Enhancing oxygen reaction kinetics in lanthanum nickelate Ruddlesden–Popper electrodes via praseodymium oxide infiltration for solid oxide cells

Abstract

This study explores the effect of praseodymium oxide (PrO_x) impregnation in lanthanum nickelate Ruddlesden–Popper (RP) type materials for use in oxygen electrodes of solid oxide cells (SOCs). These mixed conductors are free of cobalt and strontium, which are increasingly being avoided in solid oxide cell applications. We investigate two compositions, La₂NiO_4+δ (L2N1) and La₄Ni₃O_10−δ (L4N3), demonstrating distinct electrical and oxygen kinetic properties. The L2N1 material exhibits superior performance due to its higher bulk oxygen-ion diffusion, which governs the enhanced ambipolar conduction, crucial for the oxygen exchange process. In the PrO_x-impregnated samples, at 700 °C, the total polarization resistance (R_pol) values decrease to ∼0.6 Ω cm² for L2N1 + PrO_x and ∼0.8 Ω cm² for L4N3 + PrO_x, representing reductions by factors of ∼7 and ∼17, respectively, compared to the non-impregnated counterparts. Electrochemical measurements as a function of oxygen partial pressure suggest that surface-exchange processes may be rate-limiting. The impregnated PrO_x acts as a catalyst for the dissociative adsorption of oxygen and improves the charge transfer, leading to significant enhancements in the polarization processes. The electrochemical properties and stability of these RP phases in oxidizing conditions, combined with the oxygen transport capabilities and mixed oxidation state of praseodymium oxide (Pr⁴⁺/Pr³⁺), offer promising Co- and Sr-free oxygen electrodes for SOC applications.