Interfacial oxide wedging for mechanical-robust electrode in high-temperature ceramic cells

Delamination and cracking of air electrodes are two mechanical causes to the degradation of high-temperature electrochemical ceramic cells. While compositing negative thermal expansion (NTE) materials can tackle delamination by lowering the thermal expansion coefficient (TEC) of air electrode, it can exacerbate cracking due to large thermal stress between particles of NTE and positive thermal expansion perovskites (PTE). Here, we introduce interfacial oxides to "wedge" the NTE-PTE interface, thereby resisting cracking inside the bulk of the air electrode through reactive calcination at near-melting temperatures. This concept is demonstrated by compositing negative thermal expansive HfW₂O₈ with Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (perovskite), forming Co₃O₄, Fe₃O₄, BaHfO₃ and Sr₃WO₆ as wedging phases. Enhanced bulk modulus (by 102%), hardness (by 138%), and mitigated TEC (reduced by 35%) are simultaneously achieved, which enhances the durability of the air electrode over 40 rigorous thermal cycles between 600 °C and 300 °C, and even with no decay after two years of exposure to ambient air. This method offers an effective strategy for developing mechanical-robust electrodes of high-temperature electrochemical cells.