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.