Synthesis,Structure And Electrocatalytic Activity Of Transition Metal Sulfide Nanomaterials

The increasingly serious energy crisis and environmental problems have put forward a huge challenge to the sustainable development of human society.As one of the most ideal clean energy carriers,hydrogen is a very promising energy source to replace the traditional energy.Eelectrocatalytic water splitting is one of the hydrogen production methods that has no pollution but high efficiency,however,the high power consumption restricts the further application.To reduce the power consumption,Efficient,cheap and source abundant HER catalytic materials are highly needed.Among the various HER catalytic candidates to Pt,.2H MoS2 have gained a lot of attention because of the high catalytic activity,low cost,simple and reliable synthesis method.Recent studies show that the HER performance of amorphous MoSx(a-MoSx)was superior than well-crystallized MoS2 due to the abundant active sites of sulfur with various chemical states,together with its low-temperature synthesis,making it a potential candidates that can be scaled up.Therefore,It is important to study the synthesis and HER performance of a-MoSx catalyst.Based on the above discussion,the electrocatalytic performances of non-noble transition metal sulfides are studied systematically and deeply in this paper.Specific contents are as follows:The first part focuses on the preparation and HER activity of MoS2 nanoparticles.MoS2 nanoparticles were synthesized at low temperature of 200 ℃.SEM result shows that,the average diameter of the nanoparticles is～15 nm,and(002)diffraction plane can be detected in the XRD pattern,suggesting the 2H phase.The peak has much wide full width at half maximum,indicative the small crystal size,which well corresponds with the SEM result.The Raman spectra clearly exhibit the existence of Mo and S elements.Compared with the traditional MoS2 2D film or flakes,the nanoparticles counterpart has superior electrocatalytic performance with an overpotential(η10)of 170 mV and a Tafel slope of 110 mV/dec in alkaline media.Such a good performance can be attributed to the increased active sites density brought by the nanocrystal morphology.The second part mainly focuses on the microstructure and HER performance of a-MoSx based composites.A-MoSx ultrathin nanoflake-Ni3S2 nanocrystals composites were synthesized directly on NF substrate for high efficiency HER.The a-MoSx matrix was found to consist of[Mo3S13]2-nanoclusters,and its interaction with the Ni3S2 nanocrystals(size<10 nm)was convinced by obvious Raman/chemical shifts.DFT simulations reVealed that besides the active sites of shared S in a-MoS2 matrix,after composition with Ni3S2,the bridging and terminal S will become catalytically active due to the lowered ΔGH*values.The enhanced native activity with increased species of active sites,together with the high active density due to the large specific surface area,and the 3D network of Ni foam,endowed the composites with excellent HER activity,and a η10 of 102 mV and η100 of 177 mV were achieved.This work demonstrated the catalytic origin for a-MoSx and provided a rational strategy for promoting both the intrinsic and extrinsic HER activity of a-MoSx.In conclusion,MoS2 nanoparticles and a-MoSx-Ni3S2 composite materials with excellent electrocatalyst activity were synthesized through hydrothermal method,Theoretical calculations illustrate the nature and origin of the catalytic active species which provides a new research idea for the study of electrocatalytic materials.