Mn(OH)2/multi-walled carbon nanotube composite thin films prepared by spray coating for flexible supercapacitive devices

• Mn(OH)2/carbon nanotube films on flexible substrate were obtained by spray coating.
• Mn(OH)2 uniformly covers on or embeds in the carbon nanotube.
• The highest capacitance is 297.5 F/g with weight ratio of KMnO4/carbon nanotube = 1.2.

Mn(OH)2/multi-walled carbon nanotube (MWCNT) composite thin films were obtained by spray coating on flexible indium tin oxide/polyethylene terephthalate substrate. The precursors for thin film deposition were prepared by completely mixing MWCNTs and KMnO4 in deionized water. The morphological characteristics of the films were examined by field emission scanning electronic microscopy and transmission electron microscopy. Phase evolution of the thin films was characterized by X-ray diffraction and X-ray photoelectron spectroscopy. As a result of the deposition process, Mn(OH)2 did not only cover the surface of MWCNTs uniformly but also embed in MWCNTs. The capacitive properties of the thin films were investigated by electrochemical measurements and the capacitance increased as the weight ratio of KMnO4/MWCNTs increased up to 1.6. The highest specific capacitance obtained at a scan rate of 20 mV s− 1 was 297.5 F/g for the composite thin film with the weight ratio of KMnO4/MWCNTs of 1.2.