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The praseodymium oxide, Pr6O11, is regarded as a potential electrocatalyst for the oxygen reduction reaction. Its mixed conductivity properties are characterized. At 600 °C the oxygen diffusion coefficient value is as high as 3.4 × 10 −8 cm 2 s −1 , and that of the surface exchange coefficient is 5.4 × 10 −7 cm s −1 , which supposes excellent electrocatalytic properties. The measured electronic conductivity is high enough for using this material as a SOFC cathode. Herein, praseodymium nitrate is infiltrated into Gd doped ceria (GDC) backbone and fired at 600 °C to form a composite oxygen electrode Pr6O11/GDC. Electrochemical measurements show very low polarization resistance, Rp = 0.028 Ω cm 2 at 600 °C. A single cell made of a commercial Ni-YSZ/YSZ half cell and of the infiltrated cathode is able to deliver a maximum power density of 825 mW cm −2 at 600 °C. Ageing of this cell for 840 h, at 600 °C and 0.5 A cm −2 , shows a degradation rate lower than 1%.

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Aiming at a tradeoff between the chemical stability of La 2 NiO 4+ δ (LNO) and the high electrochemical performances of Pr 2 NiO 4+ δ (PNO), La 2 − x Pr x NiO 4+ 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 K 2 NiF 4 -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 pO 2 , 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 pO 2 , as requested in metal supported cell, (MSC-conditions) confirmed a decrease in polarization resistance values, R p , from 0.93 Ω cm 2 (LNO) down to 0.15 Ω cm 2 (PNO) at 600°C with increasing x.

International audienceThe present work is focused on the study of Pr4Ni3O10+δ as a new cathode material for Solid Oxide Fuel Cells (SOFCs). The structural study leads to an indexation in orthorhombic structure with Fmmm space group, this structure being thermally stable throughout the temperature range up to 1000 °C under air and oxygen. The variation of oxygen content (10+δ) as a function of temperature under different atmospheres show that Pr4Ni3O10+δ is always oxygen over-stoichiometric, which further suggests its MIEC properties. The polarization resistance (Rp) of Pr4Ni3O10+δ electrode is measured for GDC/co-sintered and two-step sintered half cells. The Rp for co-sintered sample is found to be 0.16 Ω cm2 at 600 °C under air, which is as low as the one of highest performing Pr2NiO4+δ nickelate (Rp = 0.15 Ω cm2 at 600 °C). Moreover, an anode supported (Ni-YSZ//YSZ) single cell including GDC//Pr4Ni3O10+δ co-sintered electrode shows a maximum power density of 1.60 W cm−2 at 800 °C and 0.68 W cm−2 at 700 °C. Here, the work is emphasized on the very close electrochemical performance of Pr4Ni3O10+δ compared to the one of Pr2NiO4+δ with higher chemical stability, which gives great interests to consider this material as a very interesting oxygen-electrode for SOFCs

The present study is focused on alternative oxygen electrodes for IT-SOFCs using Metal Supported Cells (MSCs) conditions. Ln 2 NiO 4+δ (Ln = La, Pr) compounds with the K 2 NiF 4 -type structure act as cathode materials for IT-SOFC due to their MIEC properties. Pr 2 NiO 4+δ (PNO) shows excellent electrochemical properties at intermediate temperature while La 2 NiO 4+δ (LNO) exhibits higher chemical stability. Thus, the properties of La 2-x Pr x NiO 4+δ (LPNO) mixed nickelates were investigated with the aim to find the best compromise between chemical stability and electrochemical performances. Herein, the chemical stability of the nickelates under air at operating temperatures as well as the evolution of the polarization resistances, R p , during ageing (i dc = 0 and i dc ≠ 0 conditions) were studied for duration up to one month. At i dc = 0 condition, the ageing of the half cells shows no change in R p . A different behavior is observed under i dc ≠ 0 conditions with an increase in R p in SOFC mode while interestingly, R p remains stable in SOEC mode.

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