Tuning the Microenvironment in Gas-Diffusion Electrodes Enables High-Rate CO₂ Electrolysis to Formate

Electroreduction of CO2 to formate on Bi-based catalyst is a promising route for CO2 recycling and sustainable fuel production. The use of gas-diffusion-electrode (GDE) flow cells has generally improved the rate of CO2 electrolysis, while the local reaction environment in GDEs and its impact on the electrolysis remain to be understood. Here, we report that tuning the microenvironment of Bi-based catalyst in a GDE by adding hydrophobic polytetrafluoroethylene (PTFE) nanoparticles in the catalyst layer can substantially enhance CO2 electrolysis, achieving a partial current density of 677 mA cm–2 for formate production and 35% single-pass CO2 conversion at −0.7 V versus RHE under 9-sccm CO2 gas flow. It is revealed that a moderate hydrophobicity of the catalyst layer can establish a microenvironment with a balance between gaseous CO2 and liquid electrolyte inside the catalyst layer, which reduces the diffusion layer thickness to accelerate CO2 mass transport and forms highly active reaction zones near solid–liquid–gas interfaces.