An investigation of chemical and electrochemical conversion of SILAR grown MnO into MnO thin films.

Manganese oxide is an interesting material for electrochemical properties. It is well known that MnO (spinel) can be electrochemically converted to MnO (birnessite) via the electrochemical route during cyclic voltammetry (CV) cycling in aqueous NaSO solution. Herein, the novel way is represented for the growth of highly adherent and compact MnO thin films by using successive ionic layer adsorption and reaction (SILAR) method. As grown MnO thin films are converted into MnO after chemical treatment by hydrochloric acid (HCl) via a disproportionate reaction. MnO thin films are converted into MnO by both chemical and electrochemical paths. During chemical conversion, at acidic pH, the crystal water insertion (HO) in MnO crystal provides the necessary driving force to transform it into MnO crystal. During electrochemical transformation, the specific capacitance was found to increase from 72 (1st CV cycle) to 393 F/g (1600th CV cycle). On the other hand, the specific capacitance was increased from 72 to 258 F/g through chemical transformation. Electrochemical and chemical conversion leads to ~5.5 and ~3.5 fold, respectively, improved supercapacitive performance than pristine MnO thin films. Both chemical and electrochemical conversion routes are extremely useful to recycle battery waste for supercapacitor applications.