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)_0.1O_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_xFe_yZr_zO_3−δ (M-BCCFZ), and a dominant proton-conducting phase, BaCe_1−(x+y+z)Co_xZr_yFe_zO_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 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.