In Situ Investigation of Oxygen Bubble Evolution at Photoanode Surface Affected by Reaction Temperature
Yonglu She, Qiang Xu, Tengfei Nie, Xinyi Luo, Mengsha Wang, Leqing Tao, Liejin Guo
Abstract
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.