| Solid oxide fuel cells are one of the friendly energy sources that have been developed in the 21st century.Solid oxide fuel cells generally have a high operating temperature.The material and structure requirements of solid oxide fuel cells are also higher at high temperatures,so the cost is also increased.Reducing the operating temperature of SOFC is an important direction of its development,and it is also an inevitable way to promote its commercial application.Cerium oxide-based electrolyte is an important material for the temperature reduction of SOFC because it has a high ionic conductivity at low temperatures.The cerium oxide-based electrolyte is a mixed ionic conductor,and the conversion of Ce4+to Ce3+is liable to occur at a relatively high temperature and a low partial pressure of oxygen,so it will cause a leakage current inside the electrolyte to affect the performance of the SOFC.The cerium oxide-based carbonate composite electrolyte has high ionic conductivity at low temperature,and the open circuit voltage and output performance of the composite electrolyte SOFC are also improved after the incorporation of carbonate.Therefore,some scholars have proposed that carbonate can suppress the electron leakage problem of cerium oxide-based electrolyte.Measurements of actual leakage currents are difficult,mostly based on numerical simulation studies.In this thesis,electrolyte materials and SOFC were prepared.The ionic conductivity of the composite electrolyte and the output performance of the SOFC were measured.According to the calculation method of leakage current proposed by our research group,whether the carbonate composite electrolyte has the effect of suppressing leakage current is explored.At the same time,this paper deeply explores the effects of temperature,fuel flow rate and carbonate content on leakage current,and draws the following conclusions:?1?In this thesis,the ionic conductivity of the electrolyte was measured by four-point method.It was found that the ionic conductivity of the carbonate composite dielectric was much higher than that of the pure SDC electrolyte,and the ionic conductivity gradually increased with the increase of the test temperature.This result is consistent with the reported literature;With the increase of the amount of carbonate doping in the composite electrolyte,the ionic conductivity first increases and then decreases.When the carbonate content is 25%,the ionic conductivity is the highest.?2?In this thesis,the sandwich structure SOFC was prepared by co-pressure method,and its I-V/I-P performance curves were tested.It is found that the open circuit voltage of the SOFC measured in this experiment is not much different from the theoretical voltage,and the SOFC with 20%carbonate content reached 0.981V at500°C,the maximum output current density reached 465mA?cm-2at 30%carbonate.In addition,the open circuit voltage values gradually decrease with the increase of the test temperature,and the open circuit voltage of the composite electrolyte SOFC is larger than the SOFC with SDC as the electrolyte.Finally,we investigated the effect of hydrogen flow on the open circuit voltage.It was found that the open circuit voltage increased first and then decreased with the decrease of hydrogen flow rate,and the open circuit voltage was the largest when the hydrogen flow rate was 30 sccm.The carbonate content has a certain influence on the output power density of the SOFC.The SOFC output power density of 20%is the largest one at 500°C and the maximum value is 115.78mW?cm-2;When the temperature is greater than or equal to 550°C,the composite SOFC with a content of 25%has the highest output power density,and the maximum output power can reach161.76mW?cm-2.?3?In this thesis,the combination of experimental measurement and calculation is used to obtain the SOFC leakage current under two different conditions.The comparison between SDC electrolyte and composite electrolyte is compared.The effects of fuel flow,test temperature and carbonate content on the leakage current are also investigated.Under the theoretical voltage,the leakage current density of the composite electrolyte is less than the leakage current density of the SDC.However,in the open state,the leakage current density of the composite electrolyte is higher than the leakage current density of the SDC.In addition,the increase of temperature will lead to the increase of leakage current;For composite SOFC,carbonate can reduce leakage current below 600°C.When the temperature is higher than 600°C,the leakage current will be accelerated with the increase of carbonate content.For composite SOFC,carbonate can reduce leakage current below 600°C.When the temperature is higher than 600°C,the leakage current will be accelerated with the increase of carbonate content.When the temperature is below 600°C,the decrease of hydrogen flow rate will lead to an increase of leakage current;when the temperature is higher than 600°C,proper reduction of hydrogen flow rate can reduce the generation of leakage current. |
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