Publication date: 10th April 2024
Symmetrical Solid Oxide Cells (SOCs) are one of the most interesting energy conversion and storage devices. The concept of symmetrical construction is associated with the use of same compounds as the anode and cathode, which can decrease the number of cell components and simplify the fabrication and later recycling processes. However, electrode materials for symmetrical design must meet certain requirements, such as good structural stability in reducing and oxidizing atmospheres, and excellent electrocatalytic activity towards fuel oxidizing and oxygen reduction [1-4]. The application of materials with the ability to in situ exsolution of nanoparticles in the SOCs electrodes is considered to be highly beneficial, allowing for the improvement of catalytic activities and stability [4]. Moreover, nanofiber-structured electrodes with highly favorable microstructure including continuous porosity and more reaction sites, efficiently contribute to a significant enhancement of the electrochemical performance of SOCs, especially in lower work temperature ranges [5].
In this work, the A-site deficient (Sm/Nd)0.9Ba0.9Mn1.8-xFexNi0.1Co0.1O6-δ perovskites with double perovskite structure (A-site cations ordering, P4/nmm space group) were successfully synthesized by the soft chemistry method. The obtained double perovskites can potentially present excellent ionic diffusion properties due to the layered structure. A continuous phase transition from P4/nmm to P4/mmm was recorded for the studied materials at around 200 °C, characterized by the second order. The measured thermal expansion coefficient (TEC) values are very close to TECs of mostly used electrolytes (including La0.9Sr0.1Ga0.8Mg0.2O3−δ and Ce0.8Gd0.2O2−δ). The obtained (Sm/Nd)0.9Ba0.9Mn1.8-xFexNi0.1Co0.1O6-δ compounds show excellent redox stability, favoring their application as potential electrode materials for symmetrical SOCs. It has been found that the A-site nonstoichiometry (Sm0.9/Nd0.9Ba0.9) favors the in situ exsolution of metallic nanocatalysts from the parent materials in reducing conditions, therefore boosting the electrochemical performance of SOCs. The presence of in situ exsolved nanoparticles (CoNix and CoNixFey) was confirmed on the surface of reduced compounds by the SEM and HR-TEM studies. Interestingly, the dissolution of exsolved nanoparticles to the parent material was also observed in the oxidizing atmosphere at elevated temperatures. Nanofiber-structured electrodes fabricated by the electrospinning technique, significantly impact the exsolution process of nanoparticles, and boost the electrochemical properties of constructed SOCs. Excellent electrochemical performance of the proposed perovskite electrodes was recorded in the reducing condition. Sm/Nd0.9Ba0.9Mn1.8-xFexNi0.1Co0.1O6-δ-based symmetrical cell exhibits as low as 0.005 Ω·cm2 electrode polarization at 850°C in 5 vol. % H2/argon, which indicates that the investigated perovskite is particularly of interest for the application as anode material.
The work is funded by the National Science Centre Poland (NCN) based on the decision number UMO-2021/43/D/ST5/00824. Jakub Lach and Kun Zheng acknowledge the financial support of research project supported by the program „Excellence Initiative – Research University” for the AGH University of Krakow.
HRTEM, EDS and SAED results were a part of CERIC-ERIC grant no. 20232033 and were conducted in Institut National Institute of Materials Physics, Măgurele in Romania.
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