Ni single-atom sites supported on carbon aerogel for highly efficient electroreduction of carbon dioxide with industrial current densities

Guo Hui; Si Duan-Hui; Zhu Hong-Jing; Li Qiu-Xia; Huang Yuan-Biao; Cao Rong

doi:10.1016/j.esci.2022.03.007

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Guo Hui, Si Duan-Hui, Zhu Hong-Jing, Li Qiu-Xia, Huang Yuan-Biao, Cao Rong. Ni single-atom sites supported on carbon aerogel for highly efficient electroreduction of carbon dioxide with industrial current densities[J]. eScience, 2022, 2(3): 295-303. doi: 10.1016/j.esci.2022.03.007

Citation:

Guo Hui, Si Duan-Hui, Zhu Hong-Jing, Li Qiu-Xia, Huang Yuan-Biao, Cao Rong. Ni single-atom sites supported on carbon aerogel for highly efficient electroreduction of carbon dioxide with industrial current densities[J]. eScience, 2022, 2(3): 295-303. doi: 10.1016/j.esci.2022.03.007

Citation:

Guo Hui, Si Duan-Hui, Zhu Hong-Jing, Li Qiu-Xia, Huang Yuan-Biao, Cao Rong. Ni single-atom sites supported on carbon aerogel for highly efficient electroreduction of carbon dioxide with industrial current densities[J]. eScience, 2022, 2(3): 295-303. doi: 10.1016/j.esci.2022.03.007

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Ni single-atom sites supported on carbon aerogel for highly efficient electroreduction of carbon dioxide with industrial current densities

doi: 10.1016/j.esci.2022.03.007

Guo Hui^{a, b},
Si Duan-Hui^a,
Zhu Hong-Jing^{a, b},
Li Qiu-Xia^a,
Huang Yuan-Biao^{a, b
,
,},
Cao Rong^{a, b, c
,
,}

a.
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, China
b.
University of Chinese Academy of Sciences, Beijing, 100049, China
c.
Fujian Science & Technology Innovation Laboratory for Optoelectronic Information of China Fuzhou, Fujian, 350108, China

More Information

Corresponding author: E-mail address: ybhuang@fjirsm.ac.cn (Y.-B. Huang); rcao@fjirsm.ac.cn (R. Cao)
Received Date: 2021-12-30
Revised Date: 2022-02-25
Accepted Date: 2022-03-31

Available Online: 2022-04-06

Abstract

Abstract

Finding highly efficient electrocatalysts for the CO₂ electroreduction reactions (CO₂RR) that have high selectivity and appreciable current density to meet commercial application standards remains a challenge. Because their reduction potentials are similar to that of the associated competitive hydrogen evolution reaction and the CO₂ activation kinetics are sluggish. Although single-atom catalysts (SACs) with high atom efficiency are one class of promising candidates for the CO₂RR to produce CO, single-atom active sites supported on microporous carbons are not fully exposed to substrates and thus lead to low current density. Carbon aerogels with interconnected channels and macropores can facilitate mass transport. But few reports describe utilizing them as supports to anchor SACs for efficient electrocatalysis. Herein, N-doped carbon aerogels supporting Ni single atomic catalyst sites (denoted as Ni-NCA-X, X = 10, 20) were fabricated by pyrolyzing Ni/Zn bimetallic zeolitic imidazolate framework (Ni/Zn-ZIF-8)/carboxymethylcellulose composite gels. Owing to abundant hierarchical micro-, meso-, and macropores and high CO₂ adsorption, the Ni single active sites in the optimal Ni-NCA-10 were readily accessible for the electrolyte and CO₂ molecules and thus achieved an industrial-level CO partial current density of 226 mA cm⁻², a high CO Faradaic efficiency of 95.6% at −1.0 V vs. the reversible hydrogen electrode, and a large turnover frequency of 271810 h⁻¹ in a flow-cell reactor at −1.0 V. Such excellent CO₂RR performance makes Ni-NCA-10 a rare state-of-the-art electrocatalyst for CO₂-to-CO conversion. This work provides an effective strategy for designing highly efficient electrocatalysts toward the CO₂RR to achieve industrial current density via anchoring single-atom sites on carbon aerogels.
- Carbon aerogel,
- ZIF-8,
- Single-atom catalyst,
- CO₂ electrocatalysis,
- CO

● Ni-NCA have abundant hierarchical pores and high CO₂ adsorption uptakes, making the Ni-NCA excellent catalyst for the CO₂RR.
● The Ni-NCA achieve an industrial level j_CO of 226 mA cm^-2, high FE_CO of 95.6% and large turnover frequency (TOF) of 271810 h^-1 in a flow-cell reactor at -1.0 V.
● Ni single-atom sites supported on carbon aerogel catalysts (Ni-NCA) were fabricated by pyrolysis of Ni/Zn-ZIF-8/CMC.

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References

[1]	J. Liang, Q. Wu, Y.B. Huang, R. Cao, Reticular frameworks and their derived materials for CO₂ conversion by thermo-catalysis, Energy Chem. 3 (2021) 100064. doi: 10.1016/j.enchem.2021.100064
[2]	Y.H. Zou, Q.J. Wu, Q. Yin, Y.B. Huang, R. Cao, Self-assembly of imidazolium-functionalized Zr-based metal-organic polyhedra for catalytic conversion of CO₂ into cyclic carbonates, Inorg. Chem. 60 (2021) 2112–2116. doi: 10.1021/acs.inorgchem.0c01199
[3]	S. Ren, D. Joulié, D. Salvatore, K. Torbensen, M. Wang, M. Robert, C.P. Berlinguette, Molecular electrocatalysts can mediate fast, selective CO₂ reduction in a flow cell, Science 365 (2019) 367–369. doi: 10.1126/science.aax4608
[4]	D. Gao, R.M. Arán-Ais, H.S. Jeon, B.R. Cuenya, Rational catalyst and electrolyte design for CO₂ electroreduction towards multicarbon products, Nat. Catal. 2 (2019) 198–210. doi: 10.1038/s41929-019-0235-5
[5]	A. Cherevotan, J. Raj, L. Dheer, S. Roy, S. Sarkar, R. Das, C.P. Vinod, S. Xu, P. Wells, U.V. Waghmare, S.C. Peter, Operando generated ordered heterogeneous catalyst for the selective conversion of CO₂ to methanol, ACS Energy Lett. 6 (2021) 509–516. doi: 10.1021/acsenergylett.0c02614
[6]	Y. Mun, S. Lee, A. Cho, S. Kim, J.W. Han, J. Lee, Cu-Pd alloy nanoparticles as highly selective catalysts for efficient electrochemical reduction of CO₂ to CO, Appl. Catal. B 246 (2019) 82–88. doi: 10.1016/j.apcatb.2019.01.021
[7]	J. Feng, H. Gao, L. Zheng, Z. Chen, S. Zeng, C. Jiang, H. Dong, L. Liu, S. Zhang, X. Zhang, A Mn-N₃ single-atom catalyst embedded in graphitic carbon nitride for efficient CO₂ electroreduction, Nat. Commun. 11 (2020) 4341. doi: 10.1038/s41467-020-18143-y
[8]	C. Zhao, G. Luo, X. Liu, W. Zhang, Z. Li, Q. Xu, Q. Zhang, H. Wang, D. Li, F. Zhou, Y. Qu, X. Han, Z. Zhu, G. Wu, J. Wang, J. Zhu, T. Yao, Y. Li, H.J.M. Bouwmeester, Y. Wu, In situ topotactic transformation of an interstitial alloy for CO electroreduction, Adv. Mater. 32 (2020) e2002382. doi: 10.1002/adma.202002382
[9]	X. Sun, L. Lu, Q. Zhu, C. Wu, D. Yang, C. Chen, B. Han, MoP nanoparticles supported on indium-doped porous carbon: outstanding catalysts for highly efficient CO₂ electroreduction, Angew. Chem. Int. Ed. 57 (2018) 2427–2431. doi: 10.1002/anie.201712221
[10]	D. Karapinar, C.E. Creissen, J.G. Rivera de la Cruz, M.W. Schreiber, M. Fontecave, Electrochemical CO₂ reduction to ethanol with copper-based catalysts, ACS Energy Lett. 6 (2021) 694–706. doi: 10.1021/acsenergylett.0c02610
[11]	F. Li, L. Chen, G.P. Knowles, D.R. MacFarlane, J. Zhang, Hierarchical mesoporous SnO₂ nanosheets on carbon cloth: a robust and flexible electrocatalyst for CO₂ reduction with high efficiency and selectivity, Angew. Chem. Int. Ed. 56 (2017) 505–509. doi: 10.1002/anie.201608279
[12]	W. Zhu, S. Kattel, F. Jiao, J.G. Chen, Shape-controlled CO₂ electrochemical reduction on nanosized Pd hydride cubes and octahedra, Adv. Energy Mater. 9 (2019) 1802840. doi: 10.1002/aenm.201802840
[13]	Y.C. Li, G. Lee, T. Yuan, Y. Wang, D.-H. Nam, Z. Wang, F.P. García de Arquer, Y. Lum, C.-T. Dinh, O. Voznyy, E.H. Sargent, CO₂ electroreduction from carbonate electrolyte, ACS Energy Lett. 4 (2019) 1427–1431. doi: 10.1021/acsenergylett.9b00975
[14]	Y. Peng, L. Wang, Q. Luo, Y. Cao, Y. Dai, Z. Li, H. Li, X. Zheng, W. Yan, J. Yang, J. Zeng, Molecular-level insight into how hydroxyl groups boost catalytic activity in CO₂ hydrogenation into methanol, Inside Chem. 4 (2018) 613–625.
[15]	D. Sheberla, J.C. Bachman, J.S. Elias, C.J. Sun, Y. Shao-Horn, M. Dinca, Conductive MOF electrodes for stable supercapacitors with high areal capacitance, Nat. Mater. 16 (2017) 220–224. doi: 10.1038/nmat4766
[16]	D.L. Meng, M.D. Zhang, D.H. Si, M.J. Mao, Y. Hou, Y.B. Huang, R. Cao, Highly selective tandem electroreduction of CO₂ to ethylene over atomically isolated nickel-nitrogen site/copper nanoparticle catalysts, Angew. Chem. Int. Ed. 60 (2021) 25485–25492. doi: 10.1002/anie.202111136
[17]	Q. Wu, M.J. Mao, Q.J. Wu, J. Liang, Y.B. Huang, R. Cao, Construction of donoracceptor heterojunctions in covalent organic framework for enhanced CO₂ electroreduction, Small 17 (2021) 2004933. doi: 10.1002/smll.202004933
[18]	Q. Wu, R.-K. Xie, M.-J. Mao, G.-L. Chai, J.-D. Yi, S.-S. Zhao, Y.-B. Huang, R. Cao, Integration of strong electron transporter tetrathiafulvalene into metalloporphyrinbased covalent organic framework for highly efficient electroreduction of CO₂, ACS Energy Lett. 5 (2020) 1005–1012. doi: 10.1021/acsenergylett.9b02756
[19]	X. Zhang, Y. Wang, M. Gu, M. Wang, Z. Zhang, W. Pan, Z. Jiang, H. Zheng, M. Lucero, H. Wang, G.E. Sterbinsky, Q. Ma, Y.-G. Wang, Z. Feng, J. Li, H. Dai, Y. Liang, Molecular engineering of dispersed nickel phthalocyanines on carbon nanotubes for selective CO₂ reduction, Nat. Energy 5 (2020) 684–692. doi: 10.1038/s41560-020-0667-9
[20]	X.-F. Qiu, H.-L. Zhu, J.-R. Huang, P.-Q. Liao, X.-M. Chen, Highly selective CO₂ electroreduction to C₂H₄ using a metal-organic framework with dual active sites, J. Am. Chem. Soc. 143 (2021) 7242–7246. doi: 10.1021/jacs.1c01466
[21]	T. Zheng, K. Jiang, N. Ta, Y. Hu, J. Zeng, J. Liu, H. Wang, Large-scale and highly selective CO₂ electrocatalytic reduction on nickel single-atom catalyst, Joule 3 (2019) 265–278. doi: 10.1016/j.joule.2018.10.015
[22]	C. Zhao, Y. Wang, Z. Li, W. Chen, Q. Xu, D. He, D. Xi, Q. Zhang, T. Yuan, Y. Qu, J. Yang, F. Zhou, Z. Yang, X. Wang, J. Wang, J. Luo, Y. Li, H. Duan, Y. Wu, Y. Li, Solid-diffusion synthesis of single-atom catalysts directly from bulk metal for efficient CO₂ reduction, Joule 3 (2019) 584–594. doi: 10.1016/j.joule.2018.11.008
[23]	L. Jiao, J. Zhu, Y. Zhang, W. Yang, S. Zhou, A. Li, C. Xie, X. Zheng, W. Zhou, S.H. Yu, H.L. Jiang, Non-bonding interaction of neighboring Fe and Ni single-atom pairs on MOF-derived N-doped carbon for enhanced CO₂ electroreduction, J. Am. Chem. Soc. 143 (2021) 19417–19424. doi: 10.1021/jacs.1c08050
[24]	J.D. Yi, R. Xie, Z.L. Xie, G.L. Chai, T.F. Liu, R.P. Chen, Y.B. Huang, R. Cao, Highly selective CO₂ electroreduction to CH₄ by in situ generated Cu₂O single-type sites on a conductive MOF: stabilizing key intermediates with hydrogen bonding, Angew. Chem. Int. Ed. 59 (2020) 23641–23648. doi: 10.1002/anie.202010601
[25]	M.-D. Zhang, D.-H. Si, J.-D. Yi, Q. Yin, Y.-B. Huang, R. Cao, Conductive phthalocyanine-based metal-organic framework as a highly efficient electrocatalyst for carbon Dioxide reduction reaction, Sci. China Chem. 64 (2021) 1332–1339.
[26]	S. Wei, H. Zou, W. Rong, F. Zhang, Y. Ji, L. Duan, Conjugated nickel phthalocyanine polymer selectively catalyzes CO₂-to-CO conversion in A wide operating potential window, Appl. Catal. B 284 (2021) 119739. doi: 10.1016/j.apcatb.2020.119739
[27]	Y.N. Gong, L. Jiao, Y. Qian, C.Y. Pan, L. Zheng, X. Cai, B. Liu, S.H. Yu, H.L. Jiang, Regulating the coordination environment of MOF-templated single-atom nickel electrocatalysts for boosting CO₂ reduction, Angew. Chem. Int. Ed. 59 (2020) 2705–2709. doi: 10.1002/anie.201914977
[28]	Q. Wu, J. Liang, Z.-L. Xie, Y.-B. Huang, R. Cao, Spatial sites separation strategy to fabricate atomically isolated nickel catalysts for efficient CO₂ electroreduction, ACS Mater. Lett. 3 (2021) 454–461. doi: 10.1021/acsmaterialslett.1c00090
[29]	Y. Hou, Y.-B. Huang, Y.-L. Liang, G.-L. Chai, J.-D. Yi, T. Zhang, K.-T. Zang, J. Luo, R. Xu, H. Lin, S.-Y. Zhang, H.-M. Wang, R. Cao, Unraveling the reactivity and selectivity of atomically isolated metal-nitrogen sites anchored on porphyrinic triazine frameworks for electroreduction of CO₂, CCS Chem. 1 (2019) 384–395. doi: 10.31635/ccschem.019.20190011
[30]	H. Yang, Y. Liu, X. Liu, X. Wang, H. Tian, G.I.N. Waterhouse, P.E. Kruger, S.G. Telfer, S. Ma, Large-scale synthesis of N-doped carbon capsules supporting atomically dispersed iron for efficient oxygen reduction reaction electrocatalysis, eScience. https://doi.org/10.1016/j.esci.2022.02.005.
[31]	K. Jiang, S. Siahrostami, A.J. Akey, Y. Li, Z. Lu, J. Lattimer, Y. Hu, C. Stokes, M. Gangishetty, G. Chen, Y. Zhou, W. Hill, W.-B. Cai, D. Bell, K. Chan, J.K. Nørskov, Y. Cui, H. Wang, Transition-metal single atoms in a graphene shell as active centers for highly efficient artificial photosynthesis, Inside Chem. 3 (2017) 950–960.
[32]	X. Rong, H.J. Wang, X.L. Lu, R. Si, T.B. Lu, Controlled synthesis of a vacancy-defect single-atom catalyst for boosting CO₂ electroreduction, Angew. Chem. Int. Ed. 59 (2020) 1961–1965. doi: 10.1002/anie.201912458
[33]	M. Zhang, T.-S. Wu, S. Hong, Q. Fan, Y.-L. Soo, J. Masa, J. Qiu, Z. Sun, Efficient electrochemical reduction of CO₂ by Ni-N catalysts with tunable performance, ACS Sustain. Chem. Eng. 7 (2019) 15030–15035. doi: 10.1021/acssuschemeng.9b03502
[34]	X. Li, W. Bi, M. Chen, Y. Sun, H. Ju, W. Yan, J. Zhu, X. Wu, W. Chu, C. Wu, Y. Xie, Exclusive Ni-N4 sites realize near-unity CO selectivity for electrochemical CO₂ reduction, J. Am. Chem. Soc. 139 (2017) 14889–14892. doi: 10.1021/jacs.7b09074
[35]	L. Jiao, W. Yang, G. Wan, R. Zhang, X. Zheng, H. Zhou, S.H. Yu, H.L. Jiang, Singleatom electrocatalysts from multivariate metal-organic frameworks for highly selective reduction of CO₂ at low pressures, Angew. Chem. Int. Ed. 59 (2020) 20589–20595. doi: 10.1002/anie.202008787
[36]	Y. Cheng, S. Zhao, H. Li, S. He, J.-P. Veder, B. Johannessen, J. Xiao, S. Lu, J. Pan, M.F. Chisholm, S.-Z. Yang, C. Liu, J.G. Chen, S.P. Jiang, Unsaturated edge-anchored Ni single atoms on porous microwave exfoliated graphene oxide for electrochemical CO₂, Appl. Catal. B 243 (2019) 294–303. doi: 10.1016/j.apcatb.2018.10.046
[37]	K. Jiang, S. Siahrostami, T. Zheng, Y. Hu, S. Hwang, E. Stavitski, Y. Peng, J. Dynes, M. Gangisetty, D. Su, K. Attenkofer, H. Wang, Isolated Ni single atoms in graphene nanosheets for high-performance CO₂ reduction, Energy Environ. Sci. 11 (2018) 893–903. doi: 10.1039/C7EE03245E
[38]	M. Wang, B. Zhang, J. Ding, N. Xu, M.T. Bernards, Y. He, Y. Shi, Three-dimensional nitrogen-doped graphene aerogel-supported MnO nanoparticles as efficient electrocatalysts for CO₂ reduction to CO, ACS Sustain. Chem. Eng. 8 (2020) 4983–4994. doi: 10.1021/acssuschemeng.0c01194
[39]	K. Ye, G. Zhang, X.-Y. Ma, C. Deng, X. Huang, C. Yuan, G. Meng, W.-B. Cai, K. Jiang, Resolving local reaction environment toward an optimized CO₂-to-CO conversion performance, Energy Environ. Sci. 15 (2022) 749–759. doi: 10.1039/D1EE02966E
[40]	M. Kuang, A. Guan, Z. Gu, P. Han, L. Qian, G. Zheng, Enhanced N-doping in mesoporous carbon for efficient electrocatalytic CO₂ conversion, Nano Res. 12 (2019) 2324–2329. doi: 10.1007/s12274-019-2396-6
[41]	S.-F. Tang, X.-L. Lu, C. Zhang, Z.-W. Wei, R. Si, T.-B. Lu, Decorating graphdiyne on ultrathin bismuth subcarbonate nanosheets to promote CO₂ electroreduction to formate, Sci. Bull. 66 (2021) 1533–1541. doi: 10.1016/j.scib.2021.03.020
[42]	M. Li, H. Wang, W. Luo, P.C. Sherrell, J. Chen, J. Yang, Heterogeneous single-atom catalysts for electrochemical CO₂ reduction reaction, Adv. Mater. 32 (2020), e2001848. doi: 10.1002/adma.202001848
[43]	S. Li, M. Ceccato, X. Lu, S. Frank, N. Lock, A. Roldan, X.-M. Hu, T. Skrydstrup, K. Daasbjerg, Incorporation of nickel single atoms into carbon paper as self-standing electrocatalyst for CO₂ reduction, J. Mater. Chem. A 9 (2021) 1583–1592. doi: 10.1039/D0TA08433F
[44]	Y. Hou, Y.-L. Liang, P.-C. Shi, Y.-B. Huang, R. Cao, Atomically dispersed Ni species on N-doped carbon nanotubes for electroreduction of CO₂ with nearly 100% CO selectivity, Appl. Catal. B 271 (2020), 118929. doi: 10.1016/j.apcatb.2020.118929
[45]	Q. Fan, P. Hou, C. Choi, T.S. Wu, S. Hong, F. Li, Y.L. Soo, P. Kang, Y. Jung, Z. Sun, Activation of Ni particles into single Ni-N atoms for efficient electrochemical reduction of CO₂, Adv. Energy Mater. 10 (2019) 1903068.
[46]	F. Zhao, Y. Shi, L. Pan, G. Yu, Multifunctional nanostructured conductive polymer gels: synthesis, properties, and applications, Acc. Chem. Res. 50 (2017) 1734–1743. doi: 10.1021/acs.accounts.7b00191
[47]	X. Zhou, Y. Guo, F. Zhao, G. Yu, Hydrogels as an emerging material platform for solar water purification, Acc. Chem. Res. 52 (2019) 3244–3253. doi: 10.1021/acs.accounts.9b00455
[48]	Z. Fang, P. Li, G Yu Gel, Electrocatalysts: An emerging material platform for electrochemical energy conversion, Adv. Mater. 32 (2020) e2003191. doi: 10.1002/adma.202003191
[49]	X. Ma, Y. Lou, X.-B. Chen, Z. Shi, Y. Xu, Multifunctional flexible composite aerogels constructed through in-situ growth of metal-organic framework nanoparticles on bacterial cellulose, Chem. Eng. J. 356 (2019) 227–235. doi: 10.1016/j.cej.2018.09.034
[50]	C. Tan, M.C. Lee, M. Arshadi, M. Azizi, A. Abbaspourrad, A spiderweb-like metalorganic framework multifunctional foam, Angew. Chem. Int. Ed. 59 (2020) 9506–9513. doi: 10.1002/anie.201916211
[51]	C. Wang, J. Kim, J. Tang, J. Na, Y.M. Kang, M. Kim, H. Lim, Y. Bando, J. Li, Y. Yamauchi, Large-scale synthesis of MOF-derived superporous carbon aerogels with extraordinary adsorption capacity for organic solvents, Angew. Chem. Int. Ed. 132 (2020) 2082–2086. doi: 10.1002/ange.201913719
[52]	K. Mou, Z. Chen, X. Zhang, M. Jiao, X. Zhang, X. Ge, W. Zhang, L. Liu, Highly efficient electroreduction of CO₂ on nickel single-atom catalysts: atom trapping and nitrogen anchoring, Small 15 (2019) e1903668. doi: 10.1002/smll.201903668
[53]	M. Wang, J. Zhang, X. Yi, X. Zhao, B. Liu, X. Liu, Nitrogen-doped hierarchical porous carbon derived from ZIF-8 supported on carbon aerogels with advanced performance for supercapacitor, Appl. Surf. Sci. 507 (2020) 145166. doi: 10.1016/j.apsusc.2019.145166
[54]	X. Xiao, Y. Xu, X. Lv, J. Xie, J. Liu, C. Yu, Electrochemical CO₂ reduction on copper nanoparticles-dispersed carbon aerogels, J. Colloid Interface Sci. 545 (2019) 1–7. doi: 10.1016/j.jcis.2019.03.005
[55]	H. Yang, Q. Lin, C. Zhang, X. Yu, Z. Cheng, G. Li, Q. Hu, X. Ren, Q. Zhang, J. Liu, C. He, Carbon Dioxide electroreduction on single-atom nickel decorated carbon membranes with industry compatible current densities, Nat. Commun. 11 (2020) 593. doi: 10.1038/s41467-020-14402-0
[56]	H.J. Qiu, Y. Ito, W. Cong, Y. Tan, P. Liu, A. Hirata, T. Fujita, Z. Tang, M. Chen, Nanoporous graphene with single-atom nickel dopants: an efficient and stable catalyst for electrochemical hydrogen production, Angew. Chem. Int. Ed. 54 (2015) 14031–14035. doi: 10.1002/anie.201507381
[57]	Y. Jia, L. Zhang, A. Du, G. Gao, J. Chen, X. Yan, C.L. Brown, X. Yao, Defect graphene as a trifunctional catalyst for electrochemical reactions, Adv. Mater. 28 (2016) 9532–9538. doi: 10.1002/adma.201602912
[58]	J. Zhang, Z. Zhao, Z. Xia, L. Dai, A metal-free bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions, Nat. Nanotechnol. 10 (2015) 444–452. doi: 10.1038/nnano.2015.48
[59]	Q. Hu, G. Li, X. Liu, B. Zhu, X. Chai, Q. Zhang, J. Liu, C. He, Superhydrophilic phytic-acid-doped conductive hydrogels as metal-free and binder-free electrocatalysts for efficient water oxidation, Angew. Chem. Int. Ed. 58 (2019) 4318–4322. doi: 10.1002/anie.201900109
[60]	R.-X. Yang, Y.-R. Wang, G.-K. Gao, L. Chen, Y. Chen, S.-L. Li, Y.-Q. Lan, Selfassembly of hydroxyl metal-organic polyhedra and polymer into Cu-based hollow spheres for product-selective CO₂ electroreduction, Small Struct. 2 (2021) 2100012. doi: 10.1002/sstr.202100012
[61]	G. Cai, P. Yan, L. Zhang, H.C. Zhou, H.L. Jiang, Metal-organic framework-based hierarchically porous materials: synthesis and applications, Chem. Rev. 121 (2021) 12278–12326. doi: 10.1021/acs.chemrev.1c00243
[62]	C. He, J. Liang, Y. H. Zou, J. D. Yi, Y. B. Huang, R Cao. Metal-organic frameworks bonded with metal N-heterocyclic carbenes for efficient catalysis. Natl. Sci. Rev. https://doi.org/10.1093/nsr/nwab157.
[63]	C. He, Q.J. Wu, M.J. Mao, Y.H. Zou, B.T. Liu, Y.B. Huang, R. Cao, Multifunctional gold nanoparticles@Imidazolium-based cationic covalent triazine frameworks for efficient tandem reactions, CCS Chem. 2 (2020) 2368–2380.
[64]	C. Yan, H. Li, Y. Ye, H. Wu, F. Cai, R. Si, J. Xiao, S. Miao, S. Xie, F. Yang, Y. Li, G. Wang, X. Bao, Coordinatively unsaturated nickel-nitrogen sites towards selective and high-rate CO₂ electroreduction, Energy Environ. Sci. 11 (2018) 1204–1210. doi: 10.1039/C8EE00133B
[65]	Y.S. Wei, M. Zhang, R. Zou, Q. Xu, Metal-organic framework-based catalysts with single metal sites, Chem. Rev. 120 (2020) 12089–12174. doi: 10.1021/acs.chemrev.9b00757
[66]	J.D. Yi, M.D. Zhang, Y. Hou, Y.B. Huang, R. Cao, N-doped carbon aerogel derived from a metal-organic framework foam as an efficient electrocatalyst for oxygen reduction, Chem. Asian J. 14 (2019) 3642–3647. doi: 10.1002/asia.201900727
[67]	Y. Zhang, X. Wang, S. Zheng, B. Yang, Z. Li, J. Lu, Q. Zhang, N.M. Adli, L. Lei, G. Wu, Y. Hou, Hierarchical cross-linked carbon aerogels with transition metalnitrogen sites for highly efficient industrial-level CO₂ electroreduction, Adv. Funct. Mater. 31 (2021) 2104377. doi: 10.1002/adfm.202104377
[68]	M.S. Dresselhaus, G. Dresselhaus, R. Saito, A. Jorio, Raman spectroscopy of carbon nanotubes, Phys. Rep. 409 (2005) 47–99. doi: 10.1016/j.physrep.2004.10.006
[69]	H.B. Yang, S.-F. Hung, S. Liu, K. Yuan, S. Miao, L. Zhang, X. Huang, H.-Y. Wang, W. Cai, R. Chen, J. Gao, X. Yang, W. Chen, Y. Huang, H.M. Chen, C.M. Li, T. Zhang, B. Liu, Atomically dispersed Ni(i) as the active site for electrochemical CO₂ reduction, Nat. Energy 3 (2018) 140–147. doi: 10.1038/s41560-017-0078-8
[70]	J.D. Yi, D.H. Si, R. Xie, Q. Yin, M.D. Zhang, Q. Wu, G.L. Chai, Y.B. Huang, R. Cao, Conductive two-dimensional phthalocyanine-based metal-organic framework nanosheets for efficient electroreduction of CO₂, Angew. Chem. Int. Ed. 60 (2021) 17108–17114. doi: 10.1002/anie.202104564
[71]	H. Zhong, M. Ghorbani-Asl, K.H. Ly, J. Zhang, J. Ge, M. Wang, Z. Liao, D. Makarov, E. Zschech, E. Brunner, I.M. Weidinger, J. Zhang, A.V. Krasheninnikov, S. Kaskel, R. Dong, X. Feng, Synergistic electroreduction of carbon Dioxide to carbon monoxide on bimetallic layered conjugated metal-organic frameworks, Nat. Commun. 11 (2020) 1409. doi: 10.1038/s41467-020-15141-y
[72]	S. Zhu, B. Jiang, W.B. Cai, M. Shao, Direct observation on reaction intermediates and the role of bicarbonate anions in CO₂ electrochemical reduction reaction on Cu surfaces, J. Am. Chem. Soc. 139 (2017) 15664–15667. doi: 10.1021/jacs.7b10462
[73]	N. Heidary, K.H. Ly, N. Kornienko, Probing CO₂ conversion chemistry on nanostructured surfaces with operando vibrational spectroscopy, Nano Lett. 19 (2019) 4817–4826. doi: 10.1021/acs.nanolett.9b01582
[74]	S. Zhu, T. Li, W.-B. Cai, M. Shao, CO₂ electrochemical reduction as probed through infrared spectroscopy, ACS Energy Lett. 4 (2019) 682–689. doi: 10.1021/acsenergylett.8b02525