Gas Bubble Stabilization Limits Tetraalkylammonium-Enhanced Hydrogen Evolution

Pt is the most active single-metal HER catalyst in acidic media, but its performance drops sharply in alkaline electrolytes. While recent studies have shown that tetraalkylammonium (TAA⁺) cations can enhance alkaline HER by restructuring interfacial water, their role under bubble-forming, high-current conditions remains unclear. Here we show that tetrabutylammonium (TBA⁺) exerts a dual, potential-dependent effect on Pt: it boosts HER rates at low overpotentials but suppresses them at higher overpotentials. Using microelectrodes with high-speed imaging, we track microbubble formation, growth and detachment, and find that TBA⁺ stabilizes bubbles through adsorption at multiple interfaces, including the electrode and surrounding insulator, leading to persistent surface blockage via pinning and coalescence. Rotating disk electrode measurements confirm that the resulting activity loss originates from mass transport limitations rather than intrinsic kinetics. These findings clarify the role of organic cations in governing gas evolution dynamics and highlight the need to account for interfacial bubble effects when interpreting alkaline HER activity.