Porous manganese oxide generated from lithiation/delithiation with improved electrochemical oxidation for supercapacitors†

For manganese oxides with low manganese oxidation states, such as MnO or Mn3O4, the electrochemical oxidation during potential cycling is critical to achieve high supercapacitor performance. In this work, dense Mn3O4 thin films are prepared by pulsed laser deposition. An electrochemical lithiation/delithiation process is applied to the Mn3O4 thin film, which leads to a nanoporous structure of the film and greatly increases the porosity of the film. The nanoporousMnOx thin film electrode exhibits significantly improved supercapacitive performance compared to the asprepared Mn3O4 thin film electrode. After 1000 cyclic voltammetric scans in 1 M Na2SO4 electrolyte between 0 and 1 V, only part of the surface of the as-prepared Mn3O4 thin film transforms into aMnO2 porous structure while the complete film of the nanoporous MnOx transforms into a MnO2 porous structure. It is believed that the nanoporous structure, which facilitates the electrolyte penetration, leads to the completion of electrochemical oxidation through the film during the potential cycling, resulting in promising supercapacitive performance of the film.