Synergy of Charge Storage Properties of CuO and Polypyrrole in Composite CuO-Polypyrrole Electrodes for Asymmetric Supercapacitor Devices

This investigation is motivated by interest in the redox properties of CuO for energy storage in supercapacitors and in the fascinating effects of charge transfer in conductive polymer–metal oxide composites on their physical and chemical properties. Various challenges are successfully addressed, such as efficient utilization of capacitive properties of charge storage materials in high active mass loading electrodes; understanding charge storage mechanisms at different electrode potentials; fabrication of anodes with high areal capacitance, which can match the capacitance of advanced cathodes; and fabrication of advanced asymmetric supercapacitor devices with high specific energy. CuO nanoparticles are prepared by hydrothermal synthesis and polypyrrole (PPy) particles are prepared by chemical polymerization for the fabrication of CuO and composite PPy-CuO anodes. An important finding is the synergistic effect of capacitive properties of PPy and CuO, which facilitates the fabrication of anodes with a record high capacitance of 7 F cm–2 in a 0.5 M Na2SO4 electrolyte. The capacitance, impedance, and charge transfer resistance of the composites are optimized by investigating electrodes with different PPy contents. The superior behavior of the composites is linked to the enhanced charge transfer, which results in a low impedance and reduced charge transfer resistance. The composite electrodes show good capacitance retention at fast charge–discharge rates and good cyclic stability. The asymmetric supercapacitor devices show high capacitance of 2.76 F cm–2 in a voltage window of 1.5 V, high energy density of 10.83 Wh kg–1, and good cyclic stability.