Design of La2−xPrxNiO4+δ SOFC cathodes: a compromise between electrochemical performance and thermodynamic stability

Abstract

Architecturally designed La_2−xPr_xNiO_4+δ (with x = 0, 0.5, 1 and 2) cathodes on the Ce_0.9Gd_0.1O_2−δ (CGO) electrolyte have been prepared with a view to take advantage of the complimentary properties of the two extreme compositions La₂NiO_4+δ and Pr₂NiO_4+δ, i.e. the superior stability of La₂NiO_4+δ and the higher electronic conductivity of Pr₂NiO_4+δ. The design consists of stacking of two layers starting with a 3D tree-like microstructure (∼20 μm thick) over a thin dense base layer (∼100 nm) fabricated in one step by electrostatic spray deposition (ESD) and then topped by using a screen-printed (SP) current collecting layer of the same composition. X-ray diffraction confirms the formation of a complete solid solution crystallizing in a single phase orthorhombic structure with the Fmmm space group. The thermodynamic stability and polarisation resistance (R_pol) decrease by increasing the Pr content. Among the complete La_2−xPr_xNiO_4+δ solid solutions, LaPrNiO_4+δ shows the best compromise between electrochemical properties (the lowest R_pol value available in the literature for this composition, 0.12 Ω cm² at 600 °C) and thermodynamic stability in air. Moreover, an anode supported single cell (Ni-3YSZ/Ni-8YSZ/8YSZ/CGO) including the LaPrNiO_4+δ double layer electrode shows a maximum power density of 438 mW cm⁻² at 700 °C.