Synthesis of MnO2–chitosan nanocomposite by one-step electrodeposition for electrochemical energy storage application

• Chitosan provides a mean for assembling manganese dioxide nanoparticles into macro-scale components.
• Chitosan promotes ions and electrons transport inside the matrix of manganese dioxide film.
• Manganese dioxide–chitosan composite presents high specific capacitance, long cycle life and superior rate capability.

MnO2–chitosan hybrid nanocomposite films with low and high chitosan's molecular weights are synthesized by one-step cathodic electrodeposition on nickel foam substrate for electrochemical capacitors (ECs) application. The films have been characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. The MnO2–chitosan hybrid nanocomposite films show better specific capacitance and rate capability than chitosan-free MnO2 film. For the MnO2–chitosan composite films, the highest specific capacitance is 424 F g−1 obtained at a current density of 1 mA cm−2. The deposited film retains a very stable capacitance over 400 cycles by charging and discharging at 3 mA cm−2, and only 3% capacity loss is observed. The presence of chitosan promotes both ion and electron transport in the matrix of MnO2. Besides, it allows the formation of porous and crack-free deposited films. A deposition mechanism for MnO2–chitosan hybrid nanocomposite films is proposed.