Electrochemical studies in room temperature ionic liquids

The work presented in this thesis involves the application of room temperature ionic liquids (RTILs) as solvents for use in electrochemical experiments. Initially, the fundamentals of electrochemistry is presented, followed by a comprehensive overview of RTILs in terms of their properties, applications and their behaviour as electrochemical solvents compared to conventional aprotic solvents. The results of 8 original studies are then presented as follows: X-Ray photoelectron spectroscopy is used to quantify the concentration of bromide ions in an ionic liquid, and is independently confirmed by potential-step chronoamperometry The reaction mechanisms and kinetics for the electrochemical reduction of some aromatic nitro compounds (namely nitrobenzene and 4-nitrophenol) are determined The electrochemistry of phosphorus trichloride and phosphorus oxychloride is studied in detail for the first time, due to the unusual stability of these highly reactive compounds in RTILs The reductions and oxidations of sodium and potassium nitrate are studied, giving rise to 'melt'-like behaviour. The electrodeposition of sodium oxide on platinum is also demonstrated The electrochemical oxidation of nitrite and the oxidation and reduction of the toxic gas, nitrogen dioxide, is presented The oxidation of hydrogen gas is studied in ten RTILs with a range of different cations and anions, and contrasting interactions with the RTIL anions are seen The electrochemical oxidation of ammonia gas is studied in five RTILs with different anions and a general reaction mechanism is suggested The reduction of benzoic acid is studied in six RTILs, and the kinetics of the dissociation step are found to be very fast The first five studies are all carried out in one particular ionic liquid, and the reactions and mechanisms are compared to that observed in conventional aprotic solvents. The last three studies employ several RTILs with different cations and anions to look at the contrasting interaction of protons with the RTIL cation/anion and ultimately help to understand the pH properties of the solvent. The overall findings from the work in this thesis are that some reactions and mechanisms (e.g bromide, nitro derivatives and ammonia) are generally the same in RTILs as in conventional aprotic solvents, but other species (e.g. nitrates, phosphorus derivatives) show remarkably different behaviour. It has also been demonstrated that RTILs are suitable media for the detection of nitrogen dioxide, hydrogen and ammonia gases. This suggests that RTILs could potentially offer many advantages when employed as solvents in electrochemical reactions and in amperometric gas sensors.