Mitigating SO2 Poisoning Effect in Electrochemical CO2 Reduction with Transition-Metal Single-Atom Molecular Catalysts

Abstract

The electrochemical CO2 reduction reaction (CO2RR) offers a promising approach for converting captured CO2 into valuable chemicals and fuels. However, CO2 streams from industrial sources often contain SO2 impurities, which compromise the performance and stability of many electrocatalysts. Herein, we report the impact of SO2 on immobilized single-atom transition-metal (TM) centers─cobalt, nickel, and copper phthalocyanines (TM-PCs) on graphene. We show how the interaction between metal centers and SO2 impurities under CO2RR conditions affects the catalytic response. Among them, the Co-Pc/graphene catalyst demonstrates notable resistance to SO2 poisoning in membrane electrode assembly flow cells, while the other two TM-PCs deactivate. In situ X-ray absorption spectroscopy combined with density functional theory calculations indicates excellent structure stability of the Co-Pc/graphene catalyst and its favorable binding affinity for CO2RR intermediates over SO2-derived species. In contrast, both Cu-Pc/graphene and Ni-Pc/graphene catalysts exhibit severe degradation of the metal-N4 coordination structure and exhibit higher binding affinity toward SO2 species, leading to substantial activity loss in CO2RR. This work highlights the potential of tuning the metal centers of molecular catalysts to enhance impurity tolerance in electrochemical systems.