Design And Performance Of Novel Perovskite Cathode Materials For Intermediate-to-Low Temperature Solid Oxide Fuel Cells

Solid oxide fuel cell?SOFC?is an energy technology that can directly convert chemical energy into electrical energy with high energy conversion efficiency at relatively high temperatures.Reducing the operating temperature to intermediate-to-low range is the main trend of SOFC field.The reduced operating temperature is expected to significantly reduce the fabricating cost and promote its commercial application.However,the development and preparation of high-performance cathode materials are the bottlenecks of developing SOFC working at medium to low temperatures.Therefore,exploring cathode materials with high performance at intermediate-to-low temperatures has become a research focus in the SOFC field in recent years.In this paper,two novel cathode materials,i.e.,Ba_0.5Sr_0.5Co_0.7Fe_0.2Ni_0.1O_3-??BSCFN?perovskite and Bi_0.7Pr_0.1Ba_0.2Fe O_3-?-Ce_0.8Sm_0.2O_1.9?BPBF-SDC?composite cathodes,have been developed for the above problems.The crystal structure,oxygen kinetics,thermal stability,electrical conductivity,electrochemical performance,stability,CO₂-resistance were investigated,and their feasibility as intermediate-to-low temperature SOFC cathode material was comprehensively evaluated.The results of this paper are as follows:Ni-doped Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-??BSCF?material,i.e.,Ba_0.5Sr_0.5Co_0.7Fe_0.2Ni_0.1O_3-??BSCFN?,was prepared by EDTA-CA combined complexation method.BSCFN retained the cubic symmetrical crystal structure of BSCF.Due to the incorporation of Ni,the crystal lattice expands slightly.The oxygen vacancy concentration of BSCFN is much higher than that of BSCF material at room temperature and high temperatures,and the bulk diffusion(D_chem)and surface adsorption coefficient(K_chem)of oxygen of BSCFN the electrolyte,the area specific resistance?ASR?at 600°C is only 0.033?cm²,which is 1/3 of the BSCF cathode at the same temperature.In addition,the symmetrical cell is able to remain the stability for 100 h at 600°C.When the symmetrical cell was exposed to an atmosphere containing 10 vol%CO₂,the area resistance increased rapidly.However,when converting the atmosphere into air,the area resistance recovered to a value that is much close to initial one in a short time.A single cell with Ni-SDC as the anode,SDC as the electrolyte,and BSCFN as the cathode can deliver a power density of?1.8W cm^-2 at 650°C.Such outstanding electrochemical performance can be ascribed to the doping of Ni,which enables the stability of cubic symmetrical structure and facilitates the oxygen kinetics.Excellent performance and stability endow BSCFN cathode materials with great application potential.The perovskite material Bi_0.7Pr_0.1Ba_0.2Fe O_3-??BPBF?was prepared by EDTA-CA combined complexation method,and was mixed with the electrolyte material SDC at a ratio of 7:3 to obtain a BPBF/SDC composite cathode material.The substitution of Pr and Ba enables a cubic symmetrical phase structure for BPBF.The mixture of BPBF and SDC was calcining at 900°C for 5 h,no secondary phase emerged,illustrating the good compatibility between BPBF and SDC at high temperature.Moreover,the oxygen bulk diffusion coefficient(D_chem)and surface exchange coefficient(k_chem)of BPBF are much higher than many novel Fe-based perovskite cathodes.The cubic structure and the enhanced phase symmetry caused by the co-substitution of Ba and Pr result in the decreasing of enthalpy of oxygen vacancy migration,thus accelerating the oxygen kinetics of BPBF.With SDC as the electrolyte and BPBF/SDC composite material as the cathode,the symmetrical cell delivered a resistance of only 0.056?cm² at 700°C.This symmetrical cell also revealed superior thermal stability and anti-CO₂ performance,which can be evidenced by the stable ASR values when exposed in air and air containing 1 vol%CO₂ each for 50 hours.Further research demonstrated that the excellent catalytic activity and stability of symmetrical cell can be attributed to the good thermal stability and CO₂resistance of the composite material.