Influence of electrode stress on proton exchange membrane fuel cell performance : experimental characterization and power optimization

Abstract

Compressive stress applied to the electrode area of a Proton Exchange Membrane (PEM) fuel cell is known to significantly affect power output. In practice, electrode stress arises during operation due to the clamping force that is necessary for sealing the cell. In traditional fuel cell designs, the sealing requirement and the clamping stress are inherently coupled and it is difficult to experimentally determine the magnitude of stress experienced by the electrodes. Investigations of the stress-performance relationship in the literature have not addressed this inherent coupling and it is uncertain whether prior stress measurement techniques are accurate. In order to address the limitations of a traditional fuel cell design in applying and measuring electrode stress, a new test setup was designed by the author in which electrode stress and sealing requirements are decoupled and applied stress is constrained to the electrode area only. This test setup allows for accurate description of the stressdependent cell performance as a function of different operating and engineering parameters. Data collected using this test setup can be used to optimize PEM fuel cell performance through consideration of the inherent coupling between parameters and their effect on power output. Performance data as a function of applied stress were obtained using the new setup for a range of cell temperatures and inlet gas pressures. In general, the peak power density was found to increase rapidly at low applied stress (below 1.6 MPa) and to level off near 4.0 MPa. Changing the cell backpressure from 0 psi to 10 psi and then 20 psi improved the power density at high stress but did not help performance below 1.6 MPa. Cell operation at 45°C yielded a power density that was 28% higher than at 23°C, but a further increase to 65°C caused cell performance to decline at all values of applied stress. Overall, increasing the applied stress from 0.8 MPa to 4.4 MPa resulted in an increase in the cell power density by a factor of 2-3 for all operating conditions.and had a greater effect on cell performance than did changing the backpressure or cell temperature.