Sodium transport through Nafion

R.L. Dotson, R.W. Lynch, and G.E. Hillard, Transport of Water Molecules and Sodium Ions Through Nafion Ion Exchange Membranes, In R.S. Yeo and R.P. Buck (eds), Ion-Exchange Transport and Interfacial Properties, PV 81-2, The Electrochemcial Society, Pennington, NJ, (1981), p. 268. 

The electroosmotic transport coefficient for water through Nafion 295 and 1150 membranes is typical and is shown to be highly dependent on the anolyte concentration to the exclusion of all the other variables studied. The water transport coefficient varies almost linearly with anolyte concentration from 6 to 17 molar caustic, giving 2.9 to 0.8 moles/F, as shown in Figure 3. The sodium ion transport number goes through a maximum of 0.82 eq/F in the 7 to 13 molar caustic range (27). 

The fundamental principle of SPE reactors is the coupling of the transport of electrical charges, i.e. an electrical current with a transport of ions (cations or anions), through a SPE membrane due to an externally applied (e.g. electrolysis) or internally generated (e.g. fuel cells) electrical potential gradient. For example, in a chlorine/alkaline SPE reactor (Fig. 13.3), the anode and cathode were separated by a cation-SPE membrane (e.g. Nafion 117) forming two compartments, containing the anolyte (e.g. 25 wt% NaCl solution) and the catholyte (e.g. dilute sodium hydroxide), respectively. 

The use of Nafion membrane as a proton conductor has been mentioned in a three-compartment electrodialysis set-up for converting sodium salicylate to salicylic acid . Use in Donnan analysis for the recovery of Cu ions from dilute solutions has been described . These metal ions are transferred through the membrane. The driving force is the proton-motive force resulting from the proton concentration difference between the two sides of the membrane. The diffusion flux of protons is coupled to a counter-transport of metal ions. 

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