Nb-doped PrBa <sub>0.8</sub>Ca <sub>0.2</sub>Co <sub>2</sub>O <sub>6</sub>-based perovskite cathode with improved oxygen reduction reaction activity and stability for solid oxide fuel cells
Depeng Zeng, Feng Zhu, Kang Xu, Hua Zhang, Yangsen Xu, Yu Chen
Abstract
The performance of a solid oxide fuel cell (SOFC) is strongly associated with the activity and durability of the cathode, where the oxygen reduction reaction occurs. In this study, we report our findings in the development of an Nb-doped PrBa<sub>0.8</sub>Ca<sub>0.2</sub>Co<sub>2</sub>O<sub>6−<i>δ</i></sub> (PrBa<sub>0.8</sub>Ca<sub>0.2</sub>Co<sub>2−<i>x</i></sub>Nb<sub><i>x</i></sub>O<sub>6−<i>δ</i></sub>, <i>x</i> = 0, 0.025, 0.05, and 0.1, denoted as PBCCN<sub><i>x</i></sub>) perovskite composite as the SOFC cathode. Analyses of X-ray diffraction (XRD) patterns and energy-dispersive transmission electron microscopy (TEM-EDS) images suggest that after being treated at 950 °C in air, PBCCN<sub>0.05</sub> mainly contains phases of Ca- and Nb-doped PrBaCo<sub>2</sub>O<sub>6−<i>δ</i></sub> double perovskite, PrCoO<sub>3</sub> perovskite with Ca and Nb doping, and Ba<sub>3</sub>Ca<sub>1.18</sub>Nb<sub>1.82</sub>O<sub>9−<i>δ</i></sub>. When evaluated as an SOFC cathode, the PBCCN<sub>0.05</sub> mixture has shown a low polarization resistance of 0.0074 Ω∙cm<sup>2</sup> at 800 °C in La<sub>0.8</sub>Sr<sub>0.2</sub>Ga<sub>0.8</sub>Mg<sub>0.2</sub>O<sub>3</sub> electrolyte symmetrical cells. Accordingly, anode-supported single cells with a configuration of Ni–Zr<sub>0.84</sub>Y<sub>0.16</sub>O<sub>2−<i>δ</i></sub> (YSZ)/YSZ/Gd<sub>0.1</sub>Ce<sub>0.9</sub>O<sub>2−<i>δ</i></sub>/PBCCN<sub>0.05</sub> display high electrochemical performance, with a peak power density of 1.81 W∙cm<sup>−2</sup> and a reasonable durability of 100 h at 800 °C. PBCCN<sub>0.05</sub> possesses a higher concentration of oxygen vacancies, a faster oxygen surface adsorption‒dissociation rate, and an increased mass ratio of PrCoO<sub>3</sub> perovskite with Ca and Nb doping compared to PrBa<sub>0.8</sub>Ca<sub>0.2</sub>Co<sub>2</sub>O<sub>6−<i>δ</i></sub> without Nb doping.