Improvement of hydrothermally synthesized MnO2 electrodes on Ni foams via facile annealing for supercapacitor applications

Nanostructured manganese dioxide (MnO 2 ) is deposited on nickel foams by a hydrothermal synthesis route. As-deposited MnO 2 thin films are largely amorphous. Facile post-deposition annealing significantly improves the electrochemical performance of the MnO 2 thin films via changing their morphology, phase, and crystallinity. The specific capacitance of the MnO 2 electrode increases with the annealing temperature and reaches an optimal value of 244 F g −1 (at the current density of 1 A g −1 ) in a neutral 1 M Na 2 SO 4 electrolyte for a specimen annealed at 500 °C. Furthermore, when an alkaline 5 M KOH electrolyte is used, an exceptionally high capacitance of 950 F g −1 is achieved at the current density of 2 A g −1 . The cost-effective facile synthesis, high specific capacitance, and good cycle stability of these MnO 2 -based electrodes enable their applications in high-performance supercapacitors.