Morphology and Electrical Capacitance Characteristics of Nanostructured MnxOy/MWCNT Composites

— Reducing potassium permanganate by a carbon matrix (multiwalled carbon nanotubes (MWCNTs)) in aqueous solutions, we have obtained Mn x O y /MWCNT nanostructured composites (NSCs). The morphology and texture of the MWCNTs and NSCs have been studied by X-ray diffraction, small angle X-ray scattering (SAXS), sorption porosimetry (SP), scanning electron microscopy, and transmission electron microscopy (TEM) with the aim of assessing the effect of the Mn x O y filler on their properties and the electrical capacitance characteristics of composite electrodes in model supercapacitor (SC) cells. Comparison of the TEM, SAXS, and SP results indicates that the MWCNTs have narrow distributions of the channel diameter (2–5 nm), outer diameter (18–23 nm), and wall thickness (2–12 nm). In addition, nanotube entanglements (“fibers”) form meso- and macropores (20–80 nm), probably slit-shaped. The filler particles in the NSCs have the form of nanometer-thick quasi-films of Mn 2 O 3 and MnO 2 nanocrystallites and aggregates on the surface of the inner channels, accessible to the electrolyte, and on the outer surface of the MWCNTs and partially block the MWCNT channels. The aggregate size and the blocking of channels and mesopores increase with increasing NSC preparation temperature and Mn x O y filler content. The electrical capacitance of the NSCs in a potential window of ±1 V exceeds the capacitance of the MWCNTs owing to the contribution of the pseudocapacitance during redox processes involving Mn x O y on the surface of the NSCs. At an optimal filler content (about 5 wt % in terms of Mn), the capacitance of NSC electrodes exceeds that of MWCNT electrodes by a factor of 1.5 (at v = 10 mV/s) and 2.5 (at v = 80 mV/s).