Time and Temperature Dependences of Electrochemical Property in Room Temperature Ionic Liquids-Water Solutions: N, N-diethyl-N-methyl-N-2-methoxyethyl Ammonium Tetrafluoroborate

Abstract

A room temperature ionic liquid (RTIL), N, N-diethyl-N-methyl-N-2- methoxyethyl ammonium tetrafluoroborate ([DEME][BF4]), shows complicated pH behaviors on a water concentration - Time diagram. The RTIL is a hydrophilic property. A strong acidic property was obtained at the water-rich region. On a contrary, at the water poor region, the pH value is around 8. The acid-base property in [DEME][BF4]-water has a relation with the specific aggregations in the liquid. On time-dependent pH measurements, a time-invariant point appears at 60 mol% H2O. Moreover, pH oscillations on t he t ime scale were observed only in t he 9 0 mol% H2O mixture. The oscillation suggests electrochemically unstable two states in the solution. An equilibrium pH value of 90 mol% H2O mixture is approximately 3. After a few days for pH measurements, by-product was formed inside the solution. As a precursor phenomenon of the by-product formation, the pH oscillations might be induced in electrochemically unstable circumstance.