Bias-free photoelectrochemical system for efficient 5-hydroxymethylfurfural oxidation using engineered silicon-based photoanode

Photoelectrochemical (PEC) oxidation provides a promising strategy to convert solar energy into high-value-added products. The oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is of particular interest, but efficient PEC conversion remains challenging due to the limitations of selectivity, stability, and energy conversion efficiency. Although n-type silicon offers the highest theoretical photocurrent, its practical application is hindered by insufficient photovoltage and sluggish interfacial catalysis. Here, we report a NiO x /Ga 2 O 3 /n-Si photoanode integrated with a Ni(OH) 2 cocatalyst for efficient HMF oxidation. The ultrathin Ga 2 O 3 interlayer facilitates the built-in electric field, thus leading to enhanced photovoltage and enabling superior HMF oxidation performance. When coupled with a commercial Pt/C cathode, the system achieves stable, bias-free FDCA production under simulated solar illumination. This work highlights the potential of engineered silicon photoanodes for sustainable light-driven biomass valorization.