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The solid oxide fuel cell (SOFC) is considered promising technology that directly converts the chemical energy stored in the fuel into electrical energy. However, the undesired oxygen reduction reaction (ORR) activity and stability of the cathode have hindered its commercialization. In this work, a series of Pr-doped Pr x Ba 1-x Fe 0.8 Co 0.2 O 3-δ (x = 0∼0.3) nanofibers and powder cathode materials with excellent performance are synthesized by electrospinning and sol-gel methods, respectively. The influence of different Pr doping amounts on the nanofiber morphology, phase structure, thermal stability and electrochemical properties of BaFe 0.8 Co 0.2 O 3-δ (BFCO) nanofibers cathode materials were investigated. Compared the microstructures and electrochemical performance of Pr 0.1 Ba 0.9 Fe 0.8 Co 0.2 O 3-δ nanofiber and powders prepared by different methods. The partial substitution of Pr for Ba (doping of a few of Pr) can effectively eliminate the BFCO hexagonal phase and induce the transformation to the cubic phase. The content of oxygen vacancies was significantly increased as well as the cathode ORR activity was well enhanced. In addition, we demonstrated by DRT that oxygen adsorption is the rate-limiting step at the cathode. Among them, Pr 0.1 Ba 0.9 Fe 0.8 Co 0.2 O 3-δ nanofiber has the best electrochemical performance and the highest oxygen surface exchange kinetics performance. The area-specific resistance (ASR) of Pr 0.1 Ba 0.9 Fe 0.8 Co 0.2 O 3-δ nanofiber is 0.1416 Ω cm2 at 700 °C. When the peak power density (PPD) of the YSZ-NiO/YSZ/GDC/PBCF1–F single cell shows 0.787 W cm−2, an anode-supported fuel cell with Pr 0.1 Ba 0.9 Fe 0.8 Co 0.2 O 3-δ nanofiber demonstrates excellent stability after 100 h of long-term stability test. Electrospinning technology is an effective method to prepare high-performance cathodes, and Pr 0.1 Ba 0.9 Fe 0.8 Co 0.2 O 3-δ nanofiber cathodes are expected to be high-performance cathode materials for IT-SOFCs. • Pr3+ and Co co-doped of BaFeO 3-δ (BFO). • Pr3+ and Co co-doped improves BaFeO 3-δ ORR activity and electrical properties. • DRT analysis of the cathodic oxygen reduction reaction process. • Pr 0.1 Ba 0.9 Fe 0.8 Co 0.2 O 3-δ nanofiber as high-performance solid oxide fuel cathode. [ABSTRACT FROM AUTHOR]

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]

• A negative expansion component SZM is used to balance the thermal expansion. • SNC/SZM heterogeneous interface is constructed by self-assembly. • Heterogeneous interface improves SNC-20SZM ORR kinetics. • The combined SZM increases the TPB length and the O2– transport pathways. • SNC-20SZM exhibits an impressive Rp value of 0.012 Ω cm2 at 700 °C. The discrepancy in thermal expansion coefficients (TECs) between the cobalt-based cathode and the electrolyte presents a notable obstacle in attaining optimal performance levels for solid oxide fuel cells (SOFCs). Here we propose to introduce negative thermal expansion (NTE) component Sm 0.85 Zn 0.15 MnO 3 (SZM) to SrNb 0.1 Co 0.9 O 3−δ (SNC) cathode to prepare SNC-xSZM (x = 0, 10, 20 and 30 %) composite cathode materials. The impact of incorporating negative thermal expansion material on the composition and properties of the matrix materials were examined by X-ray diffraction, thermal dilatometer, high-resolution transmission electron microscopy, and electrochemical workstation. The results show that SNC-xSZM can achieve more ideal thermal matching with Ce 0.8 Gd 0.2 O 1.9 (GDC), and the thermal expansion coefficient decreases observably from 25.47 × 10−6 K−1 for x = 0 to 13.74 × 10−6 K−1 for x = 30 %. The optimal comprehensive electrochemical performance is obtained for SNC-20SZM, which possesses the minimum polarization resistance (Rp) of 0.012 Ω cm2 at 700 °C. The SNC-20SZM-based cell shows a maximum peak power density (PPD) of 1.22 W cm−2 while exhibiting stable operation for a continuous duration of 120 h at a constant current of 0.8 A cm−2, with performance remaining optimal. Moreover, SNC-20SZM demonstrates exceptional durability and stability over prolonged durations even in high CO 2 atmospheres. An innovative approach for enhancing the development of intermediate-temperature solid oxide fuel cells (IT-SOFCs) involves incorporating SZM in the SNC cathode, thereby augmenting electrochemical performance and narrowing the gap in the thermal expansion coefficient among SOFC modules. [ABSTRACT FROM AUTHOR]

As a Ruddlesden-Popper (RP) phase solid oxide fuel cell (SOFC) cathode material, Pr 2 NiO 4+δ (PNO) is a critical challenge for SOFC commercialization due to the lack of oxygen vacancies and insufficient redox reaction (ORR) activity. In this paper, various concentrations of La 0.6 Sr 0.4 CoO 3-δ (LSC) nanoparticles are coated on the surface of PNO by an impregnation method, and the ORR kinetics of PNO is found to be improved by constructing a composite cathode with heterointerfaces. The formation of the heterointerface effectively enhances the transfer of interstitial oxygen in the PNO and the oxygen vacancies in LSC, which can promote the conduction of O2− in the cathode and thus improves the ORR activity of the material. When the impregnation concentration of LSC reached C LSC = 0.2 mol L−1, the ORR activity can reach the highest level. At 700 °C, the area-specific resistance of PNO-LSC reaches 0.024 Ω cm2, which is 83.4% lower than that of PNO (0.145 Ω cm2). And the peak power density of PNO-LSC reaches 0.618 W cm−2, which is 1.89 times larger than that of PNO (0.327 W cm−2). Therefore, the construction of composite cathodes with heterointerfaces via impregnation provides an alternative strategy for enhancing the ORR activity of the cathode materials in SOFC. [Display omitted] • Pr 2 NiO 4+δ -La 0.6 Sr 0.4 COO 3-δ cathode is prepared by impregnation method. • The heterointerface promotes the ORR activity of the cathode. • Pr 2 NiO 4+δ -La 0.6 Sr 0.4 COO 3-δ has excellent ORR activity. [ABSTRACT FROM AUTHOR]

Here, in situ assembly in La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ and CoFe 2 O 4 composite (LSCFC) cathode was induced by Pr to form La 0.6 Sr 0.4 Co x Fe y O 3-δ /PrCoO 3 /Co 3 O 4 /PrO 2 (LSCFC-PI) multiphase heterostructures. The surface of LSCFC-PI forms uniform nanoparticles, and the unique core-shell structure prevents Sr segregation, thereby enhancing CO 2 tolerance and increasing oxygen reduction reaction (ORR) active sites. Furthermore, compared with LSCFC, LSCFC-PI increases the oxygen vacancy content of the cathode due to the existence of multiphase heterostructure, improves the ORR kinetics, and the conductivity is also greatly improved. The peak power density (PPD) of LSCFC-PI as a single-cell cathode at 700 ℃ reached 1.51 W cm−2, which was 2.65 times higher than that of LSCFC's 0.57 W cm−2, and in the long-term stability test at a constant voltage ∼0.8 V for 100 hours, showing excellent stability. In situ assembly of multiphase heterostructures is expected to become a new strategy for developing high-performance IT-SOFC cathodes. [Display omitted] • Pr-induced in situ assembly of multiphase heterostructures. • Multiphase heterostructures facilitate the ORR kinetics of cathodes. • Optimize the oxygen vacancy content in multiphase structures. • LSCFC-PI has excellent ORR activity and CO 2 tolerance. [ABSTRACT FROM AUTHOR]

The cobalt-free cathode materials with high activity is critical to the commercial application of medium temperature solid oxide fuel cells (IT-SOFC). Herein, a series of cobalt-free Nb-doped Pr 2 Ni 1- x Nb x O 4 (x = 0, 0.05, 0.10, and 0.15) perovskite oxides were successfully prepared, and the effects of Nb-doping on the structure, thermal stability and electrochemical properties of the cathode material are studied in detail. The Pr 2 Ni 1- x Nb x O 4 exhibits a K 2 NiF 4 type structure with Fmmm space group. The Nb5+ cations that doped into Pr 2 NiO 4 replaces the Ni site, which increases the surface oxygen content, then effectively eliminates the phase transition of Pr 2 NiO 4 and significantly improves the ORR catalytic activity. The Pr 2 Ni 0.9 Nb 0.1 O 4 was found to occupy the lowest polarization resistance of 0.057 Ω cm2, and the peak power density of single cells supported by the electrolyte is 0.576 W cm−2 at 700 °C, which has good long-term stability. [Display omitted] • The structure and performance of the cobalt-free Pr 2 Ni 1- x Nb x O 4 cathodes are studied. • Nb-doping can eliminate the phase change and improve the stability of the structures. • Nb-doping can increase the ORR activity of the Pr 2 Ni 1- x Nb x O 4 cathode. • Pr 2 Ni 0.9 Nb 0.1 O 4 cathode exhibits a low polarization resistance of 0.057 Ω cm2. • The highest peak power density is 0.576 W cm−2 at 700 °C with Pr 2 Ni 0.9 Nb 0.1 O 4 cathode. [ABSTRACT FROM AUTHOR]

The electrospinning and sol-gel methods are used to prepare a Ba 0·5 Sr 0·5 Fe 0·8 Cu 0·2 O 3-δ (BSFC) cathode material with good chemical compatibility with the traditional electrolyte Ce 0.8 Gd 0.2 O 2−δ (GDC). Systematic experiments are performed to investigate the effect of sintering temperature on BSFC fibers microstructure, morphology and electrochemical properties. The results show that the three dimensional (3D) BSFC-F800 prepared by the low-temperature calcination method (800 °C) has a well-organized porous structure and larger specific surface area and porosity. In addition, the fibers are connected to each other to form a continuous electrode path, which provides an uninterrupted channel for charge transmission, and the low-temperature calcination can efficiently reduce the surface Sr segregation and increase ORR activity. At 700 °C, the 3D nanofiber cathode material BSFC-F800 has lower area specific resistance (ASR = 0.128 Ω cm2) and higher peak power density (PPD = 0.51 W cm−2). The voltage decay rate in the 100 h long-term stability test is only 0.0342% h−1. Changes of morphology and electrical properties of Ba 0·5 Sr 0·5 Fe 0·8 Cu 0·2 O 3-δ fibers prepared by electrostatic spinning at different calcination temperatures. After calcination at low temperature, a hollow 3D fiber cathode with higher specific surface area is obtained. With the increase of temperature, grain expands, fiber diameter increases, and hollow structure becomes solid structure. As the temperature continues to rise, the fibers agglomerate together, seriously damaging the specific surface area and porosity of Ba 0·5 Sr 0·5 Fe 0·8 Cu 0·2 O 3-δ fibers. Image 1 • B-site Cu doped Fe-based Ba 0·5 Sr 0·5 Fe 0·8 Cu 0·2 O 3-δ fiber cathode material. • 3D structure fiber was prepared by low temperature method. • Low temperature sintering can effectively reduce the surface Sr segregation. • 3D structure Ba 0·5 Sr 0·5 Fe 0·8 Cu 0·2 O 3-δ has excellent performance. [ABSTRACT FROM AUTHOR]

The development of cathode materials with high oxygen reduction reaction (ORR) activity and stability in intermediate temperature (IT) environments is a key factor in the commercialization of solid oxide fuel cells (SOFC). In this paper, the ORR activity of the cathode is improved by doping high-valent Sc3+ ions at the B-site of the Sr 0.5 La 0.5 Co 0.8 Cu 0.2-x Sc x O 3–δ (x = 0, 0.02, 0.04), in which Sr 0.5 La 0.5 Co 0.8 Cu 0.18 Sc 0.02 O 3–δ (SLCCS2) shows the best electrochemical performance, and the area-specific resistance of SLCCS2 at 700 °C is only 0.047 Ω cm2, much lower than the 0.087 Ω cm2 of Sr 0.5 La 0.5 Co 0.8 Cu 0.2 O 3–δ (SLCC), and the peak power density of SLCCS2 reached 1.098 W cm−2, which is 1.84 times that of SLCC (0.598 W cm−2). In addition, SLCCS2 effectively reduces the thermal expansion coefficient, improves thermal matching with traditional electrolytes, and overcomes the problem of insufficient long-term SOFC stability caused by the high thermal expansion coefficient of Co-based perovskite to a certain extent. SLCCS2 also exhibits excellent CO 2 tolerance. Considering comprehensively, SLCCS2 is expected to become an IT-SOFC cathode material with development potential. • Sc doping improves the ORR activity of Sr 0.5 La 0.5 Co 0.8 Cu 0.2 O 3–δ. • Sc doping reduces thermal expansion coefficient of Co-based perovskites. • Sr 0.5 La 0.5 Co 0.8 Cu 0.18 Sc 0.02 O 3–δ has excellent CO 2 tolerance. [ABSTRACT FROM AUTHOR]