Liquid Electrolyte Phase Research Articles

Preparation, spectroscopic characterization and electrochemical charging of the sodium-containing analogue of Prussian Blue

An electrochemical method for the preparation of thin films of the Na +-containing Prussian Blue, NaFe III [ Fe II ( CN) 6] · nH 2 O, is proposed. The system has been studied electrochemically in sodium and potassium electrolytes, as well as in solid-state, ie in the absence of contact with any liquid electrolyte phase. Hydrated-Na + counterions are sufficiently mobile in NaFe[Fe(CN) 6] to support the system's redox reactions. During voltammetric experiments in aqueous potassium solutions, structural Na + cations in the film are irreversibly replaced by smaller hydrated-K +, and the material undergoes reorganization to the commonly studied potassium-containing analogue, KFe III [Fe II(CN) 6]. The films have been analyzed using scanning electron microscopy equipped with X-ray fluorescence elemental analysis probe. Structural differences between NaFe[Fe(CN)] 6 and KFe[Fe(CN) 6] are apparent from X-ray absorption fine structure spectroscopy and ir measurements. A comparison is also made to so-called “insoluble” Prussian Blue, Fe III 4[Fe II(CN) 6] 3.

Investigations of the O 2 Reduction Reaction at the Platinum/Nafion® Interface Using a Solid‐State Electrochemical Cell

Research in solid polymer electrolyte fuel cells is gaining momentum because of the prospects of attaining high energy efficiencies and power densities essential for transportation and space applications. The most advanced solid polymer electrolytes for these fuel cells are the perfluorosulfonate ionomers (PFSIs), such as Du Pont's Nafion and the Dow PFSIs. The high oxygen solubility, chemical stability, proton conductivity and permselectivity exhibited by Nafion and the Dow PFSIs make them ideal candidates as electrolytes for fuel cells. Furthermore, the minimal anion adsorption on electrodes from fluorinated acids enhances oxygen reduction kinetics. The objectives of this work were to determine the concentration and diffusion coefficient of oxygen in Nafion, and the electrode kinetic parameters for the reduction of oxygen at the Pt/Nafion interface under totally solid‐state conditions (i.e., no contacting liquid electrolyte phase). Cyclic voltammetric and potentiostatic transient measurements were made at the Pt/Nafion interface. From cyclic voltammetric measurements, the purity of Nafion was ascertained and the roughness factor of the electrode was calculated. The slow sweep experiments yielded the Tafel parameters for oxygen reduction. From the two‐section Tafel plot, the calculated exchange current densities were found to be higher than those obtained at any other Pt/acid interface. From an analysis of the potentiostatic transients, the calculated values of oxygen solubility and diffusion coefficient in Nafion were higher than previously reported. These differences in mass‐transfer data were attributed to differences in water content of the Nafion membrane.

Prediction of vapor-liquid equilibria of binary-solvent electrolytes

An iterative method is presented that is used to predict vapor-liquid equilibria (VLE) of single-salt multisolvent electrolytes of the form solvent-cosolvent-salt. A local composition model (LCM) and an electrolyte model based on the exponential modification of the Mean Spherical Approximation (EXP-MSA) are combined with traditional phase equilibria relations to estimate the pressures and compositions of a vapor phase in equilibrium with a binary-solvent electrolyte. In addition, a pseudo-solvent model is used to obtain a variety of averaged liquid phase electrolyte properties. For our initial model system, methanol-water-LiCl, the above method accurately predicts the salt effects upon vapor composition for dilute to moderate salt concentrations up to 20 mol% LiCl, and yields good approximations of vapor pressure depression for LiCl up to 14 mol%. Three electrolyte systems are investigated: water-ethylene glycol-LiBr, ammonia-water-LiBr, and methanol-water-LiCl.