Near-Electrode Concentration Gradients of Bicarbonate and pH within Porous Gas Diffusion Electrode for Optimized Selective CO₂ Electroreduction to C₂₊ Products.

Abstract

With high current density, the intense near-electrode CO₂ reduction reaction (CO₂RR) will cause the concentration gradients of bicarbonate (HCO₃^-) and hydroxyl (OH^-) ions, which affect the selectivity of high-value C₂₊ products of the CO₂RR. In this work, we simulated the near-electrode concentration gradients of electrolyte species with different porous Cu-based CLs (catalyst layers) of GDE (gas diffusion electrode) by COMSOL Multiphysics. The higher porosity CL exhibits a better buffer ability of local alkalinity while ensuring a sufficient supply of H⁺ and local CO₂ concentration. Subsequently, the different porosity CLs were prepared by vacuum-thermal evaporation with different evaporation rate. Structural characterizations and liquid permeability tests confirm the role of the porous CL structure in optimizing concentration gradients. As a result, the high-porosity CL (Cu-HP) exhibits a higher C₂₊ Faraday efficiency (FE) of ∼79.61% at 500 mA cm^-2 under 1 M KHCO₃, far more than the FE_C2+ ≈ 38.20% with the low-porosity sample (Cu-LP).