A review on sintering technology of proton conducting BaCeO3-BaZrO3 perovskite oxide materials for Protonic Ceramic Fuel Cells

Ceramic proton conductors can reduce the operating temperature of solid oxide fuel cells (SOFCs) to the intermediate temperature range, 400-600 °C, due to their higher ionic conductivity in comparison to oxide-ion conductors under these conditions. Nonetheless, the most promising proton conducting materials, typically yttrium-doped barium cerates and zirconates with nominal compositions: BaCe1-xYxO3-δ (BCY), BaZr1-xYxO3-δ (BZY) and Ba(Ce,Zr)1-yYyO3-δ (BCZY) exhibit major challenges with respect to the production of dense electrolyte membranes. To improve the processing of these materials, liquid phase sintering (LPS) induced by the addition of transition and alkali metal oxides as sintering additives, is proposed as an effective way to promote densification, where the benefits of LPS may be further extended when this method is used in combination with solid-state reactive sintering (SSRS) to reduce the fabrication time and cost. Nonetheless, recent literature highlights that the addition of these sintering additives can have highly negative secondary impacts on bulk transport properties and overall fuel cell performance. This review summarises the recent developments and the innovative methods employed to overcome the processing difficulties in these materials, including diverse potential sintering methods, the effect of different sintering additives and their impact on densification, ionic transport and electrochemical properties.