Study on the behavior of single oxygen bubble regulated by salt concentration in photoelectrochemical water splitting

Abstract

The increase of electrolyte resistance near the electrode due to bubble evolution is the main obstacle to significantly improve the efficiency of photoelectrochemical water splitting. The oxygen bubble evolution on the TiO2 nanorod photocatalytic electrode was observed in situ by micro high-speed camera, and its corresponding current curve was measured synchronously by electrochemical workstation. The effect of single oxygen bubble evolution on current under different Na2SO4 electrolyte salt concentrations (0.01 M–1.0 M) was studied. When the salt concentration increases from 0.01 M to 0.8 M, the current in the bubble growth stage increases by about 2.5 times, while the bubble period and detachment diameter decrease by about 78.7% and 28.6%, respectively. When the salt concentration further increases, the current and bubble detachment diameter and period remain almost unchanged. The bubble growth coefficient reaches the optimum at 0.5 M, while the gas production rate reaches the optimum at 0.6 M. As the increase of electrolyte salt concentration, the increase rate of photocurrent density is lower than that of mass transfer coefficient, resulting in the decrease of solutal Marangoni force and the smaller bubble detachment diameter. The results show that regulating the concentration of electrolyte is an effective method to remove bubbles on the photocatalytic electrode.