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The successful electrochemical reduction of CO 2 (eCO 2 R) 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 eCO 2 R 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-BiO x) on porous nickel foam (NF) electrodes as electrocatalysts for eCO 2 R. The eCO 2 R 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-BiO x /NF exhibited a higher eCO 2 R 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 DFT-based 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 CO 2 electrolyzer for gas-phase CO 2 reduction containing a self-supporting C-BiO x /NF gas diffusion layer (GDL). An anion exchange membrane-based CO 2 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 CO 2 electrolyzer (FE: 25.2%, EE: 18.4%). Notably, the C-BiO x /NF catalyst exhibited remarkable stability (8 h) in the gas-phase GDL compared to that observed during the liquid-phase eCO 2 R. Our work provides new insights into utilizing improved catalyst designs in conjunction with flow cells for successful commercial implementation of this promising technology. Gas phase CO 2 electrolyzer with C-BiOx/NF gas diffusion layer for efficient and durable CO production. CO 2 electrolyzers are emerging as a promising route to convert CO 2 into fuel and alleviate the global worming problem. [Display omitted] • Carbon-derived bismuth oxide nanospheres (C-BiO x) on NF is fabricated. • High electrocatalytic activity and stability for eCO 2 RR are demonstrated. • Oxygen vacancies promote the transport of electrons for eCO 2 RR. • Self-standing ionomer free low loading C-BiO x /NF electrode for AEM and PEM reactors. • Demonstrated high catalytic stability during gas-phase CO 2 electrolysis on GDL. [ABSTRACT FROM AUTHOR]