Two-dimensional MoS2 nanosheets (NSs) with high active site density were designed for the hydrogen evolution reaction (HER) through a microdomain reaction method. The effect of the annealing temperature on the microstructure and the HER performance of MoS2 NSs was examined, and a plausible relation between the stack structures of the MoS2 catalysts and their HER performance was also explored. The MoS2 NS electrocatalyst obtained at 550 °C reveals the best HER performance with a relatively small Tafel slope of 68 mV/dec. Both the exposed surface area and active site density are very important for providing a large amount of active sites. The present work has been proved to be an efficient route to achieve a high active site density and a relatively large surface area, which might have potential use in photoelectrocatalytic water splitting.Keywords: active site density; electrocatalyst; hydrogen evolution reaction; molybdenum disulfide; nanosheets

Metastable hexagonal h-MoO3 nanorods were synthesized by a simple sonochemical method, and then were transformed into thermodynamically stable a-MoO3 microbelts by calcination. The obtained samples were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). It was found that the as-prepared h-MoO3 nanorods were of 0.2–1.2 μm in width and 1-6 μm in length. A possible formation and growth mechanism of hexagonal MoO3 nanorods is proposed, in which ultrasound plays a crucial role and cannot be ignored. Moreover, the effect of temperature on the transformation process by calcination is investigated and a possible growth process of microbelts is also discussed.

WS2 nanosheets were synthesized by a novel mechanical activation method, in which a ball-milled mixture of WO3 and S was adopted as reagent and then annealed at 600 °C for 2 h in an atmosphere of Ar. The final products were characterized by XRD, SEM and TEM. It was found that the nanosheets were obtained with thickness of only about 10 nm, through the exfoliation from the sulfurized outer layers of tungsten trioxide. The ball milling played a crucial role in the mechanical activation of reagents and promoted direct production of WS2 without any intermediate products. The effect of temperature was also discussed.

The fabrication of MoS2 nanospheres with an average diameter of 100 nm via a surfactant-assisted route was reported, in which an amorphous MoS3 precursor was obtained by the aggregation transformation of surfactant at a low temperature and then transformed to the MoS2 nanospheres with quasi-fullerene structures by thermal decomposition. The final products were characterized by XRD, IR, SEM, and TEM, respectively. The results indicate that the polyethylene glycol (PEG) promotes the formation of nanospheres and has a great effect on the microstructures, resulting in the abnormal expansion of lattice. The possible transformation mechanism of structures has been discussed based on the experimental results.

The hexagonal MoS2 nanoparticles were prepared using a surfactant-assisted method in aqueous solution at 373 K. The as-obtained samples were characterized by XRD, IR and TEM equipped with EDS. It was found that the as-prepared samples had hexagonal structures with size of 100–200 nm. The possible reaction route and formation mechanism were proposed.

The MoS2 nanoplates with hexagonal morphology have been obtained via solid-state assembly of MoS2 nanosheets, which were prepared by a normal sulfurization method. The solid-state assembly was realized by a simple calcination process, and the annealing temperature played a crucial role in the formation of the final hexagonal nanoplates. A possible mechanism about the solid-state assembly was also proposed.

The MoS2 nanoflakes have been successfully prepared by a novel mechanical activation method, in which the ball-milled mixture of MoO3 and S was used as reactants and then calcined at 600 °C for 2 h in an atmosphere of Ar. The ball milling played a crucial role not only in the reduction of particles size but also in the homogeneous distribution of reactants, and created micro-domains of reactors to produce nanoflakes. The length and thickness of the obtained MoS2 nanoflakes were less than 100 and 2 nm, respectively. These novel structures of thin nanoflakes had short and low stacked layers, providing more exposed rims and edges, which indicated potential applications in highly active catalysts. Furthermore, the closed structures like quasi-fullerene and nanotubes were also obtained by the rolling of nanoflakes at higher temperatures.