Alternative Oxidation Reactions for Solar-Driven Fuel Production

For nearly half a century, water oxidation has been extensively investigated as the electron source for solar-powered H-2 fuel production from water. However, despite a thermodynamic potential of only 1.23 V required at standard conditions, driving the oxygen evolution reaction (OER) typically requires 1.5-1.8 V resulting in a significant loss. Over the past decade, numerous researchers have begun to re-explore the idea of replacing water oxidation with more kinetically facile oxidation reactions in photoelectrochemical and photocatalytic solar H-2 production systems. Alternate photo-oxidation reactions can be employed as a means of chemical valorization, in addition to providing electrons for H-2 production from water while reducing the losses associated with the OER. In this Perspective, we discuss other possible oxidation reactions, and in particular, we highlight recent progress in the investigation of organic-based photo-oxidation reactions. We focus on oxidation reactions that have potential applications as a form of chemical valorization and that can take place in aqueous solutions to allow concurrent H-2 production via water reduction at a (photo)cathode. A critical assessment and an outlook toward the prospective large-scale implementation of this technology is finally considered.