Synchrotron Operando Spectroscopy for Electrochemical reduction of Single-Atom Alloy Ca talysts

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The well-known M-N4 coordinated catalysts show a superior catalytic activity for electrochemical CO2 reduction (ECR). However, the catalytic mechanism and the role of centered metal sites are still remaining a bitter controversy due to the lack of experimental evidence under the operating ECR conditions. Here, the cobalt phthalocyanine (CoPC) is used as a model catalyst to investigate the electronic structure evolution of reactive Co sites by HERFD-XAS and soft-XAS.(1) The graphene supported CoPc (CoPc/G) shows a potential-dependent behavior for H2 and CO production. The selectivity for CO products is increasing as the applied potentials and reaches the maximum value of ~96% Faradic efficiency at-0.8 V (vs. RHE).(2) The Co K HERFD-XAS shows that, as increasing the bias in CO2-saturated electrolyte, the peak at 7708 eV (1s→3d-4p hybridization) is gradually raising the intensity from -0.6 V and is back to the initial without the bias . Inversely, the intensity of the peak at 7715 eV (1s→4pz) is decreased. It implies that the Co site of CoPc/G could be interacted with intermediates (*COOH/*CO) and shows a reversible behavior during the reaction.(3) The Co L soft-XAS shows the intensity of the peak at 777.8 eV regarding to the transitions with components out of CoPc plane decreases at -0.6 V. It is ascribed to the intermediates absorbed on the Co site and results in a large distortion of the D4h symmetry. The spectra show same characteristic features but difference in peak intensities, indicating that the Co site of CoPc/G remains the CoII oxidation state.