A facile chemical vapor deposition method to prepare single-crystalline VS2 nanosheets for the hydrogen evolution reaction is reported. The electrocatalytic hydrogen evolution reaction (HER) activities of VS2 show an extremely low overpotential of -68 mV at 10 mA cm(-2), small Tafel slopes of ≈34 mV decade(-1), as well as high stability, demonstrating its potential as a candidate non-noble-metal catalyst for the HER.

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Depending on the charge storage mechanism, supercapacitors can be divided into two basic classes: electric double layer capacitance (EDLC) and pseudocapacitance [8]. The former generates capacitance from charge separation at the electrode/electrolyte interface [9,10], while the latter generates capacitance from the fast Faradaic reactions in electrode materials [11]. The performance of a supercapacitor is closely related to the physical and chemical features of the electrode materials. Usually, electrode materials containing carbon-based materials are regarded as typical EDLC supercapacitors, where the capacitance depends on the specific surface area, porous structure, and conductivity of active materials. Carbon-based materials possess long cycle lives and good mechanical properties. Pseudocapacitive active species include metal oxides (MnO 2 , Co 3 O 4 , RuO 2 , Fe 2 O 3 , AB 2 O 4), conducting polymers (polyaniline, polypyrrole, and polythiophene), and hydroxides [11-21]. These materials can deliver relatively high capacitance but are limited by poor stability because of structural degradation of the electrode during the redox process [ 22,23]. Thus, the capacitance can be enhanced by incorporating carbon materials with pseudocapacitive materials. Layered double hydroxides (LDHs), a kind of anionic clay, have attracted extensive attention owing to their intriguing properties, such as large surface area, positively charged surface, and compositional flexibility [24,25]. LDHs are usually expressed as the following formula: [M 2+ 1−x M x 3+ (OH) 2 ] x+ [A n− ] x/n •mH 2 O, in which M 2+ and M 3+ are divalent and trivalent metal cations, respectively, and A n− is an interlayer anion. The tunable composition and their anion exchange ability allow LDHs to be used as a variety of multifunctional materials, such as catalysts, absorbents, photoactive materials, and electroactive materials [26-29]. Thus far, LDH nanomaterials used as electrodes have been widely studied. Niu et al. [30] reported In this work, ultra-large sheet NiAl-layered double hydroxide (LDH)/reduced graphene oxide (RGO) nanocomposites were facilely synthesized via in situ growth of NiAl-LDH on a graphene surface without any surfactant or template. It was found that with a microwave-assisted method, NiAl-LDH nanosheets grew evenly on the surface of graphene. With this method, the formation of NiAl-LDH and reduction of graphene oxide were achieved in one step. The unique structure endows the electrode materials with a higher specific surface area, which is favorable for enhancing the capacity performance. The morphology and microstructure of the as-prepared composites were characterized by X-ray diffraction, Brunauer-Emmett-Teller surface area measurement, and transmission electron microscopy. The specific surface area and pore volume of the RGO/LDH composite are 108.3 m 2 g −1 and 0.74 cm 3 g −1 , respectively, which are much larger than those of pure LDHs (19.8 m 2 g −1 and 0.065 cm 3 g −1 , respectively). The capacitive properties of the synthesized...

By investigating a metastable high-entropy alloy, we report a latent strengthening mechanism that is associated with the thermally-induced epsilon-martensite-to-austenite back-transformation. We show this reversion-assisted hardening effect can be achieved in the same time-scale and temperature range as conventional bake-hardening treatment, but leads to both improved strength and cumulative ductility. Key mechanisms are discussed considering transformation kinetics, kinematics, strengthening and ductilization modules.