Studies On The Synthesis And Characterization Of Layered Double Hydroxides And Films Derived From Them

In this paper,we are trying to develop the application of Layered Double Hydroxides(LDHs) in electrochemistry.Based on this conception, a series of powdery LDHs nanomaterials and LDHs based nanostructured thin films have been synthesized by a variety of techniques.Structure and composition of the synthesized materials,electrode reaction mechanisms, the relationships among structure,composition and electrochemical properties of materials were characterized by means of XRD,ICP-AES, FT-IR,Raman,XPS,TG-MS,TEM,HR-TEM,FE-SEM,STM and electrochemical test.The main results are as follows:1.Co-Al LDHs have been synthesized by a method involving separate nucleation and aging steps.The effects of thermal treatment and Co/Al mole ratio on their microscopic morphology,surface area, crystal structure,and electrochemical behavior have also been investigated.The Co-Al LDHs with the Co/Al ratio of 2:1 retain a layered structure up to 160℃and the electrochemically active Co sites become increasingly exposed.This material obtained by heating at 160℃exhibited supercapacitor behavior with a high specific capacitance of 684 F·g^-1,a good high-rate capability,and an excellent electrochemical stability.This material can be used as electrode material for supercapacitors.2.Mg-Al LDH films have been fabricated by an electrophoretic deposition(EPD) method.The Mg-Al LDH nanoparticles were dispersed in pure acetonitrile medium to prepare the suspension solution.By applying a positive voltage,the positively charged Mg-Al LDH nanoparticles moved towards the conductive indium tin oxide(ITO)-coated glass cathode and deposited on it.A kind of Mg-Al LDH films can be obtained.The effects of EPD parameter, sucha as voltage,time,and suspensiosn concentration,have also been investigated.The deposition weight increases with the time for the same voltage and suspension concentration;the deposition weight increases with the EPD voltage for the same time and suspension concentration;the deposition weight increases linearly with the suspension concentration for the same votage and time.3.A novel Co-Al LDHs/multiwall carbon nanotubes(MWCNTs) composite film has been fabricated on the ITO substrate via an EPD method.EPD of two different charged nanoparticles,the positively charged Co-Al LDHs nanoparticles and the negatively charged MWCNTs,has been achieved due to the self-assembly of the Co-Al LDH nanoparticles to the surface of the MWCNTs.The further electrochemical investigations show that the composite films have better high-rate capability and longer cycle life than those without MWCNTs,which can be attributed to the adding of MWCNTs.4.A novel Zn-Al LDH nanosphere film has been fabricated on an ITO substrate using Zn-Al LDH nanosheets as building blocks via an EPD method.The morphology of the as-deposited films can be tailored by adjusting the deposition time and a Zn-Al mixed metal oxide(MMO) can be obtained by further heat treatment.We propose that the novel nanosphere microstructure results from the formation of diamond like carbon(DLC) precursor material,by electrolytic decomposition of formamide during the EPD process,which precipitates the Zn-Al nanosheets to lead to nuclei which develop into nanospheres.5.A serious of novel highly oriented and continuous LDH nanosheet thin film electrode materials have been fabricated using electrochemical active LDH nanosheets as building blocks by a simple evaporation method.The effects of varying the Al content,the film thickness,and the heating temperature on the electrochemical properties of the as-deposited Co-Al LDH nanosheet thin film electrode materials have been investigated.A thin film electrode material with a Co/Al molar ratio of 3:1,which has a large specific capacitance of 2500 F·cm^-3(833 F·g^-1),a good high-rate capability, and an excellent electrochemical stability,shows the best performance when used as an electrode material for thin film supercapacitors.The electrochemical investigations show that the electrode reaction of the Ni-Al LDH nanosheet thin film electrode material is controlled by proton diffusion and a high proton diffusion coefficient of 1.92×10^-9 cm²Â·s^-1 can be obtained.A high specific capacity of 660 mAh·g^-1 of Ni, an excellent high-rate capability,and a good electrochemical stability have also been obtained.This kind of thin film electrode material made up of Ni based LDH nanosheets may be an alternative electrode material for Ni-MH battery that can prove high energy density even at high-power specifications.