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)0.1O3−δ (BCCFZ) is designed via self‐assembly engineering. The material consists of a mixed ionic and electronic conducting phase, BaCo1−(x+y+z)CexFeyZrzO3−δ (M‐BCCFZ), and a dominant proton‐conducting phase, BaCe1−(x+y+z)CoxZryFezO3−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% H2O‐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. The multiphase material developed through self‐assembly engineering exhibits a high oxygen vacancy concentration. This consequently enhances its proton defect formation and transport with a low enthalpy of protonation reaching −30 ± 9 kJ mol−1. The peak power density of the single cell reaches 1054 mW cm−2 at 650 °C with good operation stability spanning over 500 h at 550 °C.