Mass transport in the cathode of a free-breathing polymer electrolyte membrane fuel cell

In small fuel cell applications, it is desirable to take care of the management of reactants, water and heat by passive means in order to minimize parasitic losses. A polymer electrolyte membrane fuel cell, in which air flow on the cathode was driven by free convection, was studied by experimental and modelling methods. The cathode side of the cell had straight vertical channels with their ends open to the ambient air. A two-dimensional, isothermal and steady state model was developed for the cathode side to identify the limiting processes of mass transport. The modelled domain consists of the cathode gas channel and the gas diffusion layer. Experimental data from current distribution measurements were used to provide boundary conditions for oxygen consumption and water production. The model results indicate that at the cell temperature of 40 degreesC the performance of the cell was limited by water removal. At the cell temperature of 60 degreesC, the current distribution was determined by the partial pressure of oxygen.