Interrelated functionalities of hierarchically CNT/CeO2/Pt nanostructured layers: synthesis, characterization, and electroactivity

We present a free-standing catalyst layer comprising current collector/CNTs (catalyst support)/CeO2/Pt (catalyst) nanostructured layers, each layer constructed upon the one below it. FESEM and TEM showed that a CeO2 layer has a fluffy morphology recalling the texture of cotton, whereas Pt nanoparticles assemble into cauliflower or broccoli-like arrangement. New insights have been gained into the effect of CeO2 on the structural properties of the beneath CNTs layer and on the above Pt layer. First, by means of Raman analysis, it was found that interaction of CeO2 with CNTs induced a decrease in the crystallinity of the latter. Second, by TEM and XPS analyses, it was observed that the size of Pt nanoparticles in the CNT/CeO2/Pt structure was inferior to that in the CNT/Pt, implying that CeO2 influenced the dispersion quality of Pt nanoparticles. For the first time, it is observed that CeO2 supported CNTs undergo oxidation/reduction reactions at low potentials in the ethanol electrolyte. The electrochemical analysis showed that entities produced from those redox processes are surface adsorbed/desorbed species most likely hydroxides. This unexpected electroactivity is due to the beneath CNTs that boosted the conductivity of CeO2. Such improved conductivity of CeO2 has fostered the electron-transfer kinetics of ethanol at Pt as demonstrated by the decreased overpotential required to oxidize ethanol and by the specific mass activity, which was greater than that of CNT/Pt.