Why is an activation procedure or break-in necessary for a membrane electrode assembly (MEA)? A large reason for performing an activation procedure or break-in is to properly humidify the membrane portion of the MEA that was dried out during the hot press stage of the membrane electrode assembly (MEA) production. MEAs will not work well when they are not fully humidified (see article: Why is Humidity / Moisture Control Important in a Fuel Cell?).
How do I Humidify a Membrane Electrode Assembly (MEA)?
You can re-humidify the MEA by soaking it in deionized water. Be aware that the membrane expands as it is hydrated, so it is possible that you will see some de-lamination of the gas diffusion electrode (GDE) from the membrane if you are using a 5-layer MEA that has the GDE bonded to it. This shouldn't significantly affect performance and you can still install the MEA into your stack or test cell even if portions of it are slightly de-laminated.
The other method to humidify the MEA is to install it in the stack or test cell and then run a break-in process in which it is operated in an air-starved mode periodically. Operate normally (with a suitable load applied) and then turn off the flow on the Air/Oxygen side until the power drops significantly and begins to settle out (around 5 minutes). Then reintroduce the air/oxygen flow until the power increases and stabilizes again. Repeat this as necessary until there are no further performance gains.
What this does is allow for the MEA to produce water (and power) as it consumes the residual oxygen in the system when the flow is removed, but not allow that humidity to escape with the gas flow (as it does during normal operation, to some extent). The hydrophobic surface of the gas diffusion layer/gas diffusion electrode (GDL / GDE) helps to keep the moisture in the membrane without wicking it away - until it's fully saturated, at which point the hydrophobic surface actually helps to push the excess water out of the GDL and into the gas stream without giving it a good place to condense and "flood" the cell.
Membrane Electrode Assembly Activation Procedure
The start-up procedure for a new fuel cell membrane electrode assembly MEA may vary somewhat from application to application. What is important in any research or production environment is to be consistent with the break-in procedure that you use. How the MEA is initially broken in can have long-lasting effects on the ultimate performance of the MEA. Published procedures vary in specifics, but almost all follow a similar sequence:
- Initial Start-Up
- Load Cycling
- Final Performance
The US Fuel Cell Council (USFCC) published a standard for single cell testing that includes specific break-in procedures(beginning on page 15):
- Fuel: Hydrogen, 1.2 Stoich, 100% RH
- Oxidant: Air, 2.0 Stoich, 100% RH
- Temperature (C): 80
- Pressures (psig): 25
Initial Startup: As required to reach 80C
- Cycle Step 1 (Perform Once): Hold 0.6V for 60 mins
- Cycling Step 2 (Perform 9 times): Hold 0.7V for 20 mins, than hold 0.5V for 20 mins
- Constant Current Operation:Hold at 200 mA/cm2 for 720 mins (12 hrs)
Verify break-in status by repeating the polarization curve sequence three times, or as necessary, to ensure that the cell is broken-in. Remain at each sequence step for 20 minutes. The cell is considered broken in when less than a 5 mV deviation from the previous polarization curve is recorded at 800 mA/cm². A waiting period of 10 minutes should be observed between polarization curves. During this period, return the gas flow rates to the equivalent of 10 stoic at 200 mA/cm² and set the current to 800 mA/cm².
For additional questions or inquiries regarding the activation/break-in procedures of membrane electrode assemblies (MEA) contact us, your membrane electrode assembly experts.
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