Manganese Oxide/Carbon Aerogel Composite: an Outstanding Supercapacitor Electrode Material

Manganese oxide/carbon aerogel composite electrodes are prepared by a self‐limiting anodic‐electrochemical deposition of manganese oxide into a binder‐enriched carbon aerogel layer, drop‐cast on a graphite substrate, using 0.1 M Mn(CH 3 COO) 2 ·4H 2 O as the electrolyte. Manganese oxide grows in the form of thin nanofibers along the backbone of the carbon aerogel, leaving adequate working space for the electrolyte and enabling a fuller extent of the utilization of the manganese oxide to make the composite an outstanding supercapacitor electrode material. The manganese oxide is determined to be Mn 3 O 4 with the Raman spectroscopy and high‐resolution transmission electron microscopy. The rectangularity of the cyclic‐voltammogram loops of the composite electrode is excellent and remains that way for scan rates up to a very‐high value of 500 mV s −1 , indicating extremely good redox reversibility and cycle efficiency. At a scan rate of 25 mV s −1 , the specific capacitance, as measured in 0.5 M Na 2 SO 4 for a potential window of 0.1–0.9 V vs. Ag/AgCl, reaches a maximum value of 503 F g −1 and experiences only a negligible decay of less than 1% at the 6000th cycle, implying an extraordinary cycling stability. The cycling efficiency is as high as 98% at a current density of 8 A g −1 cm −2 , showing an almost‐ideal capacitive behavior. The power density reaches 48.5 kW kg −1 and the energy density 21.6 W h kg −1 at a scan rate of 500 mV s −1 , well above the specifications of current state‐of‐the‐art supercapacitors.