Electrochemical storage mechanisms in non-stoichiometric cerium oxide/multiwalled carbon nanotube composites

Cerium oxide/multiwalled carbon nanotube composites with different oxide loadings (5-60 wt. %) were prepared by sol-gel deposition of the oxide onto the carbon support. The morphology, texture and surface properties of the prepared materials were studied and correlated with their electrochemical behavior. The different charge storage mechanisms occurring on the surface of the composites were successfully identified by a newly developed electrochemical method, namely the combination of sweep wave voltammetry with deconvolution analysis in 1 M H2SO4. The deposition of moderate oxide loadings (up to 10 wt. %) leads to small and well distributed oxide particles on the nanotubes surface. Therefore, the appearance of defects on the oxide structure is favored, promoting both electronic conduction and faradaic activity. Curiously, cerium oxide loadings above 10 wt. % induce a higher dispersion of the carbon support. This convenient synergism enhances the electroactive area of the composites by increasing molecular diffusion.