Facile chemical synthesis of nanoporous layered δ-MnO2 thin film for high-performance flexible electrochemical capacitors

Layered delta-MnO2 thin films with a three-dimensional nanostructure are successfully fabricated on stainless steel foil substrates for flexible electrochemical capacitors by a facile and effective chemical bath deposition technology from ethanol and potassium permanganate solution at 15 degrees C. The as-prepared thin films display nanoporous morphology and a water contact angle of 20 degrees. Energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analyses reveal that the thin films are composed of delta-MnO2. Electrochemical data demonstrate that the delta-MnO2 thin film electrodes can deliver a high special capacitance of 447 F/g at 2 mV/s, and provide a good capacitance retention ratio of 87% after 1000 continuous cycles at 10 mV/s in 0.5 M Na2SO4. Compressive and tensile bending tests show that the as-prepared electrodes can steadily work over a wide range of applied curvatures between -2.5 cm(-1) (tension) and 2.5 cm(-1) (compression). Only a small decrease in special capacitance (0.9% at a curvature of 2.5 cm(-1) under compressive strain, or 1.2% at a curvature of -2.5 cm(-1) under tensile strain) is observed even after bending for 200 cycles, indicating the excellent mechanical flexibility and electrochemical stability of the delta-MnO2 thin film electrodes. (C) 2013 Elsevier B.V. All rights reserved.