Bimetallic copper-bismuth microtubular electrodes with tunable interfaces for efficient electrochemical reduction of CO2 to formate

Bimetallic copper-bismuth microtubular electrodes with tunable interfaces for efficient electrochemical reduction of CO2 to formate

Electrochemical reduction of CO2 (CO2RR) offers a sustainable route for CO2 utilization, with emerging carbon-free gas-diffusion electrodes (GDEs) mitigating the flooding issues that limit its performance. Metal-based microtubular (hollow fiber) GDEs (HFGDEs) are particularly promising due to enhanced mass transfer by gas flow-through feed, superior charge transfer and mechanical strength. Copper-based GDEs are efficient for CO2RR but often lack selectivity. Introducing bimetallic interfaces on GDE surfaces is an effective strategy to modulate CO2RR pathways. Herein, CuBi bimetallic HFGDEs were fabricated for CO2RR through a facile premixing approach. The CuBi HFGDE with 10 wt% Bi incorporation (CuBi-10) created abundant Cu/Bi interfaces at the triple-phase boundaries, while preserving the CO2 accessibility of the HFGDEs. Operating CuBi HFGDE in flow-through GDE mode ensured sufficient CO2 supply, effectively suppressing HER and enhancing formate selectivity. CuBi-10 achieved over 90 % Faradaic efficiency (FE) for formate across a low potential window (−0.9 to −1.1 V vs. RHE), significantly outperforming monometallic Cu HFGDE (formate FE < 20 % at all applied potentials). The superior formate partial current density of CuBi-10 over Cu HFGDE (more than 5 times higher at −1.1 V vs. RHE) was due to the increased active sites and lower charge transfer resistance. In-situ Raman analysis revealed that the Cu/Bi interface effectively suppresses HER and promotes the ⁎OCHO pathway during CO2-to-formate conversion. This work presents the promise toward designing metal-based HFGDEs with bimetallic interfaces at triple-phase boundaries for selective CO2RR to formate.