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 2 ) synthesis, involving CS 2 as a sulfurizing agent and Ta 2 O 5 as a metal precursor. The structure of the created TaS 2 flakes was analyzed by Raman, XRD, XPS, SEM, and HRTEM techniques. It was demonstrated that a tuning between 1T (metallic) and 3R (semiconductor) TaS 2 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 2 were found to be 35 and 43 mV/dec for 3R-TaS 2 and 1T-TaS 2 , respectively, with the corresponding overpotentials of 63 and 109 mV required to reach a current density of 10 mA/cm 2 . 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.