Possible sources of unintended electrode, catalyst and/or membrane poisoning or contamination that may accelerate fuel cell performance degradation include:
- Humidifier source water – Recommend ASTM Type I (resistivity = 18 MW-cm)
- Tubing – Recommend tubing materials include new and clean stainless steel 316L, polypropylene (PP), high density polyethylene (HDPE), or flouropolymers such as polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) or fluorinated ethylene propylene (FEP). Do not use Nylon or polyvinylchloride (PVC). Do not use tubing that is old, soiled, moldy or that has been exposed to chemicals.
- Reactant and purges gases – Use ultra-high purity (UHP, 99.999%) hydrogen, nitrogen and oxygen. Medical grade air is acceptable.
- NOTE: Do not use grease or oils on compressed gas regulators or fittings!
- Fuel cell components including membrane and membrane electrode assembly (MEA) – Check the source. If bought from an MEA vendor, ask about potential sources of contamination. If made in-house, is there a possibility of contamination for source materials, or process chemicals and fabrication steps?
- Contaminated fuel cell hardware – Make sure all gaskets and hardware are cleaned in solvent (methanol or ethanol) and rinsed in high purity water. Wear powder free latex or nitrile gloves when handling cell hardware components during assembly and disassembly.
Diagnostics:
A cyclic voltammetry (CV) sweep commonly used for electrochemical surface area (ESA) analysis can be used as a diagnostic for impurities and / or electrode degradation. (Experimental conditions are described in the literature.) Does the electrochemical surface area decease after testing? Look for additional peaks not associated with the hydrogen adsorption/desorption process that may decrease in size with repeated CV cycles but that return after running the fuel cell. After running the CV scan, you may see a recovery in the performance of the fuel cell, which is another indication that the source of the degradation is an impurity removed during the CV experiment. Note that the impurity could occur on the anode, cathode or both electrodes, and/or the membrane. We have seen such behavior before and it was eventually attributed to substandard water used in the humidifiers.
Increase in the ohmic resistance of the fuel cell, as measured by current interrupt or high frequency resistance, during operation under constant operating conditions (flow rate, temperature, humidity and pressure) is an indication that the degradation in cell resistance may be a result of a decrease in the ionic conductivity of the membrane. Ionic conductivity can be compromised by contamination with ions, in particular cat-ions that replace the protons in the membrane.