Nickel Based Nanoparticles Modified Three-Dimensional Graphene Materials For Supercapaciotrs

Supercapacitors with high energy density and power density,as a new type of energy storage devices,have a greater application prospect than traditional capacitors,among which the performance of supercapacitors of graphene-based electrode materials-is particularly prominent.The three-dimensional graphene hydrogel is not only easily to be synthesized,but also has high specific surface area,and more importantly,it can be directly used as a binder-free electrode of the supercapacitors.The three-dimensional graphene hydrogels can be prepared directly by a mild method using ascorbic acid as reducing agent in water bath.Next,nanoparticles of metal compounds on graphene hydrogels has been prepared,introducing pseudo-capacitance for the electrode,and enhanced the conductivity of electrode materials.The specific capacitance of the three-dimensional Ni?OH?₂/rGO hydrogels prepared by the hydrothermal method is as high as 532 F g-1 in the three electrodes,and the pseudo-capacitance corresponding to the redox peak of Ni?OH?₂ appears in the CV curve.Comparing with rGO hydrogels,the rate performance and conductivity of Ni?OH?₂/rGO hydrogels are improved.The integration and electrochemical performance of Ni?OH?₂/rGO hydrogels assure the application of supercapacitors.Ni?OH?₂/rGO||rGO asymmetric supercapacitors are assembled.The highest specific capacitance of this capacitor in the voltage window of 0-1.5 V is 125 F g-1,and the highest energy density and power density are 28.88 W h Kg-1 and 5829.2 W kg-1,respectively,and the capacitance retention rate after 10,000 cycles is still 90%.In Chapter 3,we prepared the nickel sulfide hydrogel by a one-step water bath method using nickel nitrate and sodium sulfide as the nickel source and the sulfur source,respectively.Finally,two pairs of redox peaks in the CV curve were found in the electrochemical tests.TEM,Raman and XPS studies also demonstrated the successful preparation of three-dimensional nickel sulfide graphene hydrogels.The symmetric supercapacitor assembled with the nickel sulfide hydrogels has specific capacitance of 539 F g-1 and excellent electrochemical performance.In the fourth chapter,the self-restriction of atomic layer deposition?ALD?technique and deposition on the carriers of large specific surface area were used.Graphene oxide was used as the carrier and the metal source was nickel ferrocene to prepare NiO/rGO materials.The effect of deposition temperature and number of cycles on the material properties.The results revealed that the electrochemical performance of the NiO/rGO material with three cycles at 250? is the best,and the specific capacitance is as high as 1139.2 F g-1 when the current is 3 mA,is asuitable choice as the electrode material of supercapacitor.