Electrical properties in La2Sr4Ti6O19−δ: a potential anode for high temperature fuel cells

La2Sr4Ti6O19−δ has been investigated as a potential anode for fuel cells due to the high total conductivity found under reducing conditions. This mixed oxide is the n=6 member of the excess oxygen perovskite-related family La2Srn−2TinO3n+1. The structure of this family of compounds can be described as perovskite slabs joined by crystallographic shears where the characteristic excess oxygen of these mixed oxides is accommodated. Phases such as La2Sr4Ti6O19−δ could be considered as a potential oxygen ion or proton conductor due to the significant amount of interstitial oxygen found in both reduced and oxidised forms. Partial removal of the excess oxygen by reduction of Ti4+ might lead to an enhancement of the ionic conductivity together with electronic conductivity due to the presence of Ti3+. The electrical properties of this material have been studied in a range of oxygen and water partial pressure revealing the important role played by δ, i.e. the amount of Ti3+, on these phases. Under the most reducing conditions, metallic conductivity, e.g. 60 S cm−1, is observed and under slightly higher P(O2), e.g. wet hydrogen, a metal to insulator transition is observed. In addition, initial fuel cell tests were carried out to check the performance of La2Sr4Ti6O19−δ as an anode for fuel cells. Using La2Sr4Ti6O19−δ as an anode, the polarisation resistance (Rp) varies from 2.97 Ω cm2 at 900 °C in wet H2 to 8.93 Ω cm2 at 900 °C operating in wet CH4. A current value of 119 mA cm−2 at 600 mV was found, whereas the maximum power density was 76 mW cm−2 both measured in wet H2 at 900 °C.