Preparation Of Nanometer Nickle And Copper Base Supercapacitor Electrode Materials With The Diffusion Method

As a novel energy storage device,there are broad application prospects for supercapacitors in many fields owing to their high power density,long and stable cycle life,environmental benignity and mini-mal safety concerns.The electrode is an important component of supercapacitor,and electrode material is an important component of construction of electrodes.Therefore,the development of electrode materials with excellent electrochemical performances plays an important role in the development of supercapacitors.As a supercapacitor electrode,owing to small scales and higher specific surface area,the nanomaterials can shorten transport pathways of electrons and ions,enhance electrochemically active sites,improve ion adsorption and faster surface redox reactions,and the high freedom can reduce volume expansion during the process of ions adsorption/dissociation to enhance the structural stability of the electrodes.At present,there are many methods for synthesis of nanomaterials.However,most of them require complex operations,expensive equipment,harsh reaction conditions,and it is also difficult to rule out impurities.In this thesis,we have developed a novel ion diffusion method controlled by ion exchange membrane in an innovative way.We have synthesized nickel and copper based nano compounds by this method,and researched them as supercapacitor electrode materials.We have also prepared nickel based supercapacitor electrode materials with the traditional gas-liquid method and also researched growth mechanism of Ni?OH?₂ nanocrystals.The main research content and results in this paper are as follows:?1?The Ni?OH?₂ nanocrystals were synthesized by a gas-liquid method and different morphologies and structures of Ni?OH?₂ nanocrystals were obtained by adjusting the concentration of the reactants.According to the supercapacitor performance test results,the hierarchical spherical morphologies of Ni?OH?₂facilitated the electrolyte ion adsorption and diffusion and exhibited excellent supercapacitor performance.At a concentration of 0.1 mol L^-1 NiSO₄,the obtained Ni?OH?₂ electrode materials exhibited the largested specific capacitance of 1799 F g^-1at a current density of 4 A g^-1.It can retain 92.8%of the initial capacitance after 2000cycles at 4 A g^-1.The evolution of morphology and structure for Ni?OH?₂ nanocrystals with the reaction time was also investigated and the growth mechanism of Ni?OH?₂nanocrystal was discussed.?2?The Ni?OH?₂ nanocrystals with high purity were synthesized by a novel ion diffusion method controlled by ion exchange membrane under the condition of water bath heating.The different morphologies and structures of Ni?OH?₂ nanocrystals were obtained by controlling water bath heating temperature and reaction time.The study found that at a reaction condition of 50?for 12 h,the fromed Ni?OH?₂ crystals exhibited flake-like structure,higher specific surface area and larger pore size.These features can greatly enhance the contact area of the electrode-electrolyte,improve the transmission efficiency of electrons and ions,and therefore enhance the charge storage capacity.The material exhibited the largested specific capacitance of 2102 F g^-1 and can retain 85.1%of the initial capacitance after 1000 charge-discharge cycles at the current density of 4 A g^-1.?3?Based on the previous experiments,the Ni?OH?₂ precursor was synthesized by an ion diffusion method controlled by ion exchange membrane.The three NiO nanocrystals were successfully prepared by calcinating Ni?OH?₂ precursor at 400,500and 600?for 2 h respectively.It is harder for nickel atoms of NiO nanocrystals with lower binding energy to capture OH^-in the electrochemical redox reactions compared to Ni?OH?₂ materials,which decreases the utilization of active material,leading to the specific capacitance of NiO reduces obviously.Among the three NiO samples,the NiO sample obtained at 400?exhibited the largest specific surface area and owned more electrochemical active sites,leading to the largest specific capacitance of 381 F g^-1,and can retain 89.2%of the initial capacitance after 1000cycles at the current density of 2 A g^-1.The stability of NiO materials is higher than Ni?OH?₂ material.The ultraviolet visible absorption test results showed that NiO sample obtained at 400?has a broad band gap of 3.3 eV.With the increase of calcination temperature,the crystallinity of NiO samples strengthened,leading to a redshift of absorption peak for the three NiO samples and narrowed band gap.?4?Via a facile gas-liquid synthesis from nickel acetate and ammonia with sodium dodecyl sulfate?SDS?and 2-polymer sodium naphthalene sulfonate formaldehyde?NNO?as the crystal growth regulator respectively it is possible to obtain the Ni?OH?₂precursors of various morphologies depending on the structures and concentrations of surfactants.The two Ni?OH?₂ precursors were synthesized with SDS concentration of2 g L^-1and NNO concentration of 2.5 g L^-11 respectively and the two NiO samples with different morphologies were prepared by calcinating Ni?OH?₂ precursor at 400?for2 h.For the comparison,the NiO sample was also prepared at the same reaction condition without the addition of surfactants.The electrochemical test results showed that both the two NiO samples with the addition of surfactants exhibited higher specific capacitance owing to the higher binding energy.It is easier for NiO samples with higher binding energy to capture OH^-ions in the electrochemical redox reactions,which increases the utilization of active material,leading to the specific capacitance of NiO increases obviously.The obtained NiO sample assisted by SDS surfactant exhibited the highest specific capacitance of 922 F g^-1 at a current density of 2 A g^-1and can retain 89.1%of the initial capacitance after 1000 cycles.The X-ray photoelectron spectroscopy?XPS?results showed the nickel atoms of NiO nanocrystals prepared with the addition of the crystal growth regulator owned higher binding energy and it was speculated that this was one of important reasons for the mareials with excellent electrochemical performances.?5?The CuO nanocrystals were synthesized directly by the ion diffusion method controlled by ion exchange membrane.The different morphologies and structures of CuO nanocrystals were obtained by controlling water bath heating temperature.The study found that at a reaction condition of 50?for 12 h,the fromed CuO crystals was pure and exhibited fragmental morphology and the highest specific surface area.The material exhibited the largested specific capacitance of 138 F g^-1 and the capacitance loss was only 8.2%after 1000 cycles at the current density of 1 A g^-1.