New Perovskite Materials for Sensors and Low Temperature Solid Oxide Fuel Cell (LT-SOFC) Applications

This work involved the development of new perovskite oxides based on SmFeO3 and testing their performances as sensors for reducing gases (H 2, CO & CH4) and as anode materials for dry methane oxidation in solid oxide fuel cells. The new perovskite oxide materials with formula Sm0.95Ce0.05Fe1-xMxO3-δ (M= Co, Ni & Cr) were synthesized by a sol gel method using citric acid as a complexing agent. The resulting materials were characterized by using a battery of techniques including XRD, XRF, XPS, SEM and electrochemical methods.;Some materials were also selected on the basis of their reduction stability and electrical properties, and their electrochemical performances were evaluated as SOFC anodes under dry methane and dry hydrogen fuels separately. The performance tests as SOFC anode revealed that the best anode material for the oxidation of dry hydrogen fuel is Sm0.95Ce0.05FeO3-δ . Furthermore, Sm0.95Ce0.05FeO3-δ proved to be coke resistant anode under dry methane fuel and exhibited reasonably low charge transfer resistance values at temperatures between 600-700°C. The doping of Co and Ni at the B-site of Sm0.95Ce0.05FeO 3-δ found to be very effective in further improving its performance as SOFC anode towards oxidation of dry methane fuel at the lower temperatures.;Sensing experiments revealed that both cobalt doped and Cr doped materials can detect H2, CO and CH4 in air at different temperatures including room temperature. The Ni doped materials did not prove good candidates as sensors. However, their reduction treatment studies showed the formation of metallic nanoparticles on the surface which deeply influence their electrical conductivity as well as sensing ability. Consequently, this modification in surface structure and chemical composition enabled them to sense hydrogen gas at 300°C very effectively. The response of sensors based on these reduced materials was measurable and reversible.