| As a kind of efficient, environmental and new energy storage elements, supercapacitors have broad application space and development prospect. Researches on preparation and performance of electrode materials are always hotspots in the field of supercapacitors. Owing to the excellent properties of graphene, it plays a positive role for the development of supercapacitor electrode materials to study composites of graphene and materials with pseudocapacitance. In this paper, graphite oxide was prepared by modified Hummers’ method, and then graphene was acquired through microwave irradiation. Based on graphene, various graphene-based binary and ternary composites were prepared by different methods. And a variety of characterization techniques and testing approaches were used to analyze structure characteristics and micro morphologies of the as-prepared composites. Moreover, electrochemical performance, such as cyclic voltammetric behaviors, charge-discharge characteristics, rate performance, electrochemical impedance spectra and cycle stability of the composites were studied.The specific capacitance of graphene prepared through microwave irradiation is 133.6 F·g-1 at a current density of 0.5 A·g-1 in KOH electrolyte. Graphene-Mn O2 composites were synthesized by pulse electrodeposition under supergravity field, with a specific capacitance of 595.7 F·g-1 and no attenuation after 1000 cycles. The important role of supergravity field in the preparation of composite materials was demonstrated. Supergravity field is very efficient for promoting mass transfer and decreasing concentration polarization during the electrodeposition process. The strength of supergravity field was controlled by the rotating speed of the equipment. With different strength of supergravity field, the morphology of Mn O2 is different, which led to the difference of electrochemical performance of the composites. It shows that Mn O2 and graphene have given full play to the synergistic effects between transition metal oxides and carbon materials. Thus, electrochemical performance of the composites was improved.Under the presence of graphene, green reductants, such as ascorbic acid, citric acid and glucose reacted with KMn O4 at relatively low temperatures, by a hydrothermal method. Different composites of graphene with bivalent or trivalent manganese compounds were acquired from different reductants, such as Mn C2O4/graphene, Mn CO3/graphene, Mn OOH/graphene and Mn O/graphene. A series of questions were discussed, including the influence of the proportion of the reaction and temperatures of thermal treatment on composition, morphologies and electrochemical performance of composites. In addition, positive effects of graphene existing in composites were analyzed on the improvement of electrochemical performance. Mainly because that graphene with excellent conductivity was used as substrates and graphene could stablilize the microstructure of composites.Different kinds of ternary composites were synthesized by electrodeposition, such as Ni(OH)2/Ni/graphene, Ni(OH)2/CNTs/graphene and PANI/Mn O2/graphene. The specific capacitance of Ni(OH)2/Ni/graphene is 2609 F·g-1. Analyses suggest that components have given full play to their advantages and effects, which promoted the electrochemical performance of composites. The specific capacitance of Ni(OH)2/CNTs/graphene composite reaches 2868.5 F·g-1. Based on researches on morphologies and mechanisms, good supercapacitive performance is due to the special 3D architecture formed by Ni(OH)2, CNTs and graphene. The ternary composite of PANI/Mn O2/graphene has more excellent supercapacitive performance than PANI/Mn O2 binary composite and pure PANI. The reason was analyzed in the paper. Graphene acts as the substrates, on which rod-like PANI with Mn O2 nano-particles growing on distributes, forming a special hierarchical structure. |
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