Abstract: | The photo‐electrochemical performance of the Si photocathode is seriously restricted by the severe charge recombination at the Si/electrolyte interface and sluggish hydrogen evolution reaction (HER) kinetics. Herein, a facile hydrothermal process is reported to integrate Ni/Fe codoped In2S3 nanosheet arrays onto the surface of unmodified a p‐Si photocathode for water reduction. The experimental results and density functional theory calculations indicate that the Ni and Fe codoping of In2S3 contributes to small surface transfer impedance, prolonged carrier lifetime, increased charge carrier concentration, and reduced overpotential for HER. Moreover, a p–n junction formed at the interface of Si and Ni/Fe:In2S3 promotes the photogenerated electron–hole separation and reduces the recombination in the bulk. As a result, the Si–Ni/Fe:In2S3 photocathode exhibits high performance with significantly enhanced photocurrent of ?80.9 mA cm?2 at ?1.3 VRHE and positive onset potential of 0.44 VRHE. |