Determination of internal resistance and electrocatalyst utilization of fuel cells

Analytical methods have been proposed recently for determining both the internal resistance of fuel cell electrodes and the fraction of the electrocatalyst that is completely utilized. To apply these methods requires that the Tafel slope and the equilibrium exchange current for the electrolyte-electrocatalyst combination to be known when this combination is exposed to O2 and when it is exposed to H2. The Tafel parameters have been previously reported for O2 and their measurement for H2 is reported herein. Also, to apply one of these analytical methods maximum power method — requires that the current and potential to be measured when a fuel cell is operating at steady state and at maximum power. To apply the second method — approximate maximum power method — requires that the cell potential and slope of the potential versus current curve be measured at a current that is less than that corresponding to maximum power. To evaluate these methods, a series of porous carbon electrodes were constructed, and to give them different resistances nickel was electro-deposited on the one side of each. These electrodes were then assembled into fuel cells and tested. Their internal resistance was determined by the current-interrupt technique, and by using the analytical methods. These results agree to within the experimental error, 12%. Electro-depositing nickel on the gas side of the electrodes was found to decrease their internal resistance by an order of magnitude and increase the electrocatalyst utilization by a factor of three.