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

While high current density formate (HCOO - ) electrosynthesis from CO 2 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 CO 2 gas to surface-anchored Bi NSAs, resulting in numerous well-balanced triphase active interfaces for the electrocatalytic CO 2 reduction reaction (CO 2 RR). 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 CO 2 RR on a large scale.