A.Test InfrastructureFuel cell testing requires control of two different but equally important set of parameters—the reactant flow and the electronic load. Both groups are addressed briefly below. In all cases, ensure that whatever test infrastructure is put in place is in compliance with all local safety codes and facility regulations.
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Reactant Flow Control InfrastructureFuel Supply OptionsTwo methods that can be used to control the fuel supply to the stack. They are known as “dead-ended” and “continuous flow.” Dead-ended flow is based upon pressure regulation. Continuous flow is based upon flow rate control. Regardless of the option selected, the fuel source can be a pressurized hydrogen cylinder, a charged metal hydride cylinder, or a hydrogen generator. “High purity” grade (99.995% or greater) or better will ensure the catalysts in the MEAs are not contaminated by impurities in the fuel stream. If a cylinder of compressed hydrogen gas is not used as the fuel source, it is important that a filter be inserted into the fuel supply line immediately downstream of the hydrogen source to prevent contaminants from poisoning the MEAs. This is especially true if alternative hydrogen storage/supply options, such as a hydride cylinder or sodium borohydride, are employed. For both dead-ended and continuous-flow fuel supply options, the maximum fuel supply pressure is 3 psi. Two-stage regulators can be used to reduce the fuel pressure to an appropriate level. The hydrogen source must be connected to the stack and other infrastructure through appropriate tubing and tube fittings. The stack comes with push-to-connect fittings for ¼” OD flexible tubing. The tubing used should be semi-rigid and be selected based upon permeability of hydrogen gas. Recommended tubing materials include PTFE, polyurethane, polypropylene or PVC. |
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Dead-ended Fuel SupplyIf dead-ended fuel flow is selected, precise pressure regulators and gauges will be required to achieve the necessary control over the fuel delivery pressure. The recommended operating pressure range is between 0.5 and 2 psig. If hydrogen is supplied via a cylinder of compressed gas, it is likely that two or more regulators will be needed to reduce the pressure seen by the stack to the appropriate range. The hydrogen outlet of the stack should be blocked with one of the included acetal plugs. 
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For dead-ended operation, no flow controller/meter is required, though one may be used to measure the hydrogen flow into the stack. With no current load on the stack, the fuel flow rate should be zero. A non-zero flow rate at open circuit If the stack to be tested requires a forced air supply, the requirements are similar for pressure and flow control of hydrogen, in that pressure regulator(s) and a flow controller or a flow meter and an adjustable valve are required. The primary difference is in the flow rate of air selected. Again, the user should determine the appropriate air flow rate for the test that he or she wishes to run. In this case, the general rule is that the oxygen required (assuming that all oxygen reacts with hydrogen to form water) is 3.75 ccm/A /cell at room temperature and standard pressure. However, oxygen comprises only about 20% of the air, so the air flow required, again assuming complete oxygen conversion, is 18.75 ccm/A /cell. It is also necessary that the air stream be cleaned by a 10 micron filter (or better). The air should then be passed through a desiccator to dry the air prior to passing through the flow controller. Downstream from the flow control device, the air must be humidified to the maximum extent possible, as discussed above in relation to fuel humidification in continuous flow configuration. |
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Warning: Normal precautions associated with hydrogen must be taken. DO NOT use hydrogen in a sealed or unvented room. DO NOT use in close proximity to open flame or other ignition sources. Observe all local safety codes and regulations. 
Caution: Prevent electric shock through the use of proper plugs and wires and good earth ground connections. Ensure that no bare wire is exposed. Follow all safety instructions provided by the electronic load manufacturer. 