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 MoV defect species, bridging S22−, and terminal S22− 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 MoV defect species and bridging S22− ligands, or most likely dominated by the MoV 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. For the first time, various material compositions of nanosized amorphous MoSx (from amorphous MoS2 to amorphous MoS3) are successfully synthesized through photomodulation of the reaction mechanisms (from photothermal‐induced to photoinduced reduction/oxidation). The catalysts with optimized ratios of active sites of MoV defect species, bridging S22− ligands, and terminal S22− ligands exhibit excellent catalytic activity. [ABSTRACT FROM AUTHOR]