Emerging metal oxide/nitride protection layers for enhanced stability of silicon photoelectrodes in photoelectrochemical catalysis: Recent advancements and challenges

Photoelectrochemical (PEC) catalysis is considered as one of the most promising solutions to address the global energy crisis. Silicon-based photoelectrodes have been extensively studied for various PEC reactions due to their breakthroughs in the efficiency. However, stability has emerged as a major obstacle limiting commercial applications. In view of this, we have systematically summarized the main strategies for enhancing efficiency and prolonging the stability of silicon photoelectrodes, focusing on five metal oxide/nitride protection layers, namely TiO2, NiOx, CoOx, Al2O3, and GaN. In chronological order, this review presents the basic properties, synthesis processes, operation mechanisms, and application cases of these protection layers on silicon substrates. We conclude by highlighting the suitable application scenarios and the corresponding optimization solutions based on the unique characteristics of each protective layer. Lastly, we discuss the current challenges and future outlook for the development of Si-based photoelectrodes.