Transference Numbers of Alkali Chlorides and Characterization of Salt Bridges for Use in Methanol + Water Mixed Solvents

Abstract

Electromotive force measurements at 25 °C of the transference cells Ag|AgCl|MeCl (m 2)|MeCl (m 1)|AgCl|Ag and Me x Hg1 - x |MeCl (m 1)|MeCl (m 2)|Me x Hg1 - x (where Me = Li, Na, K, and Rb and Me x Hg1 - x denotes a flowing Me-amalgam electrode at Me mole fraction x) have been made at various molalities m 2 > m 1 (with m 1 fixed and m 2 varied) in methanol + water solvent mixtures with methanol mass fractions w M up to 0.8. Supplementary emf measurements have been made of the cell Pt|Li x Hg1 - x |LiCl (m 1)|AgCl|Ag|Pt to obtain the required activity coefficients for LiCl at methanol mass fractions w M = 0.2. The general trend of the ionic transference numbers of each MeCl is a t°Me + increase with w M, which is much more pronounced for those Me+'s whose primary hydration sheaths are bigger (namely, Li+ and Na+). In particular, KCl becomes exactly equitransferent (t°K + = t°Cl − = 0.5, i.e. an ideal salt bridge) at w M ≈ 0.1, but at w M > 0.6 the KCl solubility becomes insufficient for a salt bridge function. The same drawback occurs also for RbCl, which is known to be the most closely equitransferent salt in water (t°Rb + = 0.5007). NaCl, which is quite unproposable as a salt bridge in water, may be useful at high methanol concentrations, as its ionic transference numbers would approach 0.5 at w M ≥ 0.8.

Thermodynamics of the cell { Li- Amalgam | LiX (m)| AgX | Ag }(X=Cl,Br) and medium effects upon LiX in (acetonitrile + water), (1,4-dioxane + water), and (methanol + water) solvent mixtures with related solvation parameters

“…Values of the function defined by equation (7) recent literature data. (25,26) Also with NaCl and KCl, in the y S range explored, the PME is seen always to increase with y S and to be always maximum with 1,4-dioxane. It is a remarkable feature that the PME in the case of KCl varies linearly with all the co-solvents studied (but in the cases of acetonitrile and methanol the slopes are different from those observed with NaCl and LiCl), whereas for NaCl this linearity is obeyed only with acetonitrile.…”

“…This aspect is even more underlined considering the relation between the Stokes' law radii (r STOKES = 0.0082/ o t o η) and crystallographic radii for the ions Li, Na + , K + , and Cl − , that can be inferred from combining the available literature data on limiting electrolyte conductances o , limiting ionic transference numbers t o and solvent viscosities η. (14,16,25,(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42) In this context, figure 7 shows the differences (r STOKES − r CRYST ) for the above ions in (1,4-dioxane + water) and (methanol + water) solvent mixtures. It is evident that only for Li + and Na + are Stokes' radii greater than the corresponding crystallographic radii (obviously pointing to a viscous ionic motion mechanism) whereas for the others the contrary is true (that is, non-viscous motion, except Data for Na + and K + taken from the literature.…”

“…It is evident that only for Li + and Na + are Stokes' radii greater than the corresponding crystallographic radii (obviously pointing to a viscous ionic motion mechanism) whereas for the others the contrary is true (that is, non-viscous motion, except Data for Na + and K + taken from the literature. (25,26) .…”

Graphene Oxide Sieving Membrane for Improved Cycle Life in High‐Efficiency Redox‐Mediated Li–O2 batteries

“…In both electrolyte, the concentration ratio of LiTFSI to DMPZ was fixed at 5:1. m 1 was maintained at 1.0 m LiTFSI (and 0.2 m DMPZ) in TEGDME and m 2 was changed from 0.5 m LiTFSI (and 0.1 m DMPZ) down to 0.01 m LiTFSI (and 0.002 m DMPZ) in TEGDME. PTFE film and GO membrane were used as separators for liquid junction cells and gel polymer electrolyte (GPE) with cation transference number of 0.54 was used as a salt bridge for the cell without liquid junction . The transference number of GPE was measured through a potentiostatic polarization method .…”

“…Second, the obtained solution was casted onto a clean glass plate and exposed to UV‐irradiation for 30 s. The resulting membrane was used as GPE. The anion transference number can be obtained by plotting the electromotive force (emf) of cell with liquid junction (transmembrane potential, E trans ) versus the emf without liquid junction ( E ) . The slope of the E trans versus E plot was the anion transference number ( t ‐ ).…”