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Dynamic Behavior of Single-Atom Catalysts in Electrocatalysis: Identification of Cu-N 3 as an Active Site for the Oxygen Reduction Reaction

2021; American Chemical Society; Volume: 143; Issue: 36 Linguagem: Inglês

10.1021/jacs.1c03788

1943-2984

Ji Yang, Wengang Liu, Mingquan Xu, Xiaoyan Liu, Haifeng Qi, Leilei Zhang, Xiaofeng Yang, Shanshan Niu, Dan Zhou, Yuefeng Liu, Yang Su, Jianfeng Li, Zhong‐Qun Tian, Wu Zhou, Aiqin Wang, Tao Zhang,

Catalytic Processes in Materials Science

Atomically dispersed M-N-C (M refers to transition metals) materials represent the most promising catalyst alternatives to the precious metal Pt for the electrochemical reduction of oxygen (ORR), yet the genuine active sites in M-N-C remain elusive. Here, we develop a two-step approach to fabricate Cu-N-C single-atom catalysts with a uniform and well-defined Cu2+-N4 structure that exhibits comparable activity and superior durability in comparison to Pt/C. By combining operando X-ray absorption spectroscopy with theoretical calculations, we unambiguously identify the dynamic evolution of Cu-N4 to Cu-N3 and further to HO-Cu-N2 under ORR working conditions, which concurrently occurs with reduction of Cu2+ to Cu+ and is driven by the applied potential. The increase in the Cu+/Cu2+ ratio with the reduced potential indicates that the low-coordinated Cu+-N3 is the real active site, which is further supported by DFT calculations showing the lower free energy in each elemental step of the ORR on Cu+-N3 than on Cu2+-N4. These findings provide a new understanding of the dynamic electrochemistry on M-N-C catalysts and may guide the design of more efficient low-cost catalysts.