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

Abstract

A twinned Mn_0.5Cd_0.5S (T-MCS) homojunction, consisting of wurtzite and zinc-blende Mn_0.5Cd_0.5S 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 Mn_0.5Cd_0.5S, 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.

Keywords: Mn(0.5)Cd(0.5)S; NiCo(2)S(4); Photocatalytic H(2) evolution; Twinned homojunction.