Dimeric [Mo 2 S 12 ] 2− Cluster: A Molecular Analogue of MoS 2 Edges for Superior Hydrogen‐Evolution Electrocatalysis

Polysulfide induced synthesis of a MoS2 self-supporting electrode with wide-layer-spacing for efficient electrocatalytic water splitting

Efficient non-noble metal bifunctional electrocatalysts can increase the conversion rate of electric energy in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Herein, a ball & sheet MoS2/Ni3S2 composite with wide-layer-spacing and high 1T-rich MoS2 is assembled on nickel foam (NF) via a two-step solvothermal method with polymeric sulfur (S-r-DIB) as the sulfur source. The obtained material serves as both the cathode and the anode toward overall water splitting in an alkaline electrolyte. The results proved that the interpenetration of MoS2/Ni3S2-p with a ball and sheet structure increased the material active surface area and exposed more catalytic active sites, which contributed to the penetration of solution and the transfer of charge/hydrion. Meanwhile, two different semiconductors of MoS2 and Ni3S2 along with the presence of ample active sulfur edge sites and few-layer, wide-layer-spacing structures of MoS2 lead to an outstanding electrocatalytic activity. In particular, the electrodes of MoS2/Ni3S2-p only need a battery voltage of 1.55 V at 10 mA cm-2. The bifunctional electrocatalyst MoS2/Ni3S2-p also shows excellent stability at large current densities during the electrochemical test.

Single-Atom-Layer Catalysis in a MoS2 Monolayer Activated by Long-Range Ferromagnetism for the Hydrogen Evolution Reaction: Beyond Single-Atom Catalysis

Single-atom-layer catalysts with fully activated basal-atoms will provide a solution to the low loading-density bottleneck of single-atom catalysts. Herein, we activate the majority of the basal sites of monolayer MoS₂ , by doping Co ions to induce long-range ferromagnetic order. This strategy, as revealed by in situ synchrotron radiation microscopic infrared spectroscopy and electrochemical measurements, could activate more than 50 % of the originally inert basal-plane S atoms in the ferromagnetic monolayer for the hydrogen evolution reaction (HER). Consequently, on a single monolayer of ferromagnetic MoS₂ measured by on-chip micro-cell, a current density of 10 mA cm^-2 could be achieved at the overpotential of 137 mV, corresponding to a mass activity of 28, 571 Ag^-1 , which is two orders of magnitude higher than the multilayer counterpart. Its exchange current density of 75 μA cm^-2 also surpasses most other MoS₂ -based catalysts. Experimental results and theoretical calculations show the activation of basal plane S atoms arises from an increase of electronic density around the Fermi level, promoting the H adsorption ability of basal-plane S atoms.

[Mo3 S13 ]2- as a Model System for Hydrogen Evolution Catalysis by MoSx : Probing Protonation Sites in the Gas Phase by Infrared Multiple Photon Dissociation Spectroscopy

Materials based on molybdenum sulfide are known as efficient hydrogen evolution reaction (HER) catalysts. As the binding site for H atoms on molybdenum sulfides for the catalytic process is under debate, [HMo3 S13 ]- is an interesting molecular model system to address this question. Herein, we probe the [HMo3 S13 ]- cluster in the gas phase by coupling Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS) with infrared multiple photon dissociation (IRMPD) spectroscopy. Our investigations show one distinct S-H stretching vibration at 2450 cm-1 . Thermochemical arguments based on DFT calculations strongly suggest a terminal disulfide unit as the H adsorption site.

Stepwise Assembly of an Electroactive Framework from a Co6 S8 Superatomic Metalloligand and Cuprous Iodide Building Units

The design of metal-organic frameworks (MOFs) that incorporate more than one metal cluster constituent is a challenging task. Conventional one-pot reaction protocols require judicious selection of ligand and metal ion precursors, yet remain unpredictable. Stable, preformed nanoclusters, with ligand shells that can undergo additional coordination-driven reactions, provide a platform for assembling multi-cluster solids with precision. Herein, a discrete Co₆ S₈ (PTA)₆ (PTA=1,3,5-triaza-7-phosphaadamantane) superatomic-metalloligand is assembled into a three-dimensional (3D) coordination polymer comprising Cu₄ I₄ secondary building units (SBUs). The resulting heterobimetallic framework (1) contains two distinct cluster constituents and bifunctional PTA linkers. Solid-state diffuse reflectance studies reveal that 1 is an optical semiconductor with a band-gap of 1.59 eV. Framework-modified electrodes exhibit reversible redox behavior in the solid state arising from the Co₆ S₈ superatoms, which remain intact during framework synthesis.

Electrodeposition of MoSx Hydrogen Evolution Catalysts from Sulfur-Rich Precursors

Amorphous molybdenum sulfides (a-MoS_x) are known to be active electrocatalysts for the hydrogen evolution reaction (HER), but the role stoichiometry of the sulfur atoms plays in the HER activity remains unclear. In this work, we deposited thin films of a-MoS_x from two thiomolybdate deposition baths with different sulfur ratios (MoS₄^2- and Mo₂S₁₂^2-) and showed that the sulfur stoichiometry, as determined by X-ray photoelectron spectroscopy, is controlled by the precursor of choice and the electrochemical method used to deposit the thin films. Using the Mo₂S₁₂^2- precursor allows access to a MoS₆ thin film, with a higher S/Mo ratio compared with that of any previously reported electrodeposited films. We also examined the effect of electrochemistry on the resulting S/Mo ratio in the as-prepared a-MoS_x thin films. Samples with S/Mo ratios ranging from 2 to 6 were electrodeposited on glassy carbon (GC) substrates by using anodic, cathodic, or cyclic voltammetry deposition. The a-MoS_x thin films deposited on GC substrates were tested as HER catalysts in acidic electrolytes. The overpotentials needed to drive current densities of 10 mA/cm² ranged from 160 mV for MoS₆ samples to 216 mV for MoS₂ samples, signifying the important role sulfur content plays in HER activity of the prepared films. Furthermore, we characterized the deactivation of the a-MoS_x films and found that the sulfur content is gradually depleted over time, leading to a slow deactivation of the a-MoS_x thin-film catalysts. We showed a facile procedure that affords a-MoS_x films with high sulfur content by using S-rich precursors and highlighted the role of sulfur in the prepared films for HER.

Alcohol-solvothermal syntheses, crystal structures and photocatalytic properties of tin selenides with polyselenide ligands

New polyselenidostannates with Se₂²⁻ or Se₄²⁻ polyselenide ligands, [TM(en)₃]Sn₃Se₆(Se₂) (1–3), [Ni(en)₃]Sn₃Se_7.5 (4) and [TM(en)₃][Sn(Se₄)₃] (5–8), were prepared by alcohol-solvothermal methods.

Theoretical design of a series of 2D TM–C3N4 and TM–C3N4@graphene (TM = V, Nb and Ta) nanostructures with highly efficient catalytic activity for the hydrogen evolution reaction

Coupled with high structural stability and metallic conductivity, all of the new composite systems TM–C₃N₄ and TM–C₃N₄@graphene (TM = V, Nb and Ta) can possess considerably high catalytic activity for the hydrogen evolution reaction.

Two Novel Polyoxometalate-Encapsulated Metal-Organic Nanotube Frameworks as Stable and Highly Efficient Electrocatalysts for Hydrogen Evolution Reaction

Two novel polyoxometalate (POM)-encapsulated metal-organic nanotube (MONT) framework crystalline materials with unprecedented copper-mixed ligands, HUST-200 and HUST-201, have been successfully synthesized by an effective synthesis strategy. The encapsulation not only provides a shield to increase the chemical stability, but also does not affect its catalytic activity, and, therefore, the crystalline materials are very active for HER (H⁺ can diffuse easily through the pores of the MONTs). Remarkably, HUST-200 displays a low overpotential of 131 mV (catalytic current density is equal to 10 mA·cm^-2). This work thus offers a new way for devising HER electrocatalysts with low cost using POM-encapsulated MONT frameworks.

Highly efficient catalytic activity for the hydrogen evolution reaction on pristine and monovacancy defected WP systems: a first-principles investigation

A deep understanding of HER catalytic activity of tungsten phosphide at the atomic level and its effective improvement by introducing a monovacancy.

Fabrication of zero to three dimensional nanostructured molybdenum sulfides and their electrochemical and photocatalytic applications

Transition metal dichalcogenides (TMDs) are emerging as promising materials, particularly for electrochemical and photochemical catalytic applications, and among them molybdenum sulfides have received tremendous attention due to their novel electronic and optoelectronic characteristics. Several review articles have summarized the recent progress on TMDs but no critical and systematic summary exists about the nanoscale fabrication of MoS₂ with different dimensional morphologies. In this review article, first we will summarize the recent progress on the morphological tuning and structural evolution of MoS₂ from zero-dimension (0D) to 3D. Then the different engineering methods and the effect of synthesis conditions on structure and morphology of MoS₂ will be discussed. Moreover, the corresponding change in the electronic and physicochemical properties of MoS₂ induced by structure tuning will also be presented. Further, the applications of MoS₂ in various electrochemical systems e.g. hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and supercapacitors as well as photocatalytic hydrogen evolution will be highlighted. The review article will also critically focus on challenges faced by researchers to tune the MoS₂ nanostructures and the resulting electrochemical mechanism to enhance their performances. At the end, concluding remarks and future prospects for the development of better MoS₂ based nanostructured materials for the aforementioned applications will be presented.

In Situ Generation of Active Molybdenum Octahedral Clusters for Photocatalytic Hydrogen Production from Water

The photocatalytic hydrogen evolution reaction (HER) from water under homogeneous and heterogeneous conditions is explored for the {Mo6 Br(i) 8 }(4+) cluster core based unit starting from (TBA)2 [Mo6 Br(i) 8 F(a) 6 ] (TBA=tetra-n-butylammonium; "i" and "a" refer to the face-capping inner and terminal apical ligand, respectively). The catalytic activity of {Mo6 Br(i) 8 }(4+) is enhanced by the in situ generation of [Mo6 Br(i) 8 F(a) 5 (OH)(a) ](2-) , [Mo6 Br(i) 8 F(a) 3 (OH)(a) 3 ](2-) , and [Mo6 Br(i) 8 (OH)(a) 6 ](2-) , which are identified by ESIMS, luminescence, and NMR techniques. Full substitution of F(-) by OH(-) leads to the formation of (H3 O)2 [Mo6 Br(i) 8 (OH)(a) 6 ]⋅10 H2 O; its structure was determined by single-crystal XRD. The immobilization of the active {Mo6 Br(i) 8 }(4+) onto graphene oxide (GO) surfaces enhances its stability under catalytic conditions. The catalytic activity of the resulting (TBA)2 Mo6 Br(i) 8 @GO material is improved with respect to GO, but is reduced compared to the activity under homogeneous conditions because of changes in the GO semiconducting properties as well as lower activity and/or accessibility of the anchored cluster.

Synergistic WO3·2H2O Nanoplates/WS2 Hybrid Catalysts for High-Efficiency Hydrogen Evolution

Tungsten trioxide dihydrate (WO3·2H2O) nanoplates are prepared by in situ anodic oxidation of tungsten disulfide (WS2) film on carbon fiber paper (CFP). The WO3·2H2O/WS2 hybrid catalyst exhibits excellent synergistic effects which facilitate the kinetics of the hydrogen evolution reaction (HER). The electrochromatic effect takes place via hydrogen intercalation into WO3·2H2O. This process is accelerated by the desirable proton diffusion coefficient in the layered WO3·2H2O. Hydrogen spillover from WO3·2H2O to WS2 occurs via atomic polarization caused by the electric field of the charges on the planar defect or edge active sites of WS2. The optimized hybrid catalyst presents a geometrical current density of 100 mA cm(-2) at 152 mV overpotential with a Tafel slope of ∼54 mV per decade, making the materials one of the most active nonprecious metal HER catalysts.

Effects of particle size and edge structure on the electronic structure, spectroscopic features, and chemical properties of Au(111)-supported MoS2 nanoparticles

Materials based on MoS₂ are widely used as catalysts and their structure usually consists of single-layered MoS₂ nanoparticles whose edges are known to constitute the catalytically active sites. Methods based on density functional theory are used in this work to calculate the electronic structure of representative computational models of MoS₂ nanoparticles supported on Au(111). By considering nanoparticles with different edge-terminations, compositions, and sizes, we describe how the electronic structure, Mo3d core-level shifts, and chemical properties (i.e. H adsorption and S vacancy formation) depend on the MoS₂ nanoparticle size and structure. In addition, site-specific properties, largely inaccessible when using only slab models of MoS₂ edges, are reported, which reveal that the edge sites are not uniform along the nanoparticle and largely depend on the proximity to the corners of the triangular NPs, especially when interacting with a metallic support. Furthermore, a structural motif where H atoms adsorb favourably in a bridging position between two Mo atoms is proposed as an active site for the hydrogen evolution reaction.