Unraveling Crystal Phase-Driven Activity and Selectivity of WO₃ for Photoelectrochemical Biomass Valorization

Modulating the crystal phase of a photocatalyst significantly impacts its surface and photochemical properties, allowing for the adjustment of catalytic activity and selectivity, particularly in the electrooxidation reactions of biomass-derived chemicals. Herein, monoclinic and hexagonal phases of WO₃ are employed as photoanodes for the photoelectrochemical conversion of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF). The monoclinic phase demonstrated exceptional performance in photoelectrocatalytic HMF oxidation, achieving remarkable photocurrent densities (1.1 mA cm^-2), which were 5.5 times greater than those observed for hexagonal WO₃. Moreover, the yield of DFF products obtained over monoclinic WO₃ was approximately 2.5 times higher compared to that of hexagonal WO₃. A combination of experiments and theoretical calculations indicates that the superior performance of monoclinic WO₃ for HMF oxidation mainly originates from enhanced light harvesting efficiency, better charge separation and utilization, balanced adsorption energy, and stronger oxidative ability of photogenerated holes. This study emphasizes the potential of crystal phase engineering to regulate the reaction activity and selectivity and provides insights into how to design next-generation high-performance photoelectrodes for sustainable chemical production from biomass.