•Nano Sm0.2Ce0.8O1.9 particles were decorated on La0.6Ca0.4Fe0.8Ni0.2O3−δ scaffold.•Fe-Ni bimetallic nanoparticles were exsolved in-situ from LCFN perovskite.•Electrolyte-supported symmetrical SOFC showed a peak power density of 303 mW cm−2 at 800 °C.•The S-SOFC showed good operation stability in H2 and reliable redox stability in H2/air cycles.Symmetrical solid oxide fuel cells (SOFCs) have more attractive benefits such as a simplified fabrication procedure and enhanced stability and reliability compared to conventional SOFC. In this study, we fabricated a La0.6Ca0.4Fe0.8Ni0.2O3−δ (LCFN) – Sm0.2Ce0.8O1.9 (SDC) composite via infiltration and simple mixing methods and evaluated it as both anode and cathode for symmetrical SOFCs (S-SOFC). X-ray diffraction (XRD) and scanning electron microscope (SEM) results demonstrated that Fe-Ni bimetallic nanoparticles were exsolved in-situ from LCFN perovskite and distributed on the surface of LCFN backbone after H2 reduction at high temperature. The electro-activity towards oxygen reduction reaction (ORR) at the cathode side could be further improved by infiltration of SDC nanoparticles. A combined effect of in-situ ex-solution of Fe-Ni as well as infiltration of SDC nanoparticles synergistically promoted the hydrogen oxidation reaction at the anode and ORR activity at the cathode. Furthermore, the S-SOFC showed good stability in H2 at 800 °C for 140 h and reliable redox stability undergoing a repeated H2-air cycles. These recent results indicate that the LCFN-SDC composite electrodes were promising bi-electrode materials for high performance and cost-effective S-SOFCs.Download high-res image (219KB)Download full-size image

•A cation deficiency in SCNF increases oxygen non-stoichiometry.•Sr-deficient S0.95CNF electrode exhibits high ORR activity.•The rate limiting step of ORR is charge transfer process.•Electrolyte supported single cell displays a peak power density of 208 mW cm−2 at 700 °C.Solid oxide fuel cells (SOFCs) offer great promise for the most efficient and cost-effective conversion to electricity of a wide variety of fuels. The cathode materials with high electro-catalytic activity for oxygen reduction reaction is vital to the development of commercially-viable SOFCs to be operated at reduced temperatures. In present study, cobalt-based perovskite oxides SrxCo0.7Nb0.1Fe0.2O3−δ (SCNF, x = 0.95 and 1) were comparatively investigated as promising cathode materials for intermediate-temperature SOFCs. The SCNF compounds with a slight Sr deficiency (S0.95CNF) exhibited single phase of primitive cubic structure with Pm-3m symmetry. A small Sr deficiency is demonstrated to greatly enhance the electrochemical performance of stoichiometric SCNF cathode due to significantly increased oxygen vacancy. The polarization resistance of S0.95CNF at 700 °C was 0.11 Ω cm2, only about 61% of SCNF. The rate limiting step for oxygen reduction reaction (ORR) is demonstrated to be oxygen ion transfer within the bulk electrode and/or from electrode to electrolyte through the triple phase boundary. Full cells with the SCNF cathode present good performance and stable output at reduced temperatures, indicating the great potential for enhanced performance of Co-based cathodes with A-site deficiency.

•La10Si6-xCuxO27-x (0 ≤ x ≤ 2) is synthesized by sol–gel process.•La10Si6-xCuxO27-x (0 ≤ x ≤ 2) exhibits a maximum conductivity of 4.8 × 10−2 S/cm for x = 1.5 at 800 °C.•Copper doping has more significant on grain conductivity than grain boundary conductivity.•La10Si4.5Cu1.5O25.5 has a thermal expansion coefficient of 9.0 × 10−6/°C at 20–800 °C.Apatite-type Lanthanum silicate (LSO) is among the most promising electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) owing to the high conductivity and low activation energy at lower temperature than traditional doped-zirconia electrolyte. The ionic conductivity as well as the sintering density of lanthanum silicate oxy-apatite, La10Si6-xCuxO27-δ (LSCO, 0 ≤ x ≤ 2), was effectively enhanced through a small amount of doped copper. The phase composition, relative density, ionic conductivity and thermal expansion behavior of La10Si6-xCuxO27-δ was systematically investigated by X-ray diffraction (XRD), Archimedes' drainage method, scanning electron microscope (SEM), electrochemical impedance spectra (EIS) and thermal dilatometer techniques. With increasing copper doping content, the ionic conductivity of La10Si6-xCuxO27-δincreased, reaching a maximum of 4.8 × 10−2 S cm−1 at 800 °C for x = 1.5. The improved ionic conductivity could be primarily associated with the enhanced grain conductivity. The power output performance of NiO-LSCO/LSCO/LSCF single cell was superior to that obtained on NiO-LSO/LSO/LSCF at different temperatures using hydrogen as fuel and oxygen as oxidant, which could be attributed to the enhanced oxygen ionic conductivity as well as the sintering density for the copped doped lanthanum silicate. In conclusion, the apatite La10Si4.5Cu1.5O25.5 is a promising candidate electrolyte for IT-SOFCs.

Surface-decoration is a new and promising approach to improve solid oxide fuel cells (SOFC) cathode materials since it can strongly affect the oxygen reduction activity. Here we report the application of novel infiltration method to enhance the oxygen reduction reaction of LaNi0.6Fe0.4O3−δ (LNF) cathode decorated with different nano catalysts, i.e., Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF), Ba0.9La0.1FeO3−δ (BLF), Sm0.2Ce0.8O3−δ (SDC), and Pr6O11. Through surface decoration with various nano catalysts, the electrochemical activity of LNF cathode was investigated under open circuit voltage (OCV) and direct current (DC) bias voltage conditions and the inherent oxygen reduction reaction (ORR) mechanism was discussed. The strongly improved electrochemical performance at OCV suggest that infiltration is an effective way to costly promote the oxygen reduction activity of LNF electrode. Under applied cathodic potential, the electrochemical performance of various catalyst decorated LNF cathode demonstrated different oxygen reduction promotion mechanisms.

•NBCO and NBSCO as potential cathodes for IT-SOFCs have been investigated.•The TEC of NBCO and NBSCO are more compatible with electrolyte than that of cobalt-based cathodes.•The Rp of NBSCO are 0.205 Ωcm2, 0.200 Ωcm2 and 0.135 Ωcm2, at 600 °C, 700 °C and 800 °C, respectively.Cobalt-free perovskite oxides NdBaCu2O5+δ (NBCO) and NdBa0.5Sr0.5Cu2O5+δ (NBSCO) has been investigated as cathode materials in intermediate-temperature solid fuel cells (IT-SOFCs). The crystal structure, thermal expansion, electrical conductivity and electrochemical properties have been characterized by X-ray diffraction (XRD), dilatometer, four-probe dc method, electrochemical impedance spectroscopy (EIS) and cathodic polarization examinations. The average thermal expansion coefficients (TEC) values of NBCO and NBSCO are 13.0 × 10−6/°C and 14.5 × 10−6/°C, which are more desirable on combining with the electrolytes than cobalt-based cathodes. The partly substitution of Sr on B-site increases the electron hole concentration and improves the conductivity. The polarization resistances values of NBSCO are 0.205 Ωcm2, 0.200 Ωcm2 and 0.135 Ωcm2, whereas the polarization resistances values of NBCO are 8.61 Ωcm2, 3.18 Ωcm2 and 0.83 Ωcm2 at 600 °C, 700 °C and 800 °C, respectively. The improved electrochemical performance of NBSCO should be ascribed to the higher conductivity as well as the improved oxygen adsorption/desorption and oxygen ions diffusion processes.