Direct Measurement of Electrochemical Selectivity Gradients over a 25 cm2 Copper Gas Diffusion Electrode

Electrochemical CO reduction (COR) systems have increased by orders of magnitude in their accessible activities in the past decade, particularly by the implementation of the gas diffusion electrode (GDE) architecture. As GDEs are upscaled by active geometric area (cm2 to m2), reactor performance can change due to physical and chemical spatial variations which are complicated by the chemical complexity of multiphase and multiproduct electrochemical systems. This work measures and evaluates COR performance metrics by a multiport sampling reactor to measure reactant and product concentration down-the-channel of a COR GDE. It is found that the faradaic efficiency (FE) toward the hydrogen evolution reaction (HER) increases down-the-channel, largely driven by a decrease in the partial pressure of CO, while the selectivity for ethylene remains relatively constant down-the-channel. This work highlights the inhomogeneities in performance as electrochemical reactors are physically upscaled and has significant implications for future scaling of COR and CO2R systems.