Correlation between Ni Valence States Regulated by High-Electronegativity Chalcogens and Acidic CO2 Electroreduction to CO

Abstract Ni-based catalysts serve as an alternative to noble metal CO2 reduction reaction (CO2RR) catalysts. However, the excessive adsorption of *CO leads to a poisoning effect and hinders its desorption for the production of CO. Herein, we describe the systemic regulation of Ni valence by chalcogenides to regulate *CO adsorption for efficient CO2RR to produce CO in acidic media. The relationship between the oxidation state of the Ni site and the adsorption strengths of key intermediates is elucidated. We reveal that the adsorption of *COOH and *CO weakens as the oxidation state of the Ni site increases. The NiTe@C with a moderately oxidized state of +0.34 and thus suitable *COOH and *CO adsorption for efficient catalytic activity in a membrane electrode assembly achieves a CO Faradaic efficiency (FECO) of 91.8% at 300 mA cm–2 in an acidic electrolyte and a high FECO of 97.6% at 500 mA cm–2 under a neutral electrolyte. With the incorporation of a cation-immobilized layer between the cathode and cation-exchange membrane, we achieve a long stability of 70 h in an acidic electrolyte with an ultralow K+ concentration (0.05 M H2SO4 + 0.005 M K2SO4). This work reveals the effect of the chalcogen anion on optimizing CO2RR pathways, offering a viable strategy for understanding the role of valence in catalysis.