Measurement of ohmic voltage losses in individual cells of a PEMFC stack

The ohmic voltage loss in a fuel cell can be determined with the current interruption method. The method was utilized to measure the ohmic voltage loss in an individual cell of a fuel cell stack. This was achieved by producing voltage transients and monitoring them with a digital oscilloscope connected in parallel with the individual cell. In this study, the method was applied to a small polymer electrolyte membrane fuel cell (PEMFC) stack in which different air supply levels were employed on the cathode side. In the case of higher air-feed rate, the results revealed an increase of ohmic losses in the middle of the stack by up to 21% at 400 mA cm−2, compared to the unit cell with the lowest ohmic loss. This probably resulted from the decrease of membrane conductivity because of drying. Comparison to individual cell voltages showed that the decrease of conductivity would not be observed if only the individual cell voltages alone were measured. The total ohmic loss in the stack was measured using the same method to verify the reliability of the measurement system. The results indicate a good agreement between the total ohmic loss and the combined ohmic losses in the individual cells.