Preparation And Supercapacitor Properties Of Graphene-Cobalt Based Composite Materials

Supercapacitors with high power density, long cycle life and fast charging-discharging rate have increasingly attracted intense research attention in energy storage devices. According to their different energy storage mechanisms, supercapacitors usually defined into electrochemical double layer capacitors (EDLCs) and pseudocapacitors. Carbon materials are generally utilized as the electrode for EDLCs, which have a high power density with low capacitance. Among carbon materials, graphene has drawn tremendous attention as an electrode material for EDLCs owing to its unique atom-thick 2D structure and huge specific surface area, excellent electrical, perfect thermal, great mechanical strength mechanical and optical properties, high electrochemical stabilities, and can be produced on a large scale at low cost. Unfortunately, graphene nanosheets (GNs) have been hindered its practical commercial application on electrode material for its easy agglomeration. Many interleaved structures with conducting polymers or transition metal oxides/hydroxides attached to graphene have been fabricated for overcoming this problem, which can not only prevent the self-aggregation of GNs, but also enhance the specific capacitance. Among the transition metal oxides/hydroxide, Co3O4 and Co(OH)2 are promising electroactive material for supercapacitors due to its relatively low cost, high activity, superior stability, high theoretical capacitance, and environmental friendliness.In this article, GO was used as substrate to prepare graphene-cobalt based composite materials, the electrochemical properties of the composites were evaluated. The details are as follows:1. Graphene-constructed flower-like porous Co(OH)2 (GFC) composites were prepared using a one-pot hydrothermal process. The morphologies of Co(OH)2 ranged from flower petals to large flower-like microspheres. The GFC, as electrode material for supercapacitor, showed a high specific capacitance of 480 F g-1 at 1 A g-1 and outstanding cycling performance with 93.5% capacitance retained over 1000 cycles.2. We also synthesized graphene-constructed leaf-cluster Co(OH)2 (GLC) composites by one-pot hydrothermal process. The morphologies of Co(OH)2 ranged from flower-like to leaf-cluster. The GLC, as electrode material for supercapacitor, showed a high specific capacitance of 577 F g-1 at 1 A g-1 and outstanding cycling performance with 93.9% capacitance retained over 2000 cycles.3. A novel three-dimensional (3D) porous graphene/polyaniline/Co3O4 (GPC) ternary hybrid aerogels is firstly fabricated via self-assembly of graphene oxide/polyaniline (GO/PANI) by in situ polymerization and GO/cobalt salts hybrid sols through hydrothermal treatment. The 3D GPC possesses an excellent performance with high specific capacitance of 1247 F g-1 at a current density of 1 A g-1 and the capability can reach to 755 F g-1 even at 20 A g-1. Furthermore, no obvious capacitance loss is observed during 3500 cycles, indicating an outstanding cycling stability. The extraordinary electrochemical performance of the 3D GPC hybrid can be attributed to not only the high capacitance of PANI and Co3O4 with pseudocapacitive, but also the strong synergistic effect between the uniformly dispersed PANI/Co3O4 NPs and graphene aerogel.