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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 CO 3 /Zn 0.5 Cd 0.5 S 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 CO 3 served as cocatalyst stimulating the photocatalytic H 2 -evolution performance of Zn 0.5 Cd 0.5 S. The Cu 2 (OH) 2 CO 3 /Zn 0.5 Cd 0.5 S heterojunction photocatalyst containing 5 wt% of Cu 2 (OH) 2 CO 3 exhibited a prominent H 2 -evolution efficiency of 275.7 μmol h−1, which is superior to the noble metal Pt-modified Zn 0.5 Cd 0.5 S photocatalyst (237.3 μmol h−1) and much higher than bare Zn 0.5 Cd 0.5 S (90.8 μmol h−1). The active Cu+/Cu0 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 Zn 0.5 Cd 0.5 S via accelerating the charge separation, decreasing the overpotential of H 2 -generation and improving the reduction ability of photoinduced electrons. Moreover, the formed Cu+/Cu0 species during photoreaction can be readily oxidized back to Cu 2 (OH) 2 CO 3 upon exposure to air, thus restores the photoactivity and therefore enables good reusability of the Cu 2 (OH) 2 CO 3 /Zn 0.5 Cd 0.5 S heterojunction photocatalysts. This work provides a new insight into the fabrication of Cu 2 (OH) 2 CO 3 -assisted heterojunction photocatalysts with the highly stable and efficient performances for solar-to-chemical energy conversion. Unlabelled Image • A novel binary Cu 2 (OH) 2 CO 3 /Zn 0.5 Cd 0.5 S composite was successfully synthesized. • The trifunctional roles of Cu 2 (OH) 2 CO 3 cocatalyst were discussed. • Mechanism of the enhanced photocatalytic activity was illuminated. [ABSTRACT FROM AUTHOR]

• Mn 0.5 Cd 0.5 S decorated with Au and MoO 2 dual cocatalysts synthesized for H 2 -production. • Synergetic effects between the multifunctional Au NPs and MoO 2 cocatalysts discussed. • High H 2 -production rate achieved over composite, 3.73 folds higher than Mn 0.5 Cd 0.5 S. The construction of semiconductor-based nanoheterostructures toward achieving high efficient solar-to-fuel conversion is greatly limited by the insufficient electron-hole separation and the narrow spectrum range of light absorption. In this work, a novel Mn 0.5 Cd 0.5 S solid solution decorated with robust and multifunctional MoO 2 and Au nanoparticles (NPs) has been constructed by a facile two-step route: the deposition of Au NPs via an in situ deposition route and further loading of MoO 2 via an ultrasonic chemical method. Characterization results show that both MoO 2 and Au NPs can be employed as efficient cocatalytic materials to significantly promote the H 2 -production over Mn 0.5 Cd 0.5 S semiconductor. Particularly, the ternary 2MoO 2 /3Au/Mn 0.5 Cd 0.5 S nanocomposite containing 3 wt% Au NPs and 2 wt% MoO 2 exhibited the optimum H 2 -production activity (638.83 µmol h−1) under simulated sunlight conditions, more 3.73-, 1.74- and 1.35-fold enhancement relative to pristine Mn 0.5 Cd 0.5 S, binary 3Au/Mn 0.5 Cd 0.5 S and 2MoO 2 /Mn 0.5 Cd 0.5 S, respectively. Mechanistic characterizations demonstrate that the positive synergetic effects between Au NPs and MoO 2 can simultaneously boost the light absorption capacities, the separation efficiency of the interfacial charge carriers, and the thermodynamic performances of the hydrogen evolution reaction by strengthening the reduction ability of the photogenerated electrons and lowering the hydrogen evolution overpotential, which integratively resulted in the boosted photoactivity. [ABSTRACT FROM AUTHOR]

• Au decorated S-scheme Mn 0.5 Cd 0.5 S/WO 3 composite synthesized for H 2 -production. • Mechanism of charge transfer and separation in Au decorated S-scheme discussed. • High H 2 -production rate achieved over composite, 2.74 folds higher than Mn 0.5 Cd 0.5 S. Spontaneously solar-driven H 2 -production from water reduction provides a promising strategy to solve the aggravating energy and environment crises worldwide, but it is severely limited by the rapid charge-carrier recombination and the slashing redox potentials requirement. Here, a new ternary Mn 0.5 Cd 0.5 S/WO 3 /Au heterostructure photocatalyst has been designed by chemical deposition of Au nanoparticles (NPs) on Mn 0.5 Cd 0.5 S/WO 3 step-scheme (S-scheme) composite matrix to boost the photocatalytic activity through the multichannel-enhanced charge transfer/separation. By optimizing the constituent of the heterostructure photocatalyst, the prepared Mn 0.5 Cd 0.5 S/WO 3 /Au photocatalyst with 30 wt% of WO 3 and 4 wt% of Au exhibits the highest H 2 -evolution rate of 517.13 µmol h−1 under simulated solar light irradiation, more 2.74, 1.63 and 1.45 times higher than bare Mn 0.5 Cd 0.5 S and Mn 0.5 Cd 0.5 S loaded with WO 3 and Au alone, respectively. Mechanistic characterizations and control experiments have revealed that the S-scheme charge transfer in Mn 0.5 Cd 0.5 S/WO 3 heterojunction together with the "electron reservoir" resulting from the Au NPs contribute to the superior H 2 -generation activity over Mn 0.5 Cd 0.5 S/WO 3 /Au catalyst, which not only dramatically promotes the charge-carrier separation but also remains the strong redox ability of photoinduced electrons and holes in such photocatalytic system. [ABSTRACT FROM AUTHOR]