Influence of La/Pr Ratio on the Ageing Properties of La2-X Pr x NiO4+δ as Cathodes in IT-SOFCs

Abstract

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. Ln2NiO4+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). Pr2NiO4+δ shows excellent electrochemical properties at intermediate temperature (i.e. low polarization resistance Rp value, Rp = 0.03 Ω.cm² at 700 °C), while La2NiO4+δ exhibits higher chemical stability. Thus, the properties of La2 -x Pr x NiO4+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 idc = 0 and idc ≠ 0 conditions) were studied for duration up to one month. La2NiO4+δ is chemically stable whereas Pr2NiO4+δ dissociates after 1 month at 600, 700 and 800 °C. At idc = 0 condition, the ageing of the half cells during 1 month under air shows no change in Rp , despite their various degrees of chemical stability. A different behavior is observed under idc ≠ 0 conditions with a large increase in Rp for Pr-rich phases in SOFC mode while interestingly, Rp remain stable in SOEC mode. In this presentation, the electrochemical properties of La2 -x Pr x NiO4+δ under ageing and postmortem analysis will be discussed in details.