It was found that substitution of the smaller Nd3+ ion for La3+ ions in La2NiO4+δ increased the retention of mobile interstitial O defects (Oi″ ions). The concentration of the Oi″ ions in Nd2NiO4+δ stabilized at δ ≈ 0.12 in air at 800C after thermal cycling. As a mixed oxide-ion/electronic conductor, Nd2NiO4+δ gave a performance which was comparable to that of the best perovskite cathode material, SrCo0.8Fe0.2O3−δ. However, the Nd2NiO4+δ cathode exhibited a higher overpotential with La0.8Sr0.2Ga0.83Mg0.17O2.815 as the electrolyte; due presumably to the interdiffusion of La3+ and Nd3+ ions across the electrolyte/cathode interface and the subsequent formation of ion-blocking phases at the interface. On the other hand, La1.2Nd0.8NiO4+δ provided La iso-activity across the La0.8Sr0.2Ga0.83Mg0.17O2.815/cathode interface and therefore an improved performance with the La0.8Sr0.2Ga0.83Mg0.17O2.815 electrolyte. Since Nd2−xLaxNiO4+δ contained neither Sr nor Co, it was expected to be compatible with electrolytes such as yttria-stabilized zirconia; without need of a buffer layer.

Nd2−xLaxNiO4+δ, a Mixed Ionic/Electronic Conductor with Interstitial Oxygen, as a Cathode Material. J.Wan, J.B.Goodenough, J.H.Zhu: Solid State Ionics, 2007, 178[3-4], 281-6