Electrocatalytic hydrogen evolution performance of nitrogen-doped molybdenum disulfide nanocatalysts
A series of nitrogen-doped MoS2(N-MoS2)nanocatalysts were synthesized by hydrothermal method with sodium molybdate as molybdenum source,L-cysteine as sulfur source and reducing agent,and dicyandiamide as nitrogen source.The crystal structure,morphology,elemental mapping and electronic properties of N-MoS2 with different N doping contents were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),and Raman spectroscopy.The characterization results revealed that all synthesized N-MoS2 catalysts were flower-like spheres composed of nanosheets,and N atoms were successfully doped into MoS2 lattice and uniformly distributed in the N-MoS2 nanocatalysts.The doping of N atoms increases the electron densities of Mo and S atoms adjacent to N atoms,and forms more unsaturated coordination sites with high catalytic activity.The linear sweep voltammetry curves and the Tafel slopes of all catalysts were tested in acidic medium with an electrochemical workstation to evaluate their electrocatalytic hydrogen evolution(HER)performance.The results suggest that the hydrogen evolution reactions on MoS2 catalyst and N-MoS2 catalysts both proceed via the Volmer-Heyrovsky mechanism,but the rate-determining step of MoS2 catalyst is Volmer reaction,and that of N-MoS2 catalysts is Heyrovsky reaction.Compared with MoS2 catalyst,N-MoS2 catalysts exhibit better HER performance with lower Tafel slopes and faster hydrogen evolution reaction rates.Especially,N-MoS2-0.1(N/Mo=0.1)exhibits the lowest Tafel slope of 60mV/dec.The improved HER activity of N-MoS2 nanocatalysts mainly results from the increased exposure of unsaturated coordination sites and the weakening of Mo-H* due to the electron-rich Mo atoms.
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