Enhanced specific capacitance of an electrophoretic deposited MnO₂-carbon nanotube supercapacitor

Abstract

MnO₂ and MnO₂-carbon nanotubes (CNT) composite films were grown directly on stainless- steel substrates using an electrophoretic process employing supercapacitor electrodes. An electrophoretic MnO₂ film with a nanoplate-like structure was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Supercapacitor performance was studied using cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy (EIS). The specific capacitance (SC) of the electrophoretic MnO₂ film was 60 F/g at 1 A/g, with a 38.33% retention of the initial SC values after 1000 cycles. The low SC value of the MnO2 films was attributed to the high series and charge-transfer resistances of 1.70 Ω and 3.20, respectively. The MnO₂-CNT composites with the addition of 0.04, 0.06 and 0.08 g CNT to the electrophoretic MnO₂ film were found to greatly increase the SC to 300, 206 and 169 F/g at 1 A/g, respectively. The series and charge-transferred resistances of MnO₂-CNT composite films decreased to 1.38 - 1.52 Ω and 2.62 - 2.86 Ω, respectively. The SC improvement of the composite electrodes was attributed to presence of two active storage materials (MnO₂ and CNT), a high film specific surface area and electrical conductivity.