A double perovskite oxygen electrode in Zr-rich proton conducting ceramic cells for efficient electricity generation and hydrogen production

Abstract

Proton conducting ceramic fuel cells and electrolyzers are nascent technologies. An operating temperature of about 600 °C calls for the development of specific oxygen electrodes with adequate catalytic activity and stability especially at high steam concentrations. An efficient composite oxygen electrode Ba0.5Gd0.8La0.7Co2O6−δ-BaZr0.5Ce0.4Y0.1O3−δ (BGLC587-BZCY541) with low polarization resistance and high durability in either mode is reported. Electronic leakage that occurs through the electrolyte due to intrinsic materials characteristics is a major issue that limits the faradaic efficiency (ηFE) especially in steam electrolysis. An equivalent circuit model was developed to deconvolute the effect of electronic leakage in the electrolyte and the oxygen electrode reaction process. The electronic (te) and ionic (ti) transference numbers, real polarization resistance and ηFE are shown to be strongly related to pH2O, pO2, applied current density and operating temperatures. Distribution of relaxation time analysis of electrochemical impedance spectra revealed that the rate-limiting step for steam electrolysis is a surface-related oxygen electrode process in the low-frequency range and that a triple phase boundary process at the contact point BGLC587-BZCY541 is favored over a pure double phase boundary process at the surface of BGLC587 yielding the conclusion that composite electrode structures may have to be favored to achieve high performance.