Membrane ionic atmosphere

Eontanella and co-workers studied the effect of high pressure variation on the conductivity as well as the H, H, and O NMR spectra of acid form Nafionl 17 membranes that were exposed to various humidities. Variation of pressure allows for a determination of activation volume, A V, presumably associated with ionic and molecular motions. Conductivities (a) were obtained from complex electrical impedance diagrams and sample geometry, and A V was determined from the slope of linear isothermal In a versus p graphs based on the equation A E = —kJ d In a/d/j] t, where p is the applied pressure. At room temperature, A Ewas found to be 2.9 cm mol for a sample conditioned in atmosphere and was 6.9 cm mol for a sample that was conditioned in 25% relative humidity, where the latter contained the lesser amount of water. 

A fluorometric method was developed for determination of atmospheric H2O2 simultaneously with other species present at ppbv or lower levels, avoiding chromatographic separation. H2O2 is selectively collected by diffusion through a Nafion membrane, and is carried by a water stream into a reactor where it oxidizes thiamine hydrochloride (117) to a fluorescent ionic form of thiochrome (118), catalyzed by bovine hematin (75b) in alkaline solution, as shown in equation 40. The end solution containing 118 is passed through... 

The ionically bonded sodium bromide receives two electrons, and loses two +ve sodium cations to form sodium tri-bromide (see Porterfield, 1993). An alternative homogeneous reaction route to tri-bromide is to bubble bromine (Br2) through aqueous sodium bromide. Accordingly, the electrochemically formed tri-bromide has an associated atmosphere of bromine from homogeneous dissociation. Such bromine is corrosive, but is contained by the fluorinated plastic tanks and by one side of the (Na ) Nafion perm-selective membrane. Nafion is itself a compound with many fluorine atoms. Bromine is very much lower than fluorine in chemical reactivity, so that the bromine containment strategy is complete, and the selection of the bromide electrolyte seen to be a well-considered choice. 

The baseline Nafion membrane is deficient in terms of ionic conductivity above 100°C and at low relative humidity required for atmospheric-pressure building applications. Such conditions tend to dry out the membrane, drastically reducing membrane proton conductivity. Furthermore, the loss of water causes membrane embrittlement, resulting in membrane cracking, reactant cross-leakage and poor electrode-membrane contact. Therefore, a cost-effective membrane, with proton conductivity that is less sensitive to change in water content, is needed. 

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