Synthesize, Characterization And Performance Of Transition Metal Oxide For Supercapacitor Application

Due to the development of technology and society, energy issue is becoming moreand more important. Electrochemical capacitor, a energy storage and convert devicewith high power density, long cycle life, is gaining more and more attention aroundthe world. As complementary device for battery, supercapcitors overcome thedisadvantage of battery by delivering large amount of energy with a short time span,thus make electrical energy meet with more practical application. According to theenergy storage machnism, electrochemical capcitor can be divided into two classes:EDLCs and pseudocapacitors. In this article we mainly study the synthesis,characterization and performance of transition metal oxides as electrode materials forpseudocapacitors. Our works are concluded as follows:(1) One dimensional (1D) tubular Ag/MnOxnanocomposites of various morphologyare synthesized by solvothermal method via redox reaction of potassiumpermanganate with Ag nanowire templates at defferent pH level of7.00and0.76.According to XRD, SEM, TEM, BET characterizaition, the Ag/MnO2nanotubes withdiameter of around160nm and interior diameter of around120nm, which obtainspecifc surface area (SSA) of26m2/g, are prepared under neutral environment (pH=7.00); while1D hierarchical Ag/MnOxnanostructure consisted of nanosheets withdiameter of around490nm, which obtain108m2/g of SSA, are yielded under acidicenvironment (pH=0.76). When tested in three-electrode system, the Ag/MnO2nanotube and the hierarchical Ag/MnOxnanosheet-nanotube composites exhibitspecific capacitance of135F/g and180F/g at current density of0.1A/g, and stillmaintained specific capacitance of20F/g and130F/g at current density of5A/g. Thetwo kinds of material with different morphology maintain above80%of the initialcapacity after1000cycles at current density of1A/g.(2) Green (Co, Ni) hydroxide is firstly synthesized via a facial process ofelectrodeposition conducted in Ni(NO3)2, Co(NO3)2and NH4NO3solution. ThenNiCo2O4electrode material is yielded after the heat treatment of the precursor. Sincedeposition conditions would affect the growing process of the nanosheets, series ofconcetration-dependent and time-dependent experiments are carried out in order tofind out the optimized deposition condition and the growing machanism of theelectrode material during the electrodeposition process. According to SEM, TEM characterization, the as-prepared electrode material is comsisted of layer withthickness of0.78μm-6.80μm and NiCo2O4nanosheets with length of56nm-1100nm. The as-prepared samples are tested as electrodes for supercapacitors, and theoptimal electrochemical performance is acheived by sample with5.36μm thicknessof layer and600-1100nm length of nanosheets. The sample exhibit2.34F/cm2at1mA/cm2and maintain1.00F/cm2at15mA/cm2. The cyclic stability of the electrodeis also tested under current density of5mA/cm2, and70%of initial capacitance ismaintained after4000cycles.