Highly efficient photocatalytic H2 evolution over NiCo2S4/Mn0.5Cd0.5S: Bulk twinned homojunctions and interfacial heterojunctions

A twinned Mn0.5Cd0.5S (T-MCS) homojunction, consisting of wurtzite and zinc-blende Mn0.5Cd0.5S with different energy band structures, was fabricated using a facile hydrothermal method, resulting in the formation of a type-II bulk phase twinned homojunction. Furthermore, NiCo2S4 nanoparticles were deposited on the surface of T-MCS to form a surface heterojunction. The activities of T-MCS and NiCo2S4/T-MCS were tested in the photocatalytic H2 evolution reaction. T-MCS exhibits a superior H2 evolution rate of 61.4 mmol∙g−1∙h−1 under visible light (λ > 420 nm) irradiation owing to faster bulk phase charge separation, which is 8.2 and 1.9 times higher than those of wurtzite and zinc-blende Mn0.5Cd0.5S, respectively. Moreover, NiCo2S4 can facilitate interfacial electron transfer and can lower the H2 evolution overpotential; the H2 evolution rate is boosted to 127.3 mmol∙ g−1∙h−1 with an apparent quantum yield (AQY) of 23.4% with irradiation of 2 wt%-NiCo2S4/T-MCS under 400 ± 7.5 nm light. This work demonstrates that bulk phase twinned homojunctions and a surface heterojunction can combine to promote bulk and interfacial charge transfer and separation, simultaneously improving the kinetics of photocatalytic H2 evolution.