Maria Sokolikova1 Peter Sherrell1 Pawel Palczynski1 Cecilia Mattevi1

1, Imperial College London, London, , United Kingdom

Atomically thin transition metal dichalcogenides have attracted significant interest for technological use due to a wide diversity of their electronic and optical properties. Recently, nanostructured MoSe2 and WSe2 have been identified as suitable catalysts for electrochemical water splitting, considering their band edge energies with respect to the redox potential of hydrogen evolution reaction (HER) and good stability in aqueous solutions.1 Single- and few-layered nanosheets of MoSe2 and WSe2 have been mainly achieved via exfoliation of bulk powders in solution, although this approach generally yields to dispersions that are heterogeneous in flake size and thickness. On the other hand, colloidal synthesis can be significantly advantageous as it presents fine morphological and compositional control over free-standing nanostructures processed at low temperatures in liquid phase allowing for designing the material with multiplied number of active sites and desired electronic properties respectively. In this work, we report a colloidal synthesis of MoSe2, WSe2 and alloyed WxMo1-xSe2 branched nanosheets reaching 500 nm in lateral size. The materials present high crystal quality under high-resolution TEM characterization. The growth was achieved upon a reaction between transition metal carbonyls and trioctylphosphine selenide in a coordinating solvent at 300oC in inert atmosphere. The electrocatalytic activity of MoSe2, WSe2 and alloyed WxMo1-xSe2 nanostructures towards hydrogen evolution reaction was assessed in three-electrode electrochemical cell in 1M H2SO4. Alloyed WxMo1-xSe2 branched nanosheets require a smaller HER overpotential at the cathodic current density of -10 mA/cm2 (-360 mV vs RHE) than the MoSe2 branched nanosheets (-390 mV vs RHE, this work) and outperform the exfoliated MoSe2 and WSe2 counterparts.2

1. Zhuang et al, J. Phys. Chem. C, 2013, 117, 20440–20445.
2. Chia et al, ACS Nano, 2015, 9, 5164–5179.