Three-dimensionally assembled manganese oxide ultrathin nanowires: Prospective electrode material for asymmetric supercapacitors

In this report, we have forwarded a noble synthesis route for the fabrication of self-supported three-dimensional networks of manganese oxide ultrathin nanowires (3D MnO₂-UTNWs) via a simple and cost-effective process for the first time. The formation of ultrathin nanowires (5 nm in diameter with several micrometer lengths) and their 3D assembly was achieved via a slow-reduction of potassium permanganate by oleylamine under constant stirring at 80 °C for 50 h. The resultant material was characterized using FE-SEM, TEM, XRD, FTIR, BET, XPS and Raman techniques. As-fabricated 3D MnO₂-UTNWs network was used as the electrode material for supercapacitor. The electrochemical studies of the material revealed an excellent electrochemical performance with a high specific capacitance of 544.7 Fg^-1 at 1 Ag^-1 and excellent life span of 86.3% after 5000 cycles. An asymmetric supercapacitor was assembled using 3D-MnO₂ UTNWs and nitrogen-doped graphene hydrogels (NGHs) as the positive and negative electrodes; respectively. The 3D-MnO₂ UTNWs//NGHs device delivered an admirable specific capacitance of 56.5 Fg^-1 at 1 Ag^-1, energy density of 21 Whkg⁻¹ at 840 Wkg^-1, and extraordinary cyclic stability of 81.3% after 5000 cycles. This method provides a novel green synthetic route to prepare 3D MnO₂-UTNWs without utilizing non-ambient reaction parameters.