| Developing new clean and renewable energy to replace the fossil energy is an important way to deal with the energy crisis and environmental pollution.Among many energy solutions,hydrogen has been regarded as an efficient and clean new energy carrier due to its high energy density and environmentally benign quality.Exploration and development of sustainable hydrogen production technology is very important to hydrogen energy application.Water electrolysis technology has become an important research direction in many ways of hydrogen production due to its high efficiency,non-pollution and sustainability,and has shown a huge market application prospect.The design and development of low cost,high efficiency and stable electrocatalyst is the key to the wide application of water electrolysis technology.Transition metal compounds have attracted extensive attention due to their high catalytic activity and low cost.Their unique structural advantages and physical properties lay a foundation for the development of new electrocatalysts,and also provide a development platform for the exploration of structural optimization strategies of electrocatalyst materials.The goal of this dissertation is to realize function-oriented design of transition metal compounds based on the analyses of the restrictive factors of electrocatalytic water splitting performance,in order to achieve more efficient electrocatalytic water decomposition performance through the optimization of the structure and the regulation of the electronic structure.In this dissertation,the author highlights the function-oriented structure optimization of transition metal compounds by means of morphology control,element doping,interface engineering and recombination with highly conductive substrate,realizing the enhanced electrocatalytic performance and achieving the preparation of many transition metal electrocatalysts with high electrocatalytic activity.The optimization strategy by functional-oriented design of transition metal compounds explored in this dissertation will provides new ideas and feasible approaches for the design and development of high-efficiency electrocatalysts in the future.The details of this dissertation are summarized briefly as follows:Based on the perception for structural design and electronic structure regulation,the author has designed and prepared tungsten-doped molybdenum carbide and nitrogen-phosphorus co-doped carbon hybrid nanospheres electrocatalysts by means of polymerization and carbothermal reduction.The nanospheres morphology and carbon hybridization structure endow the electrocatalysts with unique structural advantages,which enable them to have a large number of active sites and good electric conductivity,thus endowing the catalyst with excellent electrocatalytic activity of electrocatalytic hydrogen evolution reaction.The effect of tungsten element doping in molybdenum carbide for hydrogen evolution reaction performance was systematically investigated by electrochemical performance test combined with theoretical calculation.The results reveal that tungsten doping in molybdenum carbide increase the density of electronic states and optimize the hydrogen adsorption energy by regulating the electronic structure,resulting in the improvement of electric conductivity and enhancement of the intrinsic activity of the electrocatalyst,thus generating the promotion of electrocatalytic activity of molybdenum carbide electrocatalyst for hydrogen evolution reaction.The molybdenum tungsten carbide electrocatalyst with structural design and electronic structure regulation requires only 133 mV overpotential to drive the current density of 10 mA cm-2,and exhibits a small Tafel slope(65 mV dec-1)and good electrochemical stability.The synthesis method of hybrid nanospheres and the regulation mode of element doping will provide a feasible reference for the function-oriented design of high efficiency electrocatalysts in the future.Based on the understanding of the synergistic regulation between the active site and the electric conductivity,a novel Ni-Co selenite nano-mesh electrocatalyst vertically grown on a highly conductive nickel foam substrate was prepared by gentle one-step electrodeposition.The porous nanomesh structure has larger specific surface area and feasible ion permeation channels,which is conducive to the exposure of more active sites.The cross-linked structure of nano-mesh electrocatalyst provides a feasible way for electron transfer within the catalyst,and the highly conductive nickel foam substrate helps to enhance the charge transfer between the electrode and the catalyst,thus ensuring the rapid electron transfer in the catalytic reaction process.The hierarchical porous structure provides sufficient buffer space for the volume change of the catalyst and feasible paths for gas release during the electrocatalytic reaction process,endowing the electrocatalyst excellent electrochemical stability.In addition,electrochemical experiment measurements and theoretical calculations show that the synergistic effect of Ni-Co bimetallic can effectively reduce the band gap of the electrocatalyst and improve the electric conductivity,which leads to the electrocatalytic activity improvement of electrocatalyst for oxygen evolution reaction.The novel Ni-Co selenite electrocatalyst synergistically optimized with active site and electric conductivity exhibits excellent electrocatalytic activity and excellent stability for oxygen evolution reaction.The optimization strategy of synergistic modulation of active site and electric conductivity offer new insight in the development of novel high efficiency electrocatalysts.Based on the exploration of structure regulation and interface effect,the author has designed and prepared the nitrogen doped carbon nanorods and Ni-Co phosphide composite materials vertically grown on carbon cloth via continuous electrodeposition and high temperature calcination processes.The introduction of nitrogen doped carbon nanorods implements more exposure of active site by increasing the dispersivity of the metal phosphide,and promotes electron transfer in the electrocatalytic reaction process by building highly conductive electron transfer channels,demonstating that the structure regulation method can realize the increase of the number of active sites and the improvement of electric conductivity at the same time.In addition,the interfacial effect between nitrogen-doped carbon nanorods and Ni-Co phosphide effectively regulates the hydrogen binding strength on the surface of the catalyst,thus improving the intrinsic activity of the electrocatalyst.After structural adjustment and effective interface construction,the composite electrocatalyst showed outstanding electrocatalytic activity for hydrogen evolution reaction and oxygen evolution reaction.The voltage required to drive the current density of 10 mA cm-2 for overall water splitting was only 1.62 V,meanwhile the electrocatalyst also showed excellent electrochemical stability.The structure regulation method of nitrogen doped carbon nanorods support and the optimization strategy of effective interface construction provide a feasible way for the design and optimization of high efficiency electrocatalysts in the future.The function-oriented design and regulation of transition metal compounds were carried out by the author via a variety of structural optimization methods,realizing the increases of the number of active sites and enhancement of electric conductivity of electrocatalysts,thus improving the electrocatalytic activity of electrocatalysts.The function-oriented optimization strategies developed in this dissertation provide a feasible reference and theoretical guidance for the design and optimization of high-efficiency electrocatalysts in the future.The electrocatalysts prepared by the function-oriented regulation show high electrocatalytic avtivity and excellent stability,making them promising substitutes for noble metal electrocatalysts,and providing a feasible electrocatalysts supply for the development of water electrolysis technology. |
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