Effects of composition of the micro porous layer and the substrate on performance in the electrochemical reduction of CO₂ to CO

With the development of better catalysts, mass transport limitations are becoming a challenge to high throughput electrochemical reduction of CO₂ to CO. In contrast to optimization of electrodes for fuel cells, optimization of gas diffusion electrodes (GDE)-consisting of a carbon fiber substrate (CFS), a micro porous layer (MPL), and a catalyst layer (CL)-for CO₂ reduction has not received a lot of attention. Here, we studied the effect of the MPL and CFS composition on cathode performance in electroreduction of CO₂ to CO. In a flow reactor, optimized GDEs exhibited a higher partial current density for CO production than Sigracet 35BC, a commercially available GDE. By performing electrochemical impedance spectroscopy in a CO₂ flow reactor we determined that a loading of 20 wt% PTFE in the MPL resulted in the best performance. We also investigated the influence of the thickness and wet proof level of CFS with two different feeds, 100% CO₂ and the mixture of 50% CO₂ and N₂, determining that thinner and lower wet proofing of the CFS yields better cathode performance than when using a thicker and higher wet proof level of CFS.