Functionally graded and homogeneous composites of La2NiO4+δ and Lan+1NinO3n+1 (n = 2 and 3) solid oxide fuel cell cathodes

Abstract

This paper presents a view to better design SOFC cathode materials based on the combination of Ruddlesden–Popper (RP) phases. The influence of composite cathodes over single phases on electrochemical properties was studied, based on nickelate compounds. These electrodes are a mixture of La₂NiO_4+δ (L2N1) and La_n+1Ni_nO_3n+1 (n = 2, L3N2 or 3, L4N3) homogeneously distributed or with a gradient in composition. All these phases crystallize in an Fmmm orthorhombic layered Ruddlesden–Popper structure. Screen printing (SP) and Electrostatic Spray Deposition (ESD) have been used to architecturally design these electrodes. The functionally graded cathodes show better electrical performance with respect to the homogeneous ones. Polarization resistance (R_pol) values as low as 0.21 and 0.22 Ω cm² at 600 °C are achieved for cathodes based on L2N1 : L3N2 and L2N1 : L4N3 phases, respectively. This grading process appears to be an attractive strategy to improve the cathode performance. Moreover, the stability of both graded composite cathodes was investigated over 15 days in air at 650 °C.