Effect of chitosan addition on the structure and capacitive characteristics of electrodeposited manganese oxides

Nano-structured MnO₂-chitosan hybrid composite electrodes containing low and high chitosan´s M_w were synthesized by one-step cathodic electrodeposition on nickel foam substrate for electrochemical capacitors (ECs) application. The effect of chitosan molecular weight (M_w) on the structure and capacitive behaviour of the tailored electrodes was examined. The electrodes have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The presence of CH promotes both ion and electron transport in the matrix of MnO₂. Furthermore, the use of CH with its inherent binding properties allowed the formation of adherent and cracks free deposits. The MnO₂-chitosan hybrid nanocomposite electrodes showed better specific capacitance and rate capability than MnO₂ electrode. The highest specific capacitance of 424 F/g was obtained for the MnO₂-chitosan composite electrode with low chitosan´s M_w at a current density of 1 mA/cm². The electrode retained a very stable capacitance over 400 cycles by charging and discharging at 3 mA/cm², as the capacity loss is only 3%, indicative of long term electrochemical cycling stability.