Preparation And Electrochemical Performance Of Graphene/Metal (Hydroxide) Oxide

Supercapacitors have been recognized as one of the key devices for rapid energystorage and delivery due to their high power density and long life cycle.Supercapacitors are used to bridge the power/energy gap between traditional dielectriccapacitors （high power output） and batteries/fuel cells （high energy density） In thisdissatation, several metal oxide/carbon based supercapacitor electrode material weredeveloped in which capacitor performance was improved by increasing theporosity/surface area and the conductivity of the electrode material. And the electrodematerials preparation, characterization and electrochemical performance weresystematic studied. The main results are as followed：（1） A easy and fast strategy was used for synthesis of Ni（OH）₂/GNS compositeby microwave heating of NiSO4·7H2O and GO. During the procedure, graphene oxidewas reduced to graphene along with Ni（OH）₂being uniformly distributed on thesurface of graphene nanosheets and then a honeycomb-like composite was formedwithout any controlling agent under microwave conditions. More importantly,Ni（OH）₂/GNS composite exhibits a high specific discharge capacitance of1823F·g^-1at0.3A·g^-1, which is higher than pure Ni（OH）^-12（1573F·g）.（2） NiO/GNS composite was fabricated through a facile microwave-assistedmethod. The product was characterized by XRD, Raman spectra, SEM and TEM. Theanalysis results have confirmed that petal-like NiO sheets are well dispersed on thesurfaces of graphene nanosheets. The as-prepared composite was electrochemicallytested by CV, GCD and EIS. The NiO/GNS composite shows a specific dischargecapacitance of799F·g^-1at0.3A·g^-1in6M KOH electrolyte. In addition, thecapacitance keeps at least about90%after1000cycles. （3） A one-step refluxing reaction was used to prepare Ni（OH）₂/GNS composite.The Ni（OH）₂and GNS were achieved simultaneously during the refluxing procedurein the presence of KOH. This method provides a facile and straightforward approachto anchor Ni（OH）₂particles onto the surface of GNS sheets. In the particle-on-sheetstructure, the aggregation or stacking of Ni（OH）₂particles are effectively preventedby GNS sheet, which maintains the active surface and leaves stable and open channelsfor ion transport. The as-prepared composite was electrochemically tested by CV andGCD test as electrode material for supercapacitors. The prepared composite exhibits abetter capacitance and the value remains1170F·g^-1when the current density increaseto3.7A·g^-1. In addition, the capacitance keeps at least about88%after1000cycles at3.7A·g^-1. The remarkable performance of the composites means that they showpromise for application in supercapacitors.（4） Ni（OH）₂/GNS composite have been successfully fabricated by a chemicalprecipitation route starting with GO, Ni（NO₃）₂·6H2O and CO（NH2）₂. The morphology,composition and microstructure of the as-obtained samples are systematicallycharacterized by XRD and FESEM. Moreover, the electrochemical performances ofcomposite was evaluated by CV and GCD. The high electronic conductivity and gooddispersive of GNS sheets can obviously enhance electrochemical properties ofNi（OH）₂. It is also found the content of GNS in composite is a key to achieve a welldispersion of composite and excellent electrochemical properties. Furthermore, thecycling test results showed that Ni（OH）₂/GNS composite exhibited cycling stabilitywith only3%decay after1000cycles.