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The commercialization of the Co-free solid oxide fuel cell (SOFC) cathode was hindered due to its insufficient oxygen reduction reaction (ORR) activity. In this paper, the ORR activity of the cathode material is effectively increased by doping a small amount of low-valence Ln3+ (Nd3+, Sm3+) ions at the B-site of Fe-based perovskite Bi 0.5 Sr 0.5 FeO 3-δ (BSF). Nd3+ increases the free volume (V free) per unit cell of perovskite due to its larger ionic radius, thus increasing the oxygen vacancy concentration of Bi 0.5 Sr 0.5 Fe 0.95 Nd 0.05 O 3-δ (BSFN). Compared with BSF, BSFN has greatly improved the surface oxygen exchange and volume diffusion rate through the electronic conductivity relaxation (ECR) method. At 700 °C, the area-specific resistance (ASR) of BSFN reached 0.062 Ω cm2, which was 65% lower than that of BSF (0.177 Ω cm2), and the peak power density (PDD) of BSFN-based single cell reached 1.10 W cm−2, which was 1.7 times higher than that of BSF-based single cell (0.64 W cm−2). Through DRT analysis, it is concluded that BSFN can accelerate the adsorption/dissociation process of oxygen due to its higher oxygen vacancy concentration compared with BSF, so that ORR is not limited to the three-phase interface but extends to the entire cathode surface. In addition, in the 80 h long-term stability test at 600 °C, the BSFN-based single cell has better long-term stability because the thermal expansion coefficient of BSFN (14.1 × 10−6 K−1) is lower than that of BSF (14.4 × 10−6 K−1). In general, BSFN is expected to become a Co-free base high-performance intermediate temperature SOFC cathode. [ABSTRACT FROM AUTHOR]

As a potential cathode material for solid oxide fuel cells, the commercial application of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) has to face the challenges in insufficient oxygen reduction reaction (ORR) activity, segregation of Sr element, and CO 2 poisoning. Therefore, the effect of A-site non-stoichiometry on the electrochemical performance of (LS) 1-x CFs (x = −0.05, 0, 0.05, 0.10, 0.15) from the aspect of microstructure/elemental surface chemical environment evolution is investigated in this paper. The results show that (LS) 0.90 CF has the best ORR activity and the highest electrochemical performance. The excellent electrochemical performance is attributed to the (LS) 0.90 CF/Co 2 FeO 4 /CoFe 2 O 4 -type heterostructure, formed by in-situ segregation induced by A-site defects, which improves the surface oxygen diffusion coefficient and chemical bulk diffusion coefficient of the cathode. At the same time, the A-site defect can effectively inhibit the segregation of Sr element in (LS) 0.90 CF, thereby improving the tolerance of CO 2. At 800 °C, the area-specific resistance (ASR) of (LS) 0.90 CF (0.023 Ω cm2) is 66.7% lower than that of LSCF (0.069 Ω cm2), and the peak power density (1.57 Wcm−2) is 1.8 times higher than that of LSCF (0.87 Wcm−2). Therefore, perovskite A-site defect-induced B-site segregation to form heterostructures provides an effective strategy for the preparation of high-performance cathode materials. [ABSTRACT FROM AUTHOR]