Influence of subatmospheric pressure on bubble evolution on the TiO2 photoelectrode surface

The increase of reaction resistance caused by bubble nucleation and long-time growth on the surface of the photoelectrode is an important factor that leads to the low efficiency of photoelectrochemical water splitting. In this study, we adopted an electrochemical workstation synchronous with a high-speed microscopic camera system to achieve in situ observation of oxygen bubble behavior on the surface of TiO2 and to study the internal relationship between the geometric parameters of oxygen bubbles and photocurrent fluctuations under different pressures and laser powers. The results indicate that with the decrease of pressure, the photocurrent decreases gradually and the bubble departure diameter increases gradually. In addition, the nucleation waiting stage and the growth stage of bubbles are both shortened. However, the difference between the average photocurrents corresponding to the moment of bubble nucleation and the stable growth stage hardly changes with the pressure. The production rate of gas mass reaches a peak near 80 kPa. In addition, a force balance model suitable for different pressures is constructed. It is found that as the pressure decreases from 97 kPa to 40 kPa, the proportion of the thermal Marangoni force in the Marangoni force decreases from 29.4% to 21.3%, while the proportion of the concentration Marangoni force increases from 70.6% to 78.7%, indicating that the concentration Marangoni force is the main factor affecting the bubble departure diameter under subatmospheric pressure conditions.

Automated summary

The increase in reaction resistance caused by bubble nucleation and long-term growth on the photoelectrode surface is a significant factor contributing to the low efficiency of photoelectrochemical water splitting. In this study, an electrochemical workstation synchronized with a high-speed microscopic camera system was used to observe the behavior of oxygen bubbles on the TiO2 surface and investigate the relationship between the geometric parameters of the bubbles and photocurrent fluctuations under different pressures and laser powers. The results showed that as the pressure decreased, the photocurrent decreased gradually, and the bubble departure diameter increased. The nucleation waiting stage and growth stage of bubbles shortened. However, the average photocurrent difference between the moment of bubble nucleation and the stable growth stage remained relatively constant with pressure. The production rate of gas mass reached its peak around 80 kPa. Additionally, a force balance model suitable for different pressures was constructed, revealing that the concentration Marangoni force is the main factor affecting the bubble departure diameter under subatmospheric pressure conditions.