Tracking Gas Diffusion Electrode Flooding in CO 2 Electrolyzers Via Electrochemical Double Layer Capacitance

As electrochemical technologies such as batteries, fuel cells, and water electrolyzers advance and transform the electric and transportation sectors, there is increasing interest around the role of electrochemistry in sustainable chemical manufacturing. As an example, blending electrochemically generated carbon monoxide (CO) and hydrogen, derived from carbon dioxide (CO 2 ) and water electrolyses respectively, could constitute a renewable scheme to produce syngas for Fischer-Tropsch gas-to-liquids processes 1 . Decades of fundamental research into electrochemical CO 2 reduction (CO 2 R) coupled with emerging engineering and economic incentives have shifted the field’s focus towards high-performance, gas-fed electrolyzers. Catalyst-coated gas diffusion electrodes facilitate such reactor configurations by providing physical separation between the gaseous reactants and the liquid electrolyte. While high geometric-area-specific electrochemical activity has been demonstrated with commercial gas diffusion electrode materials for a variety of both CO- and hydrocarbon-selective metal catalysts 2,3 , longevity remains a challenge and performance decay is often attributed to electrode deficiencies. To date, most gas diffusion layers reported in the CO 2 R literature have been repurposed from fuel cell applications, in which the transport of water to and from the catalyst layer is crucial to device operation. To this end, in fuel cells, densely-packed microporous layers serve both as catalyst-layer substrates and effective media for water management. However, the efficacy of this layer as a barrier to liquid electrolyte flooding in CO 2 R is limited by increasing hydrophilicity upon exposure to reducing potentials and high local pH. New operando diagnostic techniques are needed to probe the stability of the gas-liquid interface in gas-fed CO 2 electrolyzers with flowing liquid electrolytes 4 . In this presentation, we propose a new experimental approach for determining the relationship between cell operating conditions and the eventual degradation of CO 2 -to-CO faradaic efficiency. Specifically, we propose combining periodic in-situ electrochemical-double-layer-capacitance-based electrolyte wetting predictors with in-line gas chromatography characterization of CO 2 R products. Voltammetric- or impedance-based methods are often used to estimate electrochemically active surface area of porous carbons in supercapacitor applications, but have yet to be used to probe ele