Cu-content La_1−xSr_xNi_1−yCu_yO_3−δ perovskites with A-site strontium doping have been tuned as cobalt-free cathode materials for high-performance anode-supported SOFCs, working at an intermediate-temperature range. All obtained oxides belong to the R-3c trigonal system, and phase transitions from the R-3c space group to a Pm-3m simple perovskite have been observed by HT-XRD studies. The substitution of lanthanum with strontium lowers the phase transition temperature, while increasing the thermal expansion coefficient (TEC) and oxygen non-stoichiometry δ of the studied materials. The thermal expansion is anisotropic, and TEC values are similar to commonly used solid electrolytes (e.g., 14.1 × 10⁻⁶ K⁻¹ for La_0.95Sr_0.05Ni_0.5Cu_0.5O_3−δ). The oxygen content of investigated compounds has been determined as a function of temperature. All studied materials are chemically compatible with GDC-10 but react with LSGM and 8YSZ electrolytes. The anode-supported SOFC with a La_0.95Sr_0.05Ni_0.5Cu_0.5O_3−δ cathode presents an excellent power density of 445 mW·cm⁻² at 650 °C in humidified H₂. The results indicate that La_1−xSr_xNi_1−yCu_yO_3−δ perovskites with strontium doping at the A-site can be qualified as promising cathode candidates for anode-supported SOFCs, yielding promising electrochemical performance in the intermediate-temperature range.

Solid oxide cells (SOCs) can operate efficiently in solid oxide fuel cell (SOFC) and/or solid oxide electrolysis cell (SOEC) modes, and are one of the most promising electrochemical devices for energy conversion and storage, facilitating the integration of renewable energies with the electric grid. However, the SOC electrodes suffer performance and stability issues, especially in the case of fuel electrodes when SOCs are fueled by cheaper and more available fuels such as methane and natural gas. Typical Ni-YSZ cermet fuel electrodes suffer problems of coarsening, carbon deposition, and sulfur poisoning. Therefore, developing new electrodes using novel design strategies for SOCs is crucial. In this review work, the fuel electrode development strategies including the in situ exsolution of nanoparticles, multi-elemental nanocatalysts, and nanofiber materials have been reviewed and summarized for the design of new electrodes for SOCs. Nanofiber electrodes with in situ exsolved nanoparticles, which combine the advantages of a unique nanofiber microstructure and stable and active exsolved nanoparticles, are of great interest and significantly contribute to the development of high-performance fuel electrodes for SOCs.

In this work, A-site deficient Sm_0.9Ba_0.9Mn_1.8−xFe_xCo_0.1Ni_0.1O_6−δ (x = 0, 0.45 and 0.9) double perovskites with in situ exsolved nanoparticles were successfully obtained and evaluated as electrode materials for symmetrical Solid Oxide Cells (SOCs). All obtained oxides belong to the P4/nmm tetragonal system, and a phase transition from P4/nmm to P4/mmm was recorded by the HT-XRD in the air. The in situ exsolution of nanoparticles has been confirmed by the XRD and SEM analysis. The proposed materials present excellent redox stability and moderate thermal expansion coefficients. Electrospun nanofibers (with 150 nm diameter) were successfully fabricated, indicating an excellent potential application in the electrode. The results show the developed A-site deficient double perovskites with iron doping at Mn-site can be potentially applied as novel electrode materials for symmetrical SOCs.

Solid Oxide Cells (SOCs) are among the most promising green technologies for energy generation and storage. Electricity and heat can be produced using SOCs in fuel cell mode from traditional and renewable energy sources. When electricity consumption is low, the excess electrical energy can be stored in green hydrogen produced by SOCs in electrolysis mode. However, the excellent performance of SOCs is usually recorded rather at high temperatures (≥800 °C), which contributes to high operating costs, limitations in the choice of device materials, making SOCs commercially unviable. To increase economic competitiveness, it is imperative to reduce the working temperature to a range of ≤700 °C while still maintaining a high-power yield. At the desired low operating temperature, most electrode materials lose their excellent electrochemical properties, and the performance of SOCs decreases radically. Therefore, the development of new electrodes with improved electrocatalytic properties at a low temperature range is critical. The design of heterostructured electrodes with dual phases delivering a synergistic effect, significantly benefits the performance of SOCs, including the fabrication of heterostructured electrodes using mechanical milling, self-assembling techniques and in situ exsolution of nanocatalysts [1-3]. In this study, various strategies for engineering heterostructured electrodes have been employed and explored, targeting to boost the electrode performance for SOCs. Mechanically milled composites, one-pot synthesized electrode materials and in situ self-assembled heterostructured nanofibers were fabricated and studied as electrodes for SOCs, allowing to boost the electrochemical performance of electrodes at intermediate temperature range (≤700 °C). The assembled heterostructured electrode GdBa _0.5 Sr _0.5 CoCuO _5+δ and Ce _0.9 Gd _0.1 O _1.95 shows stable and outstanding performance with electrode polarization Rp ≈ 0.05 Ω·cm ^-2 over 480 h at 800 °C, and excellent power outputs (>1000 mW·cm ^-2 at 700 °C) were recorded. In addition, heterostructured electrodes via the formation of A-site deficient Ln _x Sr _2-x Fe _1.4 Ti _0.2 M _0.2 Ni _0.1 Co _0.1 O _6-δ (Ln = selected lanthanides; M = Mo, W, Cr, Mn) perovskites with in situ exsolved nanoparticles were designed. The in situ exsolution of nanoparticles on the surface of nanofibrous electrodes was investigated for improving the performance of SOCs. References: [1] Z. Liu, Y. Bai, H. Sun, D. Guan, W. Li, W. Huang, C. Pao, Z. Hu, G. Yang, Y. Zhu, R. Ran, W. Zhou, Z. Shao, Nature Communications, 15 (2024) 472. [2] K. Kousi, C. Tang, I.S. Metcalfe, D. Neagu, Small, 17 (2021) 2006479. [3] K. Zheng, J. Lach, P. Czaja, M. Gogacz, P. Czach, A. Brzoza-Kos, P. Winiarz, J. Luo, Journal of Power Sources, 587 (2023) 233707. Acknowledgements: The work is funded by the National Science Centre Poland (NCN) based on the decision number UMO-2021/43/D/ST5/00824. Kun Zheng also acknowledges the financial support of research project supported by the program „Excellence Initiative – Research University” for the AGH University of Krakow.