•La0.5Sr0.5Fe0.8Cu0.15Nb0.05O3−δ (LSFCN) is evaluated as oxygen electrode for RSOCs.•The LSFCN shows high performance and stability in fuel cell and electrolysis modes.•An electrolysis current density of 0.85 A cm−2 is achieved at 750 °C under 1.3 V.•No degradation is observed after 50 h electrolysis operation under 1.60 V at 800 °C.A novel cobalt-free perovskite oxide La0.5Sr0.5Fe0.8Cu0.15Nb0.05O3−δ (LSFCN) has been synthesized and evaluated as oxygen electrode for reversible solid oxide electrochemical cells (RSOCs). The performance and stability of the LSFCN based RSOCs have been characterized in fuel cell and electrolysis modes, and the reversibility of the cells has been proven. In FC mode, the cell exhibits the maximum power density of 1.10 Wcm−2 at 800 °C, and a stable output under 0.7 V at 700 °C during 108 h. The performance and stability of the cell in electrolysis mode are also remarkable. An electrolysis current of 0.85 A cm−2 is achieved at 750 °C with an applied voltage of 1.3 V, and no degradation as well as delamination are observed for the cell after 50 h electrolysis under voltage of 1.60 V (∼1.27 A cm−2) at 800 °C. The high performance of the LSFCN at both cathodic and anodic conditions may be attributed to the inherent high electrochemical activity of copper-iron based perovskites; and the incorporation of Nb5+ cations into perovskite lattice is responsible for the stability of LSFCN, which leads to the more stable crystal structure, lower thermal expansion coefficient and the reduced Sr segregation at surface.

•A composite anode with endogenous Fe-Ni alloy nanoparticles has been prepared.•The redox reversibility of the anode has been confirmed by XRD.•The Ea of H2 oxidation at the anode is much smaller than that at Ni-YSZ anode.•A ScSZ supported cell achieves MPD of 0.71 Wcm−2 and Rp of 0.16 Ω cm2 at 800 °C.•The single cell shows stable output during 105 h testing at 800 °C 0.7 V in wet H2.A redox reversible composite anode with Fe-Ni alloy nanoparticles in situ growth on SrLaFeO4-type and LaFeO3-type oxide substrates has been prepared for intermediate temperature solid oxide fuel cell (IT-SOFC) by reducing perovskite precursor La0.4Sr0.6Fe0.75Ni0.1Nb0.15O3-δ (LSFNNb) in wet H2 at 900 °C for 1 h. The anode has shown an excellent electrochemical catalytic activity for oxidation of hydrogen with much smaller Ea (25.1 ∼ 68.9 kJ mol−1) than the value (>160 kJ mol−1) at Ni-YSZ anode. A scandium stabilized zirconia (ScSZ) electrolyte supported SOFC with the anode achieves maximum power densities of 0.71, 0.52, 0.35, and 0.21 W cm−2 at 800, 750, 700 and 650 °C, respectively in wet H2 (3% H2O), and the corresponding Rp of 0.16, 0.21, 0.35, and 0.60 Ω cm2 under OCV. Moreover, the single cell shows stable power output during ∼105 h operation at 800 °C under 0.7 V in wet H2 after a initial degradation, indicating that R-LSFNNb is an excellent candidate as anode of IT-SOFC.Download high-res image (140KB)Download full-size image

As an ionic conductive functional layer of intermediate temperature solid oxide fuel cells (ITSOFC), samarium-doped ceria (SDC)–LiNaSO4 nano-composites were synthesized by a sol–gel method and their properties were investigated. It was found that the content of LiNaSO4 strongly affected the crystal phase, defect concentration, and conductivity of the composites. When the content of LiNaSO4 was 20 wt%, the highest conductivity of the composite was found to be, respectively, 0.22, 0.26, and 0.35 S cm−1 at temperatures of 550, 600, and 700 °C, which are much higher than those of SDC. The peak power density of the single cell using this composite as an interlayer was improved to, respectively, 0.23, 0.39, and 0.88 W cm−2 at 500, 600, and 700 °C comparing with that of the SDC-based cell. Further, the SDC–LiNaSO4(20 wt%)-based cell also displayed better thermal stability according to the performance measurements at 560 °C for 50 h. These results reveal that SDC–LiNaSO4 composite may be a potential good candidate as interlayer for ITSOFC due to its high ionic conductivity and thermal stability.

•Composite cathode can significantly improve the performance of cathode in SOFC.•Addition of the second phase has an optimum value for composite cathode.•Overloading second phase has a negative influence on composite cathode.•The cell shows the best performance at 40 wt% SDC as second phase.Cobalt-free composites Nd0.5Sr0.5Fe0.8Cu0.2O3−δ (NSFCu)–xSm0.2Ce0.8O1.9 (SDC) (x = 0–60 wt%) are investigated as IT-SOFC cathodes. The characteristic properties of cobalt-free composite cathodes comparing to cobalt-based composites are revealed. The DC conductivity and thermal expansion coefficient of the composite cathodes decrease with the content of SDC x, while the polarization resistance Rp shows the least value with addition of 40 wt% of SDC. The power density of the single cell with NSFCu-40% SDC composite cathode improved significantly compared with that of undoped NSFCu cathode, with peak values of 488, 623, 849 and 1052 mW cm−2 at 600, 650, 700, and 750 °C, respectively. Moreover, the performance of the composite cathode is stable within testing period of 370 h at 700 °C, indicating that the NSFCu-40% SDC is an excellent cobalt-free composite cathode applied in IT-SOFC.

Novel cobalt-free perovskite oxides NdxSr1–xFe0.8Cu0.2O3−δ (NSFCx, 0.3 ≤ x ≤ 0.7) have been prepared and evaluated as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC). Their structure, thermal expansion, electric, and electrochemical properties are investigated. The oxides exhibit all cubic structure and show excellent thermal and electrochemical performance stability. The Nd content (x) significantly affects the properties of NSCFx. NSFC0.5 has been found to be the optimum composition with a peak electrical conductivity of 124 S cm–1 at 700 °C, an average thermal expansion coefficient of 14.7 × 10–6 K–1 over 25–800 °C, a cathodic polarization resistance (Rp) of 0.071 Ω cm2 at 700 °C, and a peak power density of 900 mW cm–2 at 800 °C for samarium-doped ceria (SDC)-based single cells with NSFCx cathodes and Ni–SDC anodes. Moreover, no degradation has been observed for the Rp at 700 °C within 350 h. The concentration of surface oxygen vacancies and composition dependent crystallographic parameters have been found to be the dominating factors on performance of NdxSr1–xFe0.8Cu0.2O3−δ as IT-SOFC cathodes.

•Pr0.5Sr0.5Fe0.8Cu0.2O3−δ (PSFC) is synthesized and evaluated as SOFC cathode.•The Rp of PSFC cathode on SDC electrolyte is as low as 0.050 Ω cm2 at 700 °C.•The peak power density of a zirconia based single cell is 1077 mW cm−2 at 800 °C.A new cobalt-free perovskite oxide Pr0.5Sr0.5Fe0.8Cu0.2O3−δ (PSFC) has been synthesized and evaluated as cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The chemical compatibility of PSFC with Sm0.2Ce0.8O1.9 (SDC) electrolyte has be proven by XRD, and its electrical conductivity reaches the maximum value of 264.1 S cm−1 at 475 °C. Symmetrical cells with the configuration of PSFC/SDC/PSFC are used for the impedance study and the polarization resistance (Rp) of PSFC cathode is as low as 0.050 Ω cm2 at 700 °C. Single cells, consisting of Ni–YSZ/YSZ/SDC/PSFC structure, are assembled and tested from 550 °C to 800 °C with wet hydrogen (∼3% H2O) as fuel and static air as oxidant. A maximum power density of 1077 mW cm−2 is obtained at 800 °C. All the results suggest that the cobalt-free perovskite oxide PSFC is a very promising cathode material for application in IT-SOFC.

•Redox stable layered perovskite SrLaFeO4 (SLFO4) is firstly used as anode for SOFC.•The SLFO4 shows linear thermal expansion behavior with TEC of 14.3 × 10− 6 K− 1.•The anode achieves Pmax of 0.93 and 0.63 Wcm− 2 at 900 and 800 °C in wet H2.•The cell performance is enhanced by the existence of H2S.•The anode exhibits highly chemical and thermal stability in reducing atmosphere.Redox stable K2NiF4 type layered perovskite SrLaFeO4 − δ(SLFO4 − δ) has been prepared and evaluated as anode for solid oxide fuel cell (SOFC). The SLFO4 − δ shows linear thermal expansion behavior with TEC of 14.3 × 10− 6 K− 1. It also demonstrates excellent catalytic activity for various fuels. A scandia stabilized zirconia (ScSZ, 180 μm) electrolyte supported SOFC with the anode achieves maximum power densities (Pmax) of 0.93, 0.76, 0.63, and 0.46 Wcm− 2 at 900–750 °C, respectively, in wet H2. Pmaxs of cells supported by 250 μm ScSZ reach 0.57, 0.60 and 0.50 Wcm− 2 in H2, H2 + 50 ppm H2S and propane, respectively, at 800 °C. Moreover, the cells show stable power output during ~ 100 h operation at 800 °C under 0.7 V in various fuels. The Pmax at 800 °C in wet H2 even increases by ~ 11% in the subsequent two thermal cyclings, indicating that SLFO4 − δ is a promising anode candidate for SOFC with good electro-catalytic activity, high stability and resistance to sulfur and coking.