Lan+1NinO3n+1 (n=2 and 3) phases and composites for solid oxide fuel cell cathodes: Facile synthesis and electrochemical properties

In this work we present a modified citrate-nitrate route using citric acid as a chelating agent as an effective and facile strategy to obtain nanocrystalline La3Ni2O7+delta (L3N2) and La4Ni3O10-delta(L4N3) powders for the preparation of solid oxide fuel cell cathodes. Both samples crystallize in a Fmmm orthorhombic layered Lan+1NinO3n+1 Ruddlesden-Popper structure, with n = 2 and 3, respectively. The oxygen nonstoichiometry, determined by TGA is equal to 0.05 and 0.06 for L3N2 and L4N3, respectively. The thermal expansion coefficient values of L3N2 and L4N3 are 11.0 x 10(-6) K-1 and 11.5 x 10(-6) K-1, respectively. This study focused on L3N2, L4N3 and on novel composite electrodes with CGO (Ce0.9Gd0.1O2-delta): L3N2-CGO and L4N3-CGO with a view to taking advantage of their complimentary properties, i.e. high ionic conductivity of CGO and high electronic conductivity of Lan+1NinO3n+1 (n = 2 and 3). A significant improvement of the polarization resistance, from 1.0 to 0.03 Omega cm(2) and from 1.5 to 0.52 Omega cm(2) at 700 degrees C, is obtained when 50 wt% CGO is added to L3N2 and L4N3, respectively. In addition, the L3N2-CGO composite shows good long-term stability at 900 degrees C for 2 weeks in air, confirming its suitability as a SOFC cathode. (C) 2016 Elsevier B.V. All rights reserved.