Mathematical Modeling of Multiphysics Processes in Photoelectrochemical Water Oxidation at Near-Neutral pH

Photoelectrochemical water splitting in neutral medium offers a promising pathway toward sustainable hydrogen production. As the core of water splitting, photoelectrochemical oxygen evolution reaction (OER) involves complex processes including light transmission and attenuation, photoelectrochemical reaction, equilibrium reactions of buffer, ion transport, bubble detachment, and two-phase flow, resulting in difficulties in revealing the interplay among processes. In this paper, a mathematical model of multiphysics is proposed for photoelectrochemical OER under near-neutral pH condition. The mathematical model is solved to investigate the effect of light intensity, buffer concentration, electrolyte flow speed, electrode surface properties, and buffer types on the mass transport and electrode OER performance. The results indicate that increasing the buffer concentration and electrolyte flow speed can effectively mitigate the pH polarization and improve the OER performance. A superaerophobic surface design remarkably facilitates the bubble detachment and the ion transport, consequently increasing the electrode's OER performance. Furthermore, the bicarbonate shows a better buffer capacity than other buffers and therefore remarkably improves the OER performance of the photoanode. This paper indicates that both two-phase flow and ion transport contribute to the photoelectrochemical OER process. The developed mathematical model can enable a deeper understanding of the fundamental processes for photoelectrochemical OER in a near-neutral pH medium.