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 Ba_0.5Gd_0.8La_0.7Co₂O_6−δ–BaZr_0.5Ce_0.4Y_0.1O_3−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 (η_FE) 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 (t_e) and ionic (t_i) transference numbers, real polarization resistance and η_FE 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.