Stable, efficient and cost-competitive Ni-substituted Sr(Ti,Fe)O3 cathode for solid oxide fuel cell: Effect of A-site deficiency

In this work, a cost-competitive oxide system of Ni-substituted Sr_1-xTi_0.3Fe_0.6Ni_0.1O_3-δ (STFN, x = 0, 0.02, 0.05), is evaluated as Solid Oxide Fuel Cell cathode. All STFN oxides present cubic perovskite structure with maximum conductivities over 22 S/cm in air. The introduction of Sr deficiency yields higher oxygen vacancy and lower thermal expansion coefficient. As a result, the cathode polarization resistance of 0.107 Ω cm² is obtained for Sr_0.95Ti_0.3Fe_0.6Ni_0.1O_3-δ (STFN-95) at 750 °C and p_O2 = 0.21 atm , with weak oxygen partial pressure dependence. Specially, STFN-95 presents higher stability with slower R_p increasing rate in lower oxygen partial pressure of 0.14 atm than in 0.21 atm, which greatly facilitates the cathode practical application in SOFC stack under high air utilization condition. Finally, a stable operation of 400 h is achieved using STFN-95 cathode on anode supported single cell at 750 °C, without showing Sr and other elements diffusions.