S G. S-doping of an Fe/N/C ORR catalyst for polymer electrolyte membrane fuel cells with high power density[J]. Angew. Chem. Int. Ed., 2015, 54(34): 9907-9910. doi: 10.1002/anie.v54.34 URL
[14]	Jin Z, Nie H, Yang Z, Zhang J, Liu Z, Xu X J, Huang S M. Metal-free selenium doped carbon nanotube/graphene networks as a synergistically improved cathode catalyst for oxygen reduction reaction[J]. Nanoscale, 2012, 4(20): 6455-6460. pmid: 22955444
[15]	Gao J, Wang Y, Wu H, Liu X, Wang L L, Yu Q L, Li A W, Wang H, Song C Q, Gao Z R, Peng M, Zhang M T, Ma N, Wang J O. Construction of a sp³/sp²carbon interface in 3D N-doped nanocarbons for the oxygen reduction reaction[J]. Angew. Chem. Int. Ed., 2019, 58(42): 15089-15097. doi: 10.1002/anie.v58.42 URL
[16]	Kim D W, Li O L, Saito N. Enhancement of ORR catalytic activity by multiple heteroatom-doped carbon materials[J]. Phys. Chem. Chem. Phys., 2015, 17(1): 407-413. doi: 10.1039/C4CP03868A URL
[17]	Wei P, Li X G, He Z M, Sun X P, Liang Q R, Wang Z Y, Fang C, Li Q, Yang H, Han J T, Huang Y H. Porous N, B co-doped carbon nanotubes as efficient metal-free electrocatalysts for ORR and Zn-air batteries[J]. Chem. Eng. J., 2021, 422:130134. doi: 10.1016/j.cej.2021.130134 URL
[18]	He M, Song S J, Wang P, Fang Z, Wang W W, Yuan X L, Li C Y, Li H, Song W Y, Luo D, Li Z X. Carbon doped cobalt nanoparticles stabilized by carbon shell for highly efficient and stable oxygen reduction reaction[J]. Carbon, 2022, 196: 483-492. doi: 10.1016/j.carbon.2022.05.019 URL
[19]	Du L, Gao X Y, Li Z, Wang G Y, Wen Z, Yang C C, Jiang Q. Metal-organic frameworks derived Co/N-doped carbon nanonecklaces as high-efficient oxygen reduction reaction electrocatalysts[J]. Int. J. Hydrogen Energy, 2022, 47(92): 39133-39145. doi: 10.1016/j.ijhydene.2022.09.090 URL
[20]	Ni B X, Wu L M, Chen R, Shi C X, Chen T H. Fe/Co-based nanoparticles encapsulated in heteroatom-doped carbon electrocatalysts for oxygen reduction reaction[J]. Sci. China Mater., 2019, 62(11): 1626-1641. doi: 10.1007/s40843-019-9476-5
[21]	Gao J, Ma N, Zheng Y M, Zhang J F, Gui J Z, Guo C K, An H Q, Tan X Y, Yin Z, Ma D. Cobalt/nitrogen-doped porous carbon nanosheets derived from polymerizable ionic liquids as bifunctional electrocatalyst for oxygen evolution and oxygen reduction reaction[J]. ChemCatChem, 2016, 9(9): 1601-1609. doi: 10.1002/cctc.v9.9 URL
[22]	Wang C X, Yuan H F, Yu F, Zhang J, Li Y Y, Bao W T, Wang Z M, Lu K, Yu J, Bai G, Wang G, Peng B H, Zhang L L. Enhanced oxygen reduction reaction performance of Co@N-C derived from metal-organic frameworks ZIF-67 via a continuous microchannel reactor[J]. Chinese Chem. Lett., 2023, 34(1): 107128. doi: 10.1016/j.cclet.2022.01.021 URL
[23]	Sun M, Li Z J, Liu Y Y, Guo D F, Xie Z Y, Huang Q Z. The synthesis of Fe/N-C@CNFs and its electrochemical performance toward oxygen reduction reaction[J]. Int. J. Hydrogen Energy, 2020, 45(56): 31892-31901. doi: 10.1016/j.ijhydene.2020.08.213 URL
[24]	Deng D H, Yu L, Chen X Q, Wang G X, Jin L, Pan X L, Sun G Q, Bao X H. Iron encapsulated within pod-like carbon nanotubes for oxygen reduction reaction[J]. Angew. Chem. Int. Ed., 2013, 52(1): 389-393. doi: 10.1002/ange.v52:22 URL
[25]	Liu F, Zhang X Q, Zhang X L, Wang L L, Liu M M, Zhang J J. Dual-template strategy for electrocatalyst of cobalt nanoparticles encapsulated in nitrogen-doped carbon nanotubes for oxygen reduction reaction[J]. J. Colloid Inter. Sci., 2021, 581: 523-532. doi: 10.1016/j.jcis.2020.07.008 URL
[26]	Zulys A, Yulia F, Muhadzib N, Nasruddin. Biological metal-organic frameworks (Bio-MOFs) for CO₂ Capture[J]. Ind. Eng. Chem. Res., 2020, 60(1): 37-51. doi: 10.1021/acs.iecr.0c04522 URL
[27]	Li S, Feng C, Xie Y H, Guo C Y, Zhang L G, Wang J D. Synthesis of nitrogen-rich porous carbon nanotubes coated Co nanomaterials as efficient ORR electrocatalysts via MOFs as precursor[J]. J. Alloys Compd., 2022, 911: 11.
[28]	Xu M J, Liu J, Ge J J, Liu C P, Xing W. Research progress of metal-nitrogen-carbon catalysts toward oxygen reduction reaction inm changchun institute of applied chemistry[J]. J. Electrochem., 2020, 26(4): 464-473.
[29]	Tong H G, Wang C L, Lu J, Chen S, Yang K, Huang M X, Yuan Q, Chen Q W. Energetic metal-organic frameworks derived highly nitrogen-doped porous carbon for superior potassium storage[J]. Small, 2020, 16(43): e2002771.
[30]	Morales D M, Risch M. Seven steps to reliable cyclic voltammetry measurements for the determination of double layer capacitance[J]. J. Phys.: Energy, 2021, 3(3): 034013. doi: 10.1088/2515-7655/abee33
[31]	Nishihara Y, Nakajima Y, Akashi A, Tsujino N, Takahashi E, Funakoshi K I, Higo Y. Isothermal compression of face-centered cubic iron[J]. Am. Mineral., 2012, 97(8-9): 1417-1420. doi: 10.2138/am.2012.3958 URL
[32]	Sevilla M, Antonio B F. Catalytic graphitization of templated mesoporous carbons[J]. Carbon, 2006, 44(3): 468-474. doi: 10.1016/j.carbon.2005.08.019 URL
[33]	Yu H Y, Fisher A, Cheng D J, Cao D P. Cu, N-codoped hierarchical porous carbons as electrocatalysts for oxygen reduction reaction[J]. ACS Appl. Mater. Interfaces, 2016, 8(33): 21431-21439. doi: 10.1021/acsami.6b04189 URL
[34]	Liu M C, Guo X H, Hu L B, Yuan H F, Wang G, Dai B, Zhang L L, Yu F. Fe₃O₄/Fe₃C@nitrogen-doped carbon for enhancing oxygen reduction reaction[J]. ChemNanoMat, 2019, 5(2): 187-193. doi: 10.1002/cnma.201800432
[35]	Yan C C, Li H B, Ye Y F, Wu H H, Cai F, Si R, Xiao J P, Miao S, Xie S H, Yang F,. Li Y S, Wang G X, Bao X H. Coordinatively unsaturated nickel-nitrogen sites towards selective and high-rate CO₂ electroreduction[J]. Energy Environ. Sci., 2018, 11(5): 1204-1210. doi: 10.1039/C8EE00133B URL
[36]	Li B, Sasikala S P, Kim D H, Bak J, Kim D, Cho E A, Kim S O. Fe-N₄ complex embedded free-standing carbon fabric catalysts for higher performance ORR both in alkaline & acidic media[J]. Nano energy, 2019, 56: 524-530. doi: 10.1016/j.nanoen.2018.11.054 URL
[37]	Peng X M, Wu J Q, Zhao Z L, Wang X, Dai H L, Li Y M, Wei Y, Xu G P, Hu F P. High efficiency degradation of tetracycline by peroxymonosulfate activated with Fe/NC catalysts: Performance, intermediates, stability and mechanism[J]. Environ. Res., 2022, 205: 112538. doi: 10.1016/j.envres.2021.112538 URL
[38]	Guo J H, Zhang S, Zheng M, Tang J, Liu L, Chen J M, Wang X C. Graphitic-N-rich N-doped graphene as a high performance catalyst for oxygen reduction reaction in alkaline solution[J]. Int. J. Hydrogen Energy, 2020, 45(56): 32402-32412. doi: 10.1016/j.ijhydene.2020.08.210 URL
[39]	Li X G, Ni L, Zhou J H, Xu L, Lu C L, Yang G X, Ding W P, Hou W H. Encapsulation of Fe nanoparticles into an N-doped carbon nanotube/nanosheet integrated hierarchical architecture as an efficient and ultrastable electrocatalyst for the oxygen reduction reaction[J]. Nanoscale, 2020, 12(26): 13987-13995. doi: 10.1039/d0nr02618b pmid: 32578658
[40]	Liu D, Srinivas K, Chen X, Ma F, Zhang X J, Wang X Q, Wang B, Chen Y F. Dual Fe, Zn single atoms anchored on carbon nanotubes inlaid N, S-doped hollow carbon polyhedrons for boosting oxygen reduction reaction[J]. J Colloid Inter. Sci., 2022, 624: 680-690. doi: 10.1016/j.jcis.2022.05.167 URL
[41]	Wang N N, Li J, Hei J P, Chen X D, Yin X J, Cai C W, Li M L, Cui L F. ɛ-Fe₃N@N-doped carbon core-shell nanoparticles encapsulated in bamboo-like carbon nanotubes for oxygen reduction reaction[J]. Mater. Chem. Phys., 2022, 291: 126769. doi: 10.1016/j.matchemphys.2022.126769 URL
[42]	Talukder N, Wang Y, Nunna B B, Lee E S. An in-depth exploration of the electrochemical oxygen reduction reaction (ORR) phenomenon on carbon-based catalysts in alkaline and acidic mediums[J]. Catalysts, 2022, 12(7): 21. doi: 10.3390/catal12010021 URL
[43]	Li X, Ni L, Zhou J H, Xu L, Lu C N, Yang G X, Ding W P, Hou W H. Encapsulation of Fe nanoparticles into an N-doped carbon nanotube/nanosheet integrated hierarchical architecture as an efficient and ultrastable electrocatalyst for the oxygen reduction reaction[J]. Nanoscale, 2020, 12(26): 13987-13995. doi: 10.1039/d0nr02618b pmid: 32578658
[44]	Park S, Her M, Shin H J, Hwang W, Sung Y E. Maximizing the active site densities of single-atomic Fe-N-C electrocatalysts for high-performance anion membrane fuel cells[J]. ACS Appl. Energy Mater., 2021, 4: 1459-1466. doi: 10.1021/acsaem.0c02650 URL
[45]	Freitas W D S, Pico M P P, D’Epifanio A, Mecheri B. Nanostructured Fe-N-C as bifunctional catalysts for oxygen reduction and hydrogen evolution[J]. Catalysts, 2021, 11: 1525. doi: 10.3390/catal11121525 URL
[46]	Gao J, Ma N, Zheng Y M, Zheng J F, Gui J Z, Guo C K, An H Q, Yin Z, Ma D. Cobalt/nitrogen-doped porous carbon nanosheets derived from polymerizable ionic liquids as bifunctional electrocatalyst for oxygen evolution and oxygen reduction reaction[J]. ChemCatChem, 2017, 9(9): 1601-1609. doi: 10.1002/cctc.v9.9 URL
[47]	Yuan K, Lutzenkirchen-Hecht D, Li L B, Shuai L, Li Y Z, Cao R, Qiu M, Zhuang X D, Leung M K H, Chen Y W, Scherf U. Boosting oxygen reduction of single iron active sites via geometric and electronic engineering: nitrogen and phosphorus dual coordination[J]. J. Am. Chem. Soc., 2020, 142:2404-2412. doi: 10.1021/jacs.9b11852 pmid: 31902210
[48]	Zhang X B, Han X, Jiang Z, Xu J, Chen L N, Xue Y K, Nie A, Xie Z X, Kuang Q, Zheng L S. Atomically dispersed hierarchically ordered porous Fe-N-C electrocatalyst for high performance electrocatalytic oxygen reduction in Zn-air battery[J]. Nano Energy, 2020, 71: 104547. doi: 10.1016/j.nanoen.2020.104547 URL
[49]	Ye Y F, Li H B, Cai F, Yan C C, Si R, Miao S, Li Y S, Wang G X, Bao X H. Two-dimensional mesoporous carbon doped with Fe-N active sites for efficient oxygen reduction[J]. ACS Catal., 2017, 7: 7638-7646. doi: 10.1021/acscatal.7b02101 URL
[50]	Jiao L, Wan G, Zhang R, Zhou H, Yu S H, Jiang H L. From metal-organic frameworks to single-atom Fe implanted N-doped porous carbons: Efficient oxygen reduction in both alkaline and acidic media[J]. Angew. Chem. Int. Ed., 2018, 57: 8525-8529. doi: 10.1002/anie.201803262 pmid: 29742316
[51]	Li G N, Zhang J J, Li W S, Fan K, Xu C J. 3D interconnected hierarchical porous N-doped carbon constructed by flake-like nanostructure with Fe/Fe₃C for efficient oxygen reduction reaction and supercapacitor[J]. Nanoscale, 2018, 10(19): 9252-9260. doi: 10.1039/C8NR02337A URL
[52]	Mahmood J, Li F, Kim C, Choi H J, Gwon O, Jung S M, Seo J M, Cho S J, Ju Y W, Jeong H Y, Kim G. Fe@C₂N: A highly-efficient indirect-contact oxygen reduction catalyst[J]. Nano Energy, 2018, 44: 304-310. doi: 10.1016/j.nanoen.2017.11.057 URL
[53]	Liu S, Li C, Zachman M J, Zeng Y C, Yu H R, Li B Y, Wang M Y, Braaten J, Liu J W,. Meyer III H M, Lucero M, Kropf A P, Alp E E, Gong Q, Shi Q R, Feng Z X, Xu H, Wang G F, Myers D J, Xie J, Cullen D A, Litster S, Wu Gang. Atomically dispersed iron sites with a nitrogen-carbon coating as highly active and durable oxygen reduction catalysts for fuel cells[J]. Nat. Energy, 2022, 7(7): 652-663. doi: 10.1038/s41560-022-01062-1
[54]	Park H S, Han S B, Kwak D H, Han J H. Park K W. Fe nanoparticles encapsulated in doped graphitic shells as high-performance and stable catalysts for oxygen reduction reaction in an acid medium[J]. J. Catal., 2019, 370: 130-137. doi: 10.1016/j.jcat.2018.12.015 URL
[55]	Jiang X L, Yang Y Y, Zhu C L, Zhang R, Wu F, Wu H H, Wang J. Atomically dispersed Fe-Nx sites doped mesopore-dominated carbon nanodisks towards efficient oxygen reduction[J]. Int. J. Hydrogen Energy, 2022, 47(78): 33308-33318. doi: 10.1016/j.ijhydene.2022.07.209 URL
[56]	Wang Y, Chen Y, Wang Z W, Li P, Zhao J Y, Zhao H Y, Li D, He T X, Wei Y T, Su Y Q, Xiao C H. Boron doping induced electronic reconfiguration of Fe-Nx sites in N-doped carbon matrix for efficient oxygen reduction reaction in both alkaline and acidic media[J]. Int. J. Hydrogen Energy, 2022, 47(43): 18663-18674. doi: 10.1016/j.ijhydene.2022.04.015 URL
[57]	Bai J, Ge W, Zhou P, Xu P, Wang L, Zhang J, Jiang X, Li X, Zhou Q. Precise constructed atomically dispersed Fe/Ni sites on porous nitrogen-doped carbon for oxygen reduction[J]. J. Colloid Inter. Sci., 2022, 616: 433-439. doi: 10.1016/j.jcis.2022.02.080 URL
[58]	Gao J, Hu Y, Wang Y, Lin X, Hu K, Lin X, Xie G, Liu X, Reddy K M, Yuan Q, Qiu H J. MOF structure engineering to synthesize Co-N-C catalyst with richer accessible active sites for enhanced oxygen reduction[J]. Small, 2021, 17(49): e2104684.
[59]	Cui L F, Chen M X, Huo G, Fu X Z, Luo J G. FeCo nanoparticles wrapped in N-doped carbon derived from Prussian blue analogue and dicyandiamide as efficient oxygen reduction electrocatalysts for Al-air batteries[J]. Chem. Eng. J., 2020, 395: 125158. doi: 10.1016/j.cej.2020.125158 URL
[60]	Li W J, Wang F, Zhang Z G, Min S X. Graphitic carbon layer-encapsulated Co nanoparticles embedded on porous carbonized wood as a self-supported chainmail oxygen electrode for rechargeable Zn-air batteries[J]. Appl. Catal. B, 2022, 317: 121758. doi: 10.1016/j.apcatb.2022.121758 URL
[61]	Liu Z F, Ye D D, Zhu X, Wang S L, Zou Y N, Lan L H, Chen R, Yang Y, Liao Q. ZIF-67-derived Co nanoparticles embedded in N-doped porous carbon composite interconnected by MWCNTs as highly efficient ORR electrocatalysts for a flexible direct formate fuel cell[J]. Chem. Eng. J., 2022, 432: 134192. doi: 10.1016/j.cej.2021.134192 URL

Sample	Surface area (m²·g^-1)	Micropore area (m²·g^-1)	External surface area (m²·g^-1)	V_total (cm³·g^-1)	V_u (cm³·g^-1)	ΔV (cm³·g^-1)
Fe@N-C-30	861.4	410.4 42	450.936	1.349	0.185	1.164
Fe@N-C-60	742.3	279.085	463.248	1.185	0.125	1.060
N-C	357.2	198.504	158.665	0.77	0.098	0.672

Sample	Total nitrogen content (wt%)	Percentage of nitrogen species (%)
Sample	Total nitrogen content (wt%)	pyridinic	pyrrolic	graphitic	oxidized
N-C	8.15	33.36	22.80	36.85	7
Fe@N-C-30	7.29	31.52	16.29	45.8	6.4
Fe@N-C-60	6.14	31.64	22.30	40.14	5.92

Catalyst	Catalyst loading (mg·cm^-2)	E_onset (V vs. RHE)	E_1/2 (V vs. RHE)	Reference
Fe@N-C-30	0.3	0.97	0.89	This work
Fe@N-C NT/NSs	0.16	0.86	0.75	[43]
Co@C@TiO₂	0.25	0.867	0.68	[18]
Co@NCNTs-800	0.3	0.88	0.75	[25]
Fe-N-C Act	0.2	/	0.9	[44]
Fe-N-C	0.23	0.95	0.85	[45]
Co@N-C(DM)	1.4	0.90	0.83	[22]
Co/N-CNN	0.76	/	0.865	[19]
Co-N-pCNs	0.25	0.96	0.8	[46]
Fe-N/P-C-700	0.6	0.941	0.867	[47]
3DOM Fe-N-C	0.61	/	0.875	[48]
Fe©N-C-12	0.31	0.95	0.83	[49]
FeSA-N-C	0.28	1	0.89	[50]
Fe-CZIF-800-10	0.22	0.982	0.830	[51]
Fe@C₂N	0.7	1.015	0.876	[52]
Fe-N-C(Fe-AC)	/	/	0.915	[53]