A pseudo-phase-equilibrium approach for the calculation of liquid water saturation in the cathode gas diffuser of proton-exchange-membrane fuel cells

The cathode compartment of membrane electrode assembly (MEA) of the proton-exchange-membrane fuel cell (PEMFC) is studied theoretically. A pseudo-phase-equilibrium approach adopting an approximate phase-equilibrium equation, incorporated with the associated equations of gaseous multi-component diffusion, liquid water capillary transport, and surface electrochemical kinetics, well characterizes the performance of cathode electrode under unsaturated feed. The pseudo-phase-equilibrium approach avoids the need of explicit liquid water front tracking so that only a single domain formulation, without consideration of the interior boundary, is required for the simulation. In order to illustrate the capability of the proposed approach, a mathematical model of the cathode compartment of MEA in one-dimension is formulated, in which gas species concentration profiles, liquid water distribution, and liquid water front are calculated. The validity of the pseudo-phase-equilibrium approach is then evaluated over an extensive polarization range under specified operating temperature, pressure, and inlet humidity. The solutions obtained using the pseudo-phase-equilibrium approach and the exact phase-equilibrium equation are compared over a wide range of parameter values. In addition, the influences of important transport parameters such as water transport coefficient, gas diffuser porosity, and absolute liquid permeability are evaluated and discussed.