Manipulating metal-oxygen local atomic structures in single-junctional p-Si/WO₃ photocathodes for efficient solar hydrogen generation

Self-passivation in aqueous solution and sluggish surface reaction kinetics significantly limit the photoelectrochemical (PEC) performances of silicon-based photoelectrodes. Herein, a WO₃ thin layer is deposited on the p-Si substrate by pulsed laser deposition (PLD), acting as a photocathode for PEC hydrogen generation. Compared to bare p-Si, the single-junctional p-Si/WO₃ photoelectrodes exhibit excellent and stable PEC performances with significantly increased cathodic photocurrent density and exceptional anodic shift in onset potential for water reduction. It is revealed that the WO₃ layer could reduce the charge transfer resistance across the electrode/electrolyte interface by eliminating the effect of Fermi level pinning on the surface of p-Si. More importantly, by varying the oxygen pressures during PLD, the collaborative modulation of W-O bond covalency and WO₆ octahedral structure symmetry contributes to the promoted charge carrier transport and separation. Meanwhile, a large band bending at the p-Si/WO₃ junction, induced by the optimized O vacancy contents in WO₃, could provide a photovoltage as high as ~ 500 mV to efficiently drive charge transfer to overcome the water reduction overpotential. Synergistically, by manipulating W-O local atomic structures in the deposited WO₃ layer, a great improvement in PEC performance could be achieved over the single- junctional p-Si/WO₃ photocathodes for solar hydrogen generation.