Mechanism of pH Effect on Mass Transfer During Bubble Evolution on Photoelectrode Surfaces

• Published in: Journal of the Electrochemical Society 2024-01, Vol.171 (1), p.16501
• Main Authors: Xu, Qiang, Tao, Leqing, Nie, Tengfei, Liang, Liang, She, Yonglu, Wang, Mengsha
• Format: Article
• Language: English
• Subjects: bubble evolution; mass transfer; pH effects; photoelectrochemical water splitting; photoelectrode
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1945-7111/ad1c18

This study conducted in-depth research on the limitation problem of mass transfer of gas molecules on the surface of the photoelectrode to the efficiency of photoelectrochemical water splitting. Experimental results reveal significant differences in the dynamic characteristics of bubbles and mass transfer mechanisms during bubble growth under different pH conditions. As the pH deviates from 7.0 (vs RHE), the reaction rate increases, the bubble nucleation voltage decreases, and the terminal rising velocity increases significantly. During the rapid growth phase of bubbles, the mass transfer coefficient reaches its peak, accounting for only 1% of the entire evolution cycle. In a neutral environment (pH = 7.0), the transient mass transfer coefficient reaches a maximum at approximately 1 s of bubble growth, while in an alkaline environment (pH = 12.0), it reaches a maximum at around 0.1 s. In strongly alkaline environments (pH = 13.0), the PEC reaction rate and mass transfer rate increase, resulting in the highest gas production efficiency. The mass transfer coefficients were improved by about 72.4% and 42.8% (vs Ag/AgCl) and by about 22.2% and 33.3% (vs RHE) in the strong alkaline environment relative to the strong acid environment (pH = 1.0) and the neutral environment, respectively. Real-time monitoring and documentation of bubble evolution at different pH states. Relation between mass transfer mechanisms and bubble behavior at various pH studied. Enhanced mass transfer in strong acid and strong alkaline conditions.