Gas-phase CO2 electrolysis using carbon-derived bismuth nanospheres on porous nickel foam gas diffusion electrode

The successful electrochemical reduction of CO2 (eCO2R) into valuable fuels and chemicals relies on the development of low-cost, effective carbon-bonded metal catalysts. Carbon-bonded metal catalysts are crucial for efficient eCO2R due to their dual functionality-high electrical conductivity from carbon and catalytic activity from the metal. In this study, a facile hydrothermal method was used to synthesize carbon-derived bismuth oxide nanospheres (C-BiOx) on porous nickel foam (NF) electrodes as electrocatalysts for eCO2R. The eCO2R activity of this catalyst was evaluated in H-type cells and compared with commercially available Pd/C and Ag-nanoparticle catalysts. Our finding revealed that C-BiOx/NF exhibited a higher eCO2R activity (corresponding to the CO Faradaic efficiency (FE) of 16.2 % at -1 V vs. reversible hydrogen electrode (RHE) and HCOOH FE of 85.4 % at -0.7 V vs. RHE) than those of the Ag nanoparticle-based and Pd/C catalysts. Mechanistic insights from DFTbased studies further supported the enhanced catalytic activity of C-BiOx for HCOOH production over Ag catalysts. The fabricated catalyst was further utilized in a zero-gap CO2 electrolyzer for gas-phase CO2 reduction containing a self-supporting C-BiOx/NF gas diffusion layer (GDL). An anion exchange membrane-based CO2 electrolyzer demonstrated a higher FE for CO formation (47.1%) with an energy efficiency (EE) of 29.5% as compared to those of a polymer electrolyte membrane-based CO2 electrolyzer (FE: 25.2%, EE: 18.4%). Notably, the C-BiOx/NF catalyst exhibited remarkable stability (8 h) in the gas-phase GDL compared to that observed during the liquid-phase eCO2R. Our work provides new insights into utilizing improved catalyst designs in conjunction with flow cells for successful commercial implementation of this promising technology.