Ana Martínez-Amesti

Influence of SDC–YSZ Contact at Different Atmospheres in SOFC Operation and Processing Conditions

The intermediate operating temperature solid oxide fuel cells (SOFCs) are actually under research; one of the system developments consists in adding an interlayer between the electrodes and the electrolyte materials. In the cathodic sequence, one possible solution to improve the electrochemical performance consists of a yttria-stabilized zirconia (YSZ) and a samaria-doped ceria (SDC) bilayer. But this layer sequence is still problematic due to solid-state reactions and interdiffusion at the YSZ/SDC interface. The phase formation and element diffusion have been studied when samples are sintered at different atmospheres (oxidizing, inert, and reducing) and temperatures (1100, 1200, and 1300°C) by X-ray powder diffraction, scanning electron microscopy/energy dispersive X-ray analysis/wavelength dispersive X-ray analysis, and electrochemical impedance spectroscopy. The reaction and interdiffusion are preceded by the migration of the cerium to the YSZ lattice. Structural, microstructural, and electrochemical results can be improved when the deposited SDC is sintered at 1200°C in air atmosphere.

Composite β-AgVO3@V1.65+V0.44+O4.8 hydrogels and xerogels for iodide capture

Herein, we report on the study of silver vanadium oxide (β-AgVO3) and slightly reduced vanadium oxide (V1.65+V0.44+O4.8) composite hydrogels, which were synthesized under ambient conditions using a mixture of two solutions. Acidification of the reaction media plays a crucial role in the chemical and physical properties of the hydrogels. The non-covalent cross linked three dimensional network of silver vanadium oxide and vanadium oxide nano-ribbons traps water thus stabilizing the gel form of the materials. Xerogels of the selected materials were produced by drying the hydrogels at 70 °C. The morphology and composition of the nano-ribbons were studied using scanning (SEM) and transmission (TEM) electron microscopy and EDX and EELS compositional analyses of selected areas and punctual microanalyses. In addition, the three dimensional reconstruction of a single nano-ribbon was carried out using electron tomography. Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and double titration chemical analyses together with inductively coupled plasma mass spectroscopy (ICP-AES) chemical analyses allowed the proposal of average chemical formulas and vanadium oxidation state. EPR spectroscopy and magnetic susceptibility measurements confirm the existence of a secondary slightly reduced vanadium oxide within the silver vanadium oxide gels jellified under acidic conditions. The micro and mesoporosity of the xerogels were studied using N2 adsorption isotherms, which reveal different porous structures depending on the synthetic conditions. Finally, due to their porous and reactive nature, the hydrogels, organogels and xerogels were tested against methylene blue, crystal violet and iodide adsorption.

Performance of (Ln0.5M0.5)FeO3-δ Perovskites as Cathode for SOFCs.: Effect of Mean Radious of the A site Cations

Ceramic oxides with perovskite structure ABO3, where A is a rare earth and B a transition metal cation, have attracted a wide interest due to their utilization in various electrochemical processes. For example, compositions in the La1-xSrxFeO3-δ system tend to have a larger number of oxygen vacancies, coupled with a relatively high electronic conductivity, making them interesting candidates for oxygen separation membranes, oxygen sensors and solid oxide fuel cell applications [1]. Lowering the operating temperature of SOFCs from the traditional 1000oC will reduce cost and complexity of the stack by increasing the selection of cheaper candidate materials [2]. This requires, especially cathode materials with increased electrocatalytic activity caracterized by increased oxide ion transport in addition to high electronic conductivity. The physical properties of these perovskites materials are very sensitive to changes in the doping level, x [3,4], the average size of the A-cations, , and the effects of A cation size disorder, σ(rA), quantified by the variance of the A cation radious distribution σ(rA) = - [5]. In this study, we investigate the effect of the variation of the average size of the A-cations, , in the structure and electrical properties of a series of Ln0.5M0.5FeO3-δ perovskites (Ln = La, Pr; M = Ca, Ba, Sr) (Table 2) for its application as cathode material for SOFC. This has been achieved by keeping x and σ(rA) constant and varying the over the range 1.21 ≤ ≤ 1.25 A. Crystal structure, microstructure, electrical conductivity and electrochemical performance of a family of iron perovskites with the general formula Ln0.5M0.5FeO3-δ (Ln = La and/or Pr; M = Sr, Ca or/and Ba) (Table 1) has been studied as function of mean A cation radius .