Effects of polyelectrolyte hybridization on the crystal structure, physicochemical properties, and electrochemical activity of layered manganese oxide

The effects of polyelectrolyte intercalation on the crystal structure, physicochemical properties, and electrode performance of manganese oxide were investigated with intercalative nanohybrids composed of layered manganate nanosheets and polyelectrolytes such as polyethylenimine (PEI), poly(allylamine hydrochloride) (PAH), and poly(diallyldimethyl ammonium) chloride (PDDA). The intercalative hybridization between layered manganate nanosheets and polyelectrolytes was confirmed by X-ray diffraction, field emission-scanning electron microscopy, and FT-IR spectroscopy. N₂ adsorption-desorption isotherm analysis clearly demonstrated that the PEI-layered MnO₂ nanohybrid showed a larger surface area than the other nanohybrids. According to Mn K-edge X-ray absorption spectroscopy, the PEI-layered MnO₂ nanohybrid possessed a lower Mn oxidation state compared with the other nanohybrids, reflecting the electron transfer from Lewis basic amine groups of the PEI to the manganate layers. All the present nanohybrids exhibited pseudocapacitance behavior, suggesting their applicability as electrode for supercapacitor. The PEI-layered MnO₂ nanohybrid showed larger capacitances than the PDDA- and PAH-intercalates. The observed superior electrode performance of the former could be understood by a larger surface area and a lower Mn oxidation state of this material.