Controllable Synthesis of Nanosized Amorphous MoSx Using Temporally Shaped Femtosecond Laser for Highly Efficient Electrochemical Hydrogen Production

Amorphous molybdenum sulfide (a-MoSx) is regarded as a promising electrocatalyst for hydrogen evolution reaction (HER) due to its disorder structures with a significant number of defect-rich active sites. Here, a green, one-step, and controllable method is developed to photoregulate the chemical reactions and synthesize nanosized a-MoSx by temporally shaped femtosecond laser ablation of ammonium tetrathiomolybdate aqueous solution. By adjusting the laser energy and pulse delay to control photoinduced and/or photothermal-induced reduction/oxidation, the S to Mo ratio x can be modulated from 1.53 to 3.07 and the ratio of the Mo-V defect species, bridging S-2(2-), and terminal S-2(2-) ligands can be controlled. The optimized a-MoSx catalysts (x = 2.73) exhibit high catalytic activity with a low Tafel slope of 40 mV dec(-1), high double-layer capacitance of 74.47 mF cm(-2), and large current density of 516 mA cm(-2) at an overpotential of 250 mV. The high catalytic activity can be mainly attributed to Mo-V defect species and bridging S-2(2-) ligands, or most likely dominated by the Mo-V defect species. This study not only provides an alternatively controllable method to prepare a-MoSx as efficient HER catalysts but also contributes to the understanding of the origin of its catalytic activity.