Direct Measurement of iR-Free Individual-Electrode Overpotentials in Polymer Electrolyte Fuel Cells

A method of measuring error-free potentials of individual electrodes directly in the polymer electrolyte fuel cell and under a full range of load is introduced. Successful measurement is accomplished by placing a reference electrode in ionic contact with the active layer of a fuel cell electrode of interest, that is, away from the electrolyte membrane. Half-cell measurements with the proposed reference electrode configuration are compared with measurements in two other fuel-cell reference electrode arrangements to illustrate the conditions necessary for directly achieving correct measurement of potentials (overpotentials). Functioning of the fuel cell reference electrodes is explained through modeling of electrical potential and reactant distribution in the working fuel cell.