Gas Supersaturation-Dependent Contact Angle for Bubble Nucleation in Electrochemistry

Nucleation of surface bubbles on electrodes typically occurs under Extreme local gas supersaturation, yet the prevailing assumption treats the contact angle as constant and equal to Young's contact angle. Here, combining molecular dynamics simulations with thermodynamic analysis, we demonstrate that gas supersaturation fundamentally changes the three interfacial tensions governing bubble formation, causing substantial deviations from Young's prediction. We develop a theoretical framework that extracts interfacial parameters from atomistic simulations to predict bubble contact angles in highly supersaturated environments. Strikingly, the contact angle can either increase or decrease with supersaturation, depending on the gas-solvent-substrate combinations although all three interfacial tensions decrease with increasing supersaturation: the contact angle decreases for N₂-water-graphene but increases for H₂-water-Pt. This difference is captured by dimensionless interface competition parameters, which characterize gas-solid adsorption versus gas enrichment at the liquid-solid interface. Our findings challenge classical understanding and establish supersaturation-dependent interfacial thermodynamics as a critical design principle for gas-evolving electrocatalysts.