Synthesis and preliminary study of the double perovskite NdBaMn2O5 + δ as symmetric SOFC electrode material

NdBaMn2O5 + δ compound has been studied as a possible symmetric SOFC electrode. The A-site and charge ordered NdBaMn2O5 material has been synthesized by solid-state reaction in a reducing atmosphere at 1100 °C for 12 h; the resulting material crystallizes in a 2ap × ap × 2ap tetragonal cell of P4/nmm space group. Thermogravimetric analysis coupled to HT-XRD experiment shows that the material is completely stable to redox cycling between air and 5% H2/Ar up to at least 850 °C. In air, the phase is completely oxidized to A-site ordered NdBaMn2O6 (P4/mmm) and in anode conditions is reduced back to its initial form, with intermediate formation of orthorhombic NdBaMn2O5.5 ordered phase. Considering possible conditions of cell preparation in air (T = 1300 °C for 6 h), a loss of A-site ordering is evidenced but the material is reduced back to ordered NdBaMn2O5 at 850 °C in diluted hydrogen. Whereas the material reacts strongly with 8YSZ at 1300 °C, no particular chemical affinity with 20GDC is observed neither at high temperature in air nor at 850 °C in anodic atmosphere; TEC coefficients for NdBaMn2O5 + δ, measured in both anode and cathode conditions, are also in good agreement with reported TEC values for a ceria electrolyte. Relatively low values of electrical conductivity are found in diluted hydrogen whereas a sufficient level for the application is obtained in air.