Preparation And Performance Analysis Of Doped Cobalt-based Cathode Materials

With increasing demand for eco-friendly and renewable energy,solid-oxide fuel cells?SOFCs?have received much attention because of their high energy efficiency,less pollutant and excellent fuel flexibility compared with other types of fuel cells.To make SOFCs economically competitive with the existing power technology,the operating temperature is needed to be lowered to the intermediate range?600⁸00°C?.However,lowering the operating temperature will reduce the electrode dynamics and lead to a large interfacial polarization resistance,which has a negative impact on the output power and energy conversion efficiency of SOFC.This effect is most pronounced for the oxygen reduction reaction?ORR?at the cathode.In recent years,it is especially urgent to develop new materials with high electrocatalytic activity,excellent ion and electronic conductivity in the intermedium temperature range.The perovskite structure?ABO₃?oxide cathode material can meet the needs of this research.In this thesis,SrSc_0.2-xTa_x Co_0.8O_3-?cathode and Ba_0.5Sr_0.5Sc_0.2-xTa_x Co_0.8O_3-?are studied by which the electrochemical performance were determined from 600°C to800°C and the expected results were obtained.The SrSc_0.2-x.2-x Ta_x Co_0.8O_3-??SSTC??SSTC_x,x=0,0.015,0.025,0.050?cathode materials were prepared by solid-state method.The symmetrical fuel cell was made up of Ni_0.9Cu_0.1O_x-SDC anode,SDC electrolyte,and SrSc_0.175Ta_0.025Co_0.8O_3-?cathode which has the corresponding total interface polarization resistance of the cell as low as 0.0504?·cm² and the peak power densities about 650.76 mW·cm^-22 at 800°C.The long-term stability test shows that under the condition of test temperature of 750°C and constant voltage of 0.7 V,the single cell remains high at the current density of 0.519 A·cm^-2,and there is no obvious decrease in the current density,but there is a trend of slow rise.The stable operation time is 42 hours.It shows that Ni_0.9Cu_0.1O_x-SDC/SSTC_0.025/SDC single cell is an excellent battery.In order to obtain the cathode material with better performance,the large radius size Ba²⁺was partially replaced by the A-bit element as Ba_0.5Sr_0.5Sc_0.2-x.2-x Ta_xCo_0.8O_3-??BSSTC??BSSTC_x,x=0,0.025,0.050,0.075,0.1?cathode materials.The experimental results show that BSSTC_0.1.1 cathode material has the best electrochemical performance.The lowest polarization impedance of R_p at 800°C is0.029?·cm^-2,which is 42.46%lower than that of SSTC_0.025.The maximum power density of electrolyte-supported single cell Ni_0.9Cu_0.1O_x-SDC/BSSTC_0.1/SDC is 1075mW·cm^-2,which is 65.38%higher than that of Ni_0.9Cu_0.1O_x-SDC/SSTC_0.025/SDC.Under the same long-term stability test conditions,a single cell current density of0.618 A·cm^-22 is 19.07%higher than that of the Ni_0.9Cu_0.1O_x-SDC/SSTC_0.025/SDC single cell.There was no significant drop in the stable operation and also maintained at 30 hours of the test time.The Ni_0.9Cu_0.1O_x-SDC/BSSTC_0.1/SDC single cell is a better performance than Ni_0.9Cu_0.1O_x-SDC/SSTC_0.025/SDC,which both are better than the general electrolyte-supported single cell at the same time.