Ion-Exchange Membranes Prevent Nanobubble Detachment But Do Not Limit Electrolysis Current

Gas bubble evolution at electrochemical interfaces critically impacts electrolyzer performance and durability yet is difficult to resolve at the nanoscale. Using reactive molecular simulations at constant potential, we resolve potential-dependent nanobubble nucleation, confinement, and steady-state dynamics on Pt nanoparticles in nanometer-scale membrane-electrode gaps, providing mechanistic access that complements ensemble electrochemical measurements and operando imaging that cannot directly probe 1-2 nm confinement. We reveal that ion-exchange membrane proximity anchors nanobubbles on Pt nanoparticles, preventing detachment while maintaining average steady-state hydrogen evolution currents comparable to those of membrane-free systems. In contrast, direct ionomer adsorption onto the catalyst produces a larger reduction of the current due to active-site occlusion and enhances electroactive-area screening at higher overpotential, as the bubble spreads laterally along the polymer-solution interface. Anchored nanobubbles locally displace interfacial water, creating dehydrated regions at the membrane interface that can accelerate chemical degradation pathways in anion-exchange membranes. By connecting nanoscale bubble morphology and exposed catalytic area to macroscopic current-potential trends, our results demonstrate that membrane proximity governs bubble confinement without necessarily compromising efficiency, reframing it as a design parameter for durability management in electrolysis systems.