Assessment of Nd_1.5Pr_0.5Ni_1−xM_xO_4+δ (M = Cu, Co, Mo; x = 0, 0.05 and 0.1) as cathode materials for intermediate-temperature solid oxide fuel cell

This work presents study of the doping effect of M = Cu, Co, and Mo on the cathode properties of Nd_1.5Pr_0.5Ni_1−xM_xO_4+δ. In particular, four compositions are prepared by a modified sol–gel method, e.g., Nd_1.5Pr_0.5NiO_4+δ (NPN), Nd_1.5Pr_0.5Ni_0.9Cu_0.1O_4+δ (NPNCu), Nd_1.5Pr_0.5Ni_0.9Co_0.1O_4+δ (NPNCo), and Nd_1.5Pr_0.5Ni_0.95Mo_0.05O_4+δ (NPNMo). The crystal structure, phase stability, electrical conductivity, thermal expansion coefficient (TEC), and electrochemical performance of the oxides are systematically investigated. No chemical reactions between NPN, NPNCu, NPNCo, and NPNMo cathodes and Ce_0.8Sm_0.2O_1.9 electrolyte are found. The average TEC values of the NPN, NPNCu, NPNCo, and NPNMo are determined to be 13.9 × 10⁻⁶ K⁻¹, 13.6 × 10⁻⁶ K⁻¹, 14.7 × 10⁻⁶ K⁻¹, and 13.2 × 10⁻⁶ K⁻¹ in the range of 30–1000 °C, close to that of the typical electrolyte materials. NPN and NPNCu cathodes exhibit very low interfacial polarization resistance value of 0.033 and 0.032 Ω cm² at 800 °C, which translates to superior fuel cell performance, e.g., peak power density of 456 and 443 mW cm⁻², respectively. The electrochemical performance, however, could be significantly degraded by the Co and Mo doping in the Ni site. The presented results demonstrate that NPN and NPNCu are promising cathode candidate for intermediate-temperature solid oxide fuel cells.