Preparation And Electrocatalytic Performance Of Three-dimensional Porous Cu-based Sulfide And Phosphide Electrocatalysts

The exhaustion of fossil fuels and increase in energy demand are crucial challenging issues that cause the discovering of alternative earth abundant energies and efficient designing of energy storage devices.Therefore,sustainable and renewable energy resources?wind energy,water power and solar energy,etc.?can be used as an alternative energy sources for energy demand problems,whereas there is significant to transform those sustainable-renewable energy sources into ideal energy sources?H₂?.Hydrogen production methods include fossil fuel catalytic reforming,biomass hydrogen production and water decomposition.Hence,electrochemical water splitting is a promising technology for generating a clean chemical fuel?H₂?,which converts the renewable energy into ideal chemical energy?in the form of H₂?using highly efficient electrocatalysts.Currently,prior art precious metal electrocatalysts such as Pt/Ir based compounds used for the hydrogen evolution reaction?HER?are used as efficient electrocatalysts for water splitting with low overpotential,but their high cost and scarcity restrict their large-scale use.Therefore,the development of HER electrocatalysts for water splitting is highly efficient,stable,low overvoltage,inexpensive and earth-rich operation,which is essential for achieving inexpensive and efficient hydrogen generation.Transition metal sulfides and phosphides have requirements of high-efficiency hydrogen evolution catalysts because of their excellent electrical conductivity,chemical stability,and high catalytic performance.The nanoarray structure can improve stability of material by reducing stress and enhancing mechanical flexibility.It can also eliminate the need for polymer binder in catalytic process,which is beneficial to the exposure of active site and contact of active site with working medium.And in-situ growth techniques are beneficial to enhance conductivity and thereby promote catalysis.Therefore,this thesis focused on preparation of copper-based sulfide and phosphide nanocatalysts and their hydrogen evolution properties.The research was carried out from following three aspects:1.Firstly,based on copper foam,Cu?OH?₂nanorods were grown on copper foam by chemical oxidation method,then Cu?OH?₂was converted into Cu₂S by hydrothermal method,and N-doped Mo S₂nanosheets were coated on the surface of Cu₂S at the same time to prepare Cu₂S/Mo S₂/CF catalyst.SEM confirmed that the Cu₂S/Mo S₂nanorod arrays were uniformly grown on CF substrate.TEM and XPS confirmed the existence of heterogeneous interface and electron transfer in Cu₂S/Mo S₂/CF,respectively,which contributed to the high HER activity.Electrochemical tests shown that the overpotential required for Cu₂S/Mo S₂/CF at 10 and 100 m A cm^-2under alkaline conditions were only91 and 129 m V,and it had a low Tafel slope(41 m V dec^-1)indicated that it had a faster reaction rate in HER.The electric double layer capacitance test shows that Cu₂S/Mo S₂/CF has large electrochemical active area,and it can be stably operated in alkaline medium by chronopotentiometry for 4 h.2.Secondly,a layer of two-dimensional nanosheet-like nickel and molybdenum layered double hydroxides were grown on Cu?OH?₂nanorods to prepare hollow hierarchical structure composites by hydrothermal method.Then,hollow hierarchical structure Ni Mo P@Cu₃P/CF electrocatalyst was prepared by the low temperature phosphating method.SEM and TEM confirmed this unique three-dimensional porous structure.The electronic interaction between Ni Mo P and Cu₃P had been verified by XRD and XPS.Electrochemical tests found that Ni Mo P@Cu₃P/CF had high catalytic performance under alkaline conditions.The overpotential required at 10 m A cm^-2was only 81 m V,and it could be stably on continuously electrolyzing for 12 h.3.Finally,a layer of cobalt and manganese layered double hydroxides nanorods were grown on Cu?OH?₂nanorods by hydrothermal method to prepare hollow tree-like complex structures.Then,hollow tree-like hierarchical structure Co Mn P@Cu₃P/CF electrocatalyst was prepared by low temperature phosphating.Co Mn P@Cu₃P/CF exhibited high-efficiency and stable catalytic performance in the alkaline hydrogen evolution process.It required a low overpotential?83 m V?at 10 m A cm^-2and a low Tafel slope(79.9 m V dec^-1)and could stable and continuous electrolysis for 10 h.