Nonconductive Metal Oxide Gas Diffusion Layer for Mitigating Electrowetting during CO₂ Electrolysis.

Abstract

Gas diffusion electrodes (GDEs) are extensively used for high current density electrochemical CO₂ electrolysis (ECO₂R), enabled by significantly reducing mass transfer resistance of CO₂ to the catalyst layer. Conventionally, these GDEs are based upon hydrophobic carbon-based gas-diffusion layers (GDLs) that facilitate the gas transport; however, these supports are prone to flood with electrolyte during electrolysis. This potential-induced flooding, known as electrowetting, is related to the inherent conductivity of carbon and limits the activity of ECO₂R. To investigate the effect of electrical conductivity more carefully, a GDE is constructed based on a Cu mesh with a nonconductive microporous GDL applied to this substrate, the latter composed of a mixture of metal oxide and polytetrafluoroethylene. With alumina as the metal oxide, a stable operation is obtained at -200 mA cm^-2 with 70% selectivity for ECO₂R (with over half toward C₂₊ products) without flooding as observed by <i>in situ</i> microscopy. On the contrary, with a Vulcan carbon-based GDL, the initial activity is rapidly lost as severe flooding ensues. It is reasoned that electrowetting is averted by virtue of the nonconductive nature of alumina, providing a new perspective on alternative GDL compositions and their influence on ECO₂R performance.