Modeling different wetting states in gas diffusion electrodes for CO2 electrolysis

Continuum models can incorporate numerous gas diffusion electrode (GDE) parameters to provide insights into the interplay of mass transport and electrochemical reactions for CO 2 reduction. While experimental studies highlight the significance of the wetting state of the GDE and the catalyst layer on key metrics such as Faraday efficiency (FE), existing models do not adequately reflect these effects because they rely on the assumption of a defined wetting state of the catalyst layer, either fully saturated and impermeable for gaseous CO 2 or partially saturated and entirely accessible to the gas phase. In this work, we present a continuum model of a GDE for CO 2 reduction, allowing for the concurrence of both wetting states within the catalyst layer. The proposed modeling framework can simulate the interplay of gas-liquid interfacial area and reaction rate due to different electrolyte distributions within the catalyst layer. By utilizing the Size-Modified Nernst–Planck-Poisson equation, the salting-out effect on the CO 2 dissolution can be accurately described by considering steric effects which prevent unrealistically high ion concentrations. Additionally, this modeling approach allows for a realistic transition towards increased levels of saturation, which can be used to capture dynamic wetting behavior and flooding effects. Simulations at high saturation levels demonstrate that substantial current densities and FE can be maintained even in near-flooded states, given sufficient gas-liquid interfacial area and gas permeation depth into the catalyst layer. • Segregated saturation domains capture fully and partially saturated catalyst regions. • Smooth saturation transition to capture dynamic wetting behavior. • Interplay of gas-liquid interfacial area and flooding on partial current density. • Size-Modified Nernst–Planck-Poisson equation.