Preparation Of Graphene/Molybdate Composites And Their Uses As Electrodes For Surpercapacitor

As Faraday electrode materials, transition metal molybdate materials are mainly based on their redox reaction to form faradaic pesudocapacitance. So when used in supercapacitors, they often exhibit high specific capacitance. But these electrode materials have volume change in redox reaction, which causes low cycle stability and low rate capability. Graphene, as a new electrode material, have high electron conductivity and large specific surface area. When graphene complexed with single electrode materials (transition metal molybdate, conducting polymer, etc.), it can act as a buffer for volume change, which can improve not only the specific capacitance of the overall electrode, but also the rate capability and the cycling performance at high current densities.In our work, we have fabricated CoMoO4·0.9H2O/rGO and NiMoO4-xH2O/rGO hybrid composites via a simple and environmentally friendly hydrothermal synthesis method. Take use of SEM and TEM to observe the microstructure of the composites, and characterise the composites by XRD, Raman, FTIR, etc. It conformes the composites are Molybdate/rGO composites.For as-synthesized CoMoO4·0.9H2O/rGO nanocomposites, at the same current density (1A/g), the specific capacitance of CoMoO4·0.9H2O/rGO is802.2F/g, while the single CoMoO4·0.9H2O was only551.1F/g. when the current density increased to30A/g, the specific capacitance retention of the composite is58.2%, while the single CoMoO4-0.9H2O is48.39%. the specific capacitance retention of the composite was84.8%after5000cycles at the scan rate of50mV/s, while the single CoM0O4·0.9H2O is only77.5%. It means compositing with graphene can not only promote the specific capacitance but also improve the rate capability and the cycling performance of the overall electrode.For as-synthesized NiMoO4·xH2O/rGO nanocomposites, at the current density of1A/g, its specific capacitance is1054.4F/g, higher than that of single NiMoO4·xH2O (925.6F/g). When the current density increased from lA/g to10A/g, the two matirials have the similar specific capacitance retention,63.23%and64.82%, respectively. After2000cycles at the scan rate of50mV/s, their specific capacitance retention are106.02%and100.67%, respectively. Their electrochemical performance shows that the compositing of graphene and NiMoO4·xH2O can improve the specific capacitance and cycle stability of the composite, but the effect is not apparent. These phenomenons attribute to the amount of graphene isn’t the optimal proportion, and the single NiMoO4·xH2O material has high electrical properties and rate capability. Thus, it still has great development space in the improvement of the specific capacitance and capacitance capability. It need further study to optimize the reaction condition.