Mechanically-Enhanced, Single-Phased, and Triple-Conducting Air Electrode for Robust Oxygen-Ion and Proton Conducting Ceramic Cells

Abstract

Reversible proton-conducting fuel cells (Re-PCFCs) are poised to become the next generation of solid-state ionic devices for direct conversion between hydrogen and electricity. However, their commercialization has been hindered by the absence of a high-performance triple-conducting air electrode that combines excellent electrochemical activity with superior mechanical robustness. Here, a robust single-phased air electrode is successfully developed with its mechanical strength and electrochemical activity greatly co-enhanced, by employing high valence Nb doping to stabilize the cubic perovskite lattice of pristine BaCe_0.2Fe_0.8O_3-δ. The resulting BaCe_0.1Fe_0.8Nb_0.1O_3-δ (BCFNb) air electrode demonstrates exceptional mechanical properties in terms of Young's modulus (by 47%) and fracture toughness (by 67%). Meanwhile, the distribution of relaxation times (DRT) and Oxygen temperature-programmed desorption (O₂-TPD) characterization reveals the enhanced oxygen mobility, surface exchange kinetics, and the mixed conductivity of oxygen ions and protons that synergistically resulted in the remarkably enhanced electrochemical activity—only a low area-specific resistances of 0.262 Ω·cm² at 550 °C, translated into a high power densities of 1.091 W cm⁻² at 650 °C with degradation rates <0.005 mV h⁻¹ in fuel cell mode and 0.14 mV h⁻¹ in electrolytic mode at 550 °C. These results highlight the potential of single-phased perovskite as air electrode for mechanically and electrochemically robust Re-PCFCs.