Electrochemical reduction of carbon dioxide: IV dependence of the Faradaic efficiency and current density on the microstructure and thickness of tin electrode

Central to the conversion of CO2 in a full electrochemical cell is its cathode microstructure, which governs gas diffusion, charge exchange and transfer, and subsequently carbon dioxide reduction reaction. In this article, we report the effects of microstructure of Sn catalyst layer on the Faradaic efficiency towards formate formation as a function of Nafion loading, thickness of the catalyst layer, and catalyst particle size. Electrode with 17-20 wt.% Nafion was found to exhibit the highest partial current density towards the formation of formate when the average particle size of Sn catalysts ranged from 100 nm to 1.5 μm. This Nafion fraction is lower than what was reported, 30-36 wt.%, in the cathode of proton exchange membrane fuel cells. Moreover, the partial current density for formate formation was observed to increase with the thickness of catalyst layer, but eventually saturated because the reaction zone was limited by mass transfer. The Faradaic efficiency towards the formation of formate exhibited nearly thickness-independence due to the counteractive effects caused by increasing local proton concentration and decreasing electrical field when catalyst layer thickness was increased.