Microstructure and properties of manganese dioxide films prepared by electrodeposition

Nanostructured manganese dioxide films were obtained by galvanostatic, pulse and reverse pulse electrodeposition from 0.01 to 0.1 M KMnO₄ solutions. The deposition yield was investigated by in situ monitoring the deposit mass using a quartz crystal microbalance (QCM). Obtained films were studied by electron microscopy, X-ray diffraction analysis, energy dispersive spectroscopy, thermogravimetric and differential thermal analysis. The QCM and electron microscopy data were utilized for the investigation of deposition kinetics and film formation mechanism. It was shown that the deposition rate and film microstructure could be changed by variation of deposition conditions. The method allowed the fabrication of dense or porous films. The thickness of dense films was limited to ∼0.1 μm due to the insulating properties of manganese dioxide and film cracking, attributed to drying shrinkage. Porous and crack-free 1-2 μm films were obtained using galvanostatic or reverse pulse deposition from 0.02 M KMnO₄ solutions. It was shown that film porosity is beneficial for the charge transfer during deposition and crack prevention in thick films. Moreover, porous nanostructured films showed good capacitive behavior for applications in electrochemical supercapacitors. The porous nanostructured films prepared in the reverse pulse regime showed higher specific capacitance (SC) compared to the SC of the galvanostatic films. The highest SC of 279 F/g in a voltage window of 1 V was obtained in 0.1 M Na₂SO₄ solutions at a scan rate of 2 mV/s.