Sodium ion diffusion

Upon discharge sodium ions diffuse through the sodium-conducting /J- or -alumina or NASICON -> solid electrolyte. On the outer surface of the solid electrolyte they react with molten sulfur and/or low valency sulfide anions forming negatively charged polysulfide anions. The rather low electric conductivity of molten sulfur is improved by addition of tetracyanoethylene... 

Thus, it is suspected that strong contact ion pairing in the case of the carboxylate is responsible for the low sodium ion diffusion coefficients and high diffusional activation energies. For the sulfonate, sodium ions that function as exchange-site counterions may be less strongly bound than for the carboxylate case, resulting in more facile sodium ion self-diffusion in the polymer. 

Membrane Diffusion in Nonaqueous Solvent Environments. Self-diffusion coefficients of Na+ and Cs+ for 1200 EW Nafion membranes in dilute methanol and acetonitrile solutions have been measured (5). Arrhenius plots of these results are shown in Figure 7 along with corresponding results for aqueous experiments activation energies of diffusion are listed in Table IV. Diffusion coefficients of Na+ in methanol and water-equilibrated membranes are very similar, and the activation energy of diffusion for the methanol system is only slightly higher than the respective value for Na+ in pure methanol solvent, 12.9 kJ mol 1 (27). Thus a solution-like diffusion mechanism is inferred for both solvent systems. Cesium ion diffusion in the methanol equilibrated membrane is much slower than sodium ion diffusion in fact the... 

Figure I. Sodium ion diffusion ratio in aqueous sodium heparin solutions containing sodium sulfate. The theoretical solid line is rectified to account for the diffusion of heparin to give the broken line (8).

FIGURE4.8.14. Variation of sodium ion diffusion coefficient with temperature for perfluorocaiboxylate (open symbols) and perfluorosulfonate (dark symbols) polymers in concentrated NaOH solutions [65], The concentration of NaOH in moles liter s noted in the figure. (Reproduced with permission fivm The Electrochemical Society, Inc.)... 

H.L. Yeager, Sodium Ion Diffusion and Migration in Perfluorinated lonomer Membranes, In E.B. Yeager, B. Schumm, Jr., K. Mauritz, K. Abbey, D. Blankenship, and J. Akridge (eds.) Membranes and Ionic and Electronic Conducting Polymers, PV 83-3, The Electrochemical Society, Pennington, NJ (1982), p. 134. 

The cell is based upon a liquid sodium anode and liquid sulphur cathode, separated by a beta alumina ceramic-type electrolyte which is an electronic insulator, but through which sodium ions diffuse rapidly at 300-400 C. During discharge the reaction 2Na + 5S —> Na S. leads to an open circuit voltage (GCV) of 2.08V. Continued reaction beyond Na S results in the formation of lower polysulphides in the range Na - Na S (OCV 1.78V), after which solid separates out. The polysulphides... 

Arrhenius plots of sodium ion diffusion in aromatic carboxylate polymer films, 0.1 M NaOH solution. Q 400EW, -... 

Another interesting result in Table 6.1-1 is that the sodium ion diffuses more slowly than the chloride ion. In other words, the sodium ion does not have the same diffusion... 

---