P-Substituted Ba_0.95La_0.05FeO_3-δ as a Cathode Material for SOFCs

The need for clean and efficient energy conversion systems has stimulated tremendous research activities in the area of energy systems. Solid oxide fuel cells stand out because of their high efficiency and low emissions. In spite of the promise, to commercialize solid oxide fuel cells, the operating temperature needs to be reduced below 800 °C. Unfortunately, at such low temperatures the oxygen reduction reactions taking place at the cathode side of the solid oxide fuel cells are typically sluggish. Ferrites have recently shown that they can overcome this challenge. However, the conductivity of these materials is typically low. Here, we show by density functional theory calculations that substituting Fe in Ba_1-xLa_xFeO_3-δ with P lowers both the O vacancy formation and vacancy migration energies and promotes the creation of PO₄ groups. These factors contribute to improving the diffusional properties and oxygen reduction reaction performance. We further successfully introduce P in the Fe-site of Ba_0.95La_0.05FeO_3-δ to make a novel cathode material, Ba_0.95La_0.05Fe_0.95P_0.05O_3-δ. Consistently, we observe that Ba_0.95La_0.05Fe_0.95P_0.05O_3-δ has higher electrical conductivity and better electrocatalytic activity compared to Ba_0.95La_0.05FeO_3-δ. In light of these results, we suggest that nonmetal element doping is an effective strategy for the design of new ferrites.