Oxygen Vacancies Modulation In Manganese Oxide For High Performance Supercapacitors

With the rapid development of the global economy,problem of energy shortage has become increasingly prominent.Supercapacitors have attracted wide attention due to high power density,good rate performance and long cycle life.Manganese oxide has become very promising electrode materials for metal oxide due to high theoretical capacity,low cost,and environmental friendliness.In this dissertation,mixed-valence manganese oxide with oxygen vacancies was prepared by different methods to further improve the electrical properties of manganese oxide.The following conclusions were obtained:(1)An efficient and scalable method to improve the capacitive properties of MnO2 is reported by inducing graphene(rGO)and oxygen vacancies via a thermal treatment in air,in which graphene oxide(GO)is in situ reduced and graphene/MnOx(rGO/MnOx)composite is formed.RGO/MnOx composite exhibits a large specific capacitance(274 F g-1 at 0.5 A g-1)and excellent cycling stability(98.8%after 5000 cycles at 1 A g-1).The performance improvement of rGO/MnOx sample is mainly attributed to the moderate concentration of oxygen vacancies,rGO and special 3D porous architecture,which facilitate the rapid ionic and electronic transport and promote a facile redox reaction and surface double-layer capacitance.The asymmetric supercapacitor composed of rGO/MnOx//Kochen Black(KB)also shows an outstanding cyclic stability(89%after 5000 cycles)in all-solid-state asymmetric supercapacitor.(2)An effective strategy to intrinsically improve the conductivity and capacitive performance of MnO2 is reported by inducing oxygen vacancies via a simple thermal treatment in air,Ar or Ar/H2.MnOx-Ar delivers significantly improved electrochemical performance than MnOx-Ar and MnOx-H2.The specific capacitance of MnOx-Ar is 339 F g-1 at a current density of 0.5 A g-1.After 5000 consecutive cycles,the specific capacitance of MnOx-Ar sample shows the best specific capacitance retention(90%).The specific capacitance still maintains 88%even after 5000 cycles of the MnOx-Ar//KB asymmetric supercapacitor.The concentration of oxygen vacancies has a significant influence on the performance of manganese oxide materials.Only moderate oxygen vacancies concentration can maximize the effective active area,reduce the charge transfer resistance and improve the capacity performance of the material.(3)Another effective method to induce oxygen vacancies in MnO2 is reported by hydrogen plasma treatment.The electrochemical performance of MnO2 treated by hydrogen plasma are obviously improved.The higher output power of the plasma equipment,the better performance of MnO2.The specific capacitance of MnOx-200W sample is 300 F g'1 at a current density of 0.5 A g-1,and after 5000 consecutive cycles,the specific capacitance of MnOx-200W sample shows the best specific capacitance retention(90%).The asymmetric supercapacitor assembled by MnOx-200W//KB exhibits excellent capacitance performance.After 5000 cycles,90%of the initial specific capacitance can be maintained.