Design, Synthesis And Electrochemical Performance Of Manganese Compounds/3D Graphene

Chemical capacitor, which is also called supercapacitor, is a new kind of energy storage system. It has the advantages of faster charge and discharge performance, better cycle stability, high power density, environment friendly, wider working temperature range, et al. According to the charge storage mechanism, supercapacitors are generally classified into three types: electrochemical double layer capacitors(EDLCs), pseudocapacitors and asymmetric supercapacitors. The electrode materials usually are metals oxides, carbon materials, conductive polymers and their composite materials. 3D-rGO has been proved to be a good candidate for supercapacitor electrode materials, because it's large accessible surface areas and multilevel pore structure. Manganese oxide or hydroxide has low cost and good pesudocapacitor performance, but the weaker electronic conductivity leading to lower active material utilization. Therefore, 3D-rGO and manganese oxide or hydroxide composite material are expected to produce a composite electrode with good electrochemical performance. The main points of this paper are summarized as follows:1. Nanoporous 3D graphene was fabricated by using NH2-SiO2 particles as a sacrificial template. For further capacitance boost, MnO2 was additionally deposited onto the nanoporous 3D graphene through the reaction KMnO4 and graphene by hydrothermal method. The XRD, CV, GCD results show us that when the hydrothermal reaction temperature reaction time is 3h, we can get MnO2/3D-G-3 which showed better electrochemical performance. The excellent properties of the synthesized MnO2/3D-G-3 material have been investigated by XRD, FESEM, XPS and electrochemical properties tests. The formation of nano MnO2 powders on the surface of the nanoporous 3D graphene have been confirmed by the all results of XRD, FESEM and XPS. The specific capacitances of the MnO2/3D graphene are 310 F/g at the current densities of 0.5 A/g in 1.0 M Na2SO4 electrolyte. After 1000 cycles, the specific capacitance retention is about 88.3 %.2. A manganese oxyhydroxide/three-dimensional reduced graphene oxide(MnOOH/3D-rGO) composite was prepared by a two-step hydrothermal procedure.The SEM, CV, GCD results show that when mMn2+/mGO is 20%, we can get MnOOH/3D-rGO which showed outstanding electrochemical performance.The excellent structure of the MnOOH nanoneedles(with 1 mm in length and 15~20 nm in width) grow on the 3D-rGO skeleton have been verified by the all results of XRD, FESEM, TEM and XPS. Electrochemical performance measurements indicated that the specific capacitance of MnOOH/3D-rGO-20 was 327, 273, 242 and 200 F/g at the current density of 0.2, 0.5, 1.0 and 2.0 A/g, respectively. In addition, the capacity attenuation rate of 3.3 % after 1000 cycles at the current density 1 A/g. The asymmetric supercapacitors made with MnOOH/3D-rGO and activated carbon exhibit excellent performances in energy storage. At a power density of 378 W/kg, the devices can deliver a maximum energy density of 52.7 Wh/kg.