Visiting the roles of Sr‐ or Ca‐ doping on the oxygen reduction reaction activity and stability of a perovskite cathode for proton conducting solid oxide fuel cells

Abstract

While double perovskites of PrBaCo 2 O 6 (PBC) have been extensively developed as the cathodes for proton‐conducting solid oxide fuel cells (H‐SOFCs), the effects of Sr‐ or Ca‐doping at the A site on the activity and stability of the oxygen reduction reaction are yet to be fully studied. Here, the effect of A‐site doping on the oxygen reduction reaction activity and stability has been studied by evaluating the performance of both symmetrical and single cells. It is shown that Ca‐doped PBC (PrBa 0.8 Ca 0.2 Co 2 O 6 , PBCC) shows a slightly smaller polarization resistance (0.076 Ω cm 2 ) than that (0.085 Ω cm 2 ) of Sr‐doped PBC (PrBa 0.8 Sr 0.2 Co 2 O 6 , PBSC) at 700°C in wet air. Moreover, the degradation rate of PBCC is 0.0003 Ω cm 2 h −1 (0.3% h −1 ) in 100 h, about 1/10 of that of PBSC at 700°C in wet air. In addition, it is also confirmed that single cells with PBCC cathode show higher peak power density (1.22 W cm −2  vs. 1.08 W cm −2 at 650°C) and better durability (degradation rate of 0.1% h −1  vs. 0.13% h −1 ) than those with PBSC cathode. The distribution of relaxation time analyses suggests that the better stability of the PBCC electrode may come from the fast and stable surface oxygen exchange process in the medium frequency range of the electrochemical impedance spectrum.