Shape-tuned electrodeposition of bismuth-based nanosheets on flow-through hollow fiber gas diffusion electrode for high-efficiency CO2 reduction to formate

Abstract

Gas-phase CO2 electrochemical reduction reaction (CO2RR) requires advanced gas diffusion electrodes (GDEs) for efficient mass transport. Meantime, engineering catalyst nanostructure and tuning surface wettability are decisive to enhance three-phase interfaces formation. Herein, Bi-based nanosheets are uniformly grown on flow-through Cu hollow fiber GDE (HFGDE) to benefit from the unique shape of HFGDEs, and abundant active surface area of nanosheets. Pulse electrodeposition is used to replenish Bi3+ ions in the vicinity of HFGDEs for uniform growth of Bi nanosheets. Further, thermal oxidation of nanosheets not only maximized the active sites and improved surface wettability but also induced Bi/Bi2O3 junctions in nanosheets, enhancing formate production via switching the rate-limiting step from the initial electron transfer to hydrogenation. Consequently, a current density of 141 mA cm−2 at -1 V vs. RHE with formate faradaic efficiency of 85 % and over six times greater catalyst mass activity compared to bulk particle shaped Bi, were achieved, outperforming other reported Bi-based GDEs used for formate production in bicarbonate electrolytes. This comes from less charge-transfer resistance, higher surface roughness, and improved wettability of Bi nanosheets after oxidation. This work represents a facile strategy to engineer efficient HFGDEs as advanced electrode materials for similar electrochemical reactions with low aqueous solubility gas-phase feeds.