Enhanced Hydrogen Evolution Activity via Visible-Light-Driven Ag/MoS_2–<i>x</i>-Modified p-Type Si Micropyramid Cells with Optimized Band Alignment

Hydrogen is a clean energy carrier with the potential to address current environmental and energy challenges. One promising approach to hydrogen production is through photoelectrocatalytic water splitting, which utilizes solar energy with a minimal external bias. To improve the cell efficiency in evolving H2, a MoS2–x@Ag heterostructure was integrated on a micropyramidal p-type silicon (p-Si) substrate to form a photocathode with optimized band alignment. The cell was prepared by a sputtering method. The structural, compositional, and electronic properties of the photocathodes with varying layer thicknesses were characterized by using XRD, SEM, XPS, UPS, LEIPS, LSV, and PL techniques. The p-Si/MoS2–x/Ag heterojunction exhibited a favorable band structure for efficient charge transfer, facilitating electron accumulation for hydrogen evolution. Optimal photoelectrocatalytic performance was achieved with 50 nm MoS2–x and Ag layers, yielding a photocurrent density of 6.5 mA/cm2 at 0 VRHE. Beyond band alignment, surface defects also played a significant role in enhancing the activity by suppressing photocarrier recombination. XPS analysis revealed a high concentration of Mo6+ at the interface, indicating the presence of Mo antisite defects, which are beneficial for charge transport and catalytic efficiency. This work presents a practical design strategy that leverages both band engineering and defect modulation to improve the performance of photocathodes for solar-driven hydrogen production.