Sensitivity of Gas-Evolving Electrocatalysis to the Catalyst Microenvironment

Many electrochemical reactions for the development of renewable energy technologies are gas-evolving reactions, where the electrocatalytic performance is susceptible to the wetting properties of the catalyst microenvironment. Here, using N 2 H 4 electro-oxidation to N 2 on carbon-supported Pt nanocatalysts as a model reaction, we controlled the microenvironment using oxygen-doped and fluorine-doped carbon supports to make it more hydrophilic and more hydrophobic, respectively, and elucidated the effect on the reaction kinetics. The electrode with oxygen-doped carbon showed a 123% higher activity than that with pristine carbon, benefiting from the increased wetting and exposure of Pt catalytic sites to the electrolyte. Counterintuitively, the electrode with fluorine-doped carbon also exhibited a 46% higher activity than that with pristine carbon, despite its lower wetting of Pt. We found that the hydrophobic microenvironment accelerated the surface diffusion, coalescence, and detachment of the generated N 2 gas bubbles, which would otherwise block the Pt active sites from catalyzing the reaction.