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The development of earth-abundant and green electrocatalysts is an important research field, aiming to provide energy solutions by clean and efficient hydrogen evolution (HER). 2D transition metal dichalcogenides (TMDs) are well-known HER catalysts, and some are even biocompatible and environmentally friendly, such as WS2. Synthesizing them in a flower-like morphology that provides abundant edges, and the formation of composite structures that offer multiple interfaces, render them with promising features for electrocatalysis. Here we show the synthesis of WS2/WO3 hybrid catalysts, which facilitate the hydrogen evolution reaction. The mixture of 1T/2H-WS2 phases and doping with various transition metals (Fe, Co, and Ni) improves the pristine structures. The 5% Co-WS2/WO3 composite is the most promising HER electrocatalyst among the doped catalysts studied here. These Co-doped WS2/WO3 composites represent another TMD alternative to the precious metal electrocatalysts for the HER. [ABSTRACT FROM AUTHOR]

SnS and SnS2 are layered semiconductors, with potential promising properties for electro‐ and photocatalytic hydrogen (H2) production. The vast knowledge in preparation and modification of layered structures was still not employed successfully in this system to fully maximize its potential. Here, the first report of structural transformation of SnS2 into SnS with Mo‐doping as a bifunctional catalyst for the hydrogen evolution reaction (HER) is reported. The structural phase transition optimized the properties of the material, providing a more delicate morphology with additional catalytic sites. The electrochemical studies showed overpotential of 377 mV at 10 mA cm−2 for HER with Tafel slopes of 100 mV dec−1 in 0.5 m H2SO4 for 10 % Mo‐SnS. The same structure acts as an efficient photocatalyst in the generation of H2 from water under visible illumination with rate of 0.136 mmol g−1 h−1 of H2, which is 20 times higher than pristine SnS2 under visible light. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDCs) based materials are considered as highly active alternatives to the precious Pt‐based catalysts for the hydrogen evolution reaction (HER). In particular, MoSe2 emerges as a promising catalyst due to its abundance and electrochemical stability, but further modifications are still required to enhance its performance, specifically in alkaline conditions. Here, we developed a method to obtain MoSe2 with two cobalt doping patterns: homogeneously doped and edge doped nanoflowers, with abundant edge sites and extended surface area. The results show that low concentration of doping enhances the catalytic activity toward HER. Incorporation of cobalt as a substituent dopant within the layered structure of MoSe2 appears to have two major contributions: it changes the chemical environment providing more active sites with favored hydrogen adsorption properties, and improves the charge transfer resistance and thus facilitates the HER kinetics. Moreover, the homogeneous and edge‐doped nanoflowers show different pH‐dependence of HER activity. Edge‐doped samples exhibit significantly improved performance in acidic medium, while the overpotential increases in alkaline environment upon doping. A mechanistic explanation of the observed effect is proposed. This work opens up an additional path for improving the catalytic activity of TMDCs in acidic or alkaline medium using a simple and facile method with only small quantities of dopants. [ABSTRACT FROM AUTHOR]

Layered transition metal dichalcogenides (TMDCs) are an emerging family of catalysts. Included in this group is tungsten diselenide (WSe2), which has attracted recent attention for electro-optical applications. Tungsten is opportune because it is the heaviest transition metal in the TMDC family and is widely abundant on Earth. Moreover, WS2 and WSe2 are more benign in nature than their molybdenum counterparts. Despite this, WSe2 has been relatively unexplored as a catalyst. We report the synthesis of WSe2 doped with various transition metals (Fe, Co, Nb, Ni and Zr). Among the doped catalysts, Ni–WSe2 has been found to be the most promising electrocatalyst for the hydrogen evolution reaction (HER) as it possesses the smallest charge transfer resistance and thus facilitates a faster catalytic reaction. Upon doping with Ni, catalytic enhancement results from improved hydrogen adsorption (Hads). Beyond this threshold of Ni loading, the improved activity in alkaline medium is due to the optimized interaction of the OH/surface active sites. Using density functional theory calculations, we identified that the catalytic sites are Se atoms either bound to a substitutional Ni dopant or constituting a small patch of NiSe grafted on the WSe2 surface. [ABSTRACT FROM AUTHOR]

Self-assembled 3D hierarchical Bi2W1−xMoxO6 heterostructures with varying x (x = 0, 0.2, 0.4, 0.6, 0.8 or 1.0) with different morphologies were synthesised via a facile one-pot solvothermal method and their photocatalytic activity towards the oxygen evolution reaction (OER) from water under natural sunlight was tested. The structural properties of Bi2W1−xMoxO6 were studied by the X-ray diffraction (XRD) technique, which showed an orthorhombic Aurivillius layered crystal structure. The microstructural features were examined by FE-SEM and FE-TEM techniques which showed that the morphology of Bi2WO6 varies with substitution of Mo and each morphological structure grows via the assembly of tiny nanoparticles of size 50 nm. The effective substitution of Mo in Bi2WO6 extends the optical absorption towards the visible region. The substitution of Mo in place of W was confirmed by X-ray photoelectron spectroscopy. The photocatalytic activities were evaluated by OER under solar light irradiation. The sample Bi2W0.6Mo0.4O6 (S3) shows enhanced photocatalytic activity for OER from aqueous AgNO3 solution (652 μmol h−1 g−1) which is higher than for pristine Bi2MoO6 or Bi2WO6 photocatalysts. Enhanced photocatalytic activity can be attributed to the extended absorption in the visible light region, which enhances the photocatalytic efficiency of the photocatalysts. More significantly, the 3D intrinsically layered nanosheet structure based morphology, and the unique band structure are beneficial for efficient charge transfer, which enhances the photocatalytic activity. This work demonstrates an effective strategy for developing an active photocatalyst with greater utilization of solar light. [ABSTRACT FROM AUTHOR]

Spherically shaped plasmonic Au nanoparticles (NPs) of size 10 nm (±4 nm) have been decorated on TiO2 NPs for the synthesis of Au@TiO2 composites via an aqueous sol–gel method. The effects of the Au concentration on the optical properties, structural surface properties and photocatalytic activity have been investigated. The optical study indicated characteristics of the surface plasmon resonance (SPR) of Au NPs, which greatly red shifted the photo-absorption from UV to visible light. A Tauc plot showed a downward shift in the band gap energy due to the creation of a metal–semiconductor Schottky junction at the nano Au@TiO2 surface. The well crystallized mixed (anatase and rutile) TiO2 phase formation was investigated using X-ray diffraction studies. The decrease in the photoluminescence (PL) intensity with Au loading indicated an increase in the charge carrier separation. The porous nature of the synthesized photocatalyst material was observed in both Field Emission Scanning Electron Microscopy (FESEM) and Field Emission Transmission Electron Microscopy (FETEM). The homogeneous distribution of Au NPs over the entire TiO2 surface was examined using FETEM and was also confirmed by elemental mapping with STEM. The broadening and shifting of the Raman peak from 143.2 cm−1 to 144.7 cm−1 indicated the generation of crystalline defects such as vacancies and interstitial rearrangement, which may act as trapping sites for electrons. BET surface measurements revealed that the surface area increased from 29.19 m2 g−1 for bare TiO2 to 60.05 m2 g−1 for 2% (w/w) Au loading on TiO2. The synthesized porous Au@TiO2 composites exhibited a high photocatalytic activity for the splitting of H2O under natural solar radiation with the H2 generation rate of 399 μmol/0.1 g h−1, which is much higher than 132 μmol/0.1 g h−1 demonstrated by pristine TiO2 NPs. Along with the hydrogen (H2) generation via water splitting, photocatalytic Rhodamine-B degradation and the kinetics of the reaction were investigated in solar light. The rate was observed to be due to a pseudo-first order reaction. [ABSTRACT FROM AUTHOR]

Unique two dimensional (2D) honeycomb layered MoS2 nanostructures and hierarchical 3D marigold nanoflowers of CdMoS4 were designed using a template free and facile solvothermal method. The MoS2 structure is depicted with a sheet like morphology with lateral dimensions of 5–10 μm and a thickness of ∼200 nm and a honeycomb nanostructure architecture produced via the self-assembling of vertically grown thin hexagonal nanosheets with a thickness of 2–3 nm. The 3D CdMoS4 marigold nanoflower architecture comprised thin nanopetals with lateral dimensions of 1–2 μm and a thickness of a few nm. The CdMoS4 and MoS2 structures displayed hydrogen (H2) production rates of 25 445 and 12 555 μmol h−1 g−1, respectively. The apparent quantum yields of hydrogen production were observed to be 35.34% and 17.18% for CdMoS4 and MoS2, respectively. The 3D nanostructured marigold flowers of CdMoS4 and honeycomb like 2D nanostructure of MoS2 were responsible for higher photocatalytic activity due to inhibition of the charge carrier recombination. The prima facie observation of H2 production showed that the ternary semiconductor confers enhanced photocatalytic activity for H2 generation due to its unique structure. Such structures can be designed and implemented in other transition metal dichalcogenide based ternary materials for enhanced photocatalytic and other applications. [ABSTRACT FROM AUTHOR]

Three dimensional (3D) hierarchical nanostructures of orthorhombic Bi2WO6 with unique morphologies were successfully synthesized by a solvothermal method. The precursor concentration plays a key role in the architecture of the hierarchical nanostructures. A peony flower-like morphology was obtained at higher precursor concentrations, and a red blood cell (RBC)-like morphology with average diameter of 1.5 μm was obtained at lower concentrations. These hierarchical nanostructures were assembled by self-alignment of 20 nm nanoplates. As their band gap is in the visible region, the photocatalytic activity of the Bi2WO6 hierarchical nanostructures for the production of hydrogen from glycerol, and the degradation of rhodamine B (RhB) and methylene blue (MB) under ambient conditions in the presence of solar light was investigated. The Bi2WO6 with peony flower morphology was observed to be the most efficient photocatalyst (H2: 7.40 mmol h-1 g-1, kRhB: 0.240 and kMB: 0.100) of the reported nanostructures. The higher activity of the peony flowers was due to their porous nature, high surface area and lower band gap. Such unique 3D nanostructures of Bi2WO6 have been fabricated for the first time, and their use as photocatalysts in the production of hydrogen from glycerol has hitherto not been attempted. These nanostructures may have potential in ferroelectric, piezoelectric, pyroelectric and nonlinear dielectric applications. [ABSTRACT FROM AUTHOR]