Chromite/titanate based perovskites for application as anodes in solid oxide fuel cells

Perovskites containing lanthanides, partially substituted by alkaline-earth elements and transition metals like Cr, Ti, Fe or Co show a very broad range of physical properties. Therefore several perovskite materials, based on lanthanum chromite and strontium titanate were synthesised and investigated with regard to their application as anodes in solid oxide fuel cells. The perovskite powders were studied by thermogravimetric and differential thermal analysis (TG/DTA) and X-ray diffraction (XRD). Conductivity data in the range of 100–900°C and the thermal expansion behaviour were measured both in air and Ar–4%H2. The electrochemical properties of a screen-printed electrode were studied preliminary as function of the hydrogen partial pressure using impedance spectroscopy. In this group of materials high electronic conductivity of up to 60 S/cm at 900°C was observed. However, none of the materials investigated so far showed a combination of the advantageous properties and is therefore superior to the state-of-the-art Ni–YSZ anode

Interaction of perovskite type lanthanum-calcium-chromites-titanates La1-xCaxCr1-yTiyO3-δ with solid electrolyte materials

Lanthanum-calcium-chromites-titanates have been proposed as alternative anode material, and diffusion barrier layer material for metal supported cells3, due to their electrical conductivity and acceptable coefficients of thermal expansion. However interactions of perovskites with electrolyte materials such as doped zirconia are known to cause zirconate formation depending on temperatures and oxygen partial pressure 4. In this study we demonstrate how the presence of metallic nickel at the phase boundary affects the zirconate formation at the solid state perowskite-fluorite interface. Different compositions of La1-xCaxCr1-yTiyO3-δ (x = 1, 0.95, 0.7, 0.6, 0.5, 0.4; y = 1, 0.9, 0.8) were synthesized and reactivity with yttria doped zirconia (8YSZ) and nickel-8YSZ-cermets have been investigated by means of X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy after 80 hours at 1300 °C in reducing atmosphere (H2). The results indicate that under certain conditions there is no zirconate formation in the absence of nickel, whereas if nickel is present at the interface, calcium- and or lanthanum zirconate formation take place, depending on the La/Caratio of the A-site doping. Thermodynamic calculation and EDX spectra consistently indicate nickel-titanium alloy formation as a reason for the destabilization of the perovskite lattice within a range of 10-19.4 < a(O2) < 10-16.5 at 1300 °C

Methane electro-oxidation on a Y0.20Ti0.18Zr0.62O1.90 anode in a high temperature solid oxide fuel cell

A high temperature solid oxide fuel cell has been operated in low humidity (3 % H(2)O) methane using Y(0.20)Ti(0.18)Zr(0.62)O(1.90) (YTZ) as the anode. The mechanism of methane electro-oxidation was investigated using ac and dc techniques at different anodic overpotentials and methane concentrations in the temperature range 788 - 932 degrees C. It was found that YTZ did not support methane cracking and that its electrocatalytic activity was stable over a long period of operation. Anode performance was significantly enhanced under positive polarization. Although the system showed good stability under low humidity methane conditions, the electrochemical performance was inferior to that observed for conventional anodes, albeit under high humidity methane or hydrogen fuel conditions. The overall area specific polarization resistance decreased from 167.88 Omega cm(2) to 10.14 Omega cm(2) between open and short (E(cell) = 0 V) circuit. Altering the fuel to steam ratio showed that the steam reforming of methane was the main source of power generation at low methane concentrations. Direct methane oxidation was too slow to be discerned under these conditions, but could co-exist with steam reforming at higher methane concentrations.</p