(378ai) A Symmetrical Solid Oxide Fuel Cell with a-Site Sodium Doped Perovskite Electrode Materials

Solid oxide fuel cells (SOFCs) are electrochemical energy conversion devices those directly convert chemical energy in fuels to electrical energy with a high efficiency and low emissions. Recently, symmetrical SOFCs (SSOFCs) with a simplified configuration using the same material as both cathode and anode have raised much attention. The biggest challenge to the electrode material for a SSOFC, however, is that it must maintain structural stability and electrocatalytic activity when operating in both reducing and oxidizing environment. In this work, A-site sodium doped double-perovskites Sr_2-xNa_xFeMo_0.65Ni_0.35O_6-d (SN_xFMNi, x=0.05, 0.1 and 0.2) are synthesized and investigated as electrode materials for SSOFCs. All the samples undergo the same phase transition process from a perovskite structure to a Ruddlesden-Ropper phase (RP phase) with the exsolution of numerous Ni₃Fe nanoparticles during 10 h reduction. The phase transition process is studied with X-ray diffraction, thermogravimetric analyzer and transmission electron microscope, and the results indicate that all the samples keep a perovskite structure in an oxidizing environment while turn into a RP phase in a reducing environment. Amongst all the samples, SN_0.2FMNi shows the lowest activation energy of 0.30 eV. An electrolyte-supported symmetrical single cell with a configuration of SN_0.2FMNi|LDC|LSGM|LDC| SN_0.2FMNi gives the maximum power densities of 1157 and 335 mW cm^-2with H₂ and humidified CH₄ as the fuels at 850 ^oC, respectively.