Alternatives to water oxidation in the photocatalytic water splitting reaction for solar hydrogen production.

The photocatalytic water splitting process to produce H 2 is an attractive approach to meet energy demands while achieving carbon emission reduction targets. However, none of the current photocatalytic devices meets the criteria for practical sustainable H 2 production due to their insufficient efficiency and the resulting high H 2 cost. Economic viability may be achieved by simultaneously producing more valuable products than O 2 or integrating with reforming processes of real waste streams, such as plastic and food waste. Research over the past decade has begun to investigate the possibility of replacing water oxidation with more kinetically and thermodynamically facile oxidation reactions. We summarize how various alternative photo-oxidation reactions can be combined with proton reduction in photocatalysis to achieve chemical valorization with concurrent H 2 production. By examining the current advantages and challenges of these oxidation reactions, we intend to demonstrate that these technologies would contribute to providing H 2 energy, while also producing high-value chemicals for a sustainable chemical industry and eliminating waste.