Controlled Synthesis and Application of Nickel-based Nanomaterials

Author:Li Zhong Li

Supervisor:zhang ya fei

Database:Doctor

Degree Year:2018

Download:16

Pages:149

Size:9084K

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The development of electric drive instead of traditional fossil fuel and exploitation of clean energy resources are effective solutions in response to the environmental and energy problems.Therefore,the research of high energy density lithium ion battery and photocatalytic water splitting hydrogen production has been of great concern.Among them,nickel based nano-compounds have been extensively investigate as lithium ion battery electrode materials and substitute of noble metals due to their high specific capacity,good catalytic performance,low cost and simple fabrication.Based on this,in present work we mainly studied the controlled synthesis of Ni and nickel based oxide and sulfide nano-compounds,and their application of one-dimensional Ni/NiO nanowires and two-dimensional NiO nanosheets in lithium-ion batteries and Ni3S2 for enhanced photocatalytic H2 production of CdS.The cyclic stability and first coulombic efficiency of NiO electrode materials were improved by Ni doping in Ni/NiO and nanocrystallization of NiO nanosheets.In addition,the photocatalytic performance of Ni3S2/CdS was enhanced about 70 times than pure CdS.Detailed research progresses are as follows:(1)Hierarchical Ni nanowires with high aspect ratio about 200 have been synthesized under chemical reduction combined with magnetic-field assitance.The as-synthesized Ni NWs have an average diameter of ca.1.5μm with dense thorns on the surfaces in the length of 500-800 nm.The formation of Ni one-dimensional structure was determined by the magnetic assembly and reaction rate according to the investigations based on series of experiments.The growth mechanism of stable Ni nanowires was clarified as the directional assembly process of Ni nucleation along the lines of magnetic force,as well as the accelerated arrangement of Ni grains promoted by the magnetic dipole interaction.The magnetic performance of Ni nanowires was influenced by shape anisotropy and magnetostatic interactions.Owing to its reduced spin disorder on the surface,Ni nanowires shows Ms of 61.3 emu/g,which is the maximum among the nickel nanostructures reported.(2)Hollow NiO nanotubes were synthesized from the oxidation of Ni NWs based on Kirkendall effect and surface diffusion mechanism.Afterwards,Ni/NiO nanocomposite was prepared under 500℃via an in-suit calcination method.The lithium storage performance of NiO was improved because Ni could promote the electrode conversion reaction and enhance the conductivity.Ni/NiO(3 at%Ni)shows an initial coulombic efficiency of 72%,higher than that of NiO(65%).Its specific capacity after 100 cycles is 439.6 mAh g-1 at the current rate of 143.6 mAg-1,higher than that of NiO(213 mAh g-1).The corresponding reversible capacity retention is31.7%.While as the Ni proportion increases,the initial capacity of Ni/NiO decreases,but the charge-discharge properties become better.Ni/NiO(9 at%Ni)shows the reversible capacity retention of 104.7%with a capacity of 481.1 mAh g-1 after 100cycles.(3)Porous NiO nanosheets with a hexagonal structure have been synthesized via a simple hydrothermal approach and subsequent high-temperature calcination.The experiments illustrate that the choice and the concentration of alkali and temprature are the key factors for the formation of?-Ni(OH)2 precursor nanocrystals.As the calcination temperature rises(300℃,500℃,700℃),the better the crystallinity and the lower the BET surface area and the larger the pore size is.It was found that NiO-500 exhibits the best electrochemical performance than NiO-300 and NiO-700,which mainly ascribes to its best co-effect from the factors mentioned above.(4)A novel structure of Ni3S2/CdS hybrid structure with enhanced photocatalytic properties has been synthesized via a hydrothermal method.The structure characterizations indicate that the Ni3S2/CdS hybrid photocatalyst has well-built heterojunction structure between the two components.Hence the charge separation was promoted remarkably.As a result,the Ni3S2/CdS composite photocatalyst exhibites an enhanced photocatalytic hydrogen production rate,which is about 70 times of pure CdS nanoparticles and 1.4 times of 1 wt%Pt/CdS.The quantum efficiency at 400 nm is 12.3%,and the prepared composite catalyst shows no obvious performance decay after 3 cycles,indicating the stability of the composite catalyst.