Bangjun Guo

Hollow Structured Micro/Nano MoS2 Spheres for High Electrocatalytic Activity Hydrogen Evolution Reaction

Molybdenum disulfide (MoS2) has attracted extensive attention as a non-noble metal electrocatalyst for hydrogen evolution reaction (HER). Controlling the skeleton structure at the nanoscale is paramount to increase the number of active sites at the surface. However, hydrothermal synthesis favors the presence of the basal plane, limiting the efficiency of catalytic reaction. In this work, perfect hollow MoS2 microspheres capped by hollow MoS2 nanospheres (hH-MoS2) were obtained for the first time, which creates an opportunity for improving the HER electrocatalytic performance. Benefiting from the controllable hollow skeleton structure and large exposed edge sites, high-efficiency HER activity was obtained for stacked MoS2 thin shells with a mild degree of disorder, proving the presence of rich active sites and the validity of the combined structure. In general, the obtained hollow micro/nano MoS2 nanomaterial exhibits optimized electrocatalytic activity for HER with onset overpotential as low as 112 mV, low Tafel slope of 74 mV decade(-1), high current density of 10 mA cm(-2) at η = 214 mV, and high TOF of 0.11 H2 s(-1) per active site at η = 200 mV.

Firework-shaped TiO2 microspheres embedded with few-layer MoS2 as an anode material for excellent performance lithium-ion batteries

A three-dimensional porous hierarchical architecture of uniform TiO2 microspheres embedded with MoS2 nanosheets was prepared via a facile hydrothermal self-assembly scheme. A possible growth mechanism is presented in detail based on theoretical analysis and experimental facts. Further experiments demonstrate that MoS2 nanosheets are uniformly coated on the surface of TiO2 nanorods. Besides, the obtained F-TiO2@MoS2 possesses a large surface area and stable structure. Moreover, the F-TiO2@MoS2 microspheres were successfully assembled as an electrode material for lithium-ion batteries. As expected, the electrochemical measurement demonstrates that the F-TiO2@MoS2 shows excellent electrochemical performance, which exhibits a high reversible capacity of 971 mA h g−1 at a current density of 100 mA g−1, a markedly high rate capability of over 450 mA h g−1 at a current density of 1000 mA g−1 and a superior cycling stability of 714 mA h g−1 after 200 cycles at a current density of 100 mA g−1, as an anode material for LIBs.

Charge-Transfer Induced High Efficient Hydrogen Evolution of MoS2/graphene Cocatalyst.

The MoS2 and reduced graphite oxide (rGO) composite has attracted intensive attention due to its favorable performance as hydrogen evolution reaction (HER) catalyst, but still lacking is the theoretical understanding from a dynamic perspective regarding to the influence of electron transfer, as well as the connection between conductivity and the promoted HER performance. Based on the first-principles calculations, we here clearly reveal how an excess of negative charge density affects the variation of Gibbs free energy (ΔG) and the corresponding HER behavior. It is demonstrated that the electron plays a crucial role in the HER routine. To verify the theoretical analyses, the MoS2 and reduced graphite oxide (rGO) composite with well defined 3-dimensional configuration was synthesized via a facile one-step approach for the first time. The experimental data show that the HER performance have a direct link to the conductivity. These findings pave the way for a further developing of 2-dimension based composites for HER applications.

Novel dual-petal nanostructured WS2@MoS2 with enhanced photocatalytic performance and a comprehensive first-principles investigation

For the first time, a novel dual-petal nanostructured WS2@MoS2 heterojunction was fabricated via a facile two-step approach and explored as a photocatalyst for the photodegradation of methylene blue (MB). In the light of the results obtained from experiments, a reasonable formation mechanism for the nanopetal (NP) structured WS2 was proposed, in which the pretreatment of ball milling had played an important role in the formation of WS2 NPs that subsequently acted as the base material to grow curly MoS2 sub-NPs. Because the dual-petal nanostructured WS2@MoS2 possessed plenty of active sites that originated from its unique structural characteristics with densely stacked MoS2 nanopetals and an effective separation of photoinduced carriers, it exhibited significantly enhanced photocatalytic activity and obviously exceeded the pristine MoS2/WS2. In order to propose a scientific explanation for the corresponding enhancement mechanism, we further conducted comprehensive first-principles calculations to investigate the corresponding structural, electronic, and optical properties of this WS2@MoS2 composite. The results revealed that the calculated band gap of the WS2@MoS2 composite was narrower than that of pristine WS2 and MoS2, meanwhile, it had a well-defined staggered type-II band alignment, leading to the injection of photoexcited electrons into the conduction band minimum (CBM) of MoS2 from the CBM of WS2. This separation of carriers can restrain the photogenerated e−–h+ pair recombination and prolong the lifetime of carriers for proper interface charge distribution. In short, the calculated results fully explained the reason why the composite presented improved photocatalysis and provide valuable references for future studies.

Coral-Shaped MoS2 Decorated with Graphene Quantum Dots Performing as a Highly Active Electrocatalyst for Hydrogen Evolution Reaction

We report a new CVD method to prepare coral-shaped monolayer MoS2 with a large amount of exposed edge sites for catalyzing hydrogen evolution reaction. The electrocatalytic activities of the coral-shaped MoS2 can be further enhanced by electronic band engineering via decorated with graphene quantum dot (GQD) decoration. Generally, GQDs improve the electrical conductivity of the MoS2 electrocatalyst. First-principles calculations suggest that the coral MoS2@GQD is a zero-gap material. The high electric conductivity and pronounced catalytically active sites give the hybrid catalyst outstanding electrocatalytic performance with a small onset overpotential of 95 mV and a low Tafel slope of 40 mV/dec as well as excellent long-term electrocatalytic stability. The present work provides a potential way to design two-dimensional hydrogen evolution reaction (HER) electrocatalysts through controlling the shape and modulating the electric conductivity.

First-principle and experiment investigation of MoS2@SnO2 nano-heterogeneous structures with enhanced humidity sensing performance

In this work, we report the First-principle investigation and synthesis of MoS2@SnO2heterostructure as high-performance humidity sensor by a two-step hydrothermal method. The first-principles calculations were performed to explain water molecule adsorption mechanism by applying density of state model to simulate the interaction between water molecule and sensing base material. The higher specific surface and the lower adsorption energy theoretically predicted the improvement on humidity sensing performance, which was confirmed by experiments testing. The MoS2@SnO2heterostructure exhibited promoted humidity sensing characteristics on response time of 53 s and recovery time of 21 s, while switching the humidity between 11% relative humidity (RH) and 95% RH. The corresponding humidity sensing mechanisms of MoS2@SnO2 were elaborately interpreted. This work could bring forward a new design method on practical humidity sensing devices with an excellent stability and fast response by using MoS2@SnO2heterostructure.