On the weeping of the GDE cathode during bipolar membrane-based electrochemical CO2 reduction reaction at high current densities
Maike Wrobel, Stefanie Kriescher, T. Schiffer, Robert Keller, Matthias Weßling
Abstract
Understanding and controlling the gas–liquid–solid interface at gas diffusion electrodes (GDE) is a long-standing challenge in electrochemical engineering . Especially, flooding of gas diffusion electrodes is detrimental to high Faraday efficiencies and a long-term stable process. A detailed understanding and quantification of permeation through GDEs will contribute to enhanced control as a remedy for performance loss. Here, we present macroscopic experiments for the reduction of CO 2 in a bipolar membrane reactor configuration and focus on the effect of high current densities on the wetting, flooding, and weeping of the GDE. We monitor and quantify anolyte, catholyte , and GDE permeate to understand ion movements in the cell. We report high current densities of up to 300 mA/cm 2 and reach up to 80% Faraday efficiency for CO. However, these realistic process conditions entail an increase in the weeping rate and ion concentration up to the saturation of bicarbonate. For the first time, we observe that the permeating electrolyte gives a fingerprint of the composition inside the GDE, being significantly different compared to the bulk concentration in the feed channel, i.e., catholyte.