Porous Membrane-Mediated CO ₂ Delivery for Efficient Electrochemical CO ₂ Reduction

Microenvironment engineering offers a promising route to overcome CO2 mass transport limitations in the electrochemical CO2 reduction reaction (CO2RR). However, constructing a robust gas–liquid–solid triple-phase boundary (TPB) and ensuring continuous and sufficient CO2 supply at a high current density remain challenging. Here, a poly(4-vinylpyridine) (P4VP)-modified macroporous poly(tetrafluoroethylene) (PTFE) membrane, serving as both a gas–liquid distributor and a localized CO2 reservoir, is assembled on the bismuth oxybromide (BiOBr) electrocatalyst. The superhydrophobic PTFE membrane provides gas-filled highways for rapid CO2 transport, while the CO2-affinitive P4VP maintains a high local free CO2 concentration near the electrode, jointly ensuring a sufficient CO2 supply and a stable TPB. The resulting electrode achieves a maximum formic acid (HCOOH) partial current density of 31.13 mA cm–2. The HCOOH Faradaic efficiency (FEHCOOH) is up to 90.45% at −1.1 V in the H-cell. Moreover, it sustains a stable reaction over 27 h, markedly surpassing the durability of the unmodified electrode. In addition, its FEHCOOH remains above 80% over a broad potential range from −0.55 V to −1 V and reaches 92.9% at a constant current density of 150 mA·cm–2 in a flow cell. This work provides a novel approach to overcome the limited access of CO2 in the CO2RR.