Rational Design of Ruddlesden-Popper Perovskite Ferrites as Air Electrode for Highly Active and Durable Reversible Protonic Ceramic Cells.

Reversible protonic ceramic cells (RePCCs) hold promise for efficient energy storage, but their practicality is hindered by a lack of high-performance air electrode materials. Ruddlesden-Popper perovskite Sr3Fe2O7-δ (SF) exhibits superior proton uptake and rapid ionic conduction, boosting activity. However, excessive proton uptake during RePCC operation degrades SF's crystal structure, impacting durability. This study introduces a novel A/B-sites co-substitution strategy for modifying air electrodes, incorporating Sr-deficiency and Nb-substitution to create Sr2.8Fe1.8Nb0.2O7-δ (D-SFN). Nb stabilizes SF's crystal, curbing excessive phase formation, and Sr-deficiency boosts oxygen vacancy concentration, optimizing oxygen transport. The D-SFN electrode demonstrates outstanding activity and durability, achieving a peak power density of 596 mW cm-2 in fuel cell mode and a current density of - 1.19 A cm-2 in electrolysis mode at 1.3 V, 650 °C, with excellent cycling durability. This approach holds the potential for advancing robust and efficient air electrodes in RePCCs for renewable energy storage.

Electrokinetic Insights into the Triple Ionic and Electronic Conductivity of a Novel Nanocomposite Functional Material for Protonic Ceramic Fuel Cells.

Triple ionic and electronic conductivity (TIEC) in cathode materials for protonic ceramic fuel cells (PCFCs) is a desirable feature that enhances the spatial expansion of active reaction sites for electrochemical oxygen reduction reaction. The realization of optimal TIEC in single-phase materials, however, is challenging. A facile route that facilitates the optimization of TIEC in PCFC cathodes is the strategic development of multiphase cathode materials. In this study, a cubic-rhombohedral TIEC nanocomposite material with the composition Ba(CeCo)0.4 (FeZr)0.1 O3- δ (BCCFZ) is designed via self-assembly engineering. The material consists of a mixed ionic and electronic conducting phase, BaCo1-( x + y + z ) Cex Fey Zrz O3- δ (M-BCCFZ), and a dominant proton-conducting phase, BaCe1-( x + y + z ) Cox Zry Fez O3- δ (H-BCCZF). The dominant cerium-rich H-BCCFZ phase enhances the material's oxygen vacancy concentration and the proton defects formation and transport with a low enthalpy of protonation of -30 ± 9 kJ mol-1 . The area-specific resistance of the BCCFZ symmetrical cell is 0.089 Ω cm2 at 650 °C in 2.5% H2 O-air. The peak power density of the anode-supported single cell based on BCCFZ cathode reaches 1054 mW cm-2 at 650 °C with good operation stability spanning over 500 h at 550 °C. These promote BCCFZ as a befitting cathode material geared toward PCFC commercialization.