Choline chloride-formic acid mixture as a medium for the reduction of pertechnetates - electrochemical and spectroscopic studies.

ABSTRACT

The physicochemical properties of a choline chloride (ChCl) and formic acid (FA) mixture (1 2 molar ratio) have been studied over a broad range of temperatures (-140 to 60 °C). Differential scanning calorimetry has shown that the examined system remains in the liquid state at very low temperatures - a glass transition is observed in the range of -125 °C to -90 °C. The kinematic viscosity, ionic conductivity and the width of the electrochemical window determined for this system revealed its beneficial electrochemical properties. This indicates the suitability of ChCl FA electrolytes in electrochemical measurements. In this non-aqueous electrolyte, electrochemical reduction of Tc(VII) ions has been studied for the first time. Cyclic voltammetry and chronopotentiometry experiments revealed that the electroreduction of pertechnetates is a multi-path process which leads to the formation of a Tc(IV) ionic form. X-Ray absorption spectroscopy of the latter revealed its structure as a TcCl62- complex.