LAUSR

All inorganic perovskite CsPbBr3 nanocrystals are a promising candidate as photocathode for efficient photoelectrocatalytic (PEC) water splitting. However, the poor chemical stability severely limits its practical applications. The exploration of perovskite‐based ideal photocathode materials with efficient and highly stable PEC performance is still an ambitious and meaningful challenge. Herein, under guidance of theoretical calculations, an encapsulation strategy is proposed to prepare the CsPbBr3/Ni2P core/shell nanostructures. Compared with the pristine CsPbBr3 nanocrystals, the CsPbBr3/Ni2P nanostructures show a significant improvement of photocurrent density up to 10 000 folds with long‐term stability in aqueous solution, and present superior PEC activity for hydrogen generation with nearly 100% faradic efficiency. The encapsulation strategy opens up an avenue for rational design of perovskite‐based photocathodes for efficient and stable PEC water reduction.