Study On The Performance Of Novel Cobalt-Based Perovskite Cathode Materials For Intermediate Temperature Solid Oxide Fuel Cells

The operation temperature of traditional solid oxide fuel cell(SOFC)is?1000?,and the higher operation temperature hinders its commercialization;however,the performance of SOFC will be greatly reduced when the operating temperature is decreased.Cathode is an important component of SOFC,which will directly affect the output performance of SOFC.Therefore,it is necessary to develop novel cathode materials with high performance for solid oxide fuel cell(IT-SOFC)running at intermediate temperatures(600?850?).In this paper,three kinds of novel cobalt-based perovskite cathode materials LaxSr1-xCo0.9Sb0.103-?,La0.4Sr0.6Co0.9Sb0.1O3-?-xCe0.8Sm0.2O1.9 and BaxSr1-xCo0.9Sb0.1O3-?were prepared and the physical and chemical performances were studied systematically.The effects of La/Ba doping or electrolyte introduction on the performance of SrCoO3-based cathode were analyzed,and the feasibility of these materials used as cathodes of IT-SOFCs was assessed.Cobalt-based perovskite cathode materials LaxSr1-xCo0.9Sb0.103-?(LSCSbx,x=0.0?0.8)were prepared via a solid-state reaction method.The LSCSbx samples sintered at 1200? for 10 h have a tetragonal structure with space group P4/mmm,however,an impurity phase of La2Co2O5 was observed in the samples with x=0.6 and x=0.8,and the unit-cell volumes decrease with the doping level from x=0.0 to x=0.6.The LSCSb0.2 and LSCSb0.4 samples have a good chemical compatibility with LSGM after calcined at 1050? for 6 h,respectively.X-ray photoelectron spectroscopy(XPS)examinations indicate that the molar ratio of Co3+to Co4+increases gradually in LSCSbx samples from x=0.0 to x=0.4.The electrical conductivity increases with the doping level from x=0.0 to x=0.4 and the highest electrical conductivity of LSCSb0.4 sample is 673?1637 S cm-1 in the temperature range of 300?850?.The thermal expansion coefficients(TECs)decrease with the doping level and the minimum TEC is 18.50 × 10-6 K-1 for the LSCSb0.6 samples in the temperature range of 30?900?.The lowest polarization resistance(Rp)for the LSCSb0.2 sample on LSGM electrolyte is merely 0.069 ? cm2 at 700?.The single cells were prepared using 0.3 mm thick LSGM as electrolyte,NiO-SDC as anode and SDC as buffer layer,the LSCSb0.2 sample possesses the best cell performance,and there is almost no attenuation of performance after a 20 h testing at 700?.Composite cathode materials La0.4Sr0.6Co0.9Sb0.1O3-?-xCe0.8Sm0.2O1.9(LSCSb-xSDC,x=0,20,30,40,50 wt.%)were prepared via a physical composite method.The LSCSb0.4 samples have a good chemical compatibility with SDC after calcined at 1050? for 6 h.The electrical conductivity decreases with the increase of SDC content,but all the experimental results are still beyond 100 S cm-1 at 300?850?.The TECs of LSCSb-xSDC are reduced with increasing SDC content and the lowest TEC for the LSCSb-50SDC sample is 13.1 ×10-6 K-1 in the temperature range of 30?900?.The Rp decreases with the SDC content from x=0.0 to x=50 on the LSGM electrolyte,and the lowest Rp of LSCSb-50SDC sample is 0.086 ?cm2 at 700?.The single cells were prepared by the same way above,the maximum power density of LSCSb-50SDC sample is 793 mW cm-2 at 850?,and there is almost no attenuation of performance after a 20 h testing at 700?.Scanning electron microscopy(SEM)observations show that the introduction of SDC can enlarge the length of TPB and expand the active region of electrochemical reaction,which can improve the electrocatalytic activity of composite cathodes.Cobalt-based perovskite cathode materials BaxSr1-xCo0.95b0.1O3-?(BSCSbx,x=0.0-0.8)were prepared via a solid-state reaction method.The BSCSbx samples with x=0.0?0.4 sintered at 1050? for 10 h and with x=0.6?0.8 sintered at 1100? for 10 h are crystallized in a tetragonal structure,and the unit-cell volumes increase with the doping level.X-ray diffraction(XRD)refinement shows that all the samples have space group with P4/mmm.The BSCSb0.4 and BSCSb0.6 samples have a good chemical compatibility with LSGM electrolyte after calcined at 1050? for 6 h,respectively.XPS examinations show that the molar ratio of Co3+to Co4+increases gradually.The iodometric titration method and thermogravimetric analysis(TGA)experiments indicate that the oxygen vacancy concentration will increase with increasing content of Ba2+.The electrical conductivity decreases with the doping level.The TECs decrease with the doping level from x=0.0 to x=0.6 and the minimum TEC is 18.50 ×10-6 K-1 for the BSCSb0.6 samples in the temperature range of 30?1000?.The Rp decreases from x=0.0 to x=0.6 on the LSGM electrolyte,and the lowest Rp of BSCSb0.6 sample is 0.082 ? cm2 at 700?.The single cells were prepared by the same way above,the maximum power density increases from x=0.0 to x=0.6 and for the x=0.6 cathode,and the maximum power density of 944 mW cm-2 was attained at 850?.Furthermore,almost no attenuation of performance was observed after 20 h testing at 700?.