Stand-alone asymmetric hollow fiber gas-diffusion electrodes with distinguished bronze phases for high-efficiency CO2 electrochemical reduction

Abstract The development of advanced electrodes is of great importance to improve gas mass transfer for efficient gas-phase CO2 reduction reaction (CO2RR). Gas-diffusion electrodes (GDEs) can maximize CO2 concentration in the close proximity of electrocatalysts, and achieve high-performance catalytic conversion provided that their surface wettability and electrocatalyst nanostructure are finely tuned. Recently, hollow fiber GDEs (HFGDEs) have shown promising CO2RR efficiency, owing to their high surface area and porosity to effectively solve mass transfer issues. Unlike GDE fabrication with alloy catalysts in powder form which require a further deposition step, herein stand-alone bronze HFGDEs with distinguished alloy phases are made via a facile strategy through a two-step electrodeposition-aging process. A uniform covering layer of Cu3Sn or Cu5Sn6 phases on the surface of HFGDE was effectively obtained by controlling Sn electrodeposition thickness and aging duration. Compared to non-selective Cu HFGDE, both alloys showed less formation of H2 and hydrocarbons. Growth of Cu3Sn phase improved CO selectivity compared to Cu HFGDE at lower potentials. Cu5Sn6 HFGDE exhibited formate-selective performance with FE > 80 % over a potential window of 400 mV, reaching 89 ± 3% at -1.1 V vs. RHE. In addition, alloy-coated HFGDEs showed improved wettability and microenvironment for catalyst-electrolyte interface due to the formation of a highly rough surface. This led to more catalytically active areas and higher formate partial current density (136 mA cm−2), outperforming other bronze-based GDEs. This study contributes a facile strategy for the fabrication of bimetallic electrodes with desired alloy phases to be utilized in gas-fed electrolysis in aqueous media.