Effect of pressurization on bubble dynamics of photoelectrochemical water splitting

Energy consumption of hydrogen production significantly restricts the practical application of photoelectrochemical (PEC) water splitting technology for hydrogen production, despite its vital role in addressing the energy crisis. The direct high-pressure hydrogen production technology holds promise for reducing production costs and streamlining the overall process. This paper delved into the study of bubble dynamic characteristics of PEC water splitting reaction under elevated pressure operations by coupling a photoelectrochemical system with a high-speed microscopic camera. The results prove that the bubble growth behaviors are pressure-dependent. Pressurization leads to the simultaneous evolution of multiple bubbles along with bubble slip and coalescence on the photoelectrode surface. And the bubble detachment diameter and growth period are significantly reduced, suggesting that increasing pressure is conducive to promoting bubble detachment. Analysis of the results of linear sweep voltammetry and Tafel slope shows that elevated pressure leads to more challenging bubble nucleation. Furthermore, the time coefficient and growth coefficient of the bubble growth stage are computed, revealing that the diffusion-controlled stage dominates the bubble growth process post-pressurization. A force balance model is constructed in the initial process of bubble rising, and it is found that the terminal rise velocity of bubbles decreases when pressure increases. The effect of pressure on gas density was considered to calculate the gas production rate by bubble volume and growth period, discovering that the proportion of gas products in the form of dissolved oxygen in the liquid increases significantly under high pressure.