Regulation of bubble evolution dynamics by surfactants during water electrolysis

Facilitating rapid gas-bubble detachment is crucial for boosting water-splitting systems efficiency. However, the mechanisms governing bubble detachment dynamics remain unclarified, especially the role of electrostatic interactions. By modulating interfacial electrostatics and surface tension through surfactants with distinct charge properties, we hypothesize electrostatic forces arising from surfactant adsorption at the bubble-liquid interface have a greater influence on controlling bubble detachment than buoyancy and Marangoni stresses.

The influence of surfactant type on H₂ bubble evolution during hydrogen evolution reaction (HER) was investigated by combining high-speed imaging and electrochemical analysis. Finite-element simulations and force analysis were conducted to reveal the interplay of buoyancy, Marangoni, and electrostatic forces.

The surfactants added to the electrolyte induce electrostatic forces at the bubble interface, which become the dominant driver of the detachment process. Specifically, the anionic surfactant sodium dodecanesulfonate (SLS) increased bubble detachment frequency by 3.5-fold (micro-electrode) and enhanced HER current density by ∼34% (wire electrode) compared to surfactant-free electrolytes. Force analysis and simulations further substantiated that the surfactant-mediated electrostatic force (∼6.78 μN) dominated bubble detachment dynamics, overwhelming contributions from buoyancy (∼2.47 μN) and the Marangoni force (∼0.12 μN). In contrast, the cationic surfactant cetyltrimethylammonium bromide (CTAB) strengthened adhesion interactions through electrostatic attraction, enhancing bubble adhesion to the electrode surface and delaying bubble release. These findings establish the critical role of surfactant-derived electrostatic forces in bubble detachment at the microscale and demonstrate that rationally selecting surfactants to tune interfacial electrostatics represents a potential pathway for modulating bubble dynamics.