Study of praseodymium strontium manganite for the potential use as a solid oxide fuel cell cathode

Abstract

Extensive research has been performed on solid oxide fuel cell cathodes. These cathodes must be stable in the oxidation environment and have sufficient electrical conductivity and catalytic activity for the oxidant gas reaction at the appropriate operating temperature. Also, the cathode must be chemically and thermally compatible with the other cell components at room temperature, operating temperatures, and higher fabrication temperatures. Praseodymium strontium manganite (PSM) has shown promising electrical properties with respect to ideal properties of cathodes in solid oxide fuel cells. Various dopant levels of strontium in the perovskite structure were investigated, which include Pr 1-xSr xMnO 3-delta where x = 0.10, 0.20, 0.30 and (Pr 1- xSr x)0.98MnO 3-delta where x = 0.20 and 0.30. This cathodic material has shown electrical conductivity over twice as high as a traditionally used cathode, La 0.8Sr 0.2MnO 3. Through this investigation, the electrical and ionic conductivities of this ceramic series were measured from 200°C to 950°C. Another important electrical measurement investigated was the Seebeck coefficient within the same temperature range. This coefficient is a measurement of the change in voltage across a temperature gradient and thus can be referred to as its thermal power. Conductor types have been interpolated from the measurements. This measurement provides an improved understanding of the high electrical properties displayed within the material. Cathodic overpotential was also measured using half cell reactions performed in the temperature range of 650°C to 850°C under both air and pure oxygen. This measurement was used to calculate the current exchange density of the cathode and the area specific resistance. Overall, as the strontium concentration increased, the electrical activity of the ceramic subsequently increased. Furthermore, in relation to the traditional cathode material, La 0.8Sr 0.2MnO 3, the substitution of lanthanum with praseodymium has produced more effective cathodic performance.