Metallic MoO2 cocatalyst significantly enhances visible-light photocatalytic hydrogen production over MoO2/Zn0.5Cd0.5S heterojunction

Abstract

As semiconductor-based nanoheterostructures play a decisive role in current electronics and optoelectronics, the introduction of active heterojunctions can afford new and improved capabilities that will enhance the conversion of solar energy into chemical energy. In this work, a novel metal/semiconductor MoO₂/Zn_0.5Cd_0.5S heterojunction has been designed and prepared to significantly enhance photocatalytic H₂ production efficiency. The photocatalytic activity of the as-prepared MoO₂/Zn_0.5Cd_0.5S for H₂ generation from water under visible-light irradiation (λ ≥ 420 nm) is measured. MoO₂/Zn_0.5Cd_0.5S hybrid nanoparticles have a higher photocatalytic activity than Zn_0.5Cd_0.5S even without the noble metal cocatalyst. The results show that the rate of H₂ evolution over annealed MoO₂/Zn_0.5Cd_0.5S is about 13 times higher than that of Zn_0.5Cd_0.5S alone, and 10 times higher than that of simply mixed MoO₂/Zn_0.5Cd_0.5S. Implying that the strong coupling at the interface of MoO₂ and Zn_0.5Cd_0.5S facilitates electron transfer from the conduction band of Zn_0.5Cd_0.5S to metallic MoO₂, thus promoting the separation of photogenerated electrons and holes. MoO₂ (2 wt%)/Zn_0.5Cd_0.5S heterostructured photocatalyst calcined at 673 K achieves the optimal overall activity for H₂ evolution. The introduction of metallic MoO₂ cocatalyst leads to a remarkable improvement in the photo current and photocatalytic H₂ production activity of Zn_0.5Cd_0.5S, and the content of MoO₂ in this catalyst has an important influence on the photocatalytic activity. It is shown that 2 wt% metallic MoO₂ loaded on Zn_0.5Cd_0.5S sample produces a maximum photocatalytic H₂ production rate of 252.4 μmol h⁻¹. The junctions formed between metallic MoO₂ and semiconductor Zn_0.5Cd_0.5S by calcination play a key role in high photocatalytic water splitting to produce H₂. Our study demonstrates that metallic MoO₂ is an excellent H₂ evolution cocatalyst, and could be used as a cocatalyst for other semiconductors to improve performances.