Synthesis Of Amorphous MoS_x/CNTs Hybrid Nanospheres For Hydrogen Evolution Reaction

Developing cost-effective electrocatalysts with high activity and stability for hydrogen evolution reaction(HER)plays an important role in modern hydrogen economy.Recently,the simple and mild preparation methods along with inexpensive precursor materials make amorphous molybdenum sulfide(MoSx)as one of the most promising alternatives to Pt-based catalysts in HER,especially in acidic electrolytes.Nonetheless,the poor cystallinity of MoSx leads to relatively high solubility and poor electrochemcial stability in acidic electrolytes.The inherent poor electrical conductivity of amorphous MoSx also inhibits efficient electron transfer process,posing a major difficulty for further enhancing electrocatalytic HER performance.So far it still remains challenging to develop a viable synthetic method for the synthesis of MoSx-based electrocatalysts with abundant active sites,excellent stability,and efficient charge transfer to simultaneously achieve high HER activity and long-term stability.Here we report a simple ultrasonic spray pyrolysis method to synthesize hybrid HER catalysts composed of MoSx firmly attached on entangled carbon nanotube nanospheres(MoSx/CNTs).This synthetic process is fast,continuous and amenable to high-volume production with high yields and exceptional quality.Exploring the effects of pyrolysis temperature,the ratio of(NH4)2MoS4/CNTs and the precursor concentration on the catalytic activity of catalysts,we found that MoSx/CNTs hybrid nanospheres with an optimal synergistic structure can exhibit a low overpotential of 168 mV at the current density of 10 mA/cm2 and a small Tafel slope of 36 mV/dec.From the morphology and structure characterization of MoSx/CNTs,we found that MoSx with abundant unsaturated S atom were firmly attached on three-dimensional CNTs network nanospheres.Further X-ray photoelectron spectroscopic measurements reveal that the interaction between MoSx and CNTs not only facilitates charge transfer for HER but also stabilizes most of the active sites to improve stability.In addition,exploring the effects of pyrolysis temperatures on the structures and catalytic activities of MoSx/CNTs hybrid nanospheres,we found that the catalytic activity was consistent with the contents of S atoms with higher binding energies in MoSx/CNTs.In contrast with MoSx/CNTs prepared by solvothermal method,MoSx/CNTs hybrid nanospheres produced by USP method possess much higher catalytic activity due to the three-dimensional conductive network and rich unsaturated S atom.The highly efficient hybrid HER catalysts prepared via the scalable USP method is therefore a promising replacement for Pt-based materials in electrochemical and photoelectrochemical hydrogen production devices.