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

Electrochemical reduction of CO 2 (CO 2 RR) offers a sustainable route for CO 2 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 CO 2 RR but often lack selectivity. Introducing bimetallic interfaces on GDE surfaces is an effective strategy to modulate CO 2 RR pathways. Herein, CuBi bimetallic HFGDEs were fabricated for CO 2 RR 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 CO 2 accessibility of the HFGDEs. Operating CuBi HFGDE in flow-through GDE mode ensured sufficient CO 2 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 CO 2 -to-formate conversion. This work presents the promise toward designing metal-based HFGDEs with bimetallic interfaces at triple-phase boundaries for selective CO 2 RR to formate. Engineering bimetallic Cu/Bi interface on microtubular gas-diffusion electrodes for selective CO 2 RR to formate. • Tuning Cu/Bi interfaces at triple-phase boundaries for formate production • Flow-through HFGDEs provide sufficient CO 2 supply and effectively suppress HER. • Formate selectivity over 90 % across a low potential range (−0.9 to −1.1 V vs. RHE) • This strategy enables HFGDE design with bimetallic interfaces for selective CO 2 RR.