Tuning the morphology of manganese oxide nanostructures for obtaining both high gravimetric and volumetric capacitance

Obtaining both high gravimetric capacitance ( C s_m ) and high volumetric capacitance ( C s_V ) in supercapacitors is still a great challenge. We prepared manganese oxide (MO) nanostructures by pulsed laser deposition, using a metallic Mn target in an O 2 atmosphere with pressures ranging from 0.1 Torr to 2.0 Torr at room temperature. The morphology gradually changed from a dense film to nanofoam with different porosities and densities. Raman spectroscopy and X-ray photoelectron spectroscopy revealed a similar oxidation state despite distinct microstructures. C s_m and C s_V for the three typical nanostructures, namely thin films, perpendicular columnar structures and nanofoams, were compared. It was found that the highest C s_m value was not obtained in the nanofoam sample with the highest porosity, but it was achieved in the sample with a perpendicular columnar structure with a C s_m value of 976 F g −1 at 5 mV s −1 . Such a configuration showed the highest C s_V as well with a value of 830 F cm −3 at 5 mV s −1 . The best performance with voltage scan rates higher than 50 mV s −1 was found in the nanofoam structures with the values of 612 F g −1 at 100 mV s −1 and 352 F g −1 at 300 mV s −1 . Our research gives useful suggestions for material design in supercapacitor electrodes: a suitable microstructure can be used for applications focusing on different parameters of a supercapacitor. The results might be of general interest for the energy storage research community. We prepared three distinct MnO 2 nanostructures, and 976 F g −1 and 830 F cm −3 at 5 mV s −1 were obtained with a perpendicular columnar structure.