Electrochemical reduction of CO2 to formate at high current density using gas diffusion electrodes

The electrochemical reduction of carbon dioxide into formate was studied using gas diffusion electrodes (GDE) with Sn as electrocatalyst in order to overcome mass transport limitations and to achieve high current densities. For this purpose, a dry pressing method was developed for GDE preparation and optimized with respect to mechanical stability and the performance in the reduction of CO2. Using this approach, GDEs can be obtained with a high reproducibility in a very simple, fast, and straightforward manner. The influence of the metal loading on current density and product distribution was investigated. Furthermore, the effect of changing the electrolyte pH was evaluated. Under optimized conditions, the GDE allowed current densities up to 200 mA cm−2 to be achieved with a Faradaic efficiency of around 90 % toward formate and a substantial suppression of hydrogen production (<3 %) at ambient pressure. At higher current densities mass transport issues come into effect and hydrogen is increasingly produced. The corresponding cathode potential was found to be 1.57 V vs. SHE.