Recent Advances
Recent Developments of Atomically Dispersed Metal Electrocatalysts for Oxygen Reduction Reaction†
Ruoyu Pang,
Hongyin Xia,
Jing Li,
Shaojun Guo,
Erkang Wang,
Ruoyu Pang
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022 China
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026 China
Search for more papers by this authorHongyin Xia
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022 China
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026 China
Search for more papers by this authorCorresponding Author
Jing Li
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022 China
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026 China
E-mail: [email protected]; [email protected]Search for more papers by this authorCorresponding Author
Shaojun Guo
School of Materials Science and Engineering, Peking University, Beijing, 100871 China
E-mail: [email protected]; [email protected]Search for more papers by this authorErkang Wang
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022 China
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026 China
Search for more papers by this authorRuoyu Pang,
Hongyin Xia,
Jing Li,
Shaojun Guo,
Erkang Wang,
Ruoyu Pang
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022 China
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026 China
Search for more papers by this authorHongyin Xia
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022 China
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026 China
Search for more papers by this authorCorresponding Author
Jing Li
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022 China
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026 China
E-mail: [email protected]; [email protected]Search for more papers by this authorCorresponding Author
Shaojun Guo
School of Materials Science and Engineering, Peking University, Beijing, 100871 China
E-mail: [email protected]; [email protected]Search for more papers by this authorErkang Wang
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022 China
School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui, 230026 China
Search for more papers by this author†Dedicated to Professor Erkang Wang on the Occasion of His 90th Birthday.
Comprehensive Summary
Oxygen reduction reaction (ORR) is the pivotal portion in many electrochemical energy conversion and storage technologies. However, the complex mechanisms and sluggish kinetics of ORR have also become one of the key issues hindering the development and application of these technologies. Recently, single-atom catalysts (SACs) with well-defined atomic active centers and theoretical 100% atomic utilization have attracted broad interests in the area of electrocatalytic ORR. The electrocatalytic ORR performance of SACs is fundamentally determined by the intrinsic activity of the single-atom active site and increasing the number of active sites involved in the ORR can further enhance the ORR activity of SACs. In this review, advances in atomically dispersed metal electrocatalysts for ORR in the last three years are summarized. Three main regulation strategies for achieving SACs with excellent intrinsic activity in the context of the ORR mechanism are involved including modulation of coordination environments, the construction of intrinsic defects, and the introduction of dual active sites. Moreover, discussions on improving the loading and utilization of active sites are given. Finally, the current challenges and opportunities for the development of SACs for ORR are presented.
References
- 1 Staffell, I.; Scamman, D.; Velazquez Abad, A.; Balcombe, P.; Dodds, P. E.; Ekins, P.; Shah, N.; Ward, K. R. The role of hydrogen and fuel cells in the global energy system. Energy Environ. Sci. 2019, 12, 463–491.
- 2 Yang, H.; Han, X.; Douka, A. I.; Huang, L.; Gong, L.; Xia, C.; Park, H. S.; Xia, B. Y. Advanced Oxygen Electrocatalysis in Energy Conversion and Storage. Adv. Funct. Mater. 2020, 31, 2007602.
- 3 Stephens, I. E.; Rossmeisl, J.; Chorkendorff, I. Toward sustainable fuel cells. Science 2016, 354, 1378–1379.
- 4 Zaman, S.; Huang, L.; Douka, A. I.; Yang, H.; You, B.; Xia, B. Y. Oxygen Reduction Electrocatalysts toward Practical Fuel Cells: Progress and Perspectives. Angew. Chem. Int. Ed. 2021, 60, 17832–17852.
- 5 He, Y.; Liu, S.; Priest, C.; Shi, Q.; Wu, G. Atomically dispersed metal-nitrogen-carbon catalysts for fuel cells: advances in catalyst design, electrode performance, and durability improvement. Chem. Soc. Rev. 2020, 49, 3484–3524.
- 6 Debe, M. K. Electrocatalyst approaches and challenges for automotive fuel cells. Nature 2012, 486, 43–51.
- 7 Nie, Y.; Li, L.; Wei, Z. Recent advancements in Pt and Pt-free catalysts for oxygen reduction reaction. Chem. Soc. Rev. 2015, 44, 2168–201.
- 8 Sun, M.; Chen, C.; Wu, M.; Zhou, D.; Sun, Z.; Fan, J.; Chen, W.; Li, Y. Rational design of Fe-N-C electrocatalysts for oxygen reduction reaction: From nanoparticles to single atoms. Nano Res. 2021, 15, 1753–1778.
- 9 Ball, P. Single-atom catalysis: a new field that learns from tradition. Natl. Sci. Rev. 2018, 5, 690–693.
- 10 Roduner, E. Size matters: why nanomaterials are different. Chem. Soc. Rev. 2006, 35, 583–92.
- 11 Yang, X. F.; Wang, A.; Qiao, B.; Li, J.; Liu, J.; Zhang, T. Single-atom catalysts: a new frontier in heterogeneous catalysis. Acc. Chem. Res. 2013, 46, 1740–8.
- 12 Qiao, B.; Wang, A.; Yang, X.; Allard, L. F.; Jiang, Z.; Cui, Y.; Liu, J.; Li, J.; Zhang, T. Single-atom catalysis of CO oxidation using Pt1/FeOx. Nat. Chem. 2011, 3, 634–41.
- 13 Wei, P. J.; Yu, G. Q.; Naruta, Y.; Liu, J. G. Covalent grafting of carbon nanotubes with a biomimetic heme model compound to enhance oxygen reduction reactions. Angew. Chem. Int. Ed. 2014, 53, 6659–63.
- 14 Yang, H.; Shang, L.; Zhang, Q.; Shi, R.; Waterhouse, G. I. N.; Gu, L.; Zhang, T. A universal ligand mediated method for large scale synthesis of transition metal single atom catalysts. Nat. Commun. 2019, 10, 4585.
- 15 Han, A.; Wang, X.; Tang, K.; Zhang, Z.; Ye, C.; Kong, K.; Hu, H.; Zheng, L.; Jiang, P.; Zhao, C., et al. An Adjacent Atomic Platinum Site Enables Single-Atom Iron with High Oxygen Reduction Reaction Performance. Angew. Chem. Int. Ed. 2021, 60, 19262–19271.
- 16 Chen, Y.; Gao, R.; Ji, S.; Li, H.; Tang, K.; Jiang, P.; Hu, H.; Zhang, Z.; Hao, H.; Qu, Q., et al. Atomic-Level Modulation of Electronic Density at Cobalt Single-Atom Sites Derived from Metal-Organic Frameworks: Enhanced Oxygen Reduction Performance. Angew. Chem. Int. Ed. 2021, 60, 3212–3221.
- 17 Chen, H.; Liang, X.; Liu, Y.; Ai, X.; Asefa, T.; Zou, X. Active Site Engineering in Porous Electrocatalysts. Adv. Mater. 2020, 32, e2002435.
- 18 Wang, Y.; Su, H.; He, Y.; Li, L.; Zhu, S.; Shen, H.; Xie, P.; Fu, X.; Zhou, G.; Feng, C., et al. Advanced Electrocatalysts with Single-Metal-Atom Active Sites. Chem. Rev. 2020, 120, 12217–12314.
- 19 He, Y.; Yang, X.; Li, Y.; Liu, L.; Guo, S.; Shu, C.; Liu, F.; Liu, Y.; Tan, Q.; Wu, G. Atomically Dispersed Fe-Co Dual Metal Sites as Bifunctional Oxygen Electrocatalysts for Rechargeable and Flexible Zn-Air Batteries. ACS Catal. 2022, 12, 1216–1227.
- 20 Khan, K.; Yan, X. X.; Yu, Q. M.; Bae, S. H.; White, J. J.; Liu, J. X.; Liu, T. C.; Sun, C. J.; Kim, J.; Cheng, H. M., et al. Stone-Wales defect-rich carbon-supported dual-metal single atom sites for Zn-air batteries. Nano Energy 2021, 90, 106488.
- 21 Liu, X.; Zhang, Y.; Zhao, Z.; Gao, H.; Kang, J.; Wang, R.; Ge, G.; Jia, X. Highly exposed discrete Co atoms anchored in ultrathin porous N, P-codoped carbon nanosheets for efficient oxygen electrocatalysis and rechargeable aqueous/solid-state Zn-air batteries. J. Mater. Chem. A 2021, 9, 22643–22652.
- 22 Gao, L.; Gao, X.; Jiang, P.; Zhang, C.; Guo, H.; Cheng, Y. Atomically Dispersed Iron with Densely Exposed Active Sites as Bifunctional Oxygen Catalysts for Zinc-Air Flow Batteries. Small 2022, 18, e2105892.
- 23 Wroblowa, H. S.; Yen Chi, P.; Razumney, G. Electroreduction of oxygen. J. Electroanal. Chem 1976, 69, 195–201.
- 24 Yeager, E. Electrocatalysts for O2 reduction. Electrochim. Acta 1984, 29, 1527–1537.
- 25 Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I.; Norskov, J. K.; Jaramillo, T. F. Combining theory and experiment in electrocatalysis: Insights into materials design. Science 2017, 355, eaad4998.
- 26 Gong, H.; Wei, Z.; Gong, Z.; Liu, J.; Ye, G.; Yan, M.; Dong, J.; Allen, C.; Liu, J.; Huang, K., et al. Low-Coordinated Co-N-C on Oxygenated Graphene for Efficient Electrocatalytic H2O2 production. Adv. Funct. Mater. 2021, 32, 2106886.
- 27 Zhao, Q.; Wang, Y.; Lai, W.-H.; Xiao, F.; Lyu, Y.; Liao, C.; Shao, M. Approaching a high-rate and sustainable production of hydrogen peroxide: oxygen reduction on Co-N-C single-atom electrocatalysts in simulated seawater. Energy Environ. Sci. 2021, 14, 5444–5456.
- 28 Shi, G.; Tryk, D. A.; Iwataki, T.; Yano, H.; Uchida, M.; Iiyama, A.; Uchida, H. Unparalleled mitigation of membrane degradation in fuel cells via a counter-intuitive approach: suppression of H2O2 production at the hydrogen anode using a Ptskin-PtCo catalyst. J. Mater. Chem. A 2020, 8, 1091–1094.
- 29 Ye, C. W.; Xu, L. Recent advances in the design of a high performance metal-nitrogen-carbon catalyst for the oxygen reduction reaction. J. Mater. Chem. A 2021, 9, 22218–22247.
- 30 Luo, E.; Chu, Y.; Liu, J.; Shi, Z.; Zhu, S.; Gong, L.; Ge, J.; Choi, C. H.; Liu, C.; Xing, W. Pyrolyzed M-Nx catalysts for oxygen reduction reaction: progress and prospects. Energy Environ. Sci. 2021, 14, 2158–2185.
- 31 Kulkarni, A.; Siahrostami, S.; Patel, A.; Norskov, J. K. Understanding Catalytic Activity Trends in the Oxygen Reduction Reaction. Chem. Rev. 2018, 118, 2302–2312.
- 32 Nørskov, J. K.; Rossmeisl, J.; Logadottir, A.; Lindqvist, L.; Kitchin, J. R.; Bligaard, T.; Jónsson, H. Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode. J. Phys. Chem. B 2004, 108, 17886–17892.
- 33 Zhang, L.; Doyle-Davis, K.; Sun, X. Pt-Based electrocatalysts with high atom utilization efficiency: from nanostructures to single atoms. Energy Environ. Sci. 2019, 12, 492–517.
- 34 Shi, Z.; Zhang, J.; Liu, Z. S.; Wang, H.; Wilkinson, D. P. Current status of ab initio quantum chemistry study for oxygen electroreduction on fuel cell catalysts. Electrochim. Acta 2006, 51, 1905–1916.
- 35 Sun, T.; Xu, L.; Wang, D.; Li, Y. Metal organic frameworks derived single atom catalysts for electrocatalytic energy conversion. Nano Res. 2019, 12, 2067–2080.
- 36 Zhao, C. X.; Li, B. Q.; Liu, J. N.; Zhang, Q. Intrinsic Electrocatalytic Activity Regulation of M-N-C Single-Atom Catalysts for the Oxygen Reduction Reaction. Angew. Chem. Int. Ed. 2021, 60, 4448–4463.
- 37 Jasinski, R. A New Fuel Cell Cathode Catalyst. Nature 1964, 201, 1212–1213.
- 38 Bisen, O. Y.; Nanda, K. K. Alkaline earth metal based single atom catalyst for the highly durable oxygen reduction reaction. Appl. Mater. Today 2020, 21, 100846.
- 39 Lin, Z.; Huang, H.; Cheng, L.; Hu, W.; Xu, P.; Yang, Y.; Li, J.; Gao, F.; Yang, K.; Liu, S., et al. Tuning the p-Orbital Electron Structure of s-Block Metal Ca Enables a High-Performance Electrocatalyst for Oxygen Reduction. Adv. Mater. 2021, 33, e2107103.
- 40 Shi, C.; Maimaitiyiming, X. Biomass-derived precious metal-free porous carbon: Ca-N,P-doped carbon materials and its electrocatalytic properties. J. Alloys Compd. 2021, 883, 160726.
- 41 Qin, Y.; Wu, H.-H.; Zhang, L. A.; Zhou, X.; Bu, Y.; Zhang, W.; Chu, F.; Li, Y.; Kong, Y.; Zhang, Q., et al. Aluminum and Nitrogen Codoped Graphene: Highly Active and Durable Electrocatalyst for Oxygen Reduction Reaction. ACS Catal. 2018, 9, 610–619.
- 42 Liu, H.; Zhu, S.; Cui, Z.; Li, Z.; Wu, S.; Liang, Y. Boosting oxygen reduction catalysis with abundant single atom tin active sites in zinc-air battery. J. Power Sources 2021, 490, 229483.
- 43 Wang, T.; Cao, X.; Qin, H.; Shang, L.; Zheng, S.; Fang, F.; Jiao, L. P-Block Atomically Dispersed Antimony Catalyst for Highly Efficient Oxygen Reduction Reaction. Angew. Chem. Int. Ed. 2021, 60, 21237–21241.
- 44 Yang, H.; Chen, Z.; Kou, S.; Lu, G.; Chen, D.; Liu, Z. Carbon-supported catalysts with atomically dispersed metal sites for oxygen electroreduction: present and future perspectives. J. Mater. Chem. A 2021, 9, 15919–15936.
- 45 Li, R.; Wang, D. Understanding the structure-performance relationship of active sites at atomic scale. Nano Res. 2022, 15, 6888–6923.
- 46 Xu, H.; Jia, H.; Li, H.; Liu, J.; Gao, X.; Zhang, J.; Liu, M.; Sun, D.; Chou, S.; Fang, F., et al. Dual carbon-hosted Co-N3 enabling unusual reaction pathway for efficient oxygen reduction reaction. Appl. Catal. B 2021, 297, 120390.
- 47 Miao, Z.; Wang, X.; Zhao, Z.; Zuo, W.; Chen, S.; Li, Z.; He, Y.; Liang, J.; Ma, F.; Wang, H. L., et al. Improving the Stability of Non-Noble-Metal M-N-C Catalysts for Proton-Exchange-Membrane Fuel Cells through M-N Bond Length and Coordination Regulation. Adv. Mater. 2021, 33, e2006613.
- 48 Jia, Y.; Xue, Z.; Yang, J.; Liu, Q.; Xian, J.; Zhong, Y.; Sun, Y.; Zhang, X.; Liu, Q.; Yao, D., et al. Tailoring the Electronic Structure of an Atomically Dispersed Zinc Electrocatalyst: Coordination Environment Regulation for High Selectivity Oxygen Reduction. Angew. Chem. Int. Ed. 2022, 61, e202110838.
- 49 Wang, Y.; Shi, R.; Shang, L.; Waterhouse, G. I. N.; Zhao, J.; Zhang, Q.; Gu, L.; Zhang, T. High-Efficiency Oxygen Reduction to Hydrogen Peroxide Catalyzed by Nickel Single-Atom Catalysts with Tetradentate N2O2 Coordination in a Three-Phase Flow Cell. Angew. Chem. Int. Ed. 2020, 59, 13057–13062.
- 50 Jiang, K.; Back, S.; Akey, A. J.; Xia, C.; Hu, Y.; Liang, W.; Schaak, D.; Stavitski, E.; Norskov, J. K.; Siahrostami, S., et al. Highly selective oxygen reduction to hydrogen peroxide on transition metal single atom coordination. Nat. Commun. 2019, 10, 3997.
- 51 Li, X.; Yang, X.; Liu, L.; Zhao, H.; Li, Y.; Zhu, H.; Chen, Y.; Guo, S.; Liu, Y.; Tan, Q., et al. Chemical Vapor Deposition for N/S-Doped Single Fe Site Catalysts for the Oxygen Reduction in Direct Methanol Fuel Cells. ACS Catal. 2021, 11, 7450–7459.
- 52 Wang, M.; Yang, W.; Li, X.; Xu, Y.; Zheng, L.; Su, C.; Liu, B. Atomically Dispersed Fe-Heteroatom (N, S) Bridge Sites Anchored on Carbon Nanosheets for Promoting Oxygen Reduction Reaction. ACS Energy Lett. 2021, 6, 379–386.
- 53 Sun, T.; Zang, W.; Yan, H.; Li, J.; Zhang, Z.; Bu, Y.; Chen, W.; Wang, J.; Lu, J.; Su, C. Engineering the Coordination Environment of Single Cobalt Atoms for Efficient Oxygen Reduction and Hydrogen Evolution Reactions. ACS Catal. 2021, 11, 4498–4509.
- 54 Chen, K.; Liu, K.; An, P.; Li, H.; Lin, Y.; Hu, J.; Jia, C.; Fu, J.; Li, H.; Liu, H., et al. Iron phthalocyanine with coordination induced electronic localization to boost oxygen reduction reaction. Nat. Commun. 2020, 11, 4173.
- 55 Hu, L.; Dai, C.; Chen, L.; Zhu, Y.; Hao, Y.; Zhang, Q.; Gu, L.; Feng, X.; Yuan, S.; Wang, L., et al. Metal-Triazolate-Framework-Derived FeN4 Cl1 Single-Atom Catalysts with Hierarchical Porosity for the Oxygen Reduction Reaction. Angew. Chem. Int. Ed. 2021, 60, 27324–27329.
- 56 Xin, C.; Shang, W.; Hu, J.; Zhu, C.; Guo, J.; Zhang, J.; Dong, H.; Liu, W.; Shi, Y. Integration of Morphology and Electronic Structure Modulation on Atomic Iron-Nitrogen-Carbon Catalysts for Highly Efficient Oxygen Reduction. Adv. Funct. Mater. 2021, 32, 2108345.
- 57 Li, L.; Huang, S.; Cao, R.; Yuan, K.; Lu, C.; Huang, B.; Tang, X.; Hu, T.; Zhuang, X.; Chen, Y. Optimizing Microenvironment of Asymmetric N,S-Coordinated Single-Atom Fe via Axial Fifth Coordination toward Efficient Oxygen Electroreduction. Small 2022, 18, e2105387.
- 58 Liu, F.; Shi, L.; Song, S.; Ge, K.; Zhang, X.; Guo, Y.; Liu, D. Simultaneously Engineering the Coordination Environment and Pore Architecture of Metal-Organic Framework-Derived Single-Atomic Iron Catalysts for Ultraefficient Oxygen Reduction. Small 2021, 17, e2102425.
- 59 Liu, X.; Zhai, X.; Sheng, W.; Tu, J.; Zhao, Z.; Shi, Y.; Xu, C.; Ge, G.; Jia, X. Isolated single iron atoms anchored on a N, S-codoped hierarchically ordered porous carbon framework for highly efficient oxygen reduction. J. Mater. Chem. A 2021, 9, 10110–10119.
- 60 Shao, C.; Wu, L.; Zhang, H.; Jiang, Q.; Xu, X.; Wang, Y.; Zhuang, S.; Chu, H.; Sun, L.; Ye, J., et al. A Versatile Approach to Boost Oxygen Reduction of Fe-N4 Sites by Controllably Incorporating Sulfur Functionality. Adv. Funct. Mater. 2021, 31, 2100833.
- 61 Qin, J.; Liu, H.; Zou, P.; Zhang, R.; Wang, C.; Xin, H. L. Altering Ligand Fields in Single-Atom Sites through Second-Shell Anion Modulation Boosts the Oxygen Reduction Reaction. J. Am. Chem. Soc. 2022, 144, 2197–2207.
- 62 Yin, H.; Yuan, P.; Lu, B.-A.; Xia, H.; Guo, K.; Yang, G.; Qu, G.; Xue, D.; Hu, Y.; Cheng, J., et al. Phosphorus-Driven Electron Delocalization on Edge-Type FeN4 Active Sites for Oxygen Reduction in Acid Medium. ACS Catal. 2021, 11, 12754–12762.
- 63 Yu, L.; Li, Y.; Ruan, Y. Dynamic Control of Sacrificial Bond Transformation in the Fe-N-C Single-Atom Catalyst for Molecular Oxygen Reduction. Angew. Chem. Int. Ed. 2021, 60, 25296–25301.
- 64 Tang, C.; Chen, L.; Li, H.; Li, L.; Jiao, Y.; Zheng, Y.; Xu, H.; Davey, K.; Qiao, S. Z. Tailoring Acidic Oxygen Reduction Selectivity on Single- Atom Catalysts via Modification of First and Second Coordination Spheres. J. Am. Chem. Soc. 2021, 143, 7819–7827.
- 65 Li, B. Q.; Zhao, C. X.; Liu, J. N.; Zhang, Q. Electrosynthesis of Hydrogen Peroxide Synergistically Catalyzed by Atomic Co-Nx-C Sites and Oxygen Functional Groups in Noble-Metal-Free Electrocatalysts. Adv. Mater. 2019, 31, e1808173.
- 66 Zhang, E.; Tao, L.; An, J.; Zhang, J.; Meng, L.; Zheng, X.; Wang, Y.; Li, N.; Du, S.; Zhang, J., et al. Engineering the Local Atomic Environments of Indium Single-Atom Catalysts for Efficient Electrochemical Production of Hydrogen Peroxide. Angew. Chem. Int. Ed. 2022, 61, e202117347.
- 67 Yan, D.; Li, Y.; Huo, J.; Chen, R.; Dai, L.; Wang, S. Defect Chemistry of Nonprecious-Metal Electrocatalysts for Oxygen Reactions. Adv. Mater. 2017, 29, 1606459.
- 68 Zhong, W. X.; Zhao, X. R.; Qin, J. Y.; Yang, J. An Active Hybrid Electrocatalyst with Synergized Pyridinic Nitrogen-Cobalt and Oxygen Vacancies for Bifunctional Oxygen Reduction and Evolution. Chin. J. Chem. 2021, 39, 655–660.
- 69 Wang, X.; Jia, Y.; Mao, X.; Liu, D.; He, W.; Li, J.; Liu, J.; Yan, X.; Chen, J.; Song, L., et al. Edge-Rich Fe-N4 Active Sites in Defective Carbon for Oxygen Reduction Catalysis. Adv. Mater. 2020, 32, e2000966.
- 70 Xiao, M.; Xing, Z.; Jin, Z.; Liu, C.; Ge, J.; Zhu, J.; Wang, Y.; Zhao, X.; Chen, Z. Preferentially Engineering FeN4 Edge Sites onto Graphitic Nanosheets for Highly Active and Durable Oxygen Electrocatalysis in Rechargeable Zn-Air Batteries. Adv. Mater. 2020, 32, e2004900.
- 71 Zong, L.; Fan, K.; Wu, W.; Cui, L.; Zhang, L.; Johannessen, B.; Qi, D.; Yin, H.; Wang, Y.; Liu, P., et al. Anchoring Single Copper Atoms to Microporous Carbon Spheres as High-Performance Electrocatalyst for Oxygen Reduction Reaction. Adv. Funct. Mater. 2021, 31, 2104864.
- 72 Cui, L.; Fan, K.; Zong, L.; Lu, F.; Zhou, M.; Li, B.; Zhang, L.; Feng, L.; Li, X.; Chen, Y., et al. Sol-gel pore-sealing strategy imparts tailored electronic structure to the atomically dispersed Ru sites for efficient oxygen reduction reaction. Energy Stor. Mater. 2022, 44, 469–476.
- 73 Cui, L.; Zhao, J.; Liu, G.; Wang, Z.; Li, B.; Zong, L. Rich edge-hosted single-atomic Cu-N4 sites for highly efficient oxygen reduction reaction performance. J. Colloid Interface Sci. 2022, 622, 209–217.
- 74 Rao, P.; Wu, D.; Qin, Y. Y.; Luo, J.; Li, J.; Jia, C.; Deng, P.; Huang, W.; Su, Y.; Shen, Y., et al. Facile fabrication of single-atom catalysts by a plasma-etching strategy for oxygen reduction reaction. J. Mater. Chem. A 2022, 10, 6531–6537.
- 75 Yuan, S.; Zhang, J.; Hu, L.; Li, J.; Li, S.; Gao, Y.; Zhang, Q.; Gu, L.; Yang, W.; Feng, X., et al. Decarboxylation-Induced Defects in MOF-Derived Single Cobalt Atom@Carbon Electrocatalysts for Efficient Oxygen Reduction. Angew. Chem. Int. Ed. 2021, 60, 21685–21690.
- 76 Ying, Y.; Luo, X.; Qiao, J.; Huang, H. “More is Different:” Synergistic Effect and Structural Engineering in Double-Atom Catalysts. Adv. Funct. Mater. 2020, 31, 2007423.
- 77 Zheng, X.; Li, B.; Wang, Q.; Wang, D.; Li, Y. Emerging low-nuclearity supported metal catalysts with atomic level precision for efficient heterogeneous catalysis. Nano Res. 2022, 15, 7806–7839.
- 78 Wang, J.; Xu, R.; Sun, Y.; Liu, Q.; Xia, M.; Li, Y.; Gao, F.; Zhao, Y.; Tse, J. S. Identifying the Zn-Co binary as a robust bifunctional electrocatalyst in oxygen reduction and evolution reactions via shifting the apexes of the volcano plot. J. Energy Chem. 2021, 55, 162–168.
- 79 Wang, D.; Xu, H.; Yang, P.; Lu, X.; Ma, J.; Li, R.; Xiao, L.; Zhang, J.; An, M. Fe-N4 and Co-N4 dual sites for boosting oxygen electroreduction in Zn–air batteries. J. Mater. Chem. A 2021, 9, 13678–13687.
- 80 Chen, Z.; Liao, X.; Sun, C.; Zhao, K.; Ye, D.; Li, J.; Wu, G.; Fang, J.; Zhao, H.; Zhang, J. Enhanced performance of atomically dispersed dual-site Fe-Mn electrocatalysts through cascade reaction mechanism. Appl. Catal. B 2021, 288, 120021.
- 81 Cheng, Y.; Wang, M.; Lu, S.; Tang, C.; Wu, X.; Veder, J.-P.; Johannessen, B.; Thomsen, L.; Zhang, J.; Yang, S.-z., et al. First demonstration of phosphate enhanced atomically dispersed bimetallic FeCu catalysts as Pt-free cathodes for high temperature phosphoric acid doped polybenzimidazole fuel cells. Appl. Catal. B 2021, 284, 119717.
- 82 Tong, M.; Sun, F.; Xie, Y.; Wang, Y.; Yang, Y.; Tian, C.; Wang, L.; Fu, H. Operando Cooperated Catalytic Mechanism of Atomically Dispersed Cu-N4 and Zn-N4 for Promoting Oxygen Reduction Reaction. Angew. Chem. Int. Ed. 2021, 60, 14005–14012.
- 83 Chao, G.; Zhang, Y.; Zhang, L.; Zong, W.; Zhang, N.; Xue, T.; Fan, W.; Liu, T.; Xie, Y. Nitrogen-coordinated single-atom catalysts with manganese and cobalt sites for acidic oxygen reduction. J. Mater. Chem. A 2022, 10, 5930–5936.
- 84 Samireddi, S.; Aishwarya, V.; Shown, I.; Muthusamy, S.; Unni, S. M.; Wong, K. T.; Chen, K. H.; Chen, L. C. Synergistic Dual-Atom Molecular Catalyst Derived from Low-Temperature Pyrolyzed Heterobimetallic Macrocycle-N4 Corrole Complex for Oxygen Reduction. Small 2021, 17, e2103823.
- 85 Zhang, X.; Li, Y.; Jiang, M.; Wei, J.; Ding, X.; Zhu, C.; He, H.; Lai, H.; Shi, J. Engineering the coordination environment in atomic Fe/Ni dual-sites for efficient oxygen electrocatalysis in Zn-air and Mg-air batteries. Chem. Eng. J. 2021, 426, 130758.
- 86 Ye, W.; Chen, S.; Lin, Y.; Yang, L.; Chen, S.; Zheng, X.; Qi, Z.; Wang, C.; Long, R.; Chen, M., et al. Precisely Tuning the Number of Fe Atoms in Clusters on N-Doped Carbon toward Acidic Oxygen Reduction Reaction. Chem 2019, 5, 2865–2878.
- 87 Xiao, M.; Zhang, H.; Chen, Y.; Zhu, J.; Gao, L.; Jin, Z.; Ge, J.; Jiang, Z.; Chen, S.; Liu, C., et al. Identification of binuclear Co2N5 active sites for oxygen reduction reaction with more than one magnitude higher activity than single atom CoN4 site. Nano Energy 2018, 46, 396–403.
- 88 Wang, Z.; Jin, X.; Zhu, C.; Liu, Y.; Tan, H.; Ku, R.; Zhang, Y.; Zhou, L.; Liu, Z.; Hwang, S. J., et al. Atomically Dispersed Co2-N6 and Fe-N4 Costructures Boost Oxygen Reduction Reaction in Both Alkaline and Acidic Media. Adv. Mater. 2021, 33, e2104718.
- 89 Wang, K.; Liu, J.; Tang, Z.; Li, L.; Wang, Z.; Zubair, M.; Ciucci, F.; Thomsen, L.; Wright, J.; Bedford, N. M. Establishing structure/ property relationships in atomically dispersed Co-Fe dual site M-Nx catalysts on microporous carbon for the oxygen reduction reaction. J. Mater. Chem. A 2021, 9, 13044–13055.
- 90 Yu, D.; Ma, Y.; Hu, F.; Lin, C. C.; Li, L.; Chen, H. Y.; Han, X.; Peng, S. Dual-Sites Coordination Engineering of Single Atom Catalysts for Flexible Metal-Air Batteries. Adv. Energy Mater. 2021, 11, 2101242.
- 91 Kong, F.; Si, R.; Chen, N.; Wang, Q.; Li, J.; Yin, G.; Gu, M.; Wang, J.; Liu, L.-M.; Sun, X. Origin of hetero-nuclear Au-Co dual atoms for efficient acidic oxygen reduction. Appl. Catal. B 2022, 301, 120782.
- 92 Ma, Y.; Fan, H.; Wu, C.; Zhang, M.; Yu, J.; Song, L.; Li, K.; He, J. An efficient dual-metal single-atom catalyst for bifunctional catalysis in zinc-air batteries. Carbon 2021, 185, 526–535.
- 93 Hai, X.; Xi, S.; Mitchell, S.; Harrath, K.; Xu, H.; Akl, D. F.; Kong, D.; Li, J.; Li, Z.; Sun, T., et al. Scalable two-step annealing method for preparing ultra-high-density single-atom catalyst libraries. Nat. Nanotechnol. 2022, 17, 174–181.
- 94 Yuan, K.; Lutzenkirchen-Hecht, D.; Li, L.; Shuai, L.; Li, Y.; Cao, R.; Qiu, M.; Zhuang, X.; Leung, M. K. H.; Chen, Y., et al. Boosting Oxygen Reduction of Single Iron Active Sites via Geometric and Electronic Engineering: Nitrogen and Phosphorus Dual Coordination. J. Am. Chem. Soc. 2020, 142, 2404–2412.
- 95 Sa, Y. J.; Seo, D. J.; Woo, J.; Lim, J. T.; Cheon, J. Y.; Yang, S. Y.; Lee, J. M.; Kang, D.; Shin, T. J.; Shin, H. S., et al. A General Approach to Preferential Formation of Active Fe-Nx Sites in Fe-N/C Electrocatalysts for Efficient Oxygen Reduction Reaction. J. Am. Chem. Soc. 2016, 138, 15046–15056.
- 96 Li, J.; Xia, W.; Tang, J.; Gao, Y.; Jiang, C.; Jia, Y.; Chen, T.; Hou, Z.; Qi, R.; Jiang, D., et al. Metal-Organic Framework-Derived Graphene Mesh: a Robust Scaffold for Highly Exposed Fe-N4 Active Sites toward an Excellent Oxygen Reduction Catalyst in Acid Media. J. Am. Chem. Soc. 2022, 144, 9280–9291.
- 97 Yasuda, S.; Furuya, A.; Uchibori, Y.; Kim, J.; Murakoshi, K. Iron- Nitrogen-Doped Vertically Aligned Carbon Nanotube Electrocatalyst for the Oxygen Reduction Reaction. Adv. Funct. Mater. 2016, 26, 738–744.
- 98 Cheng, Y.; Zhang, J.; Wu, X.; Tang, C.; Yang, S.-z.; Su, P.; Thomsen, L.; Zhao, F.; Lu, S.; Liu, J., et al. A template-free method to synthesis high density iron single atoms anchored on carbon nanotubes for high temperature polymer electrolyte membrane fuel cells. Nano Energy 2021, 80, 105534.
- 99 Zhou, Y.; Chen, G.; Wang, Q.; Wang, D.; Tao, X.; Zhang, T.; Feng, X.; Müllen, K. Fe-N-C Electrocatalysts with Densely Accessible Fe-N4 Sites for Efficient Oxygen Reduction Reaction. Adv. Funct. Mater. 2021, 31, 2102420.
- 100 Jiang, M.; Wang, F.; Yang, F.; He, H.; Yang, J.; Zhang, W.; Luo, J.; Zhang, J.; Fu, C. Rationalization on high-loading iron and cobalt dual metal single atoms and mechanistic insight into the oxygen reduction reaction. Nano Energy 2022, 93, 106793.
- 101 Wu, X.; Wang, Q.; Yang, S.; Zhang, J.; Cheng, Y.; Tang, H.; Ma, L.; Min, X.; Tang, C.; Jiang, S. P., et al. Sublayer-enhanced atomic sites of single atom catalysts through in situ atomization of metal oxide nanoparticles. Energy Environ. Sci. 2022, 15, 1183–1191.
- 102 Malko, D.; Kucernak, A.; Lopes, T. In situ electrochemical quantification of active sites in Fe-N/C non-precious metal catalysts. Nat. Commun. 2016, 7, 13285.
- 103 Wan, X.; Liu, X.; Li, Y.; Yu, R.; Zheng, L.; Yan, W.; Wang, H.; Xu, M.; Shui, J. Fe-N-C electrocatalyst with dense active sites and efficient mass transport for high-performance proton exchange membrane fuel cells. Nat. Catal. 2019, 2, 259–268.
- 104 Jaouen, F.; Lefevre, M.; Dodelet, J. P.; Cai, M. Heat-treated Fe/N/C catalysts for O2 electroreduction: are active sites hosted in micropores? J. Phys. Chem. B 2006, 110, 5553–8.
- 105 Fu, X.; Zamani, P.; Choi, J. Y.; Hassan, F. M.; Jiang, G.; Higgins, D. C.; Zhang, Y.; Hoque, M. A.; Chen, Z. In Situ Polymer Graphenization Ingrained with Nanoporosity in a Nitrogenous Electrocatalyst Boosting the Performance of Polymer-Electrolyte-Membrane Fuel Cells. Adv. Mater. 2017, 29, 1604456.
- 106 Antolini, E. Carbon supports for low-temperature fuel cell catalysts. Appl. Catal. B 2009, 88, 1–24.
- 107 Yang, L.; Wang, T.; Wu, D. Porous Nitrogen-doped Reduced Graphene Oxide Gels as Efficient Supercapacitor Electrodes and Oxygen Reduction Reaction Electrocatalysts. Chin. J. Chem. 2020, 38, 1123–1131.
- 108 Hong, Y.; Li, L.; Huang, B.; Tang, X.; Zhai, W.; Hu, T.; Yuan, K.; Chen, Y. Deciphering the Precursor-Performance Relationship of Single-Atom Iron Oxygen Electroreduction Catalysts via Isomer Engineering. Small 2022, 18, e2106122.
- 109 Liang, S.; Zou, L. C.; Zheng, L. J.; Li, F.; Wang, X. X.; Song, L. N.; Xu, J. J. Highly Stable Co Single Atom Confined in Hierarchical Carbon Molecular Sieve as Efficient Electrocatalysts in Metal–Air Batteries. Adv. Energy Mater. 2022, 12, 2103097.
- 110 Liu, M.; Wang, L.; Zhang, L.; Zhao, Y.; Chen, K.; Li, Y.; Yang, X.; Zhao, L.; Sun, S.; Zhang, J. In-Situ Silica Xerogel Assisted Facile Synthesis of Fe-N-C Catalysts with Dense Fe-Nx Active Sites for Efficient Oxygen Reduction. Small 2022, 18, e2104934.
- 111 Xie, X.; Shang, L.; Xiong, X.; Shi, R.; Zhang, T. Fe Single-Atom Catalysts on MOF-5 Derived Carbon for Efficient Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells. Adv. Energy Mater. 2021, 12, 2102688.
- 112 Xie, X.; Peng, L.; Yang, H.; Waterhouse, G. I. N.; Shang, L.; Zhang, T. MIL-101-Derived Mesoporous Carbon Supporting Highly Exposed Fe Single-Atom Sites as Efficient Oxygen Reduction Reaction Catalysts. Adv. Mater. 2021, 33, e2101038.
- 113 Xu, H.; Wang, D.; Yang, P.; Du, L.; Lu, X.; Li, R.; Liu, L.; Zhang, J.; An, M. A hierarchically porous Fe-N-C synthesized by dual melt-salt- mediated template as advanced electrocatalyst for efficient oxygen reduction in zinc-air battery. Appl. Catal. B 2022, 305, 121040.
- 114 Hao, J.; Wang, Y.; Qiu, X.; Liu, M.; Li, W.; Li, J. Dual Inorganic Sacrificial Template Synthesis of Hierarchically Porous Carbon with Specific N Sites for Efficient Oxygen Reduction. ACS Appl. Mater. Interfaces 2021, 13, 28140–28149.
- 115 Wang, D.; Xu, H.; Yang, P.; Xiao, L.; Du, L.; Lu, X.; Li, R.; Zhang, J.; An, M. A dual-template strategy to engineer hierarchically porous Fe-N-C electrocatalysts for the high-performance cathodes of Zn–air batteries. J. Mater. Chem. A 2021, 9, 9761–9770.
- 116 Li, L.; Zhang, L.; Xu, Z.; Yan, D.; Xiao, G. Hierarchically porous carbons fabricated by dual pore-forming approach for the oxygen reduction reaction. Carbon 2022, 189, 634–641.
- 117 Wang, Q.; Yang, Y.; Sun, F.; Chen, G.; Wang, J.; Peng, L.; Chen, W. T.; Shang, L.; Zhao, J.; Sun-Waterhouse, D., et al. Molten NaCl-Assisted Synthesis of Porous Fe-N-C Electrocatalysts with a High Density of Catalytically Accessible FeN4 Active Sites and Outstanding Oxygen Reduction Reaction Performance. Adv. Energy Mater. 2021, 11, 2100219.
- 118 Li, P.; Qi, X.; Zhao, L.; Wang, J.; Wang, M.; Shao, M.; Chen, J. S.; Wu, R.; Wei, Z. Hierarchical 3D porous carbon with facilely accessible Fe-N4 single-atom sites for Zn-air batteries. J. Mater. Chem. A 2022, 10, 5925–5929.
- 119 Han, J.; Bao, H.; Wang, J. Q.; Zheng, L.; Sun, S.; Wang, Z. L.; Sun, C. 3D N-doped ordered mesoporous carbon supported single-atom Fe-N-C catalysts with superior performance for oxygen reduction reaction and zinc-air battery. Appl. Catal. B 2021, 280, 119411.
- 120 Gao, J.; Hu, Y.; Wang, Y.; Lin, X.; Hu, K.; Lin, X.; Xie, G.; Liu, X.; Reddy, K. M.; Yuan, Q., et al. MOF Structure Engineering to Synthesize CoNC Catalyst with Richer Accessible Active Sites for Enhanced Oxygen Reduction. Small 2021, 17, e2104684.
- 121 Zhao, X.; Yang, X.; Wang, M.; Hwang, S.; Karakalos, S.; Chen, M.; Qiao, Z.; Wang, L.; Liu, B.; Ma, Q., et al. Single-Iron Site Catalysts with Self-Assembled Dual-size Architecture and Hierarchical Porosity for Proton-Exchange Membrane Fuel Cells. Appl. Catal. B 2020, 279, 119400.
- 122 Tang, Y.; Liu, R.; Liu, S.; Zheng, B.; Lu, Y.; Fu, R.; Wu, D.; Zhang, M.; Rong, M. Cobalt and nitrogen codoped ultrathin porous carbon nanosheets as bifunctional electrocatalysts for oxygen reduction and evolution. Carbon 2019, 141, 704–711.
- 123 Wu, Y.; Ye, C.; Yu, L.; Liu, Y.; Huang, J.; Bi, J.; Xue, L.; Sun, J.; Yang, J.; Zhang, W., et al. Soft template-directed interlayer confinement synthesis of a Fe-Co dual single-atom catalyst for Zn-air batteries. Energy Stor. Mater. 2022, 45, 805–813.
- 124 Cui, T.; Wang, Y. P.; Ye, T.; Wu, J.; Chen, Z.; Li, J.; Lei, Y.; Wang, D.; Li, Y. Engineering Dual Single-Atom Sites on 2D Ultrathin N-doped Carbon Nanosheets Attaining Ultra-Low-Temperature Zinc-Air Battery. Angew. Chem. Int. Ed. 2022, 61, e202115219.
- 125 Chen, L.; Zhang, X.; Chen, A.; Yao, S.; Hu, X.; Zhou, Z. Targeted design of advanced electrocatalysts by machine learning. Chinese J. Catal. 2022, 43, 11–32.
- 126 Shang, Y.; Duan, X.; Wang, S.; Yue, Q.; Gao, B.; Xu, X. Carbon-based single atom catalyst: Synthesis, characterization, DFT calculations. Chin. Chem. Lett. 2022, 33, 663–673.
- 127 Yang, L.; Zhang, X.; Yu, L.; Hou, J.; Zhou, Z.; Lv, R. Atomic Fe-N4/C in Flexible Carbon Fiber Membrane as Binder-Free Air Cathode for Zn-Air Batteries with Stable Cycling over 1000 h. Adv. Mater. 2022, 34, e2105410.
