Hybrid MnO₂–disordered mesoporous carbon nanocomposites: synthesis and characterization as electrochemical pseudocapacitor electrodes

Abstract

MnO2–mesoporous carbon hybrid nanocomposites were synthesized to achieve high values of redox pseudocapacitance at scan rates of 100 mV s−1. High-resolution transmission electron microscopy (HRTEM) along with energy dispersive X-ray spectroscopy (EDX) demonstrated that ∼1 nm thick MnO2 nanodomains, resembling a conformal coating, were uniformly distributed throughout the mesoporous carbon structure. HRTEM and X-ray diffraction (XRD) showed formation of MnO2 nanocrystals with lattice planes corresponding to birnessite. The electrochemical redox pseudocapacitance of these composite materials in aqueous 1 M Na2SO4 electrolyte containing as little as 2 wt% MnO2 exhibited a high gravimetric MnO2 pseudocapacitance (CMnO2) of 560 F gMnO2−1. Even for 30 wt% MnO2, a high CMnO2 of 137 F gMnO2−1 was observed at 100 mV s−1. Sodium ion diffusion coefficients on the order of 10−9 to 10−10 cm2 s−1 were measured using chronoamperometry. The controlled growth and conformal coating of redox-active MnO2–mesoporous carbon composites offer the potential for achieving high power energy storage with low cost materials.