Cu 2 O is a typical photoelectrocatalyst for sustainable hydrogen production, while the fast charge recombination hinders its further development. Herein, Ni 2+ cations have been doped into a Cu 2 O lattice (named as Ni-Cu 2 O) by a simple hydrothermal method and act as electron traps. Theoretical results predict that the Ni dopants produce an acceptor impurity level and lower the energy barrier of hydrogen evolution. Photoelectrochemical (PEC) measurements demonstrate that Ni-Cu 2 O exhibits a photocurrent density of 0.83 mA cm À2 , which is 1.34 times higher than that of Cu 2 O. And the photostability has been enhanced by 7.81 times. Moreover, characterizations confirm the enhanced light-harvesting, facilitated charge separation and transfer, prolonged charge lifetime, and increased carrier concentration of Ni-Cu 2 O. This work provides deep insight into how acceptordoping modifies the electronic structure and optimizes the PEC process. Developing hydrogen energy plays a critical role in revolutionizing the current fossil-fuel-based energy system. [1] In various sustainable hydrogen production routes, photoelectrochemical (PEC) water splitting has drawn increasing attention since 1972. [2] Numerous materials, including Si, [3] g-C 3 N 4 , [4] metal oxides, [5] metal-chalcogenides, [6]