Numerical and Experimental Analysis of Current Density Distribution and Transient Response for Polymer Electrolyte Membrane Fuel Cell

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Polymer Electrolyte Membrane Fuel Cell (PEFC), which can achieve high energy efficiency and small load on environment, is expected to apply to power sources for electric vehicles and distributed power sources. Because the ionic conductivity and electro-osmosis coefficient of the polymer electrolyte membrane (PEM) are depend on its water uptake and temperature, it is important to control the water uptake and the temperature so that FC can generate electricity uniformly, understanding the temperature distribution and water molecule behavior in PEFC.And it is also important to grasp the transient response of cell potential to load and reactant flow gas change.First, to analyze the steady state characteristics of the power generation, we developed numerical code of PEFC considering the mass, charge and energy balance, and analyzed its characteristics corresponding the experimental condition, such as cell temperature, utilization ratio, etc. Where the activation overpotential was given so a … More s to agree with the measured current-potential characteristics. As the numerical result, it was understood that the current distribution changed due to the water uptake change in PEM, which was controlled by the humidifier temperature. To verify this numerical current distribution change, we actually measured it by use of segmented electrode. The experimental result of current distribution agreed with the analytical.Next, we experimentally and numerically investigated the transient response of cell potential, quickly changing the load current and reactant gas flow rate. In case of constant H_22/O_2 flow rate, the cell potential response to the load current change was describable by the representative time of electric double layer capacitance and reaction resistance. In case of constant simulated reformed gas/air flow rate, the response time was longer because of the larger diffusive resistance. In case of constant load current, the cell potential response to the gas flow rate change was about 10 seconds due to the re-distribution of water molecule in PEM. Less