Artificial photosynthesis for high-value-added chemicals: Old material, new opportunity

Solar energy utilization has drawn attention due to ever-increasing environmental and energy issues. Photoelectrochemical (PEC) and photocatalytic (PC) water splitting for hydrogen production, which is the most popular and well-established solar-to-chemical conversion process, has been studied thoroughly to date but is now facing limitations related to low conversion efficiency. To resolve this issue, research in PEC cells or photocatalysts has recently aimed to produce alternative value-added chemicals by modifying their redox reactions, which potentially enables high economic reward to compensate for the low efficiency. Here, various kinds of redox reactions that decouple classic water splitting reactions to produce value-added chemicals via PEC and PC processes are introduced. Successful coupling of CO2 reduction, O-2 reduction and organic synthesis with either water oxidation or water reduction is comprehensively discussed from the perspective of basic fundamental and product selectivity in terms of the band structure of materials, cocatalyst design, and thermodynamics and kinetics of the reactions. Throughout the review, future challenges and opportunities are suggested with respect to the redesigned artificial synthesis, which might be an alternative development for the commercialization of PEC or PC value-added chemical production technologies in the near future.