Residence time distributions and reaction kinetics in a fuel cell anode

A method which treats the fuel cell anode as a chemical reactor is developed to predict fuel cell performance. The method is based on experimentally measured residence time distribution parameters and differential cell kinetic data. The apparatus and experimental technique used to obtain the gas-phase residence time distributions are described. Kinetic data obtained from differential cell tests of the electrodes are used to evaluate an empirical rate expression.Axial dispersion model solutions for flow with volume change are obtained, based on the measured Peclet numbers and empirical rate expressions, and compared with experimental data from operating large high-temperature molten carbonate fuel cells. Agreement between the model and the experimentally determined data is very good, but only for low conversions of the fuel.Notation A cross-sectional area, cm² - C concentration of hydrogen. (g mole/cm³) - c=C/C_o dimensionless concentration of hydrogen - D dispersion coefficient cm²/s - d_e equivalent diameter, cm - F Faraday's constant - I total current, A - J current density, mA/cm² - k reaction rate constant, appropriate units - L length, cm - M number of moles - N =D/UL dispersion number - n order of reaction - n_e number of electrons transferred - –r rate of reaction based on volume of fluid, moles of reactant reacted/ cm³ s - S_e surface of electrode, cm² - T absolute temperature, °K - mean residence time, s - U velocity component in Z direction, cm/s - u = U/U₀ dimensionless velocity - V_a volume of system, cm³ - V operating voltage, V - v volumetric flow rate, cm²/s - fractional conversion, degree of conversion of hydrogen - y mole fraction of hydrogen - Z space coordinate, cm - z =Z/L fractional lengthGreek letters coefficient of expansion - _m molar density of fuel, g mole/cm³ - overvoltage, V - dimensional variance, s² - ² dimensionless variance - =V_a/v₀ space time, s