Effect of Mn on the electrochemical properties of a layered perovskite NdBa_0.5Sr_0.5Co_2−xMn_xO_5+δ (x = 0, 0.25, and 0.5) for intermediate-temperature solid oxide fuel cells

Highlights: • The electrical conductivity of NdBa_0.5Sr_0.5Co_2−xMn_xO_5+δ is evaluated in air. • Symmetrical half cells based on GDC electrolyte are used for the impedance studies. • A Ni-GDC anode-supported cell is used to measure the electrochemical performance. • The partial substitution of Co by Mn lowers TEC value of NdBa_0.5Sr_0.5Co_2−xMn_xO_5+δ. - Abstract: NdBa_0.5Sr_0.5Co_2−xMn_xO_5+δ (x = 0, 0.25, and 0.5) specimens are synthesized and investigated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The interaction between two different transition metals, Mn and Co, may affect the electronic conducting properties and electrochemical performance. The substitution of Mn for Co lowers the thermal expansion coefficient (TEC) of Co-based materials by suppression of the spin state transition of Co³⁺ which might consequently improve the mechanical compatibility with the electrolyte. The electrochemical performance, however, could be slightly degraded by trapping of the effective mobile charge with increasing Mn content. Such a substitution of Co by Mn would provide a tradeoff relationship between TEC and electrochemical performance in IT-SOFCs. In this paper, the tradeoff between electrochemical and thermal expansion is explored