The MoS 2 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 MoS 2 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.In recent years, the demands for the renewable and clean energy resources gradually become urgent for the growing problems of environmental pollution. Hydrogen, as a clean and efficient fuel source, has been vigorously pursued as a promising candidate for future energy carrier. The traditional way to produce hydrogen involving CO 2 release and the high temperature reaction condition will be phased out gradually for the related disadvantages 1 , therefore, developing techniques to produce hydrogen from economic and renewable resources can be beneficial to a significant reduction in consumption of fossil fuel and a lower CO 2 emissions. Recently, massive efforts have been devoted to producing hydrogen by electrochemical or photoelectrocatalytic processes from water splitting [2][3][4] . So far, many kinds of materials including nickel alloy, carbides, polymeric carbon nitride and transition metal chalcogenides have been attempted to serve as the HER catalysts [5][6][7] . Among these, the most common catalysts used for HER are noble metals, such as ruthenium, iridium and platinum 8,9 . In general electrochemical routines, nickel alloy catalysts present high activity for the HER in alkaline electrolytes, while they are often degraded in acidic solutions. Pt has very small over potential for HER and exhibits excellent electrocatalytic activity, but the scarcity and high prices of these kinds of noble metals prohibit their widespread applications 10

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.

In this work, we studied the synthesis and electrochemical performance of MoS 2 and reduced graphene oxide (rGO) hybrid nanoflowers for use as anode material in lithium ion batteries (LIBs). The morphology and microstructure of the samples were characterized by field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Xray diffraction (XRD) and X-ray photoelectron spectrometry (XPS). Herein, the composite nanoflowers delivered a significant enhanced reversible specific capacity and charge/discharge cycle stabilities as anode in comparison with pristine MoS 2 . Electrochemical impedance spectroscopy (EIS) measurements indicated that the incorporation of rGO significantly reduced the contact resistance and the improved electrochemical performances could be attributed to the synergy effect between the functions of MoS 2 and rGO. A high reversible capacity of 1150 mAh/g at a current of 0.1 A/g could retain without fading after 60 cycles. The rate performance of the composite was also improved, and the specific capacity remained a relative high value of mAh/g even at a current of 1000 mA/g. In order to further systematically study the mechanism of the improved LIBs performances for composite, we constructed the corresponding models based on experiment data and conducted first-principles calculation. Nudged elastic band (NEB) method was employed to study the diffusion of Li in different structures. The calculated results proved that the diffusion barrier for Li in MoS 2 /graphene was significantly lower than that of in pristine MoS 2 and presented a theoretical explanation for a better diffusivity property. The high specific capacity and excellent cycling stability of these hybrid nanoflowers are competent as a promising anode material for high-performance LIBs.

The flower-like MoS 2 /BiVO 4 composite with heterojunction has been successfully fabricated by a two-step approach. A possible formation mechanism of this heterostructure was investigated. The calculated valence band offset (VBO) and conduction band offset (CBO) of MoS 2 /BiVO 4 heterojunction showed that the VBO and CBO of MoS 2 /BiVO 4 are 1.4 and 0.3 eV, respectively, implying the formation of well-defined staggered type II band alignment. The photodegradation of methylene blue (MB) was adopted to assess the photocatalytic ability of the pristine MoS 2 and BiVO 4 as well as MoS 2 /BiVO 4 composites. It exhibited that the MoS 2 /BiVO 4 composite structures performed much better than that of the pristine MoS 2 and BiVO 4 , which was due to the staggered band alignment formed between the two structures. Besides, the corresponding mechanism of enhanced photocatalysis regarding the separation of the photogenerated electron−hole pairs for the heterojunction has also been investigated by the first-principles calculation.

The growing demand for lithium-ion (Li-ion) battery in electric vehicles has expedited the need for new optimal charging approaches to improve the speed and reliability of the charging process without deteriorating battery performances. Many efforts have been deployed to develop optimal charging strategies for commercial Li-ion batteries over the last decade. The active optimal charging strategies have great potential to meet the requirement. This paper is a review of the studies on constructing the optimal charging algorithms for Li-ion batteries. The battery models on which these protocols rest are stated, the generalized structures are examined, the advantages and the drawbacks of the mathematical controller algorithms are discussed, and their applications are presented. Suggestions for overcoming the shortcomings of the proposed strategies are proposed. Challenges and future directions in the development of optimal charging strategies for commercial Li-ion batteries are also discussed.INDEX TERMS Fast charging, optimal charging strategies, lithium-ion battery.