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

Nanostructured manganese dioxide (MnO2) is deposited on nickel foams by a hydrothermal synthesis route. As-deposited MnO2 thin films are largely amorphous. Facile post-deposition annealing significantly improves the electrochemical performance of the MnO2 thin films via changing their morphology, phase, and crystallinity. The specific capacitance of the MnO2 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 Na2SO4 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 MnO2-based electrodes enable their applications in high-performance supercapacitors.