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The rational design of durable and nonprecious nanocomposite photocatalysts with efficient charge separation and abundant active sites is still a grand challenge for photocatalytic hydrogen production from water reduction. Herein, a novel ternary nanocomposite, MoO 2 decorated Mn 0.5 Cd 0.5 S/Cu 2 O p-n heterojunction has been constructed via a facile two-step route employing the energy band engineering theory. Impressively, the optimized ternary Mn 0.5 Cd 0.5 S/Cu 2 O/MoO 2 nanocomposite displays a robust photocatalytic H 2 -evolution rate of 733.24 μmol h−1 under simulated solar light irradiation, more 4.2 times higher than pure Mn 0.5 Cd 0.5 S. The results demonstrated that the p-n heterojunction formed between n-type Mn 0.5 Cd 0.5 S and p-type Cu 2 O could markedly promote the interfacial charge transfer/separation through the internal electric field, whereas the MoO 2 cocatalyst with low overpotential could effectively collect photoinduced electrons and dramatically facilitate the H 2 -evolution kinetics. Moreover, both Cu 2 O and MoO 2 could improve the light-harvesting ability of pristine Mn 0.5 Cd 0.5 S, further contributing to the boosted hydrogen generation activity. [Display omitted] • MoO 2 decorated Mn 0.5 Cd 0.5 S/Cu 2 O p-n heterojunction synthesized for H 2 -production. • Multichannel charge-carrier transfer between Mn 0.5 Cd 0.5 S, Cu 2 O and MoO 2 discussed. • High H 2 -production rate achieved over composite, 4.2 folds higher than Mn 0.5 Cd 0.5 S. [ABSTRACT FROM AUTHOR]

[Display omitted] • WS 2 decorated Mn 0.5 Cd 0.5 S/CuInS 2 p-n heterojunction synthesized for H 2 -production. • Multichannel charge-carrier transfer between Mn 0.5 Cd 0.5 S, CuInS 2 and WS 2 discussed. • High H 2 -production rate achieved over composite, 3.98-fold higher than Mn 0.5 Cd 0.5 S. Effective charge separation and sufficient light harvesting are crucial for photocatalytic water splitting into renewable and storable hydrogen energy. Employing WS 2 as cocatalyst and CuInS 2 as p-type semiconductor and photosensitizer, a novel WS 2 /Mn 0.5 Cd 0.5 S/CuInS 2 hierarchical tandem p-n heterostructure was constructed based on the energy band engineering theory. In this tandem p-n heterostructure, Mn 0.5 Cd 0.5 S nanoparticles adhere closely to CuInS 2 nanosheets to form a p-n junction along with the strong and monodirectional inner-built electric field, which can regulate the directional transfer/migration of photoinduced electrons-hole pairs and significantly boost the charge separation. Furthermore, the WS 2 cocatalyst employed in the ternary heterostructure further expedites the spatial charge separation and directional migration of photoexcited electrons, as well as simultaneously provides plentiful reaction active sites to decrease the activation barrier for hydrogen generation reaction. Benefiting from the synergetic cooperation of WS 2 cocatalyst and the p-n junction charge transfer channels, the smartly designed ternary WS 2 /Mn 0.5 Cd 0.5 S/CuInS 2 heterostructure displays the optimal photoactivity toward hydrogen production (681.7 μmol h−1), more 3.98-fold enhancement than individual Mn 0.5 Cd 0.5 S under simulated sunlight irradiation. This research provides a new avenue for constructing multi-hierarchical systems with remarkably boosted charge separation and light-harvesting abilities for high-efficiency solar energy conversion. [ABSTRACT FROM AUTHOR]