| Summary: | The principles of potentiometry from liquid phase electrochemistry have already been applied to the gas phase by considering a flame as an ionised gaseous environment which can behave as a dilute electrolyte. This study focused on the design, construction and optimisation of a 3-electrode electrochemical cell for direct electron transfer in the gas phase. Three electrochemical cells were developed with the final design deemed satisfactory to conduct electrochemical measurements. Particular attention was given to the development of the reference electrode, which allows for stable voltage measurements. The reference electrodes analysed for their voltage stability and polarisability were metal wires, a dynamic type electrode and metal / metal oxide powders packed into ceramic supports. Through extensive studies, titanium wire (which forms a solid oxide layer once placed in the flame) was deemed to behave as a stable reference electrode. In conjunction with the electrode assembly and the titanium metal wire reference electrode, two metal salt clusters were individually introduced into the flame. The metal salt clusters were characterised by their reproducible electrochemical responses through cyclic voltammetry. Three negative peaks were observed when ammonium molybdate tetrahydrate was introduced into the flame. In contrast, four negative peaks were observed (at different voltage positions) when the metal salt cluster was replaced with ammonium metatungstate hydrate. The results suggest that electroreduction is indeed possible in the gas phase with reproducible Faradaic current responses being observed. The results are well supported by unambiguous correlation of the reduction potentials for peaks observed for the metal salt clusters to the vertical electron detachment energies obtained from photoelectron emission spectroscopy. The developed electrochemical cell and technique can be used to further characterise other chemical compounds.
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