Regulation of electronic and ionic transport in Ni-doped La0.6Sr0.4FeO3−δ for enhanced oxygen reduction in intermediate-temperature solid oxide fuel cells

Abstract

This study systematically investigates the effect of Ni doping on the electrochemical performance of La_0.6Sr_0.4Fe_1−xNi_xO_3−δ (LSFN_x) cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). By tuning the Ni content at the Fe site (x = 0–0.2), the composition with x = 0.15 exhibits the optimal overall performance. Ni doping enhances the material's properties through a dual mechanism: on one hand, it regulates the Fe³⁺/Fe⁴⁺ redox couple, optimizing the balance between charge carrier concentration and mobility, resulting in a conductivity of 479.68 S cm⁻¹ at 800 °C—approximately double that of undoped LSF (224.41 S cm⁻¹); on the other hand, it promotes the formation of oxygen vacancies, thereby improving oxygen ion transport. Combined analysis using distribution of relaxation times (DRT) and electrochemical impedance spectroscopy (EIS) confirms that Ni incorporation reduces the activation energy of the oxygen reduction reaction (ORR). As a result, LSFN_0.15 achieves a polarization resistance of only 0.071 Ω cm² at 800 °C, a 70.54% reduction compared to LSF (0.241 Ω cm²). Single-cell tests further demonstrate a peak power density (PPD) of 852.65 mW cm⁻² for LSFN_0.15 at 800 °C, nearly twice that of the undoped counterpart (434.36 mW cm⁻²). This study reveals the synergistic enhancement mechanisms of Ni doping in LSF-based cathode materials, highlighting the excellent potential of LSFN_0.15 as a high-performance IT-SOFC cathode.