Colloidal Processing of Mn₃O₄-Carbon Nanotube Nanocomposite Electrodes for Supercapacitors

This investigation addresses the challenges in the development of efficient nanostructured Mn₃O₄ cathodes for supercapacitors. A high areal capacitance and the ability to avoid a time-consuming activation procedure for electrodes with high active mass loading of 40 mg cm^-2 are reported. This facilitates practical applications of Mn₃O₄ based electrodes. The highest capacitance of 6.11 F cm^-2 (153 F g^-1) is obtained from cyclic voltammetry at a scan rate of 2 mV s^-1 and 6.07 F cm^-2 (151.9 F g^-1) from the chronopotentiometry at a current density of 3 mA cm^-2 in a potential window of 0.9 V in a neutral Na₂SO₄ electrolyte. The new approach is based on the application of rhamnolipids (RL) as a capping agent for the synthesis of Mn₃O₄ particles and a co-dispersant for Mn₃O₄ and carbon nanotubes, which are used as conductive additives. The size and shape of the Mn₃O₄ particles are influenced by RL. The enhanced performance of the electrodes is linked to the chemical structure and properties of RL molecules, which exert influence on Mn₃O₄ particle size and shape during synthesis, reduce agglomeration, facilitate RL adsorption on Mn₃O₄ and carbon nanotubes, and influence their co-dispersion and mixing at the nanometric scale.