| dc.description.abstract | Fuel cell performance was obtained as functions of the humidity at the anode and
cathode sites, back pressure, flow rate, temperature, and channel depth. The fuel cell
used in this work included a membrane and electrode assembly (MEA) which possessed
an active area of 25, 50, and 100 cm2 with the Nafion® 117 and 115 membranes.
Higher flow rates of inlet gases increase the performance of a fuel cell by increasing
the removal of the water vapor, and decrease the mass transportation loss at
high current density. Higher flow rates, however, result in low fuel utilization. An important
factor, therefore, is to find the appropriate stoichiometric flow coefficient and
starting point of stoichiometric flow rate in terms of fuel cell efficiency. Higher air supply
leads to have better performance at the constant stoichiometric ratio at the anode, but
not much increase after the stoichiometric ratio of 5.
The effects of the environmental conditions and the channel depth for an airbreathing
polymer electrolyte membrane fuel cell were investigated experimentally. Triple
serpentine designs for the flow fields with two different flow depths was used. The shallow flow field deign improves dramatically the performance of the air-breathing fuel
cell at low relative humidity, and slightly at high relative humidity.
For proton exchange membrane fuel cells, proper water management is important
to obtain maximum performance. Water management includes the humidity levels of the
inlet gases as well as the understanding of the water process within the fuel cell. Two
important processes associated with this understanding are (1) electro-osmotic drag of
water molecules, and (2) back diffusion of the water molecules. There must be a neutral
water balance over time to avoid the flooding, or drying the membranes. For these reasons,
therefore, an investigation of the role of water transport in a PEM fuel cell is of
particular importance.
In this study, through a water balance experiment, the electro-osmotic drag coefficient
was quantified and studied. For the cases where the anode was fully hydrated and
the cathode suffered from the drying, when the current density was increased, the electro-
osmotic drag coefficient decreased. | en |
