Influence of La/Pr Ratio on the Ageing Properties of La2-XPrxNiO4+δ as Cathodes in IT-SOFCs

The present study is focused on alternative oxygen electrodes for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs) using Metal Supported Cells (MSCs) conditions. To prevent detrimental oxidation of the metal support, sintering of the cell components at high temperature under low pO₂ is required. Ln₂NiO_4+δ (Ln = La, Pr) compounds with the K₂NiF₄-type structure act as cathode materials for IT-SOFC due to their mixed ionic and electronic conductivity (i.e. MIEC properties). Pr₂NiO_4+δ shows excellent electrochemical properties at intermediate temperature (i.e. low polarization resistance R_p value, R_p = 0.03 Ω.cm² at 700 °C), while La₂NiO_4+δ exhibits higher chemical stability. Thus, the properties of La_2-xPr_xNiO_4+δ mixed nickelates were investigated with the aim to find 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 during ageing (recorded under air at i_dc = 0 and i_dc ≠ 0 conditions) were studied for duration up to one month. La₂NiO_4+δ is chemically stable whereas Pr₂NiO_4+δ dissociates after 1 month at 600, 700 and 800 °C. At i_dc = 0 condition, the ageing of the half cells during 1 month under air shows no change in R_p, despite their various degrees of chemical stability. A different behavior is observed under i_dc ≠ 0 conditions with a large increase in R_p for Pr-rich phases in SOFC mode while interestingly, R_p remain stable in SOEC mode. In this presentation, the electrochemical properties of La_2-xPr_xNiO_4+δ under ageing and postmortem analysis will be discussed in details.