Passivation\nEffect of Rock-Salt Nitride Materials\non a Planar <i>p</i>‑Si Photocathode for Solar Water\nReduction

Photoelectrochemical\nwater splitting, which uses sunlight to produce\nclean hydrogen fuel, is gaining traction with rising concerns about\nfossil fuels and pollution. Silicon (Si) photocathodes are promising\nfor this process due to their light absorption and favorable band\nalignment for hydrogen production. However, limitations such as reflectance,\nlow photovoltage, and rapid photocorrosion hinder their overall performance\nand stability. An interfacial insulating layer such as SiO<sub><i>x</i></sub> ensures superior durability to <i>p</i>-Si photocathodes. However, the inherent heterogeneity and intrinsic\ndefects pose challenges to effective surface passivation. This study\ninvestigates the challenges of photocorrosion and utilization of a\nthin titanium nitride (TiN) passivation layer deposited using direct-current\nmagnetron sputtering to protect the native silicon oxide (SiO<sub><i>x</i></sub>) layer. Additionally, a molybdenum oxynitride\n(Mo(O,N)<sub><i>x</i></sub>) bifunctional layer is employed\nto enhance both the electrocatalytic activity and durability of the\nphotocathode. The presence of oxygen and nitrogen within this cocatalyst\nlayer modifies the surface chemistry of the <i>p</i>-Si\nphotocathode, promoting favorable interfacial interactions with electrolyte\nspecies during PEC reactions. This modification facilitates efficient\ncharge transfer processes and accelerates reaction kinetics, ultimately\noptimizing the performance and operational lifetime of the photocathode.\nThe resulting Mo(O,N)<sub><i>x</i></sub>/TiN/<i>p</i>-Si photocathode exhibited a remarkable onset potential of +0.46\nV<sub>RHE</sub> in harsh acidic conditions under simulated sunlight\n(AM 1.5G illumination, 100 mW·cm<sup>–2</sup>). Notably,\nthe photocathode demonstrated exceptional long-term stability exceeding\n140 h, highlighting the combined TiN passivation and Mo(O,N)<sub><i>x</i></sub> cocatalyst as a protection strategy.