Activity and Stability of (Pr1-xNdx)(2)NiO4 as Cathodes for Solid Oxide Fuel Cells III. Crystal Structure, Electrical Properties, and Microstructural Analysis

This study is to complement an early article (Dogdibegovic et al., J. Electrochem. Soc., 163(13), F1344 (2016)) on the electrochemical activity and performance stability of (Pr1-xNdx)(2)NiO4+delta (PNNO) electrodes. Here, we report the crystal structure, electrical properties, and microstructures of PNNO series as the cathodes for solid oxide fuel cells. Rietveld refinements on powders (x = 0, 0.25, 0.50, 0.75, and 1) show that the unit cell volume decreases with an increase in x, primarily due to a decrease in the c lattice parameter. Larger cell volume (similar to 1.50%) and higher total electrical conduction (40%) in Pr2NiO4+delta are in favor with its mixed conducting properties during operation, but Pr2NiO4+delta cathode exhibits a severe phase evolution. Substitution of Pr with Nd shows the suppression of phase evolution in both thermally annealed powders and electrodes. An increase in Nd content leads to a full preservation of the parent phase in both (Pr0.25Nd0.75)(2)NiO4+delta and Nd2NiO4 after 2,500 hour annealing at elevated temperatures. Reaction with GDC buffer layer was also suppressed with the presence of Nd, which was shown by a reduction of Pr and Ni elemental diffusion into GDC bulk. STEM analysis confirms multiple phases present in an operated Pr2NiO4+delta electrode, while suppressed phase transition was observed in electrodes with high Nd content. (c) 2016 The Electrochemical Society

Activity and Stability of (Pr1-xNdx)(2)NiO4 as Cathodes for Solid Oxide Fuel Cells: Part V. In Situ Studies of Phase Evolution

This study is to complement an early report (the manuscript is attached for review purpose) on the role of interlayer on activity and performance stability in praseodymium nickelates. The aforementioned report showed a remarkable 48% increase in power density while switching from common GDC interlayer to a new interlayer chemistry (PGCO). Furthermore, a stable long-term performance was linked with suppressed reaction between the cathode and PGCO interlayer. In this article, we report in situ studies of the phase evolution. The high energy XRD studies at a synchrotron source showed fully suppressed phase transition in praseodymium nickelates with PGCO interlayer, while the electrodes on the GDC interlayer undergo substantial phase transformation. Furthermore, in operando and post-test XRD analyses shown fully suppressed structural changes in electrodes operated in full cells at 750 degrees C and 0.80 V for 500 hours. SEM-EDS analysis showed that the formation of PrOx at the cathode-interlayer interface may play a role in a decrease of mechanical integrity of the interfaces, due to thermal expansion mismatch, leading to a local stress between the two phases. Consequently, phase evolution at a narrow interface may propagate toward the electrode bulk, leading to structural changes and performance degradation. (C) The Author(s) 2017. Published by ECS. All rights reserved

The Role of Interlayer on the Catalytic Activity and Performance Stability of (Pr1-xNdx)(2)NiO4 as Cathodes for Solid Oxide Fuel Cells

Design optimization; reaction sphere; support vector machines; finite element metho