Near-Electrode\nConcentration Gradients of Bicarbonate\nand pH within Porous Gas Diffusion Electrode for Optimized Selective\nCO<sub>2</sub> Electroreduction to C<sub>2+</sub> Products

With high current density, the intense near-electrode\nCO<sub>2</sub> reduction reaction (CO<sub>2</sub>RR) will cause the\nconcentration\ngradients of bicarbonate (HCO<sub>3</sub><sup>–</sup>) and\nhydroxyl (OH<sup>–</sup>) ions, which affect the selectivity\nof high-value C<sub>2+</sub> products of the CO<sub>2</sub>RR. In\nthis work, we simulated the near-electrode concentration gradients\nof electrolyte species with different porous Cu-based CLs (catalyst\nlayers) of GDE (gas diffusion electrode) by COMSOL Multiphysics. The\nhigher porosity CL exhibits a better buffer ability of local alkalinity\nwhile ensuring a sufficient supply of H<sup>+</sup> and local CO<sub>2</sub> concentration. Subsequently, the different porosity CLs were\nprepared by vacuum-thermal evaporation with different evaporation\nrate. Structural characterizations and liquid permeability tests confirm\nthe role of the porous CL structure in optimizing concentration gradients.\nAs a result, the high-porosity CL (Cu-HP) exhibits a higher C<sub>2+</sub> Faraday efficiency (FE) of ∼79.61% at 500 mA cm<sup>–2</sup> under 1 M KHCO<sub>3</sub>, far more than the FE<sub>C2+</sub> ≈ 38.20% with the low-porosity sample (Cu-LP).