Protecting Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode with SrSn0.8Sc0.2O3-δ proton conductor for protonic ceramic fuel cells

Abstract

Improving chemical stability and performance is desirable for protonic ceramic cathodes (PCFCs). In this study, the proton conductor SrSn0.8Sc0.2O3-δ (SSSc) is used to couple the classically unstable Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathode to increase the chemical stability of the composite cathode. Compared to the conventional BSCF + BaCe0.7Zr0.1Y0.2O3-δ (BCZY) composite cathode, the new BSCF + SSSc cathode demonstrates enhanced chemical stability. This is a result of the superior chemical stability of SSSc, which protects BSCF. Moreover, the formation of oxygen vacancies is easier at the BSCF/SSSc interface than at the BSCF/BCZY interface, thereby enhancing the cathode oxygen reduction reaction (ORR) activity. The closer proximity of the O p-band center to the Fermi level in BSCF + SSSc compared to BSCF + BCZY further validates the higher ORR activity of the BSCF + SSSc cathode. The peak power density of the PCFC with BSCF + SSSc cathode, which reaches 1404 mW cm−2 at 700 °C, is significantly greater than that with BSCF + BCZY cathode. The protection of SSSc to BSCF is also reflected in the fuel cell's long-term operation, as the BSCF + SSSc cell operates without detectable degradations for more than 150 h, whereas the BSCF + BCZY cell exhibits observable degradation. These findings indicate that utilizing the SSSc proton conductor to couple the cathode material is a feasible and effective strategy for producing the composite cathode with high chemical stability and superior electrochemical performance for PCFCs.