Surface modification of MnO2 and carbon nanotubes using organic dyes for nanotechnology of electrochemical supercapacitors

Abstract

Efficient dispersion and electrophoretic deposition (EPD) of multiwalled carbon nanotubes (MWCNTs) was achieved using organic dyes, such as pyrocatechol violet (PV) and m-cresol purple (CP). The problem of MnO₂ nanoparticle dispersion in concentrated suspensions was addressed by the use of PV as a dispersant. The analysis and comparison of experimental data for PV and CP provided insight into the influence of chemical structures of the dyes on their adsorption on MWCNTs and MnO₂. The adsorption of PV on MWCNTs and MnO₂ was attributed to π–π interactions and catecholate type bonding, respectively. The EPD yield can be varied by the variation of the PV concentration in the suspensions, deposition voltage and time. It was found that PV can be used as a co-dispersant for EPD of MWCNTs and MnO₂ and the fabrication of MnO₂–MWCNT composites. The proposed approach offers advantages of uniform distribution of individual components and low binder content in the composite. MnO₂–MWCNT films were prepared by EPD for thin film electrodes of electrochemical supercapacitors (ES). Bulk MnO₂–MWCNT electrodes with a material loading of 40 mg cm⁻² were obtained by the impregnation of Ni foam current collectors. The highest specific capacitance of 5.9 F cm⁻² (148 F g⁻¹) was achieved. The composite materials are promising for ES applications.