Ternary hybrid nanocomposites based on polypyrrole/manganese dioxide/palygorskite clay for electrochemical supercapacitor applications

Abstract

Ternary nanocomposites containing polypyrrole (PPy), manganese dioxide (MnO₂), and two distinct acid-treated palygorskite (Pal) clays were prepared by in situ chemical oxidative polymerization for electrochemical supercapacitor applications. The resulting composites were fully characterized in terms of structure, morphology, and electrochemical properties. MnO₂ nanorods were hydrothermal synthesized, while natural Pal clay was modified by two sequential acid treatments not only for clay purification but also to increase its specific surface area and porosity. The Pal clay was initially treated with a 1 M HCl solution, designated as Pal1, and subsequently treated with a 5 M H₂SO₄ solution to yield Pal2. Pal clay was incorporated in order to increase the dimensional stability during the doping-dedoping process. Two ternary nanocomposites, designated as PMP1 and PMP2 were formed through in-situ polymerization of pyrrole on Pal1/MnO₂ or Pal2/MnO₂ mixtures, respectively. The ternary electrodes exhibited a notable enhancement in the cycle life of the supercapacitors due to the incorporation of acid-treated clays, retaining up to 98 % of their initial capacitance after 1600 charge-discharge cycles. In contrast, the device containing PPy/MnO₂ electrodes (PM) retained only 78 % of its initial capacitance. Furthermore, the highest specific capacitance of 205 mF cm⁻² at 3 mA cm⁻² was obtained for the PMP1 supercapacitor by the GCD method, which delivered a maximum energy density of 13 mW h cm⁻² with a power density of 335 mW cm⁻². These results demonstrate for the first time the potential application of acid-treated Pal clays in improving cycle stability of the PPy/MnO₂ electrode materials. This approach could also be adapted for other types of binary electrode materials.