Park, Yong Hun (2007-12). Investigation of the performance and water transport of a polymer electrolyte membrane (pem) fuel cell. Doctoral Dissertation. Thesis uri icon

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(R) 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.
  • 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(R) 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.

publication date

  • December 2007