Study on pseudocapacitance mechanism of aqueous MnFe2O4 supercapacitor

The electrochemical mechanism leading to the pseudocapacitance of MnFe2O4 in aqueous electrolyte solutions has been investigated by, in addition to electrochemical characterization, synchrotron X- ray absorption near-edge spectroscopy (XANES) and X- ray diffraction (XRD) analyses using KCl solution as the model electrolyte. The ferrite crystallites, prepared by a solution method, contain Mn and Fe ions randomly distributed over the tetrahedral and octahedral sites of the spinel structure and exhibit an average capacitance exceeding 100 F/g- ferrite. Based on the data from the in situ XANES and XRD measurements and open-circuit- potential dependence on solution pH, it is concluded that the pseudocapacitance of MnFe2O4 involves charge transfer at both the Mn- and Fe- ion sites, balanced by insertion/ extraction of proton into/ from the lattice. In addition, compared with MnO2 . nH(2)O electrode, the ferrite exhibits a far reduced, by similar to 90%, lattice expansion upon cycling. (c) 2006 The Electrochemical Society.