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.