Enhanced capacitance of manganese oxide driven by hierarchically structured carbon nanotube-carbon nanowall composite

Abstract

The deposition of transition metal oxides on hierarchically grown carbon‑carbon nanostructures improves the storage properties of electrode materials for next-generation energy storage devices. Usually, a thin layer of oxide covering the carbon nanostructure is deposited to avoid high series resistance values. However, increasing the energy storage density of the electrode requires the deposition of a larger amount of electrochemically active material. Here we demonstrate the improvement in performance of the metal oxide layer when hierarchically grown carbon‑carbon nanostructures are present on the substrate. Optimum capacitance, series resistance, and cycling stability are found to be after 20 min manganese oxide electrodeposition time on carbon‑carbon nanocomposites. The asymmetrical supercapacitor devices prepared under these conditions present high energy density (2.9 mWh·cm−2), moderate power density (2.8 mW·cm−2), and high cycling stability (80% capacitance retention after 20,000 cycles).