Wettability of Gas Diffusion Electrode Materials for CO 2 Reduction

Rapidly decreasing cost of wind and solar electricity coupled with the increasingly urgent need to reduce carbon emissions motivate the decarbonization of the electric power sector and offer exciting opportunities for the electrification of the chemical industry. The development of efficient carbon dioxide (CO 2 ) electroreduction processes, which leverage renewable electrons, would simultaneously curb anthropogenic CO 2 emissions and provide sustainable pathways to a range of fuels, chemicals, and plastics. While progress has been made in CO 2 electrocatalysis, most materials are evaluated in electrochemical cells that operate at relatively low current density (ca. 1 – 10 mA·cm -2 ). In contrast, practical electrolyzers must achieve current densities in the range of 0.5 – 1 A·cm -2 , typical of existing industrial electrochemical processes (e.g., chlor-akali electrolyzers), which are needed to enable cost-effective scaling, without sacrificing efficiency 1 . Aqueous-phase CO 2 delivery at ambient conditions is hampered by low solubility and diffusivity which, in turn, lead to mass transport limitations that set an upper limit on current density of 10 – 20 mA·cm -2 . Gas-phase delivery offers an alternative configuration whereby gaseous CO 2 is fed into an electrolysis cell and interfaces with a liquid electrolyte or ion-selective membrane via catalyst-coated gas diffusion electrodes (GDEs), which were originally developed to manage gas, liquid, electron, and heat transport at electrochemical interfaces within polymer electrolyte fuel cells (PEFCs). In this configuration, the high diffusive rates of gaseous CO 2 and shorter diffusion lengths enable increased current densities, typically an order of magnitude or larger, over atmospheric liquid-phase cell designs. As such, most emerging gas-fed CO 2 electrolyzers employ GDEs based on repurposed PEFC materials, which demonstrate high geometric-area-specific electrochemical activity for a variety of both CO- and hydrocarbon-selective metal catalysts although longevity remains a challenge 2 . While differential conditions are typical of laboratory scale flow cells, industrial electrolyzers will likely operate near maximum single-pass conversion to reduce the necessity for material recycling and to avoid high separation costs associated with dilute product streams. Achieving high conversion requires either high current densities and/or long residence times which, for gas-to-liquid electrolysis, lead to organic p