(540d) Tuning Gas Diffusion Electrode Construction to Mitigate Flooding and Degradation Processes for Electrochemical CO2 Reduction

A critical limitation of overall electrochemical CO₂ reduction (ECR) performance is suboptimal construction of gas diffusion electrodes (GDEs). GDEs separate the gaseous CO₂ reactant feed from the liquid electrolyte, thereby enhancing mass transfer in an otherwise solubility-limited electrocatalytic reaction and enabling efficient operation at high current densities. However, commercialized GDEs starts to lose their hydrophobicity after ~2hrs of electrocatalytic reaction, leading to flooding and failure of the entire reactor system. Compared to catalyst development, there is scant work towards fundamentally understanding GDE’s local reaction environment and the process of electrode degradation. Herein, we prepare 2 different catalysts (Cu and CuO) with varied loadings of PTFE particles and carbon black deposited on PTFE membrane or carbon paper supports to investigate overall GDE properties and monitor time-dependent changes. We alternate ECR reaction with electrochemical impedance spectroscopy (EIS) and goniometer contact angle measurements to track changes in impedance and hydrophobicity as a function of GDE construction and operating conditions (i.e. time, applied potential). EIS data is fit to appropriate equivalent circuit models to provide insights regarding possible charge transfer mechanisms for the system. We analyze contact angle measurements using the Cassie Baxter equation to explicitly quantify the fractional surface area of gas-dominated regions that are caused by the varied PTFE loading and ECR operating conditions. We find that GDE made from PTFE membrane/spray casted carbon black/catalyst to be incompatible for further analysis at different time intervals as the PTFE membrane is innately insulating and leads to high ohmic loss. Low carbon loading leads to high series resistance (>20 Ω) while higher carbon loading favors undesirable hydrogen evolution reaction (HER). Results from this work will guide continuing investigation and improved GDE construction to mitigate degradation processes.