Fe3O4 spinel-Mn3O4 spinel supercapacitor prepared using Celestine blue as a dispersant, capping agent and charge transfer mediator

An asymmetric spinel-spinel supercapacitor is fabricated with negative and positive electrodes respectively consisting of Fe3O4 and Mn3O4 nanoparticles, where carbon nanotubes (CNT) serve as conductive additives. High performance of the individual electrodes and devices is achieved at a high active mass (AM) loading of 40 mg cm−2 of the individual electrodes. We implement a conceptually new strategy using multifunctional Celestine blue (CB) dye, which is strongly adsorbed on the spinel phases and CNT, facilitates dispersion, acts as a capping agent and allows for the fabrication of spinel decorated CNT. CB is an efficient charge transfer mediator, which allows for significant improvement of capacitive behavior. The use of CB as a charge transfer mediator allows for good utilization of capacitive properties of spinels at high AM. Mechanisms of spinel-CB-CNT interactions and charge transfer mediation are discussed. The capacitive properties of electrodes with different spinel/CNT mass ratios are tested by cyclic voltammetry, chronopotentiometry and impedance spectroscopy. The areal capacitances of 6.17 and 5.15 F cm−2 are obtained for Fe3O4 and Mn3O4 based electrodes, respectively in 0.5 M Na2SO4 electrolyte. The high capacitances are achieved for the electrodes that have low resistance. Using these electrodes, an asymmetric device is fabricated that has a capacitance of 2.41 F cm−2 in a voltage window of 1.6 V.