La2-xPrxNiO4+δ as suitable cathodes for metal supported SOFCs
Résumé
Aiming at a tradeoff between the chemical stability of La2NiO4 + δ (LNO) and the high electrochemical performances of Pr2NiO4 + δ (PNO), La2 − xPrxNiO4 + δ mixed nickelates, further referred as LPNO, were studied as possible oxygen electrodes for solid oxide fuel cells (SOFCs). LPNO phases were synthesized using the modified citrate–nitrate route followed by a heat treatment at 1200 °C for 12 h under air. Structural characterizations of those K2NiF4-type compounds show the existence of two solid solutions with orthorhombic structure, namely a La-rich one from x = 0 to 0.5 with Fmmm space group, and a Pr-rich one from x = 1.0 to 2.0 with Bmab space group. The mixed ionic and electronic conducting (MIEC) properties of LPNO phases were investigated through the evolution of the oxygen over-stoichiometry, δ, measured as a function of temperature and pO2, the electrical conductivity, the diffusion and surface exchange coefficients versus x, showing that all compositions exhibit suitable characteristics as cathode materials for SOFCs. In particular, the electrochemical performances measured in symmetrical cells using LPNO materials sintered under low pO2, as requested in metal supported cell, (MSC-conditions) confirmed a decrease in polarization resistance values, Rp, from 0.93 Ω cm2 (LNO) down to 0.15 Ω cm2 (PNO) at 600 °C with increasing x.
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