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

Abstract

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 (CO₂ RR), which together with the competing hydrogen evolution reaction (HER) exert changes in the local OH^- and H₂ O activity that in turn can possibly affect activity, stability, and selectivity of the CO₂ RR. We determine the local OH^- and H₂ O activity in close proximity to a CO₂ -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/CO₂ 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.

Keywords: carbon dioxide reduction; electrocatalysis; gas diffusion electrodes; local pH gradient; silver.