Piezo-catalytic Hydrogen Evolution Of Few-layer 2D WS₂ Nanosheets Through Harvesting Vibration Energy

In recent years,with the continuous development of industrial level,people have more and more demands for energy.Fossil energy is the most widely used energy form at present,but the over exploitation and use of fossil energy make people face a series of problems such as energy shortage and environmental pollution.Hydrogen has been regarded as the most potential new energy in the future because of its zero pollution and abundant source of reaction products,and has been widely concerned by domestic and foreign researchers.Because of its simple method,high purity and no pollution,electrolysis water is recognized as one of the effective ways to produce hydrogen in large scale industry.In order to improve the efficiency of electrolysis water,catalyst plays an important role.The highly efficient electric catalyst should have the characteristics of good conductivity,high catalytic activity and large specific surface area.At present,platinum is the most efficient catalyst for hydrogen evolution,but it is limited in wide application because of its low reserves and high cost.Therefore,it is of great practical significance to develop a kind of hydrogen evolution catalyst with low cost,abundant reserves and high catalytic activity.In this paper,the piezoelectric catalytic effect of two-dimensional tungsten disulfide nanosheets with few layers was studied.Under the action of ultrasound,the piezoelectric effect of tungsten disulfide can enhance the catalytic performance of hydrogen evolution and significantly improve the efficiency of hydrogen evolution reaction.Tungsten disulfide belongs to transition metal sulfide,which is a typical layered material.Due to its abundant reserves and good chemical stability,it is widely used in the field of catalysis.A few layers two-dimensional tungsten disulfide nanosheets were prepared by simple liquid phase stripping technique.Transmission Electron Microscope(TEM)showed that the prepared nanosheets had hexagonal structure,ultra-thin single-layer and few layers structure,and clear lattice stripes,which indicated that the crystallinity of the nanosheets was better.The valence and structure of tungsten disulfide nanosheets were analyzed by X-ray Photoelectron Spectroscopy(XPS),X-ray Diffraction(XRD)and laser Raman spectroscopy(Raman).X-ray photoelectron spectroscopy shows that the valence states of tungsten and sulfur are+6 and-4,respectively.There are a few W-O peaks,which may be caused by oxidation in air.The characteristic peaks measured by X-ray diffractometer are in good agreement with the standard card,which shows that the tungsten disulfide prepared by liquid phase stripping method has high purity.Raman spectra show that E¹_2g and A_g¹ are two distinct vibration modes.The existence of the two vibration modes indicates that the synthesized tungsten disulfide has an ultra-thin layer with atomic thickness.Piezoresponse Force Microscope(PFM)and Atomic Force Microscope(AFM)have verified the piezoelectric properties and thickness of the prepared tungsten disulfide nanosheets.The electrochemistry test was carried out to compare the electrocatalytic hydrogen evolution of tungsten disulfide nanosheets with piezoelectric and piezoelectric assisted.The results show that the hydrogen evolution efficiency increases by 6 times when the overpotential is-1 V,and the impedance decreases by 4times when the overpotential is-0.8 V.The effects of different ultrasound power and frequency on the piezoelectric catalysis of tungsten disulfide nanosheets was also compared.The results showed that the hydrogen evolution performance was the best under the condition of 40 W power and 40 k Hz.In a word,through the research on the piezoelectric catalytic performance of tungsten disulfide nanosheets,the catalytic efficiency can be significantly improved by using the energy of external vibration,which provides another effective strategy for the development of non-noble metal hydrogen evolution catalysts and promoting the development of clean energy.