Failure of protonic ceramic fuel cells (PCFCs) under gaseous Cr and CO₂ exposure and the introduction of a protective barrier layer for mitigation

Protonic ceramic fuel cells (PCFCs) are attracting widespread interest due to their high efficiency and relatively low operating temperatures. However, the stability of PCFCs under realistic operating conditions, which include exposure to volatile Cr species and CO₂ in the air electrode compartment, has rarely been examined. Here, we test a PCFC composed of BaCe_0.4Zr_0.4Y_0.1Yb_0.1O_3−δ as the electrolyte and PrBa_0.5Sr_0.5Co_1.5Fe_0.5O_5+δ as the air electrode, with a metallic interconnect and atmospheric air as an oxidant gas. The complete phase decomposition of the electrolyte and the formation of BaCO₃ at the air electrode/electrolyte interface were observed after sudden cell failure within 20 hours of operation. Detailed analyses and control tests confirm the effects of Cr and CO₂ species on cell degradation. In contrast, the PBSCF air electrode remains relatively stable. We also report on the effectiveness of applying a thin and dense PBSCF protective barrier layer between the electrolyte and the air electrode, which significantly improves stability under realistic operating conditions.