Highly Efficient and Robust Composite Cathode with an In Situ Formed Proton Conductor for Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) are efficient energy-conversion devices that provide great potential to realize a clean and sustainable energy future. However, the low catalytic activity and stability of the cathode at intermediate temperatures present significant obstacles to their commercial application. To overcome these challenges, we developed a strategy to modify a Ba(Co 0.7 Fe 0.2 Zr 0.1 ) 0.95 O 3−δ (BCFZ95) cathode surface by Pr 6 O 11 (PO) nanoparticles (NPs) and in situ formed BaPrO 3 proton conductor. Oxygen molecules adsorb and dissociate rapidly on the NPs, leading to a significant enhancement of the oxygen reduction reaction (ORR) activity for the B(CFZ)95 cathode. The polarization resistance ( R p ) of the B(CFZ)95–15 wt % PO composite cathode was 0.064 Ω cm 2 at 700 °C, exhibiting a substantial reduction of 50% compared with B(CFZ)95. Through the rational adjustment of the calcination temperature, proton-conductor BaPrO 3 was in situ generated at the Pr 6 O 11 /B(CFZ)95 interface, which promoted the hydration process and facilitated the proton transmission of the composite cathode. Moreover, the stability of the composite cathode against CO 2 was synchronically promoted by the Pr 6 O 11 conformal coating due to a more stable Pr 6 O 11 and a higher acidity of Pr 3+ /Pr 4+ than that of Ba 2+, as confirmed by carbonate decomposition chemical potential computations. The composite cathode also has good recovery performance; after the treatment with a high concentration of CO 2, the R p of the composite cathode can be restored to the initial level. The infiltration of Pr 6 O 11 and in situ formed proton conductor comprehensively improved the ORR activity, hydration activity, and stability of the B(CFZ)95 cathode, and the modification method provides an inspiring technical solution for not only PCFCs but also other types of energy-conversion and -storage systems, including solid oxide electrolysis cells and metal–air batteries.