A-site element tuning in Nd2NiO4-based Ruddlesden-Popper cathodes: Enhanced electrochemical performance and stability for intermediate-temperature SOFCs

Developing high-performance cathodes for intermediate-temperature SOFCs (IT-SOFCs, 600–800 °C) faces persistent challenges due to sluggish oxygen reduction reaction (ORR) kinetics and thermal incompatibility issues. In this work, A-site Ba and Pr doping effectively optimizes both the electrochemical performance and stability of Nd 2 NiO 4 -based Ruddlesden-Popper cathodes. Firstly, Nd 1.5 M 0.5 NiO 4 (M = Ba, Pr, Nd) powders were synthesized via a modified Pechini method. Secondly, Rietveld refinement confirmed an orthorhombic structure with Fmmm (No. 69) space group for all compositions. X-ray photoelectron spectroscopy (XPS) analysis revealed that Pr and Ba ion doping effectively increases oxygen vacancy concentration while simultaneously modulating the valence states of Ni and Pr. Scanning electron microscopy (SEM) images showed well-developed porous microstructures favorable for gas diffusion. Electrochemical impedance spectroscopy (EIS) measurements demonstrated remarkably low area-specific polarization resistances of 0.104 and 0.072 Ω cm 2 for NPNO and NBNO, respectively, at 850 °C. Distribution of relaxation times (DRT) analysis further confirmed the enhanced ORR kinetics, showing improved performance across all elementary steps including gas adsorption, dissociation, and charge transfer following A-site optimization. Single-cell tests achieved peak power densities of 0.61 and 0.87 W cm −2 for NPNO and NBNO cathodes at 850 °C, respectively. Notably, the cells exhibited exceptional operational stability, attributable to well-matched thermal expansion coefficients between the cathodes and conventional electrolytes. Finally, these findings establish NBNO as a highly promising cathode material for IT-SOFC applications, offering both superior performance and long-term durability.