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 La3Ni2O7þd (L3N2) and La4Ni3O10d (L4N3) powders for the preparation of solid oxide fuel cell cathodes. Both samples crystallize in a Fmmm orthorhombic layered Lanþ1NinO3nþ1 Ruddlesden-Popper structure, with n ¼ 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 11.0 106 K1 and 11.5 106 K1, respectively.
This study focused on L3N2, L4N3 and on novel composite electrodes with CGO (Ce0.9Gd0.1O2d): 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 Lanþ1NinO3nþ1 (n ¼ 2 and 3). A significant improvement of the polarization resistance, from 1.0 to 0.03 U cm2 and from 1.5 to 0.52 U cm2 at 700 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 C for 2 weeks in air, confirming its suitability as a SOFC cathode.
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