The identification of the active sites in heterogeneous catalysis requires a combination of surface sensitive methods and reactivity studies. We determined the active site for hydrogen evolution, a reaction catalyzed by precious metals, on nanoparticulate molybdenum disulfide (MoS2) by atomically resolving the surface of this catalyst before measuring electrochemical activity in solution. By preparing MoS2 nanoparticles of different sizes, we systematically varied the distribution of surface sites on MoS2 nanoparticles on Au(111), which we quantified with scanning tunneling microscopy. Electrocatalytic activity measurements for hydrogen evolution correlate linearly with the number of edge sites on the MoS2 catalyst.

http://science.sciencemag.org/content/sci/317/5834/100.full.pdf

Identification of active edge sites for electrochemical H2 evolution from MoS2 nanocatalysts.

Advanced materials for electrocatalytic and photoelectrochemical water splitting are central to the area of renewable energy. In this work, we developed a selective solvothermal synthesis of MoS2 nanoparticles on reduced graphene oxide (RGO) sheets suspended in solution. The resulting MoS2/RGO hybrid material possessed nanoscopic few-layer MoS2 structures with an abundance of exposed edges stacked onto graphene, in strong contrast to large aggregated MoS2 particles grown freely in solution without GO. The MoS2/RGO hybrid exhibited superior electrocatalytic activity in the hydrogen evolution reaction (HER) relative to other MoS2 catalysts. A Tafel slope of ∼41 mV/decade was measured for MoS2 catalysts in the HER for the first time; this exceeds by far the activity of previous MoS2 catalysts and results from the abundance of catalytic edge sites on the MoS2 nanoparticles and the excellent electrical coupling to the underlying graphene network. The ∼41 mV/decade Tafel slope suggested the Volmer–Heyrovsky mec...

MoS2 Nanoparticles Grown on Graphene: An Advanced Catalyst for the Hydrogen Evolution Reaction

Promising catalytic activity from molybdenum disulfide (MoS2) in the hydrogen evolution reaction (HER) is attributed to active sites located along the edges of its two-dimensional layered crystal structure, but its performance is currently limited by the density and reactivity of active sites, poor electrical transport, and inefficient electrical contact to the catalyst. Here we report dramatically enhanced HER catalysis (an electrocatalytic current density of 10 mA/cm2 at a low overpotential of −187 mV vs RHE and a Tafel slope of 43 mV/decade) from metallic nanosheets of 1T-MoS2 chemically exfoliated via lithium intercalation from semiconducting 2H-MoS2 nanostructures grown directly on graphite. Structural characterization and electrochemical studies confirmed that the nanosheets of the metallic MoS2 polymorph exhibit facile electrode kinetics and low-loss electrical transport and possess a proliferated density of catalytic active sites. These distinct and previously unexploited features of 1T-MoS2 make ...

Enhanced Hydrogen Evolution Catalysis from Chemically Exfoliated Metallic MoS2 Nanosheets

Controlling surface structure at the atomic scale is paramount to developing effective catalysts. For example, the edge sites of MoS(2) are highly catalytically active and are thus preferred at the catalyst surface over MoS(2) basal planes, which are inert. However, thermodynamics favours the presence of the basal plane, limiting the number of active sites at the surface. Herein, we engineer the surface structure of MoS(2) to preferentially expose edge sites to effect improved catalysis by successfully synthesizing contiguous large-area thin films of a highly ordered double-gyroid MoS(2) bicontinuous network with nanoscaled pores. The high surface curvature of this catalyst mesostructure exposes a large fraction of edge sites, which, along with its high surface area, leads to excellent activity for electrocatalytic hydrogen evolution. This work elucidates how morphological control of materials at the nanoscale can significantly impact the surface structure at the atomic scale, enabling new opportunities for enhancing surface properties for catalysis and other important technological applications.

Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis

Nanoparticles of nickel phosphide (Ni2P) have been investigated for electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in acidic solutions, under which proton exchange membrane-based electrolysis is operational. The catalytically active Ni2P nanoparticles were hollow and faceted to expose a high density of the Ni2P(001) surface, which has previously been predicted based on theory to be an active HER catalyst. The Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quantitative faradaic yield, while also affording stability in aqueous acidic media.

http://pubs.acs.org/doi/pdf/10.1021/ja403440e

Nanostructured Nickel Phosphide as an Electrocatalyst for the Hydrogen Evolution Reaction

Single layer transition metal sulfides (SLTMS) such as MoS2, WS2, and ReS2, play an important role in catalytic processes such as the hydrofining of petroleum streams, and are involved in at least two of the slurry‐catalyst hydroconversion processes that have been proposed for upgrading heavy petroleum feed and other sources of hydrocarbon fuels such as coal and shale oils. Additional promising catalytic applications of the SLTMS are on the horizon. The physical, chemical, and catalytic properties of these materials are reviewed in this report. Also discussed are areas for future research that promise to lead to advanced applications of the SLTMS.

Catalytic Properties of Single Layers of Transition Metal Sulfide Catalytic Materials

Single layer transition metal sulfides (SLTMS) such as MoS{sub 2}, WS{sub 2}, and ReS{sub 2}, play an important role in catalytic processes such as the hydrofining of petroleum streams, and are involved in at least two of the slurry-catalyst hydroconversion processes that have been proposed for upgrading heavy petroleum feed and other sources of hydrocarbon fuels such as coal and shale oils. Additional promising catalytic applications of the SLTMS are on the horizon. The physical, chemical, and catalytic properties of these materials are reviewed in this report. Also discussed are areas for future research that promise to lead to advanced applications of the SLTMS.

Catalytic properties of single layers of transition metal sulfide catalytic materials.

Unsupported transition metal sulfide catalysts: 100 years of science and application

Periodic effects form the basis for progress in understanding the role of structure/function relationships in hydrodesulfurization (HDS). Theoretical results of Toulhoat, and Raybaud et al. based on ab initio calculations using density functional theory calculations as well as experimental results of Berhault et al. have recently confirmed the initial proposal of Pecoraro and Chianelli about the Sabatier principle interpretation for HDS activity either for transition metal binary bulk sulfides or for cobalt promotion of MoS2-based catalysts. An optimum HDS activity corresponds to a moderate active site-organic sulfur-containing reactant interaction. An update is presented here with a special attention to the electronic foundations of the Sabatier principle as applied to HDS catalysis.

Periodic trends in hydrodesulfurization: in support of the Sabatier principle

A simple preparation method of high surface area MoS2 using reactions in aqueous solution in the presence of an organic surfactant has been reported. Molybdenum sulfide was obtained from the reactions of aqueous (NH4)2MoS4 with N2H4 or NH2OH·H2SO4, followed by thermal treatment under nitrogen flow. The solids were characterized by X-ray diffraction, chemical analysis, surface and porosity measurements, photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HREM). Addition of the cetyltrimetylammonium chloride surfactant to the reaction mixtures led to the increase of specific surface area up to 210 m2/g and disappearance of MoS2 layers stacking. Single layer, short fringes of MoS2 were observed by HREM. The solids contained 4−8 wt % of carbon impurity, which probably acts as a textural stabilizer.

Gilles Berhault

Papers

Catalytic Properties of Single Layers of Transition Metal Sulfide Catalytic Materials

Catalytic properties of single layers of transition metal sulfide catalytic materials.

Unsupported transition metal sulfide catalysts: 100 years of science and application

Periodic trends in hydrodesulfurization: in support of the Sabatier principle

Surfactant-assisted synthesis of highly dispersed molybdenum sulfide