Influence of La/Pr Ratio on the Ageing Properties of La_2-X Pr _x NiO_4+δ as Cathodes in IT-SOFCs

Abstract

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.

Structural transformations of the La2−xPrxNiO4+δ system probed by high-resolution synchrotron and neutron powder diffraction

“…This adds considerable new detail to previous investigations which reported only orthorhombic structures across the La2-xPrxNiO4+δ (LPNO) series. [15][16][17][18][19]48 A lower resolution diffraction study of the related La2-xNdxNiO4+δ system reports similar trends, with quasi-tetragonal La-rich compositions and smaller orthorhombically strained Nd-rich unit cells. 62 It is possible that future studies of the La2-xNdxNiO4+δ system will reveal additional complexity analogous to that observed in this current study.…”

“…Promising electrochemical properties of the PNO end member (x = 2.0) are undermined by poor chemical stability at elevated temperatures corresponding to SOFC operating conditions. [10][11][12][13][14]18 The monoclinic distortion and supercell ordering seen at ambient temperature here may therefore reflect a highly strained structure that readily decomposes to more thermodynamically stable compositions.…”

“…However, in bulk ceramics, this more Prrich composition is unstable at operating temperatures vs. time. 18…”

“…[10][11][12][13][14] For this reason, there has been recent interest in mixed PNO-LNO compositions which could offer a compromise of chemical stability and electrochemical performance. [15][16][17][18][19] However, despite investigations spanning three decades, the phase diagram of the La2-xPrxNiO4+δ system; as a function of composition, oxygen stoichiometry, and temperature, is still unclear. In the current work, a fundamental crystallographic study of the La2-xPrxNiO4+δ series has been performed using high resolution synchrotron and neutron powder diffraction data.…”

Структура, стабильность и термомеханические свойства Ca-замещенного Pr-=SUB=-2-=/SUB=-NiO-=SUB=-4+delta-=/SUB=-

“…Это приводит к быстрому старению электродов на его основе, особенно в режиме топливного элемента [14].…”