Efficiency and selectivity of CO₂ reduction to CO on gold gas diffusion electrodes in acidic media

The electrochemical reduction of CO₂ to CO is a promising technology for replacing production processes employing fossil fuels. Still, low energy efficiencies hinder the production of CO at commercial scale. CO₂ electrolysis has mainly been performed in neutral or alkaline media, but recent fundamental work shows that high selectivities for CO can also be achieved in acidic media. Therefore, we investigate the feasibility of CO₂ electrolysis at pH 2–4 at indrustrially relevant conditions, using 10 cm² gold gas diffusion electrodes. Operating at current densities up to 200 mA cm⁻², we obtain CO faradaic efficiencies between 80–90% in sulfate electrolyte, with a 30% improvement of the overall process energy efficiency, in comparison with neutral media. Additionally, we find that weakly hydrated cations are crucial for accomplishing high reaction rates and enabling CO₂ electrolysis in acidic media. This study represents a step towards the application of acidic electrolyzers for CO₂ electroreduction.