The construction of efficient semiconductor/cocatalyst heterojunction is a promising strategy to promote the photocatalytic H-2-production efficiency from water reduction. Herein, a novel Cu-2(OH)(2)CO3/Zn0.5Cd0.5S heterojunction composite with superior photocatalytic H-2-generation activity and stability was prepared via a facile in situ synthetic route, in which Cu-2(OH)(2)CO3 served as cocatalyst stimulating the photocatalytic H-2-evolution performance of Zn0.5Cd0.5S. The Cu-2(OH)(2)CO3/Zn0.5Cd0.5S heterojunction photocatalyst containing 5 wt% of Cu-2(OH)(2)CO3 exhibited a prominent H-2-evolution efficiency of 275.7 mu mol h(-1), which is superior to the noble metal Pt-modified Zn0.5Cd0.5S photocatalyst (237.3 mu mol h(-1)) and much higher than bare Zn0.5Cd0.5S (90.8 mu mol h(-1)). The active Cu+/Cu-0 species generated during the photoreaction process is responsible for the prominent H-2-production activity of the heterojunction photocatalyst, which plays triple roles in enhancing the photoactivity of Zn0.5Cd0.5S via accelerating the charge separation, decreasing the overpotential of H-2-generation and improving the reduction ability of photoinduced electrons. Moreover, the formed Cu+/Cu-0 species during photoreaction can be readily oxidized back to Cu-2(OH)(2)CO3 upon exposure to air, thus restores the photoactivity and therefore enables good reusability of the Cu-2(OH)(2)CO3/Zn0.5Cd0.5S heterojunction photocatalysts. This work provides a new insight into the fabrication of Cu-2(OH)(2)CO3-assisted heterojunction photocatalysts with the highly stable and efficient performances for solar-to-chemical energy conversion.