Probing the Local Reaction Environment During High Turnover Carbon Dioxide Reduction with Ag‐Based Gas Diffusion Electrodes

Discerning the influence of electrochemical reactions on the electrode microenvironment is an unavoidable topic for electrochemical reactions that involve the production of OH(−) and the consumption of water. That is particularly true for the carbon dioxide reduction reaction (CO(2)RR), which together with the competing hydrogen evolution reaction (HER) exert changes in the local OH(−) and H(2)O activity that in turn can possibly affect activity, stability, and selectivity of the CO(2)RR. We determine the local OH(−) and H(2)O activity in close proximity to a CO(2)‐converting Ag‐based gas diffusion electrode (GDE) with product analysis using gas chromatography. A Pt nanosensor is positioned in the vicinity of the working GDE using shear‐force‐based scanning electrochemical microscopy (SECM) approach curves, which allows monitoring changes invoked by reactions proceeding within an otherwise inaccessible porous GDE by potentiodynamic measurements at the Pt‐tip nanosensor. We show that high turnover HER/CO(2)RR at a GDE lead to modulations of the alkalinity of the local electrolyte, that resemble a 16 m KOH solution, variations that are in turn linked to the reaction selectivity.