Defect-induced pyrochlore Pr2Zr2O7 cathode rich in oxygen vacancies for direct ammonia solid oxide fuel cells

In this study, pyrochlore Pr2B2O7 oxides (BZr, ZrSn, Sn, PZO/PZSO/PSO) and perovskite (BTi, PTO) were prepared as direct ammonia solid oxide fuel cell (DA-SOFC) cathode with oxygen reduction reaction activity induced by B-site cationic defects. Compared with PTO, the pyrochlore PBO with unoccupied 8a-oxygen sites are high in inherent oxygen vacancies (ca. 12.5%), leading to enhanced migration of lattice oxygen. Among the n-type semiconductors, PZO is with a more negative flat-band potential and is more effective in terms of overcoming energy barriers. As a result, the conductivity of PZO is two orders of magnitude higher than that of PTO at 800 °C. The oxygen transport performance reveals that the surface exchange coefficient of PZO is about one order of magnitude higher than that of La0.7Sr0.3MnO3-δ at 900 °C. Owing to high conductivity, fast oxygen transport, and matched thermal expansion coefficient, an anode-supported DA-SOFC using the PZO-based cathode can offer a maximum power density of 0.25 W cm−2 at 600 °C and 1.22 W cm−2 at 800 °C, operating continuously over 100 h without obvious degradation. The electrochemical performance is 2.3 folds higher than those of SOFCs using other PBO-based cathode, and higher than most reported SOFCs with the cathodes using A-site Pr.