The issue of increased reaction resistance due to bubble growth has always been a major bottleneck limiting the efficiency improvement of photoelectrochemical water splitting. In this study, we developed a synchronized measurement system with a micro-high-speed camera and an electrochemical workstation to observe oxygen bubble evolution on the surface of a fixed TiO2 film electrode in situ. The intrinsic relationship between the nucleation and growth of oxygen bubbles and photocurrent at different pH values (1.0–13.0) was investigated. The results indicate that higher pH can promote bubble nucleation at lower potentials. Additionally, increasing pH from 1.0 to 13.0 at 0.1 V vs Ag/AgCl, the photocurrent in the bubble growth stage increases by about 35 times, and the average period of bubble growth decreases by about 15 times. Compared with pH = 9.0, the gas production rates of pH = 1.0 and pH = 13.0 are improved by 13 times and 22 times at 0.71 V vs RHE, respectively. Then, we developed a force balance model for oxygen bubbles at the anode surface, and the predicted bubble detachment diameters are in good agreement with the experimental results. The Marangoni force induced by the nonuniform distribution of dissolved oxygen was found to be increased with pH, which leads to the larger detachment diameter of bubbles. The results show that the strong alkali environment is an effective means to remove oxygen bubbles from the surface of the photoelectrode.

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A significant challenge associated with photoelectrochemical water splitting is the reduction of the anode photocurrent due to bubble adhesion. To achieve in situ observation of bubble evolution on the electrode surface, an electrochemistry system coupled with a high-speed camera was developed. The relations between photocurrent curves and bubble morphology were clarified on a fixed TiO 2 thin-film electrode at various reaction temperatures (303.15−343.15 K). The photocurrent during the nucleation waiting, growth, and detachment of bubble evolution increased approximately linearly with the reaction temperature, indicating a higher reaction rate and a reduction in the impedance that must be overcome during bubble growth. The shortened nucleation waiting period was illustrated via a homogeneous nucleation model. The study found that the required concentration of dissolved gas for bubble nucleation decreased with an increasing reaction temperature. The bubble oscillations (∼25 Hz) under high reaction temperatures promoted the bubble mass transfer from the perspective of gas evolution efficiency. Besides, a force balance model was established based on the experimental data of bubbles. Because of the decrease of solutal Marangoni force with the increase of reaction temperature, the bubble growth periods were shortened, along with the relatively large bubble detachment diameter, thereby efficiently accelerating bubble removal from the electrode surface.

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