Hydrogen has been deemed as an ideal substitute fuel to fossil energy because of its renewability and the highest energy density among all chemical fuels. One of the most economical, ecofriendly, and high‐performance ways of hydrogen production is electrochemical water splitting. Recently, 2D transition metal dichalcogenides (also known as 2D TMDs) showed their utilization potentiality as cost‐effective hydrogen evolution reaction (HER) catalysts in water electrolysis. Herein, recent representative research efforts and systematic progress made in 2D TMDs are reviewed, and future opportunities and challenges are discussed. Furthermore, general methods of synthesizing 2D TMDs materials are introduced in detail and the advantages and disadvantages for some specific methods are provided. This explanation includes several important regulation strategies of creating more active sites, heteroatoms doping, phase engineering, construction of heterostructures, and synergistic modulation which are capable of optimizing the electrical conductivity, exposure to the catalytic active sites, and reaction energy barrier of the electrode material to boost the HER kinetics. In the last section, the current obstacles and future chances for the development of 2D TMDs electrocatalysts are proposed to provide insight into and valuable guidelines for fabricating effective HER electrocatalysts.

The crystallization behavior of poly(1-butene) (P1b) was investigated by polarized light microscopy (PLM), atomic force microscopy (AFM), wide-angle X-ray scattering (WAXS), dilatometry, and also by time-and temperature-resolved small-angle X-ray scattering experiments (SAXS). Observations in the PLM indicate a temperature-dependent change in the mechanism of crystallization. When crossing a certain critical crystallization temperature, the morphology changes from spherulites to quadratic, platelike single crystals. Investigations of samples with different molar mass show that the transition temperature is molar mass-dependent; on decreasing the molar mass the transition shifts to lower temperatures. As proved by WAXS, both the spherulites and the single crystals are of the metastable form II. The morphological change is also observed in AFM images obtained after a rapid cooling of the samples to room temperature; the difference in the morphological appearance is preserved through the transformation from form II to form I. According to dilatometric measurements, the change in the crystallization mechanism leads to variations in the temperature dependence of the crystallization rate and also to a steplike increase in the crystallinity. The results of SAXS experiments show that the formation of P1b crystallites is governed by the same general laws as for other polymers studied before. Both the crystallization temperature, T c, and the melting temperature, Tf, are linearly dependent on the reciprocal crystalline layer thickness, dc -1 , but with different slopes and different limiting temperatures for dc -1 f 0. The observations are again indicative for a crystal development in two steps: First an initial form appears which then transforms into the final lamellar crystallites. As a new feature, in direct correspondence to the two different crystallization mechanisms observed microscopically, two different crystallization lines (dc -1 vs Tc) show up, indicating the occurrence of two different initial states. On the other hand, only one common melting line (Tf vs dc -1 ) is found, which means that the two crystallization mechanisms produce crystallites with similar surface free energies. We discuss the peculiar crystallization properties of P1b by comparing the radius of gyration Rg of the chains in the melt with the crystal thickness dc and propose that the change in the crystallization mechanism could be due to a change from foldedchain to chain-extended crystallization, taking place when dc gets larger than Rg.

Developing earth-abundant and low-cost electrocatalysts for water splitting is important for the conversion systems of renewable and clean energy. Herein, under the guidance of theoretical calculations, a new type of skutterudite-type ternary cobalt nickel phosphide (Co1–x Ni x P3) nanoneedle arrays (NAs) is fabricated on carbon cloth for the splitting of water. The electronic structure was tuned by doping an appropriate amount of Ni, and the resultant Co0.93Ni0.07P3 displayed good catalytic activity toward hydrogen evolution reaction (HER) with an overpotential (η10) of 87 mV versus reversible hydrogen electrode (RHE) when the current density reaches −10 mA cm–2 and the Tafel slope of the catalyst is 60.7 mV dec–1 in alkaline electrolyte. In addition, the Co0.93Ni0.07P3 also exhibited an OER activity (η20 of 221 mV vs RHE and the Tafel slope of 83.7 mV dec–1). These skutterudite-based Co1–x Ni x P3 electrocatalysts show promising potential in the applications of overall water splitting in an alkaline environment.

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To ensure sustainable hydrogen production by water electrolysis,robust, earth-abundant, and high-efficient electrocatalysts are required. Constructing ahybrid system could lead to further improvement in electrocatalytic activity.I nterface engineering in composite catalysts is thus critical to determine the performance,a nd the phase-junction interface should improve the catalytic activity.H ere,w es howt hat nickel diphosphide phase junction (c-NiP 2 /m-NiP 2)i sa ne ffective electrocatalyst for hydrogen production in alkaline media. The overpotential (at 10 mA cm À2)f or NiP 2-650 (c/m) in alkaline media could be significantly reduced by 26 %a nd 96 % compared with c-NiP 2 and m-NiP 2 ,respectively.The enhancement of catalytic activity should be attributed to the strong water dissociation ability and the rearrangement of electrons around the phase junction, which markedly improved the Volmer step and benefited the reduction process of adsorbed protons.

Generally, electrocatalytic hydrogen evolution reaction (HER) by water splitting is a pH-dependent reaction, which limits the widespread harvesting of hydrogen energy. Herein, we present a simple way for chemical bonding of MoS2 (002) planes and α-MoC {111} planes to form in-plane heterostructures capable of efficient pH-universal HER. Due to the lattice strain from mismatched lattice parameters between α-MoC and MoS2, this catalyst changes the electronic configuration of the MoS2 and thus acquires the favorable proton adsorption and desorption activity, suggested by the platinum (Pt)-like free Gibbs energy. Consequently, only a low 78 mV overpotential is needed to achieve the current density of 10 mA cm–2 in acidic solution along with a favorable Tafel kinetic process with a Tafel slope of 38.7 mV dec–1. Owing to the synergistic interaction between MoS2 (002) planes and α-MoC {111} planes with strong water dissociation activities, this catalyst also exhibits high HER performances beyond that of Pt in neutral and alkaline. This work proves the advances of in-plane heterostructures and illustrates the production of low-cost but highly efficient pH-universal HER catalytic materials, promising for future sustainable hydrogen energy.

Nanofibrillated cellulose (NFC) was incorporated to reduced graphene oxide (rGO) for fabrication of multifunctional amphiphilic aerogels. The as-prepared amphiphilic aerogel showed excellent recoverability, superior absorption capacity for both organic solvents and water, and an electrical conductivity sensitive to compressive strain making it highly potential to be used as a pressure-responsive sensor.

Highly efficient platinum-alternative bifunctional catalysts by using abundant non-noble metal species are of critical importance to the future sustainable energy reserves. Unfortunately, current electrocatalysts toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are far from satisfactory because of lacking reasonable design and assembly protocols. A type of 1-nm molybdenum carbide nanoparticles confined in mesh-like nitrogen-doped carbon (Mo 2 C@NC nanomesh) with high specific surface area is reported here. In addition to the superior ORR performance comparable to platinum, the catalyst offers a high HER activity with small Tafel slope of 33.7 mV dec −1 and low overpotential of 36 mV to reach −10 mA cm −2 . Theoretical calculations indicate that the active sites of the catalyst are mainly located at Mo atoms adjacent to the N-doped carbon layer, which contributes the high HER activity. These findings show the great potential of Mo 2 C species in wide electrocatalysis applications.