Durability Testing of Electrolyte Membranes in Solid Polymer Membrane Fuel Cells
The electrolyte membrane is an indispensable part of solid polymer fuel cells. Significant technical development work has been conducted to enhance the functionality of the electrolyte membrane, with a focus on the moisture content, permeability, and chemical stability.
Meanwhile, it has become more important to evaluate the mechanical characteristics with due consideration given to external forces resulting from electrolyte pressure and temperature fluctuations.
This page introduces the endurance testing of the electrolyte membrane with respect to repeated tensile loads using a Shimadzu Microservo fatigue tester.
One method of evaluating the durability of electrolyte membranes attracting interest is determining the changes in mechanical characteristics under a repeated, external force. This method models the deflection of the electrolyte membrane in a vehicle-mounted fuel cell due to pressure fluctuations in the electrolyte and thermal expansion caused by temperature fluctuations.
The endurance testing was conducted by repeatedly applying stresses (85%, 90%, and 95% tensile strength obtained by static tensile testing) to unused samples as a 5 Hz sine wave. The fatigue life was evaluated as the number of cycles for the distance between the grips to increase 50% over its initial value.
Fig. 2 shows the S-N curve for fatigue testing of the electrolyte membrane. The vertical axis shows the maximum value of the repeated stress applied to the sample and the horizontal axis shows the number of cycles for the distance between the grips to increase 50% over its initial value (10 mm elongation).
These test results do not produce a precise estimate of the fatigue life of the electrolyte membrane to 50% deformation. However, an estimate on durability due to thermal expansion and external forces could be obtained by increasing the load levels and the number of samples tested at each load level.
The Shimadzu Microservo electromagnetic force micro material testers are tabletop instruments that apply repeated micro loads to polymers, electronic components, and other small samples. They can analyze the durability of electrolyte membranes with respect to external forces in a constant-temperature, constant-humidity environment. Closed-loop servo control of the electromagnetic loading mechanism provides accurate control of the micro forces. This offers a range of dynamic force patterns applied to the sample, down to the milligram/submicron order. Different microscopes can be attached for observations during testing.