Preparation Of Nitrogen-Doped Reduced Graphene Oxide/metal Compound Electrode Materials And Studies Of Their Electrochemical Properties

Electrode materials, as the crucial components of supercapacitors, have been the research hotspot in the field of supercapacitors. Currently, the electrode materials mainly contain carbon materials, metal compounds and conducting polymers. Because various electrode materials have their own advantages and disadvantages, combination of electrode materials can adopt their strong points and overcome their weak points to achieve the optimization of electrochemical performance. Graphene, owing to its superior chemical and physical properties, have attracted much attention in the fields of material and chemistry since it was discovered. Nitrogen doping for graphene can modulate its electronic structure, effectively enhance its properties, and broaden its practical application in supercapacitors. Therefore, nitrogen-doped graphene-based composite materials supply a possibility for improving the performance of supercapacitors.This paper aimed at preparing various nitrogen-doped reduced graphene oxide/metal compound composite electrode materials based on the interaction between nitrogen-doped reduced graphene oxide and metal compound to meet the need of supercapacitors with high capacitance via using low-cost raw materials and easy hydrothermal method. The formation mechanisms of composite electrode materials were explored, and the influences of chemical constitutions, structures and morphologies on electrochemical performances were investigated.The research contents of this paper were as follow:(1) Nitrogen-doped reduced graphene oxide/nickel hydroxide(N-RGO&Ni(OH)2)composite was prepared by two-step hydrothermal method, where nickel acetate and urea served as nickel source, reducing agent and nitrogen source. Detailedly, N-RGO was first synthesized,and then served as the carrier for Ni(OH)2. The structure, composition, morphology and electrochemical property of N-RGO&Ni(OH)2 were analyzed. Moreover, the formation mechanism of the morphology of composite by nitrogen doping was explored. The results showed that N-RGO had less oxygen-containing functional groups, which caused the number of nuclear centers for Ni2+was reduced and more Ni2+was consequently absorbed on less nuclear centers. As a result, the three-dimensional flower-like structure of N-RGO&Ni(OH)2 was formed through self-assembly. With the three-dimensional flower-like structure and the synergistic effect between N-RGO and Ni(OH)2, N-RGO&Ni(OH)2 composite showed excellent electrochemical performance.(2) Nitrogen-doped reduced graphene oxide/nickel hydroxide(N-r GO&Ni(OH)2) composite electrode material was synthesized in situ by one-step hydrothermal method, where urea and nickel acetate served as nitrogen source and nickel source. The formation mechanism of composite electrode material was explored. In addition, the composition, structure, morphology and electrochemical performance were investigated. The experimental results showed that the reduction and nitrogen doping of graphene oxide and the formation of Ni(OH)2 were achieved simultaneously under the hydrothermal condition. With the effect of nitrogen doping, the nitrogen-doped site, especially the pyridinic site could act as active site, which enhanced the interaction between N-r GO and Ni(OH)2, leading to the better dispersion of Ni(OH)2 with smaller size and the tighter contact between N-r GO and Ni(OH)2. As a result, the synthesized N-r GO/Ni(OH)2 electrode displayed superior electrochemical performance, including high capacitance, excellent rate capability and good cycle life.(3) Nitrogen-doped reduced graphene oxide/iron oxide(N-r GO/Fe2O3) composite material was prepared via one-step hydrothermal method, where urea served as nitrogen source, reducing agent and precipitant and iron nitrate acted as iron source. The results showed that Fe2O3 nanoparticles with sizes of ca. 30-40 nm were tightly contacted on the surface of N-r GO. The electrochemical tests indicated that N-r GO/Fe2O3 electrode had better electrochemical properties than r GO/Fe2O3 electrode, which could be ascribed to the positive synergistic effect between N-r GO and Fe2O3.