A Cu hollow fiber with coaxially grown Bi nanosheet arrays as an integrated gas-penetrable electrode enables high current density and durable formate electrosynthesis

Abstract

While high current density formate (HCOO⁻) electrosynthesis from CO₂ reduction has been achieved in a flow cell assembly, the inevitable flooding and salt precipitation of traditional gas-diffusion electrodes (GDEs) severely limit the overall energy efficiency and stability. In this work, an integrated gas-penetrable electrode (GPE) for HCOO⁻ electrosynthesis was developed by coaxially growing vertically aligned high density Bi nanosheet arrays on a porous Cu hollow fiber (Bi NSAs@Cu HF) via controllable galvanic replacement. The interior porous Cu HF serves as a robust gas-penetrable and conductive host for continuously delivering CO₂ gas to surface-anchored Bi NSAs, resulting in numerous well-balanced triphase active interfaces for the electrocatalytic CO₂ reduction reaction (CO₂RR). The most active Bi NSAs@Cu HF GPE exhibits a high HCOO⁻ faradaic efficiency (FE_HCOO⁻) of over 80% in a wide potential window (330 mV) with a linearly increased partial current density (j_HCOO⁻) up to −261.6 mA cm⁻² at −1.11 V vs. the reversible hydrogen electrode (RHE). The Bi NSAs@Cu HF GPE also sustains a FE_HCOO⁻ of >80% at a high total current density of −300 mA cm⁻², corresponding to a j_HCOO⁻ of >−240 mA cm⁻², for more than 60 h. This work provides new perspectives on designing efficient and durable integrated GPEs for a sustainable CO₂RR on a large scale.