Ternary Earth-Abundant Catalyst Enabling Stable Silicon Photocathodes for Solar Hydrogen Generation

Silicon-based photocathodes offer great promise for scalable photoelectrochemical (PEC) hydrogen production due to their earth abundance and optimal bandgap, yet their practical deployment remains hindered by interfacial instability and sluggish catalytic kinetics. Herein, we report a CoMoS ternary bimetallic catalyst, deposited via a photoelectrodeposition method onto a TiO₂-passivated Si substrate, enabling efficient and durable PEC hydrogen evolution. The research found that Co-Mo has a strong electronic interaction and charge distribution. The incorporation of Mo into CoS optimizes its electronic structure and regulates the hydrogen adsorption free energy, thereby enhancing HER activity. Mo incorporation lowers the reaction energy barriers for hydrogen adsorption and desorption, providing highly active sites that facilitate intermediate transfer, reduce activation energy, and boost intrinsic catalytic activity. These improvements originate from the robust electronic coupling between Mo and Co, as well as the synergistic effects at the heterogeneous interface, which effectively modulate the local electronic structure and band alignment, thereby enhancing charge transfer kinetics. Comprehensive carrier dynamics analyses based on IMVS, IMPS, EIS, OCP, and transient photocurrent measurements demonstrate substantially reduced interfacial resistance, extended carrier lifetime, and faster charge transport. The optimized CoMoS/TiO₂/Si photocathode delivers an onset potential of 0.69 V_RHE, a high photocurrent density of 31.2 mA cm^-2 at 0 V_RHE, and an applied bias photon-to-current efficiency (ABPE) of 7.04%, while maintaining exceptional operational stability. These results highlight the viability of nonprecious metal catalysts and structural tuning strategies for advancing silicon-based PEC devices toward real-world applications.