Large-scale production of transition metal dichalcogenide nanocatalysts for hydrogen evolution reaction

Clean hydrogen produced using renewable energy sources is an important energy carrier that can serve as an alternative to fossil fuels. In recent years, transition metal dichalcogenides (TMDs) have emerged as promising catalyst materials for the hydrogen evolution reaction (HER). In this thesis, molybdenum sulfide (MoS2) and molybdenum selenide (MoSe2) nanosheets were synthesized under an argon (Ar) atmosphere using a mechanochemical production method that enables large-scale synthesis. In each synthesis, approximately 2 g of MoS2 and MoSe2 nanopowder were produced with yields of 94.3% and 90.9%, respectively. Molybdenum (Mo) powder was used as the transition metal source and sulfur (S) and selenium (Se) powders as the chalcogen sources. Synthesis parameters such as ball-to-powder weight ratio, milling time, reaction atmosphere, and solid dispersant content were optimized to achieve the highest production yield. Structural and chemical characterizations of the obtained samples were performed using X-ray diffraction (XRD), photoluminescence spectroscopy (PL), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) analyses, scanning electron microscopy (SEM), as well as UV-Vis Spectroscopy. Electrochemical hydrogen evolution tests were conducted in a borosilicate glass cell using a three-electrode setup and a potentiostat (Gamry Interface 1000). As a result of structural and electrochemical characterizations, the optimum synthesis conditions yielding the highest efficiency were determined to be a 100:1 ball-to-powder weight ratio, 72 hours of milling, and a 1:1 NaCl:(Mo+S/Se) molar ratio. Under these optimum conditions, the synthesized materials exhibited high HER activity. To achieve a current density of 10 mA cm-2, the MoS2 and MoSe2 catalysts required overpotentials of 191 mV and 165 mV, respectively, and showed low Tafel slopes of 75 and 48 mV dec-1. The high catalytic activity of the synthesized nanocatalysts was attributed to the partially amorphous nature of the nanosheets, crystal defects, and the presence of S and Se vacancies. This facilitates hydrogen adsorption and desorption processes and contributes to the acceleration of HER kinetics. The proposed method also shows great promise for the large-scale production of other nano-TMDs.