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

•Varied the structure and composition of gas diffusion electrodes for CO2 reduction.•Identified optimum levels of hydrophobicity of the microporous layer.•Identified optimum levels of wet proofing and thickness of the carbon substrate.•Optimized GDEs outperform commercially available GDEs.•Optimized GDEs exhibit no decay in performance during continuous operation.

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.