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

Architecturally designed La2-xPrxNiO4+ delta (with x = 0, 0.5, 1 and 2) cathodes on the Ce0.9Gd0.1O2- delta (CGO) electrolyte have been prepared with a view to take advantage of the complimentary properties of the two extreme compositions La2NiO4+ delta and Pr2NiO4+ delta , i.e. the superior stability of La2NiO4+ delta and the higher electronic conductivity of Pr2NiO4+ delta . The design consists of stacking of two layers starting with a 3D tree-like microstructure ( similar to 20 mu m thick) over a thin dense base layer ( similar to 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 (Rpol) decrease by increasing the Pr content. Among the complete La2-xPrxNiO4+ delta solid solutions, LaPrNiO4+ delta shows the best compromise between electrochemical properties (the lowest Rpol value available in the literature for this composition, 0.12 Omega cm2 at 600 degree C) and thermodynamic stability in air. Moreover, an anode supported single cell (Ni-3YSZ/Ni-8YSZ/8YSZ/CGO) including the LaPrNiO4+ delta double layer electrode shows a maximum power density of 438 mW cm-2 at 700 degree C.