Study On Numerical Simulation And Electrochemical Performance Of SOFC Using H₂-CO As Fuel Gas

As an energy conversion device,solid oxide fuel cell（SOFC）can convert chemical energy into electrical energy.When hydrocarbon fuel is used as fuel gas,SOFC has great development potential.Because the operating temperature of SOFC is too high and the size of SOFC is too small,it is difficult to measure the key physical parameters of SOFC by experimental methods,and the operating parameters and microstructure characteristics of SOFC directly affect the electrochemical performance of SOFC.It is the key to improve the performance of the battery to obtain the key physical parameters under the working state of the battery.Therefore,it is necessary to use the numerical simulation method to determine the physical parameters.Firstly,the experimental test device of anode supported SOFC single cell was built.The three-dimensional numerical model of the plate SOFC with H₂-CO as fuel was established.The model was solved by mass transfer,momentum transfer,heat transfer,component transfer,charge transfer and electrochemical reaction coupling.The distribution of physical parameters such as component concentration,temperature,velocity and current density were investigated.The effects of operating parameters such as gas flow direction,operating temperature,fuel flow rate,air flow rate,fuel gas ratio and microstructure parameters such as porosity,tortuosity,particle size and pore size on the electrochemical performance of SOFC were studied in order to provide help for the design and operation of SOFC.The results show that the mole fraction of fuel in the anode gas channel is larger than that in the functional layer along the gas flow direction,and the mole fraction decreases rapidly in the anode gas channel.The mole fraction of oxygen in the cathode gas channel is much larger than that under the electrode connectors on both sides of the channel,and the temperature of the cell increases,The results show that the anode temperature is higher than the cathode temperature,the gas velocity at the outlet of the anode gas channel is higher than that at the inlet,the gas velocity at the outlet of the cathode gas channel is lower than that at the inlet,the current density of the electrode connector is lower than that at the center of the channel,and the current density at the wall of the channel is higher than that at the center of the channel,The average current density of electrolyte layer decreases gradually from outlet to inlet.When the operating voltage is constant at 0.7 V,the fuel flow rate is 200 sccm and the air flow rate is 500 sccm,the maximum power density of SOFC increases with the increase of operating temperature,the performance of SOFC increases,the concentration overpotential increases,and the activation overpotential and ohmic overpotential decrease.When the current density is low,the performance curves of SOFC under forward current and reverse current are basically coincident;When the current density increases to 0.4 A/cm²,the downward trend of the voltage in the forward flow is higher than that in the reverse flow,and the reverse flow has advantages over the forward flow.However,the temperature gradient at the fuel outlet is the largest when the reverse flow mode is adopted,resulting in greater thermal stress on the battery module and reduced service life of the battery.When the operating temperature is 800℃,the operating voltage is constant at 0.7 V,and the air flow rate is 1000 sccm,the cell temperature,power density and cathode concentration overpotential first increase and then decrease with the increase of fuel flow rate;The fuel utilization rate of H₂ and CO,the overpotential of anode concentration difference,and the composition change of anode and cathode at the inlet and outlet all show a downward trend;The activation overpotential,ohmic overpotential and the average current density of the electrolyte layer at the outlet increase.When the current density is more than 0.8 A/cm²,the larger the proportion of H₂ in the fuel,the better the performance of the cell.When the fuel flow is 100 sccm,the power density increases with the increase of air flow;When the air flow rate increases to 800 sccm,the battery performance remains unchanged,while the air flow utilization rate decreases gradually.When the operating temperature is 800℃,the operating voltage is 0.7 V,the fuel flow rate is 100 sccm,and the air flow rate is 1000 sccm,the performance of the cell is improved with the increase of porosity.However,when the porosity rises to 0.5,the fuel utilization of H₂ increases and the fuel utilization of CO decreases.When the tortuous degree decreases from 3.5 to 1.5,the particle size decreases from 1μm to 0.2μm,the pore size increases from0.1μm to 0.9μm,the battery performance,maximum power density,electrode temperature at the outlet,composition changes of anode and cathode at the inlet and outlet,fuel utilization ratio and average current density of electrolyte layer at the outlet increase,and changes of three kinds of overpotential at the inlet and outlet increase,the concentration overpotential,activation overpotential and ohmic overpotential of the battery at the inlet and outlet increase.