Effect of Doping on Hydrogen Evolution Reaction of Vanadium Disulfide Monolayer

Molybdenum Atom Engineered Vanadium Disulfide for Boosted High-Capacity Li-Ion Storage

A drawback with lithium-ion batteries (LIBs) lies in the unstable lithium storage which results in poor electrochemical performance. Therefore, it's of importance to improve the electrochemical functionality and Li-ion transport kinetics of electrode materials for high-performance lithium storage. Here, a subtle atom engineering via injecting molybdenum (Mo) atoms into vanadium disulfide (VS2 ) to boost high capacity Li-ion storage is reported. By combining operando, ex situ monitoring and theoretical simulation, it is confirmed that the 5.0%Mo atoms impart flower-like VS2 with expanded interplanar spacing, lowered Li-ion diffusion energy barrier, and increased Li-ion adsorption property, together with enhanced e- conductivity, to boost Li-ion migration. A "speculatively" optimized 5.0% Mo-VS2 cathode that exhibits a specific capacity of 260.8 mA h g-1 at 1.0 A g-1 together with a low decay of 0.009% per cycle over 500 cycles is demonstrated. It is shown that this value is ≈1.5 times compared with that for bare VS2 cathode. This investigation has substantiated the Mo atom doping can effectively guide the Li-ion storage and open new frontiers for exploiting high-performance transition metal dichalcogenides for LIBs.

Synthesis of Phase Junction Cadmium Sulfide Photocatalyst under Sulfur-Rich Solution System for Efficient Photocatalytic Hydrogen Evolution

Photocatalyst with excellent semiconductor properties is the key point to realize the efficient photocatalytic hydrogen evolution (PHE). As a representative binary metal sulfide (BMS) semiconductor, cadmium sulfide (CdS) possesses suitable bandgap of 2.4 eV and negative conduction band potential, which has a great potential to realize efficient visible-light PHE performance. In this work, CdS with unique cubic/hexagonal phase junction is facilely synthesized through a sulfur-rich butyldithiocarbamate acid (BDCA) solution process. The results illustrate that the phase junction can efficiently enhance the separation and transfer of photogenerated electron-hole pairs, resulting in an excellent PHE performance. In addition, the sulfur-rich property of BDCA solution leads to the absence of additional sulfur sources during the synthesis of CdS photocatalyst, which greatly simplifies the fabrication process. The optimal PHE rate of the BDCA-synthesized phase junction CdS photocatalyst is 7.294 mmol g^-1  h^-1 and exhibits a favorable photostability. Moreover, density function theory calculations indicated that the apparent redistribution of charge density in the cubic/hexagonal phase junction regions gives a suitable hydrogen adsorption capacity, which is responsible for the enhanced PHE activity.

Triple-Shelled Co-VSex Hollow Nanocages as Superior Bifunctional Electrode Materials for Efficient Pt-Free Dye-Sensitized Solar Cells and Hydrogen Evolution Reactions

Complex nanostructures with distinct spatial architectures and more active sites hold broad prospects in new energy conversion fields. Herein, a facile strategy was carried out to construct triple-shelled Co-VSe_x nanocages, starting with an ion-exchange process between Co-based zeolitic imidazolate framework-67 (ZIF-67) nanopolyhedrons and VO₃^- followed by the formation of triple-shelled Co-VSe_x hollow nanocages during the process of increasing the solvothermal temperature under the assistance of SeO₃^2-. Meanwhile, triple-shelled Co-VS_x and yolk-double shell Co-VO_x nanocages were fabricated as references by a similar process. Benefiting from the larger surface areas and more electrolyte adsorption sites, the triple-shelled Co-VSe_x nanocages exhibited excellent electrocatalytic performances when applied as the electrochemical catalysts for dye-sensitized solar cells (DSSC) and hydrogen evolution reactions (HER). More concretely, the DSSC based on the Co-VSe_x counter electrode showed outstanding power conversion efficiency of 9.68% when its Pt counterpart was 8.46%. Moreover, the Co-VSe_x electrocatalyst exhibited prominent HER performance with a low onset overpotential of 40 mV and a small Tafel slope of 39.1 mV dec^-1 in an acidic solution.

Reversing the charge transfer between platinum and sulfur-doped carbon support for electrocatalytic hydrogen evolution

Metal-support interaction is of great significance for catalysis as it can induce charge transfer between metal and support, tame electronic structure of supported metals, impact adsorption energy of reaction intermediates, and eventually change the catalytic performance. Here, we report the metal size-dependent charge transfer reversal, that is, electrons transfer from platinum single atoms to sulfur-doped carbons and the carbon supports conversely donate electrons to Pt when their size is expanded to ~1.5 nm cluster. The electron-enriched Pt nanoclusters are far more active than electron-deficient Pt single atoms for catalyzing hydrogen evolution reaction, exhibiting only 11 mV overpotential at 10 mA cm^-2 and a high mass activity of 26.1 A mg^-1 at 20 mV, which is 38 times greater than that of commercial Pt/C. Our work manifests that the manipulation of metal size-dependent charge transfer between metal and support opens new avenues for developing high-active catalysts.

Titanium carbide sheet: metallic 2D structure with intrinsic and high catalytic activity for the hydrogen evolution reaction

Searching for a metallic material that possesses intrinsic and high catalytic activity is interesting for the hydrogen evolution reaction (HER) in the electrochemical reduction of water. In this work, via density functional theory, we identified a promising two-dimensional (2D) catalyst material, namely TiC (1 0 0) sheet, which is composed of two atomic layers. Phonon spectrum calculation shows that all vibrational modes of the TiC (1 0 0) sheet are real. Even at 1200 K, the geometrical structure of TiC (1 0 0) sheet is still well kept. Interestingly, TiC (1 0 0) sheet is metallic, which means that TiC (1 0 0) sheet can possess high conductivity. Moreover, the Gibbs free energy ([Formula: see text]) of hydrogen on TiC (1 0 0) sheet at a low coverage is about 0.13 eV, which can be further optimized to an ideal value of 0 eV by introducing a strain. Besides, the effect of thickness on its catalytic activity is also assessed. We observed that TiC (1 0 0) sheet with a large thickness is also metallic. Calculated values of [Formula: see text] for four-layered and six-layered TiC (1 0 0) sheets at a moderate coverage can be about  -0.06 and  -0.04 eV, respectively. Our results highlight a new promising 2D catalyst material for the HER in the electrochemical reduction of water.

Modulation of the electronic properties and spin polarization of 2H VS2 nanoribbons by tuning ribbon widths and edge decoration

VS₂ magnetic nanoribbons with different edges and widths show abundant electrical and magnetic properties.

Facile Synthesis of Vanadium-Doped Ni3S2 Nanowire Arrays as Active Electrocatalyst for Hydrogen Evolution Reaction

Ni₃S₂ nanowire arrays doped with vanadium(V) are directly grown on nickel foam by a facile one-step hydrothermal method. It is found that the doping can promote the formation of Ni₃S₂ nanowires at a low temperature. The doped nanowires show excellent electrocatalytic performance toward hydrogen evolution reaction (HER), and outperform pure Ni₃S₂ and other Ni₃S₂-based compounds. The stability test shows that the performance of V-doped Ni₃S₂ nanowires is improved and stabilized after thousands of linear sweep voltammetry test. The onset potential of V-doped Ni₃S₂ nanowire can be as low as 39 mV, which is comparable to platinum. The nanowire has an overpotential of 68 mV at 10 mA cm^-2, a relatively low Tafel slope of 112 mV dec^-1, good stability and high Faradaic efficiency. First-principles calculations show that the V-doping in Ni₃S₂ extremely enhances the free carrier density near the Fermi level, resulting in much improved catalytic activities. We expect that the doping can be an effective way to enhance the catalytic performance of metal disulfides in hydrogen evolution reaction and V-doped Ni₃S₂ nanowire is one of the most promising electrocatalysts for hydrogen production.

Tension-Enhanced Hydrogen Evolution Reaction on Vanadium Disulfide Monolayer

Water electrolysis is an efficient way for hydrogen production. Finding efficient, cheap, and eco-friendly electrocatalysts is essential to the development of this technology. In the work, we present a first-principles study on the effects of tension on the hydrogen evolution reaction of a novel electrocatalyst, vanadium disulfide (VS2) monolayer. Two electrocatalytic processes, individual and collective processes, are investigated. We show that the catalytic ability of VS2 monolayer at higher hydrogen coverage can be efficiently improved by escalating tension. We find that the individual process is easier to occur in a wide range of hydrogen coverage and the collective process is possible at a certain hydrogen coverage under the same tension. The best hydrogen evolution reaction with near-zero Gibbs free energy can be achieved by tuning tension. We further show that the change of catalytic activity with tension and hydrogen coverage is induced by the change of free carrier density around the Fermi level, that is, higher carrier density, better catalytic performance. It is expected that tension can be a simple way to improve the catalytic activity, leading to the design of novel electrocatalysts for efficient hydrogen production from water electrolysis.

Hydrogenation-controlled phase transition on two-dimensional transition metal dichalcogenides and their unique physical and catalytic properties

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been widely used from nanodevices to energy harvesting/storage because of their tunable physical and chemical properties. In this work, we systematically investigate the effects of hydrogenation on the structural, electronic, magnetic, and catalytic properties of 33 TMDs based on first-principles calculations. We find that the stable phases of TMD monolayers can transit from 1T to 2H phase or vice versa upon the hydrogenation. We show that the hydrogenation can switch their magnetic and electronic states accompanying with the phase transition. The hydrogenation can tune the magnetic states of TMDs among non-, ferro, para-, and antiferro-magnetism and their electronic states among semiconductor, metal, and half-metal. We further show that, out of 33 TMD monolayers, 2H-TiS₂ has impressive catalytic ability comparable to Pt in hydrogen evolution reaction in a wide range of hydrogen coverages. Our findings would shed the light on the multi-functional applications of TMDs.