Fabrication of Mn₃O₄-carbon nanotube composites with high areal capacitance using cationic and anionic dispersants

Mn₃O₄-multiwalled carbon nanotube (MWCNT) electrodes for supercapacitors with high active mass loadings have been fabricated with the goal of achieving a high area normalized capacitance (C_S) and enhanced capacitance retention at high charge-discharge rates. Poly(4-styrenesulfonic acid-co-maleic acid) sodium salt P(SSA-MA) was used as a charging and dispersing agent for the fabrication of Mn₃O₄. The unique bonding properties of the MA monomers allowed efficient P(SSA-MA) adsorption on Mn₃O₄, whereas SSA monomers imparted a negative charge. Cationic ethyl violet (EV) and pyronin Y (PY) dyes were used for dispersion and charging of MWCNT. Good dispersion of the individual components and their electrostatic heterocoagulation facilitated efficient mixing, which allowed enhanced capacitive behavior at mass loadings of 28.4 mg cm^-2, which meet requirements for practical applications. The highest capacitance of 2.8 F cm^-2 was obtained at a scan rate of 2 mV s^-1 for the composites, prepared using PY. However, the composites, prepared using EV showed better capacitance retention of 88% in the scan rate range of 2-100 mV s^-1 and the capacitance of 2.1 F cm^-2 was obtained at a scan rate of 100 mV s^-1. The composites showed activation behavior during cycling, which resulted in a capacitance increase and electrical resistance reduction. The results of this investigation showed that Mn₃O₄-MWCNT composites, prepared by new colloidal methods are promising materials for practical applications in electrochemical supercapacitors.