A modified hydrothermal route for preparing γ-MnOOH nanorods and its isomorphous conversion to α-MnO2 with inherited morphology for remarkable performance supercapacitors

Currently it is a huge challenge in preparing inorganic nanomaterials with special morphology. In the present work, nitrilotriacetic acid is firstly introduced to prepare γ-MnOOH nanorods with approximately 15 nm in diameter and 100 nm in length. α-MnO2 with the inherited morphology is also obtained under calcination at 400 ℃. The structures of the resultant samples are analyzed by several techniques in detail. When investigated as the electrode of supercapacitors, both nanorods deliver the satisfied electrochemical performances including high specific capacitances, excellent capacitance retentions and kinetics, which can be attributed to the unique nanorods structure providing short distance for ionic/electron diffusion and lower strain relaxation. Moreover, the asymmetric supercapacitors made by applying activated carbon as negative electrode exhibit the maximum energy/power densities with 30.5 Wh kg−1/0.7 kWh kg−1 for γ-MnOOH nanorods and 18.2 Wh kg−1/0.5 kWh kg−1 for α-MnO2 nanorods, respectively, demonstrating a promising application in supercapacitors.