Validation of calcium-doped neodymium nickelates as SOFC air electrode materials

The search for new electrode materials that can be applied to the solid oxide fuel cell (SOFC) technology is an active field of research. In continuing our studies of Ca-substituted layered nickelates, in this work we investigated Nd2−xCaxNiO4+δ materials synthesized via the solution assistant solid state reaction method to evaluate their prospective usage as cathode materials for the intermediate temperature SOFC. It was found that Ca doping resulted in the temperature decreasing for the Fmmm → I4/mmm transition in Nd2NiO4+δ (NNO) and the tetragonal structure stabilizing at room temperature at x ≥ 0.2 in ambient air. The coefficient of thermal expansion calculated from the linear expansion under heating and cooling was different; however there was a common tendency for it to decrease when the Ca content was increased above 5 mol% (x = 0.1). The dc four-probe measurements revealed an increase in total electrical conductivity with doping. The polarization resistance of the Nd2−xCaxNiO4+δ electrodes in contact with Ce0.8Sm0.2O1.9 depended non-linearly on the Ca content with a moderate maximum at x = 0.1. Ca-doping was found to decrease the interaction of the electrode materials with the electrolyte. It resulted in the polarization resistance of the composite electrodes containing doped materials decreasing compared to the composite electrodes based on Nd2NiO4+δ. The polarization resistance of the Nd1.7Ca0.3NiO4+δ-Ce0.8Sm0.2O1.9 (NCNO3-SDC) electrode formed at 1200 °C is equal to 0.56 Ω cm2 at 700 °C in ambient air and comparable with the resistance of the NNO electrode (0.51 Ω cm2). Due to its superior stability and lower interaction with the electrolyte this electrode composition can be recommended for preferential usage in IT-SOFCs.