RESUMEN
Polymethylmethacrylate (PMMA)/ceria composite fibres were synthesized by using a sequential combination of polymer electrospinning, spray-coating with a sol, and a final calcination step to yield microstructured ceria tubes, which are composed of nanocrystalline ceria particles. The PMMA template is removed from the organic/inorganic hybrid material by radio frequency (rf) plasma etching followed by calcination of the ceramic green-body fibres. Microsized ceria (CeO(2)) tubes, with a diameter of ca. 0.75 µm, composed of nanocrystalline agglomerated ceria particles were thus obtained. The 1-D ceramic ceria material was characterized by X-ray diffraction, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV-vis and photoluminescence spectroscopy (PL), as well as thermogravimetric analysis (TGA). Its catalytic performance was studied in the direct carboxylation of methanol with carbon dioxide leading to dimethyl carbonate [(CH(3)O)(2)CO, DMC], which is widely employed as a phosgene and dimethyl sulfate substitute, and as well as a fuel additive.
RESUMEN
The electrochemical delithiation of LiCo(0.6)M(0.4)PO(4) phosphates (M = Mn, Fe, Ni) was studied by in situ synchrotron diffraction. In all three metallophosphates the oxidation-reduction of 3d-elements proceed via two-phase mechanisms leading to two-phase regions, corresponding to the Co(2+)/Co(3+) and M(2+)/M(3+) reactions. The Ni(2+)/Ni(3+) reaction was not revealed, neither by the potentiostatic intermittent titration technique (PITT) nor by diffraction. In the two-phase reaction, the olivine-like structure of the cathode remains preserved, which is characteristic of this type of materials. Pronounced solid-solution domains were observed during both lithium extraction and insertion. The thermal stability of the charged cathodes is limited by the presence of Co(3+) and its intrinsic instability in these compounds.