Single bubble dynamics on a TiO2 photoelectrode surface during photoelectrochemical water splitting

Abstract

The bubble evolution on the photoelectrode surface in photoelectrochemical water splitting can change the mass transfer of gaseous products and induce additional resistance. In this paper, the growth and nucleation of a single oxygen bubble over a titanium dioxide (TiO2) nanorod-array electrode was investigated. The results indicate that the resistance decreases significantly due to the decrease of dissolved gas concentration at the beginning of bubble growth period. Because the effect of electrolyte constriction offsets the concentration-lowering effect, the resistance is almost constant in the later stage of bubble growth. The increase of light intensity leads to longer bubble waiting time and growth time, larger bubble diameter and smaller contact angle. Moreover, the bubble nucleation frequency increases due to the improved reaction rates at higher potential. A force balance model is constructed to predict the bubble departure diameter. It is found that the forces preventing the bubble departure from the photoelectrode surface are mainly surface tension and Marangoni force, which account for 82% and 18%, respectively.