A-Site Cation Deficiency in Mixed Nickelate Nd _2-X Pr _x NiO₄₊ _δ Cathodes for Solid Oxide Fuel Cells

Rare-earth nickelates Ln 2 NiO 4+ δ (Ln = Pr, Nd) with perovskite-related structure are very promising cathodes materials for SOFCs ( Solid Oxide Fuel Cells ) due to their high ionic and electronic conductivities as well as their electrocatalytic properties. 1 Theses phases crystallize in the a Ruddlesden-Popper (RP) structure, with the intergrowth of n LnNiO 3 perovskite layers for one NaCl-type LnO layer. Electronic conductivity is provided by the NiO 6 octahedra in the perovskite layer, while anionic diffusion takes place mainly via interstitial oxygen sites in the NaCl layer. Neodymium nickelate (Nd 2 NiO 4+ ⸹ ) exhibits excellent chemical stability and a moderately good electrochemical performance. In contrast, praseodymium nickelate Pr 2 NiO 4+ ⸹ , presents a very low ASR ( Area Specific Resistance ) but shows a limited chemical stability especially during SOFC operation. Aiming to find a trade-off between the high electrochemical performance of Pr 2 NiO 4+ ⸹ and the excellent chemical stability of Nd 2 NiO 4+ ⸹ , the solid solution with the general formula Nd 2-x Pr x NiO 4+ ⸹ (x = 0.5, 1, and 1.5) has been studied. The different compositions were successfully synthesised via the citrate-nitrate route. The solid solution was characterised by XRD, and the lattice parameters exhibit intermediate values between those of Pr 2 NiO 4+ ⸹ and Nd 2 NiO 4+ ⸹ . Their crystallographic structure was studied and the oxygen content of each material was measured. The electrochemical performances measured on symmetrical cells showed lower ASR values for the NdPrNiO 4+ ⸹ compound. For further investigations, we aimed to introduce a limited cation vacancies amount into the lanthanide (Ln) sub-lattice, which could influence the oxygen non-stoichiometry, the electronic structure and conductivity as well as the electro-catalytic activity. Original compositions such as (NdPr) 2-x NiO 4+ ⸹ with x = 0, 0.05, 0.1 were successfully prepared. The electrochemical performance studies carried on the corresponding half symmetrical cells showed an ASR of 40 mΩ.cm 2 at 700 °C, i.e; among the best ones reported in the literature. Ageing measurements are currently in progress. Morales-Zapata, M. A., Larrea, A. & Laguna-Bercero, M. A. Lanthanide nickelates for their application on Solid Oxide Cells. Electrochimica Acta 444 , 141970 (2023).