Dual Protection Layer Strategy to Increase Photoelectrode–Catalyst Interfacial Stability: A Case Study on Black Silicon Photoelectrodes

Photoelectrode degradation under harsh solution conditions continues to be a major hurdle for long‐term operation and large‐scale implementation of solar fuel conversion. In this study, a dual‐layer TiO 2 protection strategy is presented to improve the interfacial durability between nanoporous black silicon and photocatalysts. Nanoporous silicon photocathodes decorated with catalysts are passivated twice, providing an intermediate TiO 2 layer between the substrate and catalyst and an additional TiO 2 layer on top of the catalysts. Atomic layer deposition of TiO 2 ensures uniform coverage of both the nanoporous silicon substrate and the catalysts. After 24 h of electrolysis at pH = 0.3, unprotected photocathodes layered with platinum and molybdenum sulfide retain only 30% and 20% of their photocurrent, respectively. At the same pH, photocathodes layered with TiO 2 experience an increase in photocurrent retention: 85% for platinum‐coated photocathodes and 91% for molybdenum sulfide–coated photocathodes. Under alkaline conditions, unprotected photocathodes experience a 95% loss in photocurrent within the first 4 h of electrolysis. In contrast, TiO 2 ‐protected photocathodes maintain 70% of their photocurrent during 12 h of electrolysis. This approach is quite general and may be employed as a protection strategy for a variety of photoabsorber–catalyst interfaces under both acidic and basic electrolyte conditions.