Solutal Marangoni effect influencing bubble dynamics with varied electrolyte compositions

Abstract

In the photoelectrochemical (PEC) water splitting system, the intricate interplay between bubble evolution and charge transfer at the electrode-electrolyte interface underscores the paramount importance of studying electrolyte properties. In this paper, the bubble dynamics and gas-liquid interface mass transfer on TiO₂ nanorod and nanotube film electrodes are investigated by changing the cation types (K⁺, Na⁺, Li⁺) and concentrations (0.1 M-1.5 M) in alkaline electrolytes. The results indicate that the photocurrent and gas production follow the order of K⁺ > Na⁺ > Li⁺ under the same concentration, which is affected by the solvation of metal cations in aqueous solution and the adsorption on the photoanode surface. Compared with the nanotube electrode, the nanorod electrode enables the bubble to detach at a smaller size and faster rate. The trend of bubble detachment diameter variation with concentration in different cation electrolytes is the same, and follows the order of K⁺ > Na⁺ > Li⁺, which indicates that the force caused by Marangoni effect shows similar rules. The results reveal that the surface tension variation rate induced by ion concentration gradient varies significantly under different cation concentrations, while the variation rate driven by temperature gradient remains notably stable. This confirms that the bubble growth and detachment depend on the solutal Marangoni effect caused by the surface tension variation rate of different alkaline electrolytes with concentration. Therefore, the suitable choice of electrolyte composition is pivotal for regulating the bubble evolution at the electrode-electrolyte interface and improving the PEC system efficiency.