Photocatalysts for hydrogen evolution coupled with production of value-added chemicals

Abstract

The conversion of water into clean hydrogen fuel using renewable solar energy can potentially be used to address global energy and environmental issues. However, conventional photocatalytic H₂ evolution from water splitting has low efficiency and poor stability. Hole scavengers are therefore added to boost separation efficiency of photoexcited electron–hole pairs and improve stability by consuming the strongly oxidative photoexcited holes. The drawbacks of this approach are increased cost and production of waste. Recently, researchers have reported the use of abundantly available hole scavengers, including biomass, biomass‐derived intermediates, plastic wastes, and a range of alcohols for H₂ evolution, coupled with value‐added chemicals production using semiconductor‐based photocatalysts. It is timely, therefore, to comprehensively summarize the properties, performances, and mechanisms of these photocatalysts, and critically review recent advances, challenges, and opportunities in this emerging area. Herein, this paper: 1) outlines reaction mechanisms of photocatalysts for H₂ evolution coupled with selective oxidation, C–H activation and C–C coupling, together with nonselective oxidation, using hole‐scavengers; 2) introduces equations to compute conversion/selectivity of selective oxidation; 3) summarizes and critically compares recently reported photocatalysts with particular emphasis on correlation between physicochemical characteristics and performances, together with photocatalytic mechanisms, and; 4) appraises current advances and challenges.