Synthesis And Electrocatalytic Application Of Two-dimensional Transition Metal Sulfide

With the increasing of energy crisis and environment problems,the development of renewable and environmental friendly energy sources to replace traditional fossil fuels has become a hot issue of global concern.In the preparation of clean energy,the appropriate efficiency and selective electrocatalysts have become the key factors,which have aroused wide concern.Two-dimensional（2D）inorganic nanomaterials,especially 2D transition metal sulfide,have good applications in optoelectronic devices,electronic devices,sensors,electrocatalysis and energy storage because of their unique physical,chemical or electronic properties.This paper aims to controllable preparation and property modulation of 2D transition metalsulfide,using X-ray absorption spectroscopy characterization techniques to build the relationship between the fine structure of materials and the properties,in order to provide new method and train of thought for the optimization of their catalytic activity and stability as electrocatalysts,which makes it get more extensive application in energy conversion reaction.The specific works are as follows:1.Controllable preparation of a new class of ultrathin metallic CuFeS₂ nanosheets（NSs）with abundant exposed high-index（02?）facets by the high temperature pyrolysis method.They serve as a robust catalyst for the HER with a lower onset potential of 28.1 mV,an overpotential of only 88.7mV at 10 mA cm^-2 in 0.5 M H₂SO,which superior to most non-noble-metal based HER catalysts reported.The CuFeS₂ NSs are also stable for HER.In addition,the nanosheet structure and high-index facets are well retained after the stability test.The theoretical calculations reveal that the ultrathin metallic Cu FeS₂ nanosheets（NSs）with abundant exposed high-index（02?）facets exhibit an appealingΔG_H value of 0.1 eV,which would provide a fast proton/electron-transfer step to facilitate the overall HER processes.2.Design synthesis of the metallic CuCo₂S nanosheets with-atom-thick to 6-atom-thick layer.The EXAFS spectra clarify that the coordination deficiency from Cu and the disordered surface structure with vacancy for increasing active sites of the CuCo₂S NSs.Thus,the CuCo₂S NSs exhibit excellent reversible oxygen catalytic performance with an overpotential of 287 mV(at j=10 mA cm^-2)for oxygen evolution reaction（OER）and onset potential of 0.90 V for oxygen reduction reaction（ORR）.Additionally,the portable-flexible Zn-air battery used CuCo₂S NSs as the air-cathode displays a high energy density of 2 Wh kg^-1 and good cycling durability for more than 18–22 h.3.The FeS₂/CoS₂ interface nanosheets with rich defects were successfully prepared.The HRTEM indicates the interface with rich defects and disordered structure,the EXAFS spectra further clarify the surface structure of the FeS₂/CoS₂ NSs,which provides more active sites for catalytic reaction and enhances the electrocatalytic performance.The FeS₂/CoS₂ NSs show a remarkable HER performance with a low overpotential of 78.2 mV at 10 mA cm^-2 as well as a superior stability for80 h in alkaline medium,also an overpotential of 302 mV at 100 mA cm^-2 for OER.As an excellent catalyst for overall water splitting,the FeS₂/CoS₂ NSs only need a cell voltage of 1.7 V to achieve current density of 10 mA cm^-2 and maintain the activity for at least 21 h.