Concurrent utilization of e- and h+ for water splitting to H2 and biomass component to value added products: Sustainable solar driven photocatalysis towards meeting SDG7, 12 and 13

Abstract

Photocatalytic water splitting is considered as one of the efficient methods for producing green hydrogen. However, the sluggish oxygen evolution reaction (OER) kinetics with four electrons limits the overall efficiency of water splitting. Biomass components/biomass derivatives are the renewable carbon feedstock and abundantly available in nature. It is prudent to make use of electrons and holes concurrently in photocatalysis for H2 production and oxidation of biomass components, respectively, due to latter’s occurrence at low potential (≤1 V) than OER (>1.23 V), to value-added products (VAPs); this approach makes the entire process to be energy-efficient and kinetically superior. This potential approach could effectively utilize the charge carriers as well as abundant renewable resources of water and biomass simultaneously, thus meeting the sustainability, energy conversion and economic goals together. Parallel utilization of the charge carriers for redox reactions also enhances the sustainability of the catalyst system employed. Interestingly, biomass component oxidation to VAPs occur in several steps, which not only enhances holes utilization, but also provides an opportunity to design better catalyst to enhance selectivity of the targeted product. Carrying out such reactions under aerobic or anaerobic conditions, and different pH conditions offer to fine tune the product selectivity. Current review provides a detailed overview of the recent developments in this emerging area with three different types of photocatalyst systems, such as oxide, chalcogenide, carbon-based materials. Among them, the oxide-based system demonstrated the higher activity with sustainability, maintaining performance over 300 h. While many of these systems exhibited high selectivity towards a single product, 100 % selectivity to lactic acid from glycerol was observed with BiVO4 integrated TiO2 catalyst. Finally, the challenges, opportunities and future perspectives in this thriving field is listed, and they underscore the role of carbon-neutral economy towards achieving a potentially sustainable future.