Balancing oxygen vacancy formation and thermal stability in A-site-deficient Mn-substituted NdBaCoFe-based double perovskite oxygen electrodes

Double perovskites are promising oxygen electrodes for intermediate-temperature solid oxide cells, but their practical application is often limited by the trade-off between electrochemical activity and thermomechanical stability. Herein, A-site deficiency and Mn substitution were jointly introduced into (NdBa) 2-α CoFe 1-x Mn x O 5+δ to regulate oxygen vacancy formation, thermal expansion, and electrode polarization. X-ray diffraction studies confirmed the formation of double perovskites, and their good compatibility with electrolytes. Thermogravimetric and dilatometric analyses revealed that A-site deficiency promotes oxygen vacancy formation, whereas increasing Mn content suppresses oxygen loss and lowers the thermal expansion owing to stronger Mn–O bonding and reduced Co-related chemical expansion. Among investigated electrodes, (NdBa) 2 CoFeO 5+δ delivered the lowest ASR (0.059 Ω cm 2 ) at 750 °C, while A-site-deficient (NdBa) 1.9 CoFeO 5+δ exhibited a comparable ASR (0.062 Ω cm 2 ) with significantly improved long-term stability. Incorporating 30 wt% GDC markedly improved the Mn-rich electrodes by extending oxygen-ion transport pathways and increasing reaction sites. The (NdBa) 1.9 CoFe 0.25 Mn 0.75 O 5+δ –GDC composite achieved an ASR of 0.067 Ω cm 2 and stable operation over 100 h. Oxygen partial pressure and DRT analyses indicate that the composite architecture mainly facilitates oxygen adsorption/ionization and surface transport processes. These results highlight the importance of balancing vacancy concentration and structural stability when designing double-perovskite oxygen electrodes for solid oxide cells.