NAFION Hydrogen-Form Membrane Expansion

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NAFION Hydrogen-Form Membrane Expansion ( nafion-hydrogen-form-membrane-expansion )

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NAFIONTM Hydrogen-Form Membrane Expansion Technical Information Bulletin 93-01 Many NAFIONTM perfluorinated membranes* are produced in the hydrogen ionic form (H+) to meet specific customer needs. Prior to using these membranes, it is necessary to expand them before installation so that during operation, the membranes will shrink slightly and remain wrinkle-free. Because there are many different applications and electrolyzers that these membranes are used in, we recommend that membrane expansion be discussed with your equipment supplier or your representative. Special Expansion Considerations • Membranes expand more in deionized (DI) water when they are in the hydrogen ionic form (H+) than they do when they are in the sodium ionic form (Na+) or potassium ionic form (K+). Consequently, many applications processing dilute electrolytes require that membranes be pre-expanded in DI water. • Membranes expand more when the expansion bath is heated. Consequently, some applications may require elevated bath temperatures to prevent wrinkling during USC. • The hydrogen-form membranes are relatively free of other cations. In special cases where purity is essential, such as fuel cell applications, the membrane is typically expanded in high purity HNO3 or HCI followed by a DI water rinse. • Hydrogen-form membranes expanded in DI water will be slightly acidic (pH 2 to 7). This may cause corrosion of certain types of electrodes before start-up. Corrosion of some electrodes (activated nickel, for example) could result in nickel absorption in the membranes and subsequent high voltage during normal operation. If this is the case, alkaline expansion is recommended as detailed next. If in doubt about possible corrosion of your electrodes, contact your hardware supplier for specific recommendations. • If alkalinity is required to protect the electrodes, or if there is uncertainty about your electrodes, we recommend that the membrane be converted to the sodium form, except that only NaOH should be used for the conversion. If NaHC03 were used, CO2 gas would be generated and the bubbles would coat the membrane and inhibit wetting. • Some electrode types are not affected by slight acidity, and water expansion is a convenient way to expand membranes. When expanding the hydrogen-form membranes in DI water, follow the guidelines presented below. *NAFIONTM 117 perfluorinated membrane (abbreviated N-117), NE-112, NE-115, N-417, N-450, N-120, N-324, and N-350 are some of the hydrogen-form membranes available. (979) 703-1925

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