Ce-induced phase separation in Sm0.6Sr0.4Co1-xCexO3−δ to form multiphase nanocomposite air electrodes for solid oxide and protonic ceramic cells

Ce-induced phase separation orchestrates a tri-phase nanocomposite architecture. • Optimized fluorite SDC ratio maximizes the triple-conducting transport network. • Excess pure ion-conducting SDC phase critically impedes charge transfer pathways. • SSCC1 delivers 1.64 and 1.30 W cm −2 in SOFC and PCFC modes at 650 °C. • The optimized cell shows exceptional reversible cycling stability over 240 h. Developing multiphase nanocomposite is an interesting approach for the air electrodes with high activity and durability for both solid oxide fuel cells and protonic ceramic cells. Herein, a Ce-induced phase separation strategy is reported to construct a multiphase nanocomposite (Sm 0.6 Sr 0.4 Co 0.9 Ce 0.1 O 3−δ ) comprising single-perovskite Sm 0.5 Sr 0.5 CoO 3-δ (SP-SSC), Ruddlesden-Popper SrSm 2 Co 2 O 7 (RP-SSC), and fluorite Sm 0.4 Ce 0.6 O 1.8 (SDC) phases. By precisely tailoring the phase proportions to balance proton, oxygen-ion, and electron conducting networks while maximizing active heterointerfaces, the optimized architecture unlocks exceptional oxygen electrocatalytic kinetics. The results reveal that exceeding the optimal ratio of the fluorite phase impedes charge transfer, highlighting the crucial role of delicate phase regulation. Furthermore, Density Functional Theory calculations reveal that this multiphase network enables a phase-specific division of labor, successfully achieving spatial decoupling of O 2 and H 2 O adsorption to mitigate their competitive adsorption. Consequently, the optimized composite electrode achieves remarkable peak power densities of 1.64 W cm −2 in SOFC mode and 1.30 W cm −2 in protonic ceramic fuel cell mode at 650 °C. Furthermore, an outstanding electrolysis current density of −2.19 A cm −2 at 1.3 V is attained, alongside robust reversible cycling stability over 240 h. This work provides significant insights into designing highly efficient multiphase air electrodes intended for future reversible ceramic electrochemical energy conversion.