Modeling mass transfer limitations driven by electrowetting in electrochemical CO2 reduction at silver gas diffusion electrodes

Abstract

A one-dimensional mathematical model of a silver gas diffusion electrode (GDE) in electrochemical CO2 reduction (eCO2R) is presented. A Leverett approach is utilized to describe the coexistence of gaseous and liquid phases in the porous GDE, accounting for the potential-dependent contact angle of silver influenced by electrowetting. The model is fit to a set of experimental steady state results for sprayed electrodes with a range of diluted feeds (25−100vol%CO2). The model results ascertain a high electrolyte saturation in the GDE as the main cause for the inherent mass transfer limitations during eCO2R at elevated current densities. Furthermore, precipitation as a result of increased local K2CO3 concentration that surpasses the solubility limit is determined as degradation mechanism at current densities > 3kAm−2. It is demonstrated how the model can be used to examine the effects of design parameters, indicating benefits of more hydrophobic and thinner GDEs.