(Invited) Local pH in the (Photo/Electro) Catalytic Environment

Abstract

(Photo)electrodes designed for improved efficiency and selectivity for CO2 reduction are often nanostructured, for example highly roughened metal films, nanowire arrays, and catalyst particles within a gas diffusion electrode. In all cases, local pockets of water with dissolved CO2 and ions are necessary for the reduction reaction. Although these regions are thought of as having a pH, they are often too small to have a well-defined pH or be at thermodynamic equilibrium until a minimum electrolyte pool size is reached. Computational studies using stochastic chemical kinetics provide a window into this environment, bridging the nanometer scale to the bulk-like scale. The calculations show that the compositions of these regions are characterized by large concentration fluctuations including periods of time when some ions are not present at all. The calculations enable useful trends in electrolyte composition to be identified as a function of electrolyte pool size, providing insights to the complex environments surrounding the catalytic center.