Analytical method for determining the internal resistance and electrocatalyst utilization of fuel cells

Two analytical methods are developed that each allows one to determine: (i) the internal resistance of fuel cell electrodes, and (ii) the fraction of the electrocatalyst that is effectively used. To apply either method requires knowledge of the Tafel parameters for the electrocatalyst electrolyte combination. In addition, one method —the maximum power method —requires that the potential and current of a fuel cell be measured when the cell is operating under steady-state conditions and at maximum power. Thus, its application is limited to fuel cells that are not damaged by operating at these conditions. The second method is approximate, but it does not require that the voltage and current be measured at the maximum power condition. To apply the second method—approximate maximum power method—requires the measurement of the fuel cell potential and slope of the potential-current relation of the fuel cell at a current that is less than the current corresponding to the maximum power condition. Using data available from the literature, the two techniques are used to evaluate these characteristics for a KOH fuel cell. They are also used to predict the voltage-current relation for the fuel cell. The results are found to be in close agreement with the reported measurements over a range of currents. The range is larger for the ‘maximum power method’ than for the ‘approximate maximum power method’.