Enhancing CO₂ Electroreduction Selectivity toward Multicarbon Products via Tuning the Local H₂O/CO₂ Molar Ratio

Mass transfer plays an important role in controlling the surface coverage of reactants and the kinetics of surface reactions, thus significantly adjusting the catalytic performance. Herein, we reported that H₂O diffusion was modulated by controlling the thicknesses of the carbon black (CB) layer between the gas diffusion electrode (GDE) of Cu and the electrolyte. As a consequence, the product distribution over the GDE of Cu was effectively regulated during CO₂ electroreduction. Interestingly, a volcano-type relationship between the thickness of the CB layer and the faradaic efficiency (FE) for multicarbon (C₂₊) products was observed over the GDE of Cu. Especially, when the applied total current density was set as 800 mA cm^-2, the FE for the C₂₊ products over the GDE of Cu coated by a CB layer with a thickness of 6.6 μm reached 63.2%, which was 2.8 times higher than that (16.8%) over the GDE of Cu without a CB layer.