Various recast Nafion® composite membranes containing ceramic oxide fillers with different surface characteristics (SiO2, SiO2-PWA, Al2O3, ZrO2) have been investigated for application in high temperature direct methanol fuel cells (DMFCs). Cell resistance at 145 °C increases as a function of the pH of slurry of the inorganic filler indicating a strong influence of the acid-base characteristics on the electrolyte conductivity. This effect has been attributed to the different water retention capabilities of the various membranes. Fuel cell performance at 145 °C, expressed as both maximum power density and current density at 0.5 V cell potential, increases almost linearly as the pH of slurry of the oxide materials decreases. Appropriate selection of the surface properties for the inorganic fillers allows to enhance the proton conductivity and extends the operating temperature range of composite membranes. An infrared spectroscopic investigation of inorganic fillers employed in composite membranes has been carried out. The surface acidity of the fillers appears to influence the bending and stretching vibrational frequencies of the water physically adsorbed on the filler surface. Inorganic fillers characterised by acidic properties undergo a strong interaction with water and enhance the DMFC performance at high temperature.

In this study, we incorporated vanadium pentoxide xerogel into an alumina matrix and into a silica matrix in order to improve the structural stability by incorporating the electroactive material into an inert matrix which provides structural stability to the electrode. The novel materials were characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, cyclic voltammetry and impedance spectroscopy. V2O5/SiO2 and V2O5/Al2O3 xerogel composites prepared by soft chemistry present conductivity almost five orders of magnitude higher than other related systems. The electrochemical behavior is quite similar to that found for V2O5 xerogel. In addition, the cyclic voltammetric and electrochemical impedance spectroscopy studies demonstrated that the alumina and silica matrices provide an improvement of the electrochemical properties mainly in relation to the kinetics of the lithium electroinsertion into the oxide matrix with little decrease of total charge during successive redox cycles. Overall, the synthetic approach applied in this study is extremely attractive due to its simplicity and can provide new strategies for tailoring new materials and future family members for electrochromic devices, batteries and chemical sensing.

LiFePO4-based powders prepared through various synthesis conditions are presented. Depending on whether the precursors contain carbon or not, LiFePO4-based composites obtained contain significant amounts of carbon as well. We did not succeed in doping LiFePO4 with Nb and produced, instead, crystalline β-NbOPO4 and/or an amorphous (Nb, Fe, C, O, P) matrix around LiFePO4 particles. The total electrical conductivity is of ∼10−9 S.cm−1 at 25°C with an activation energy of ca. 0.65 eV for pure LiFePO4 and LiFePO4/β-NbOPO4 composite. C-containing LiFePO4 samples, including those that had been tentatively doped with Nb, are much more conductive (up to 1.6.10−1 S.cm−1) with an activation energy ΔE ∼ 0.08 eV.

The layered oxide LiMn0.4Ni0.4Co0.2O2 was synthesized by heating the mixed hydroxide precursor. This 442 composition was found to show high capacity. It has the optimum cobalt concentration to both substantially order the lattice, yet leave enough nickel on the lithium sites to minimize conversion to the 1T structure of CoO2 on deep charging. A combined x-ray and neutron diffraction study showed conclusively that only nickel, not manganese or cobalt is found on the lithium sites at room temperature. Magnetic measurements also confirmed the presence of nickel on the lithium sites, and showed the effectiveness of cobalt at minimizing nickel disorder. Heating above 800°C always leads to nickel disorder. The structural and thermal stability of reduced lithium content materials was studied; the structure remains rhombohedral except for x≤0.05, and cobalt substitution improves the thermal stability of the layered compound, but not the chemical stability.

The metastable-to-equilibrium phase evolution over a wide range of compositions in the TiO2-YO3/2-ZrO2 system was investigated. The competing phases are all derivatives of the fluorite structure and compositions within the fluorite and pyrochlore fields exhibit technologically interesting ionic and mixed ionic-electronic conductivity. Powders of various compositions were synthesized by precursor routes, pyrolyzed and subsequently heat-treated in a stepwise manner at progressively higher temperatures to explore the sequence of phase evolution. Extended solid solutions with amorphous, fluorite and ordered pyrochlore structures were produced over significant composition ranges within the ternary. The study also sheds new light on the correct form of the phase equilibria at 1300°C.

Pure tin reacts readily with four lithium atoms, and so is a prime candidate as the host for the anode of lithium batteries. Tin foil and an expanded tin grid (microporous tin) have a capacity of >600 mAh/g over more than 10 deep reaction cycles, indicating the inherent reversibility of tin anode. The microporous tin showed superior chemical capacity retention. Different phases are observed during the intercalation of lithium. Capacity loss was observed after 10 cycles though, consistent with the significant increase of the cell impedance. For comparison aluminum expanded grids were also examined as hosts, where LiAl is formed. Capacities approaching 1 Ah/g were obtained. LiBOB (lithium bis(oxalato)borate) was also studied as the electrolyte salt for comparison with the reactive and high cost LiPF6 salt.

The influence of the grain boundaries on the ionic conductivity of yttrium stabilized zirconia (YSZ) was investigated. The initially nanocrystalline samples were prepared using a tape casting process. The samples were annealed at different temperatures in the range from 1000 to 1400°C to overlap the grain size from 100nm to ∼10μm and investigated using impedance spectroscopy. Two distinct semicircles were found on all YSZ samples corresponding to the influence of the grain and grain boundary on the resistance. The activation energies for both resistances are very close (1.00 and 1.03eV correspondingly). The grain resistance does not change significantly during the annealing process, but the grain boundary resistance decreases after high temperature annealing which causes a decrease in the overall resistance of the material. The calculations show that the decrease in the grain boundary resistance is connected only with the increase in the grain size and the specific grain boundary resistance (per unit surface area of grain boundary) does not change with annealing.

CuBr films are used to design an ammonia gas microsensor operating at ambient temperature, with high sensitivity and much improved selectivity in comparison with usual conductometric microsensors. The specific detection mechanism relies on adsorption of ammonia molecules and interactions with mobile Cu+ ions in the ionic conductor film. The CuBr films can be prepared by r.f. sputtering, but more simply and cost efficiently by chemical reaction of copper metal with bromine ions. Photolithographic techniques are applied to miniaturize the sensor.