Dense and long carbon nanotube arrays decorated with Mn3O4 nanoparticles for electrodes of electrochemical supercapacitors

Mn3O4 nanoparticles have been homogenously deposited within highly dense, millimeter-long carbon nanotube array (CNTA) by dip-casting method from non-aqueous solutions. After modified with Mn3O4 nanoparticles, CNTAs have been changed from hydrophobic to hydrophilic without their alignment and integrity being destroyed. The hydrophilic Mn3O4/CNTA composite electrodes present improved performance for supercapacitors, compared with as-grown CNTA electrodes. The maximum specific capacitance of the Mn3O4/CNTA composite electrode was found to be 143 F/g, leading to an exceptionally high area-normalized capacitance (Faraday per geometric area of the electrode) of 1.70 F/cm2, while the specific capacitance for as-grown CNTA electrode is only 1–2 F/g. When normalized to the deposited Mn3O4 nanoparticles, the specific capacitance was estimated to be as high as 292 F/g. The method is promising for producing high performance area-limited electrochemical supercapacitors and provides a new route of decorating highly dense CNTAs with active materials.