Chromium deposition and poisoning of the proton-conducting BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ electrolyte of protonic ceramic cells

Due to their low activation energy and high mobility of proton transfer, protonic ceramic cells (PCCs), including protonic ceramic fuel cells (PCFCs) and protonic ceramic electrolysis cells (PCECs), working at relatively low temperatures (400-700 °C) have gained increasing attention as promising and highly efficient energy conversion and storage technologies to replace the oxide ion-conducting, high-temperature solid oxide cells (SOCs). However, similar to SOCs, Fe-Cr based alloys are also commonly used as metallic interconnects in PCCs. Thus, the practical applicability of Ba-containing proton conducting electrolytes in PCCs is fundamentally related to their tolerance and resistance towards the deposition and poisoning of the volatile chromium species from the Fe-Cr based interconnect. This study focuses on the interaction between the Cr species and the most widely used proton conducting electrolyte BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb1711) within a temperature range from 400 °C to 700 °C. Results indicated that barium oxide and the BZCYYb1711 powder reacted with the Cr₂O₃ powder at 250 °C and 400 °C, respectively, while the deposition of Cr species on the BZCYYb1711 electrolyte surface occurred at temperatures as low as 500 °C. Ba segregated from the BZCYYb1711 electrolyte and reacted with gaseous Cr species, forming BaCrO₄ and causing a significant depreciation in Ba content in the electrolyte. The Cr species also diffused into the inner layer of BZCYYb1711, leading to the segregation of CeO₂ and degrading the conductivity of the electrolyte. This study demonstrates that the deposition and poisoning of the Cr species from the Fe-Cr based metallic interconnect are serious issues for the practical and long-term applicability of Ba-containing protonic ceramic materials in PCCs.