Superior Photocatalytic Hydrogen Evolution Performances of WS<sub>2</sub> over MoS<sub>2</sub> Integrated with CdS Nanorods
B. Archana, Nagaraju Kottam, Sanjay Nayak, K. B. Chandrasekhar, M. B. Sreedhara
Abstract
Fabrication of noble metal-free semiconductor heterojunction composed of transition metal dichalcogenides (TMDs) and CdS is observed to be an efficient and economical photostable system for hydrogen evolution. In this report, ultrathin nanosheets of MoS2, Mo1–xWxS2 (x = 0.5 and 0.8), and WS2 integrated with CdS nanorods; hierarchical nanocomposites have been developed to improve the efficiency and durability of CdS nanorods for H2 generation. These nanocomposites exhibit outstanding H2 evolution activity with notable efficiency and excellent stability. The activity of pure MoS2, Mo1–xWxS2, and WS2 nanosheets are negligible, suggesting their cocatalytic action. The H2 evolution activities of MoS2–CdS, MoWS2–CdS, and WS2–CdS nanocomposites have been systematically studied and compared. The highest H2 evolution rates of 19.2 mmol g–1 h–1 was recorded for WS2–CdS nanocomposite (9.7 mmol g–1 h–1 for MoS2–CdS), which is 35 times higher than that of pure CdS (0.53 mmol g–1 h–1). The activity of these nanocomposites were notably superior in acidic medium (lactic acid sacrificial donor) than alkaline medium (Na2S–Na2SO3 sacrificial donor). The apparent quantum yield of 10.19% was observed in lactic acid sacrificial electron donor medium. The rational design presented here not only substantially surges H2 evolution rates but also reduces the photocorrosion of CdS. The possible mechanism has been investigated by analyzing the electronic band alignment of materials with respect to the vacuum level. Furthermore, the H2 evolution reactions were carried out under direct sunlight and in seawater to assess the performance of these nanocomposites in the practical applications.