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 N2H4 electro-oxidation to N2 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 N2 gas bubbles, which would otherwise block the Pt active sites from catalyzing the reaction.