A mathematical model of a hydrogen/oxygen alkaline fuel cell

Abstract

A mathematical model of a hydrogen/oxygen alkaline fuel cell is presented that can be used to predict the polarization behavior under various power loads. The major limitations to achieving high power densities are indicated and methods to increase the maximum attainable power density are suggested. These performance indications can help future research and the design of alkaline fuel cells. The alkaline fuel cell model describes the phenomena occurring in the solid, liquid, and gaseous phases of the anode, separator, and cathode regions based on volume averaging of the three phases. Fundamental equations of chemical engineering that describe conservation of mass and charge, species transport, and kinetic phenomena in the homogeneous regions are volume averaged over a heterogeneous region giving expressions that contain the averages of the properties of each phase. Gas phase diffusional resistances are considered by calculating the spatial variation of the partial pressures of oxygen, hydrogen, and water vapor in the gas phase. The liquid phase diffusional resistances are accounted for by considering the concentration distributions of dissolved oxygen and hydrogen in KOH. The variation of the KOH electrolyte concentration is also accounted for by including the ionic resistance effects. Electronic resistances are considered by calculating the solid electrode potential drops in the porous gas diffusion electrodes. By developing a complete model of the alkaline fuel cell, the interaction of these various resistances can be investigated under conditions that simulate actual fuel cells. A sensitivity analysis of the various transport and electrokinetic parameter indicates which parameters have the most influence on the predicted current density and over which range of potentials these parameters affect the fuel cell performance the most. This information can be used to decide which parameters should be optimized or determined more accurately through further modeling or experimental studies. The effect of various design parameters on the limiting current density are also investigated to determine if optimal values exist for the parameters. These parameter sensitivities and optimal design parameters can help in the development of better three-phase electrodes and separators for the alkaline fuel cell.