Photoreforming lignocellulosic biomass for hydrogen production: Optimized design of photocatalyst and photocatalytic system

Using renewable solar energy for clean hydrogen (H2) fuel production via photocatalysis is a promising low carbon intensity strategy to address the energy crisis and environmental pollution issues. Biomass photorefinery is an emerging technology platform where biomass or its derivatives are employed as hole (h+) scavengers during photocatalysis, which not only reduces the thermodynamic barrier of the energy-demanding oxygen evolution reaction (OER, Delta E degrees =-1.23 V) in water splitting to favor H2 generation, but also endows the potential of biomass valorization. This review provides an in-depth comprehensive overview of the co-production of H2 and value-added biochemicals via lignocellulosic biomass photoreforming, with the special focuses on catalyst's struc-ture and photocatalytic system design. The photocatalyst structure is mainly elaborated from its band gap, morphology and size, crystal phase, cocatalyst and surface group modification. Among them, the band gap structure is crucial for the regulation of catalyst redox ability, which determines the high selectivity of photo -catalyst to generate the desired biochemicals. As well as the catalytic system such as pH, solvent, the concen-tration of catalyst and substrates, and the reaction temperature, matter much to enhance the solubility of lignocellulose and the accessibility of catalysts to substrates. The performance of using raw and pretreated biomass as h+ scavengers to boost H2 production as well as insights into their valorization pathways are deeply discussed. Future perspectives and challenges for the further advancement of biomass photoreforming tech-nologies are given at the end of this review.