J. P. Donoso

Characterisation of PEO–Al2O3 composite polymer electrolytes

Abstract The behaviour of PEO 8 LiClO 4 with different quantities of α-Al 2 O 3 or γ-Al 2 O 3 was investigated using DSC, AC conductivity and 7 Li NMR experiments. DSC results showed that the presence of the filler does not change the glass transition temperature of the electrolyte but, on the other hand, modifies the quantity of its crystalline phase. From the AC impedance measurements, it was observed that the sample with the highest conductivity at room temperature is PEO 8 LiClO 4 5.3 wt.% α-Al 2 O 3 . The change in the quantity of crystalline phase cannot alone explain the conductivity data, and it is suggested that the space charge contribution in the interphase of the filler particles and the polymeric chains influences the behaviour of the samples. The 7 Li NMR results showed that line width narrowing begins at temperatures close to T g . From the hydrogen decoupling experiments it was possible to estimate the LiH average distances as 2.7 A. The LiLi distance was calculated as being between 2.6 and 3.5 A depending on the number of near neighbours lithium nuclei used in the model.

Nuclear magnetic relaxation study of poly(ethylene oxide)-lithium salt based electrolytes

We have studied the low‐temperature NMR line shape for three nuclei (1H, 7Li, and 19F) in poly(ethylene oxide)‐lithium salts (LiClO4, LiBF4, and LiAsF6) solid polymer ionic conductors and measured their spin–lattice relaxation rates as functions of frequency and temperature. The three nuclei probe the dynamics of the polymer segments, the cations, and the anions. We find that the Li+ cations follow the segmental motion of the chain, while the anions move independently. Homonuclear interactions and heteronuclear interactions with the polymer and the anion contribute to the 7Li line shape. When the heteronuclear contributions were selectively eliminated by the decoupling method, it was found that the Li–H interaction accounts for 80%–90% of the linewidth. Additional evidence for the correlation between the cationic and the polymeric motions is provided by the remarkably similar temperature dependences of the measured relaxation rates for 7Li and 1H, which differ significantly from the dependence for 19F. Th...

Nuclear magnetic resonance and conductivity study of starch based polymer electrolytes

Abstract Nuclear magnetic resonance (NMR) spectroscopy and complex impedance spectroscopy have been used to study the polymer electrolytes formed by amylopectin rich starch, plasticized with glycerol and containing lithium perchlorate. The 7 Li and 1 H NMR linewidth narrowing occurs close to the glass transition temperature ( T g ) of the plasticized electrolytes. The heteronuclear decoupling NMR experiments suggest a weaker Li–polymer interaction in the plasticized electrolyte when compared with the unplasticized ones. The effects of the plasticizer on the ionic mobility in these starch-based electrolytes, as measured by NMR spin-lattice relaxation and conductivity, are discussed. The 7 Li NMR relaxation results indicate that the ionic mobility in these plasticized electrolytes seems to be controlled by the plasticizer molecules. The dynamical parameters obtained from the conductivity and NMR data demonstrate that the Li + mobility in our systems is comparable to those found in others plasticized polymer electrolytes.

Nuclear magnetic resonance study of PEO-based composite polymer electrolytes

Abstract The effect of carbon black and ceramic (a-Al 2 O 3 and g-Al 2 O 3 ) particles on the cationic and polymer chain mobilityhave been investigated in poly(ethylene oxide)–lithium salt (LiClO 4 and LiBF 4 ) solid composite polymer electrolytesby using nuclear magnetic resonance (NMR) techniques. Proton ( 1 H) and lithium ( 7 Li) lineshapes and spin–latticerelaxation times were measured as a function of temperature. The 7 Li data indicates that the lineshape and relaxationis affected by the coupling of its quadrupolar moment to the surrounding electric field gradients. Activation energiesextracted from the 7 Li relaxation data are in the range 0.20–0.25 eV. Results show that the addition of a-Al 2 O 3 influenced both, the relative cation mobility and the polymer chain motion. Calculation shows that this result is inquantitative agreement with the conductivity data.

Nuclear magnetic resonance and conductivity study of HEC:polyether-based polymer electrolytes

Measurements of 1H and 7Li nuclear magnetic resonance (NMR) and ionic conductivity are reported for the polymer electrolytes formed by hydroxyethylcelluloses (HEC), poly(ethylene oxide) diisocyanate (DPEO) and LiClO4. The NMR experiments exhibit the qualitative features associated with Li+ and polymer chain mobilities in polymer electrolytes, namely the presence of well-defined 7Li and 1H spin–lattice relaxation rate maxima (T1−1). The single absorption band in the proton spectra and the observed 1H and 7Li exponential relaxation indicate that the HEC/DPEO/LiClO4 polymer electrolytes are predominantly amorphous. The conductivity values obtained by a.c. measurements rise above 10−4 S/cm at 370 K and are slightly higher for the samples with a greater oxygen content in the HEC molecule. The parameters estimated from the data indicate that the conductivity and the mobilities of Li+ and polymer chains are comparable to those found in the PEO8LiClO4 polymer electrolyte.

Electrical conductivity and lithium diffusion in molybdenum disulfide intercalated with poly(ethylene oxide)

Abstract Electrical conductivity and lithium diffusion coefficients of nanocomposites prepared by intercalation of molybdenum disulfide with poly(ethylene oxide), Li0.1MoS2(PEO)y, are informed. The products show a semiconductor behaviour with relatively high electrical conductivity. Lithium diffusion coefficients are higher than those observed for the disulfide alone.

NMR and conductivity study of PEO-based composite polymer electrolytes

The influence of the space charge created by the presence of TiO2 nanoparticles on the lithium and polymer chain mobility have been investigated in solid composite polymer electrolytes (CPE), poly(ethylene oxide) (PEO) LiClO4, by using complex impedance spectroscopy and nuclear magnetic resonance (NMR). Special care was taken with the synthesis and the characterization of the TiO2 particles and with the composite preparation. The conductivity and NMR measurements were undertaken in composite samples nanoparticles having constant total surface area. Proton (1H) and lithium (7Li) lineshapes and spin-lattice relaxation times were measured as a function of temperature. Activation energies extracted from the 7Li relaxation data are in the range 0.20–0.22 eV. The NMR decoupling experiment suggests that the Li–Li interactions are stronger in the composites when compared with those of the ceramic free electrolytes.

V2O5/TiO2 catalyst xerogels: Method of preparation and characterization

This work describes a modified sol-gel method for the preparation of V2O5/TiO2 catalysts. The samples have been characterized by N2 adsorption at 77 K, X-ray Diffractometry (XRD), Scanning Electronic Microscopy (SEM/EDX) and Fourier Transform Infrared Spectroscopy (FT-IR). The surface area increases with the vanadia loading from 24 m2 g−1 for pure TiO2 to 87 m2 g−1 for 9 wt% of V2O5. The rutile form is predominant for pure TiO2 but becomes enriched with anatase phase when vanadia loading is increased. No crystalline V2O5 phase was observed in the diffractograms of the catalysts. Analysis by SEM showed heterogeneous granulation of particles with high vanadium dispersion. Two species of surface vanadium were observed by FT-IR spectroscopy: a monomeric vanadyl and polymeric vanadates. The vanadyl/vanadate ratio remains practically constant. Ethanol oxidation was used as a catalytic test in a temperature range from 350 to 560 K. The catalytic activity starts around 380 K. For the sample with 9 wt% of vanadia, the conversion of ethanol into acetaldehyde as the main product was approximately 90% at 473 K.

Nuclear magnetic relaxation study of poly(propylene oxide)complexed with lithium salt

Abstract Measurements of 7 Li, 1 H and 19 F nuclear relaxation times and 7 Li linewidths are reported for poly(propylene oxide) complexed with lithium salts (LiClO 4 , LiBF 4 and LiAsF 6 ). For PPO 6 LiBF 4 and PPO 8 LiClO 4 the onset of the 7 Li motional line narrowing, occurs at approximately T G . The NMR decoupling methods was used to eliminate heteronuclear contribution to 7 Li line shape. It was found that the Li- H interaction accounts for 80–90% of the linewidth. The remarkably similar temperature dependence of the measured 1 H and 7 Li spin-lattice relaxation rates, which shows rate maxima at 340–350 K in this PPOLi salts complexes, gives additional evidences for correlation between the cationic and the polymeric motions. The nuclear spin-lattice relaxation rates of the PPO complexes always peak at higher temperatures than the POE complexes, suggesting a lower ionic mobility for the former complexes. The frequency dependence of the relaxation rates cannot be described in the framework of the BPP theory.

V2O5/TiO2 Catalytic Xerogels Raman and EPR Studies

Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V2O5/TiO2 catalysts prepared by a modified sol-gel method in order to identify the vanadium species. Two species of surface vanadium were identified by Raman measurements, monomeric vanadyls and polymeric vanadates. Monomeric vanadyls are characterized by a narrow Raman band at 1030 cm−1 and polymeric vanadates by two broad bands in the region from 900 to 960 cm−1 and 770 to 850 cm−1. The Raman spectra do not exhibit characteristic peaks of crystalline V2O5. These results are in agreement with those of X-ray Diffractometry (XRD) and Fourier Transform Infrared (FT-IR) previously reported (C.B. Rodella et al., J. Sol-Gel Sci. Techn., submitted). At least three families of V4+ ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V4+ ions are located in sites with octahedral symmetry substituting for Ti4+ ions in the rutile structure. Magnetically interacting V4+ ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V2O5, a partial oxidation of V4+ to V5+ is apparent from the EPR results.