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

Abstract 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 O 3− δ (BCCFZ) is designed via self‐assembly engineering. The material consists of a mixed ionic and electronic conducting phase, BaCo 1−( x + y + z ) Ce x Fe y Zr z O 3− δ (M‐BCCFZ), and a dominant proton‐conducting phase, BaCe 1−( x + y + z ) Co x Zr y Fe z O 3− 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 cm 2 at 650 °C in 2.5% H 2 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.