(201o) Solvent Engineering of Molybdenum Disulfide Electro-Catalysts for Hydrogen Evolution

Hydrogen can be obtained via water splitting. However, the state of art catalysts is dominated by Platinum and its alloys. Transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS₂), are abundant and have recently shown promising results for the hydrogen evolution reaction. Hydrothermal synthesis of MoS₂ using a precursor, ammonium tetra-thiomolybdate, is a common route for obtaining the TMD. However, results show thermodynamic and kinetic limitations using water as a solvent. Here, we have investigated the electrochemical performance of MoS₂ obtained using asolvothermal synthesis route. We have explored a variety of solvents based on the Hansen solubility parameter. The electrochemical studies reveal increases in onset potentials of approximately 50 mV and 100 mV at current density of -2.75 mA cm^-2 using ethylene glycol and triethylamine solvents, respectively. Results show that MoS₂ synthesized in water exhibits the best tafel slope of 60 mV decade^-1, followed by triethylamine and ethylene glycol at 62.5 mV decade^-1 and 75 mV decade^-1, respectively. Scanning electron microscopy images reveal more deeply exfoliated MoS₂ catalysts synthesized in triethylamine and ethylene glycol, potentially producing more active edge sites and allowing for better hydrogen proton adsorption. This study concludes that the thermodynamic potential is the rate-limiting reaction, and improvements in adsorption properties of exfoliated MoS₂ can be achieved using solvent engineering. Further studies will examine effects of solvent polarity and boiling point on the thermodynamic performance of MoS₂ catalysts.