Enhanced capacitor effects in polyoxometalate/graphene nanohybrid materials: a synergetic approach to high performance energy storage

A synergetic combination of a chemical redox reaction and a physical capacitor effect in one electrochemical cell is a promising route to realize both high-energy and high-power-density energy storage. In the present work, we studied the electrochemical properties of a nanohybrid system of polyoxometalate (POM) and graphene (RGO), in which individual POM molecules are adsorbed on the RGO surfaces. The molecular cluster battery (MCB) in which the POM/RGO hybrid was adopted as a cathode active material exhibited a higher battery capacity than the POM/SWNT (single-walled carbon nanotube)-MCB and the microcrystal POM-MCB. The observed capacity for the POM/RGO-MCB was found to be much larger than the theoretical one, as calculated from the redox changes in POM, indicating a cooperative enhancement of the capacitor effects of RGO, induced by the POMs on the RGO surfaces.