The Exploration Of Nickel Cobaltite With Oxygen Vacancies And The Preparation Of Flexible Nickel-hemp Capacitor

For a long time,the energy problem is the sword of Damocles which hanging on all human beings.Especially,in recent years,the energy crisis has become increasingly prominent.Among kinds of energy devices,electrochemical capacitor which owns high power output,excellent power utilization,long cycle life and reliable performance has been inspired the people's research enthusiasm.Nickel cobalt compound,as a type of representative electrochemical capacitor active material,has large capacitance and excellent cycle performance.More oxygen vacancies are introduced into nickel cobaitite to further improve the capacitance and conductivity.After that,we prepared novel flexible nickel hemp substrate which owns high conductivity and excellent mechanical strength and applied this novel substrate in electrochemical capacitance application.Specific contents are as follows:(1)In this paper,to explore the electrochemical influence of the oxygen vacancy in NiCo2O4 material,we introduced more oxygen vacancies into NiCo2O4 electrode with different nanostructures.NiCo2O4 nanosheet electrode and NiCo2O4 nanowire electrode were prepared by electrodeposition and hydrothermal method,respectively.Then,both electrodes were soaked into NaBH4 solution to increase oxygen vacancies in active materials.Oxygen vacancies,as the intrinsic defects in metal oxides,have a closely relationship with materials' conductivity.Electrochemical data show increasing oxygen vacancies in NiCo2O4 can significantly improve its specific capacitance.Specifically,at the current density of I A/g,the soaking reduction caused the specific capacitance of NiCo2O4 nanosheets electrode improved from 945 F/g to 1375 F/g and the NiCo2O4 nanowire electrode capacity was improved from 863.3 F/g to 1163 F/g.After 10000 cycles,the capacitance retentions of the NiCo2O4 nanosheets electrode and the reduced NiCo2O4 nanosheets electrode are 79.16%and 76.92%,respectively.Besides,after 5000 cycles,the capacitance retention of the NiCo2O4 nanowires electrode and the reduced NiCo2O4 naonwire electrode are 84.90%and 85.56%respectively.These data show the method of increasing oxygen vacancies in NiCo2O4 is an effective method to improve the capacitance ability.It is a useful method for prepare better electrochemical capacitor material.(2)Ramie fiber is a kind of natural organic material with wide source and low price.In this paper,the two step nickel plating method was used for the first time on the natural ramie fiber(the two steps nickel plating including electro-less plating and electro-deposition)to prepare the nickel ramie fiber substrate.Compared with metal,the nickel hemp fiber has same conductivity but better folding resistance ability.Then,the Ni-Co hydroxyl carbonate was grown directly on the substrate by hydrothermal method to prepare flexible electrode.This electrode shows a high capacitance of 1258 mF/cm at a current density of 1 mA/cm.Due to there is no high-temperature process,this kind of electrode can maintain good flexibility and excellent mechanical strength.Besides,the non-toxic Ni-Co hydroxyl carbonate guarantees the electrode is safe for users.This kind of electrode owns a certain degree commercial potential.To sum up,the method of introducing more oxygen vacancies in NiCo2O4 makes the capacitance of NiCo2O4 material has been significantly improved.Besides,nickel hemp fiber,which owns high conductivity and folding resistance,is an excellent substrate.Both works mentioned above have certain application value in electrochemical capacitor.