Synergistic Ga³⁺-Zr⁴⁺ B-Site Co-doping Enabling Highly Active and CO₂-resistant Fe-based Perovskite Cathodes for Intermediate-temperature Solid Oxide Fuel Cells

Abstract

A Ga³⁺-Zr⁴⁺ co-doping strategy at the B-site is developed to simultaneously enhance oxygen reduction reaction (ORR) activity, structural stability, and CO₂ tolerance of La_0.6Sr_0.4FeO_3−δ (LSF64) cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The synergistic charge compensation between lower-valence Ga³⁺ (ionic compensation) and higher-valence Zr⁴⁺ (electronic compensation) significantly increases oxygen vacancy concentration and optimizes the Fe³⁺/Fe⁴⁺ redox equilibrium, thereby accelerating both oxygen surface exchange and bulk diffusion. XPS and EPR analyses confirm substantially enriched oxygen vacancy populations in the co-doped material. Electrical conductivity relaxation measurements further reveal enhanced oxygen surface exchange and bulk diffusion coefficients, indicating accelerated oxygen transport kinetics. As a result, the optimized La_0.6Sr_0.4Fe_0.8Ga_0.1Zr_0.1O_3−δ (LSFGZ) cathode exhibits a low polarization resistance of 0.12 Ω·cm² at 700 °C, approximately 76% lower than that of pristine LSF64, and delivers a peak power density of 0.94 W/cm² in single-cell operation. In addition, modulation of surface acidity effectively suppresses SrCO₃ formation under CO₂-containing atmospheres, ensuring excellent long-term stability. This work demonstrates a general B-site co-doping strategy for designing high-performance and durable Fe-based perovskite cathodes for IT-SOFCs.

Keywords

Solid oxide fuel cell / Cathode / Co-doping / Oxygen reduction reaction (ORR) / CO₂ tolerance

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