How does one identify the problem if the MEA in a single cell being tested does not reach a desired OCV?
The OCV of most low temperature fuel cells operating on H2 and Air should be in the range 0.95 to 1.0 V and slightly higher under H2/O2. Lower OCV value indicates high reactant cross-over and/or electronic short through the membrane, or poisoning of the catalyst or electrolyte. For PEM fuels cells, a low OCV may also indicate total dehydration of the membrane.
Linear sweep voltammetry of the cell under H2/N2 conditions can be used to diagnose the presence and magnitude of cross-over and electronic short through the membrane. Cyclic voltammetry of the cell under the same H2/N2 conditions can be used for in-situ analysis of the electrode catalysts, including the presence of poisoned catalysts or poor electrode properties. Both of these diagnostic methods and the analysis procedure are described in detail the Scribner’s book “Experimental Methods and Data Analysis for Proton Exchange Membrane Fuel Cells”.
If there is an unexpected low OCV which is not explained by the information above, a volt meter can be used to verify the test system reading.
To perform this check: Apply Fuel and Apply Temperature with the same settings as previous OCV measurement; disconnect the main load cables and sense leads from the fuel cell fixture; and measure the cell voltage with an accurate digital voltmeter. Ensure that the other cell hookups stay connected (fuel lines, vent lines, cell heaters, and thermocouple) during this test.
There should be little or no measurable difference between the voltage on the meter and the voltage reported by the software with ‘Apply Fuel’ selected but ‘Apply Load’ not selected. If the readings agree, the low OCV is real and is likely related to MEA construction. If the voltage measurements do not agree closely, please contact support for further troubleshooting assistance.