Performance improvement of oxygen electrode in reversible protonic ceramic electrochemical cell by co-doping of La and F

Abstract

Reversible protonic ceramic electrochemical cell (R-PCEC) has demonstrated high potential as an energy storage and conversion device. Efforts have primarily concentrated on the development of oxygen electrodes being to increase their performance and reduce performance degradation. In this work, three perovskite materials, namely Ba0.9Co0.2Fe0.7Nb0.1O3-δ (BCFN), Ba0.8La0.1Co0.2Fe0.7Nb0.1O3-δ (BLCFN), and Ba0.8La0.1Co0.2Fe0.7Nb0.1F0.1O2.9-δ (BLCFNF) are investigated. Both doping with La and co-doping with La and F lead to a notable reduction in the average valence states of Fe, Co, and Nb elements, further resulting in an increase in oxygen vacancy concentration, thereby enhancing the oxygen migration ability of the material. The H2O partial pressure does not have a significant impact on the polarization resistance (Rp) of the oxygen electrode. Conversely, the rise in Rp is highly correlated with the decrease in oxygen partial pressure, suggesting that the primary factor influencing the reaction rate of the oxygen electrode process is the exchange of oxygen ions on the surface of the electrode. BLCFNF exhibits the best oxygen migration and surface exchange ability, resulting in the lowest Rp. When BLCFNF was used as the oxygen electrode in a R-PCEC with the humidity air (10%H2O) and humidified H2 (3%H2O) as oxidant and fuel, respectively, it exhibits the highest maximum power density of 472 mW cm−2, and a current density of −682.6 mA cm−2 (1.3 V) at 650 °C. In addition, BLCFNF also shows good durability in both discharge and electrolysis process. The results indicate that La and F co-doped BLCFNF material is a promising oxygen electrode material for R-PCECs.