MoS2 is a typical 2D transition metal dichalcogenide, and have exhibit superior electrocatalytic HER activity. The MoS2's HER catalysis was developed 15 years ago, various nanofabrication strategies are applied to boost the performance. It is promising that MoS2 would take place of Pt in HER catalysis. Various active catalytic sites, including edge, vacant, basal plane, etc. are developed and the catalytic performance were compared. Hybrid composition were developed, like modification with atoms, clusters, loading on substrates were developed. We make a summary on HER mechanisms varies with active sites and operation solutions. MoS2 synthesis, characterization, HER performance, mechanisms, to make a holistic understanding on the interplay between the structure, chemistry, HER performance, and mechanism. It is believed that the review will help researchers to get a better understanding on MoS2's superior HER performance, and provide a wealth of catalyst tool box to promote next-generation catalysts development. Main textHydrogen energy is perceived as the most promising clean energy without any carbon emission like CO2. For the greenhouse effect is becoming increasingly serious issue caused by large application of fossil fuel, hydrogen fuel is an innovative solution and show great potential in resolute carbon emission. Electrocatalytic water splitting is the best achievable approach nowadays for achieving large amount of H2. MoS2 are facile, stable, non-toxic, affordable materials with reasonable price, and have exhibit its superior potential in catalysis, sensing, opt electrochemical, environmental relate application 1 , etc. Modification of MoS2 materials has been widely applied for adjusting and formulate the relative performance in certain application field. MoS2 is a typical transition metal dichalcogenide 2 (TMD) compound with a two-dimensional S-Mo-S tri-atom layer structure. MoS2 is predicted to be a promising substitute catalyst for platinum 15 years ago 3 . While pristine MoS2 shows low electrocatalysis performance, via vacancies engineering, phase engineering, heterojunction engineering, hetero-atom doping strategies, the catalytic active sites quantities are elevated and catalysis performance is magnitude improved. We summarize on MoS2 synthesis, characterization, HER performance, mechanisms, to make a holistic understanding on the interplay between the structure, chemistry, HER performance, and mechanism, which will give directions to elevate other electrochemical reaction by MoS2. Structural, fundamental physical and chemical properties of MoS2:MoS2 has been applied as lubricant materials at industrial level in alleviate worn out phenomenon [4][5] . Generally, two-dimensional MoS2 exist 4 main crystal structure, which are 1H, 1T, 2H, 3R 6 . Figure 3. Phase transition between 1T and 2H mechanism based on the crystal field theory 11 . Schematic models of single-layered MoS2 with 2H (a) (Adapted with permission from ref. 10.

Bottom-up design of functional device components based on nanometer-sized building blocks relies on accurate control of their self-assembly behavior. Atom-precise metal nanoclusters are well-characterizable building blocks for designing tunable nanomaterials, but it has been challenging to achieve directed assembly to macroscopic functional cluster-based materials with highly anisotropic properties. Here, we discover a solvent-mediated assembly of 34atom intermetallic gold-silver clusters protected by 20 1-ethynyladamantanes into 1D polymers with Ag-Au-Ag bonds between neighboring clusters as shown directly by the atomic structure from single-crystal X-ray diffraction analysis. Density functional theory calculations predict that the single crystals of cluster polymers have a band gap of about 1.3 eV. Fieldeffect transistors fabricated with single crystals of cluster polymers feature highly anisotropic p-type semiconductor properties with ≈1800-fold conductivity in the direction of the polymer as compared to cross directions, hole mobility of ≈0.02 cm 2 V −1 s −1 , and an ON/OFF ratio up to ≈4000. This performance holds promise for further design of functional cluster-based materials with highly anisotropic semiconducting properties.

The edge sites of MoS2 are catalytically active for hydrogen evolution reactions (HER). However, pristine edge sites usually contain only intrinsic atoms or defects, limiting the tuning of on‐site hydrogen species adsorption and desorption, the critical steps for HER. In addition, the number of atoms on pristine edges is small compared to that of electrochemically inert atoms in bulk. Thus, it is desirable to develop a scalable technique of creating a large number of highly HER‐active edge sites. Here, a plasma etching strategy is developed for creating MoS2 edge electrodes with a controllable number of active sites that enable the quantitative characterization of their HER activity using a local probe method. Fluorine atoms with large electronegativity are doped on the MoS2 edge sites that lead to a fivefold activity enhancement compared to that from pristine edges and is attributed to the more moderate binding energy for hydrogen species. The scalability of such a method is further demonstrated by activating MoS2 catalyst in macroscopic quantities with enhanced HER performance and stability. The work provides two‐dimensional materials as a platform for understanding the doping effect on the edge sites at atomic‐level, and offers a novel route for the design of efficient catalysts.