MnPO4·H2O as Electrode Material for Electrochemical Capacitors

The preparation of MnPO4·H2O and its study as electrode material for electrochemical capacitors is reported. The charge storage mechanism is pseudocapacitive and involves insertion of hydroxyl ions into the 1D tunnels of the crystalline structure of MnPO4·H2O, that together with the diverse functional groups of this manganese phosphate allows the successive surface redox reactions. The active thickness is around 4.5 nm for one electron process. The coupled charge stored process leads to a high areal capacitance of 1350 μFcm−2. The specific capacitance is 210 Fg−1 in 3M KOH with a potential window of 0.6V and can increase up to 250 Fg−1 with a potential window of 0.9V. MnPO4·H2O-based electrodes show only a slight drop of 7% in specific capacitance in a symmetric cell configuration during the first 5000 cycles.