Multiwalled carbon nanotube supported polypyrrole manganese oxide composite supercapacitor electrode: Role of manganese oxide dispersion in performance evolution

We report the effect of manganese oxide (MnO2) dispersion in Polypyrrole (PPy) matrix for supercapacitor electrode. Multiwalled carbon nanotubes (MWCNTs) are used as a large area conductive support to enable the dispersion at nano-scale. PPy and MnO2 nanocomposites are synthesized in two different structural forms i.e. mixed (MWCNT/PPy:MnO2) and co-axial multilayered (MWCNT/PPy/MnO2). Dispersion of MnO2 is studied from molecular level to layered nanostructure. Electrical and electrochemical investigations show that MWCNT/PPy:MnO2 is more conducting and capacitive as compared to MWCNT/PPy/MnO2. Galvanostatic charge discharge measurement shows that MWCNT/PPy:MnO2 stores high energy density (∼44 Wh/kg) compared to ∼36 Wh/kg for MWCNT/PPy/MnO2. The improved performance in mixed composite is attributed to molecular level dispersion of MnO2 which forms a percolative path between two PPy chains. Increase in PPy wt (%) leads to thick PPy layer over MWCNT in MWCNT/PPy/MnO2 structure and significantly affects the electronic conduction whereas MWCNT/PPy:MnO2 nanocomposite is capable of loading high PPy wt (%) with improved charge storage. Cyclic voltammogram of MWCNT/PPy:MnO2 at 5 mV/s shows maximum capacitance ∼365 F/g at ∼70 wt (%) PPy in PPy/(PPy + MnO2) while co-axial nanostructure exhibits maximum ∼270 F/g at ∼ 50 wt (%) PPy. This work suggests that in situ incorporation of MnO2 in PPy matrix yields molecular level dispersion of MnO2 which leads to enhanced performance instead of using layers of PPy and MnO2 over MWCNT. Besides, this study also proposes the tuning of supercapacitor device characteristics by tailoring the electrode material composition.