Exsolution of phase-separated nanoparticles via trigger effect toward reversible solid oxide cell

• Cu and Fe-doped perovskites are explored as electrode for a reversible SOCs. • Pre-exsolved Cu played a key role in triggering Fe exsolution via seeded effect. • The exsolved Cu/Fe nanoparticles are formed in heterogeneous Janus structure. • A reversible cell shows high power and current densities under H 2 /H 2 O and CO/CO 2 . • The high performance was achieved by electrical reduction and Cu/Fe nano-catalysts. The electrocatalytic characteristics of heterostructure nanoparticles have attracted attention for use in devices addressing energy and environmental issues. Among the various features, exsolved alloy or core–shell nanoparticles display high reactive surface area and strong interaction between the metal and substrate oxide. Herein, we report multifunctional heterostructure nanoparticles, namely Fe/Cu Janus nanoparticles (JN) and verify an exsolution trigger effect using Cu as a seed in the La 0.43 Sr 0.37 Fe 0.09 Cu 0.03 Ti 0.88 O 3-δ (Fe75) perovskite substrate. During the exsolution process, the exsolved Cu particles played a key role in triggering the Fe exsolution by contributing additional surface energy. These Fe/Cu JNs exhibited outstanding catalytic activity in a reversible solid oxide cell fed with H 2 O/H 2 and CO/CO 2 fuels. A single cell with Fe75 showed an impressive current density of − 1.11 A cm −2 at 1.3 V and 900 °C. Our study experimentally elucidated the mechanism of the triggering of co-exsolution and demonstrated a multifunctional catalyst using Fe/Cu JNs.