Controlled exsolution-dissolution in double perovskites enables symmetrical-capable high-performance SOFC electrodes

In situ exsolution has emerged as a powerful strategy for tailoring fuel electrode catalysts in solid oxide fuel cells (SOFCs), yet its integration with reversible exsolution-dissolution processes and its application to symmetrical-capable electrode design remain largely unexplored. Here, we demonstrate controlled exsolution-dissolution in nanofiber double perovskites as a rational route to engineer high-performance SOFC electrodes operable in both symmetrical and anode-supported configurations. Sm 0.9 Ba 0.9 Mn 1.8−x Fe x Co 0.1 Ni 0.1 O 5+δ nanofiber perovskites enable composition-dependent control of nanoparticle evolution. Under reducing conditions, socketed Co–Ni–Fe alloy nanocatalysts exsolve and partially embed into the perovskite lattice, while oxidation induces their transformation into Fe 3−x−y Ni x Co y O 4 -type hollow core–shell nano-oxides via a Kirkendall-type mechanism. The nanofiber architecture promotes smaller and more densely distributed nanoparticles compared to powders, enhancing catalytic activity and redox stability. The optimized composite electrode delivers a low polarization resistance of 0.046 Ω cm 2 at 800 °C. Anode-supported cells achieve a peak power density of 1112 mW cm −2 at 850 °C and 877 mW cm −2 at 800 °C, while symmetrical cells deliver 816 mW cm −2 at 800 °C with stable operation. This work establishes controlled exsolution-dissolution as a versatile platform for designing symmetrical-capable high-performance SOFC electrodes and highlights hollow core–shell nanostructure engineering as a powerful strategy for durable solid oxide electrochemical systems.