Beyond the Platinum Era─Scalable Preparation and Electrochemical Activation of TaS 2 Flakes.

Among 2D materials, transition-metal dichalcogenides (TMDCs) of group 5 metals recently have attracted substantial interest due to their superior electrocatalytic activity toward hydrogen evolution reaction (HER). However, a straightforward and efficient synthesis of the TMDCs which can be easily scaled up is missing. Herein, we report an innovative, simple, and scalable method for tantalum disulfide (TaS) synthesis, involving CS as a sulfurizing agent and TaO as a metal precursor. The structure of the created TaS flakes was analyzed by Raman, XRD, XPS, SEM, and HRTEM techniques. It was demonstrated that a tuning between 1T (metallic) and 3R (semiconductor) TaS phases can be accomplished by varying the reaction conditions. The created materials were tested for HER, and the electrocatalytic activity of both phases was significantly enhanced by electrochemical self-activation, up to that comparable with the Pt one. The final values of the Tafel slopes of activated TaS were found to be 35 and 43 mV/dec for 3R-TaS and 1T-TaS, respectively, with the corresponding overpotentials of 63 and 109 mV required to reach a current density of 10 mA/cm. We also investigated the mechanism of flake activation, which can be attributed to the changes in the flake morphology and surface chemistry. Our work provides a scalable and simple synthesis method to produce transition-metal sulfides which could replace the platinum catalyst in water splitting technology.