Hydrophilic or Hydrophobic? Optimizing the Catalyst Microenvironment for Gas‐Involving Electrocatalysis

Abstract Electrocatalysis plays a key role in the development of renewable energy technologies. Along with the design of electrocatalysts, the microenvironment around catalytic sites has received increasing attention because it affects the distribution and mass transport of reaction species and impacts the reaction kinetics. In this Concept article, we highlight some mechanistic insights into the effect of microenvironment on gas‐involving electrocatalytic reactions, including CO 2 reduction, 2‐electron oxygen reduction, and hydrazine oxidation, demonstrating their sensitivity to the wetting properties of microenvironment. For reactions with a gaseous reactant, a moderately hydrophobic microenvironment can greatly enhance the mass transport of gaseous species to accelerate the reaction kinetics while improving the stability of gas‐diffusion electrodes. In contrast, for reactions with a liquid reactant and gaseous product, a hydrophilic microenvironment improves the exposure of catalytic sites to the reactant, while a hydrophobic microenvironment benefits the reaction on the other end by accelerating the diffusion and detachment of generated gas bubbles, which would otherwise block the catalytic sites from the reactant. These understandings and insights can provide important guidelines on the control and optimization of catalyst microenvironment for the development of efficient electrolyzers.