Synthesis and Characterization of Functional Nanomaterials and Their Application for Hydrogen Evolution Reaction

Author:Li Qun

Supervisor:yang xiu rong

Database:Doctor

Degree Year:2019

Download:214

Pages:130

Size:16195K

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With excessive consumption of fossil fuels and accompanying environmental crises,the renewable and green energy have attracted increasing attention.Globally,measures are taken to exploit various clean energy resource such as solar,ocean and wind.Nevertheless,the discontinuity of these new energy sources in time and space becomes a significant bottleneck for further improve their utilization efficiency.Converting these renewable energy sources into easily stored and transported chemical energy is therefore one of the most effective measures.Currently,the electrolysis of water is widely used in new energy conversion system,which can be used to transform electric energy into high energy density hydrogen energy.In practice,however,the energy conversion efficiency of commercial electrolysis equipment is only about 56-73%.In order to reduce the energy waste caused by the high cathode overpotential,exploiting the highly active and stable electrocatalyst for hydrogen evolution reaction(HER)is of paramount importance.Although Pt-group materials are still the most effective electrocatalysts for HER,the scarcity and high cost greatly hamper their large-scale practical application.Recently,high performance and low-cost nanomaterials have attracted intense attention.In the thesis,we focused on the synthesis,characterization,and applications of these functional nanomaterials.The main points of this thesis include following three aspects:1.Cobalt phosphide nanoparticles film was developed on carbon cloth(CoP NPs/CC)through a facile two-pot thermal decomposition strategy with cobalt chloride hexahydrate and sodium hypophosphite as precursors.The direct growth of CoP NPs on the flexible and conductive CC substrate enables intimate contact and facilitate to increase the electrochemical surface area and loading amounts of active CoP NPs.In addition,the uniformly dispersed CoP NPs on the carbon cloth substrate can effectively avoid the mutual accumulation and covering of active sites.The CoP NPs/CC electrode exhibits high performance and long-term stability.CoP NPs/CC electrode shows high performance with a low onset overpotential of 33 mV,and a high Faradaic efficiency of nearly 100%,CoP NPs/CC can maintain its high catalyic activity at least for 30 h and with only slight degradation.Furthermore,we also investigated the influence of CoP loading on catalytic performance by changing the concentration of cobalt chloride hexahydrate in the ink.2.We reported the development of nitrogen-doped carbon-coated tungsten oxynitride(WON@NC NWs/CC)and bromine,nitrogen-codoped metallic tungsten(W/BrN NWs/CC)nanowire arrays on carbon cloth by annealing the WO3 NWs/CC nanowire arrays precursor by using dicyandiamide and ammonium bromide as doping agent,respectively.The analyses show that doping of nonmetallic elements plays a significant role in regulating the electronic structure of tungsten-based nanomaterials.In WON@NC NWs/CC system,the coating of carbon layer is beneficial to improve the stability of WON NWs/CC core.In addition,nitrogen doping into the carbon layer can improve the hydrophilicity,conductivity and catalytic activity of carbon shell.In the W/BrN NWs/CC system,the doped non-metallic elements can optimize the active sites of tungsten through the electron transfer process,which is conducive to improving the catalytic activity of W/BrN NWs/CC.The electrochemical activity test show both WON@NC NWs/CC and W/BrN NWs/CC reveal high HER activity at all pH values,suggesting the non-metallic doping has a significant effect for the improvement of the HER activity of tungsten-based materials.3.We reported thermally prepared heterostructure nanomaterials,containing CoMn-S@NiO/CC,NiS/NiS2,and RuO2/SrRuO3.Firstly,the nature of the lattice mismatch between multicomponent nanomaterial result in the tensile or compressive strain on the interface of heterostructure,which is conducive to increase the disorder of the multicomponent material as well as create more active catalytic sites.Secondly,the close bonding of different lattices at the heterogeneous interface lead to the strong interactions between the two components,which greatly affects the surface energy at the heterogeneous interface.In addition,the interaction between multiple components can also significantly optimize the active sites of each component near the heterogeneous interface.All the heterostructure materials show substantially better HER activity than that of the corresponding single-component catalysts.The analyses indicate that the positive synergistic interplay between different components in producing a favorable atomic and electronic structure that enhance the energetics for HER.