Microwave-Enhanced Electrochemistry in Locally Superheated Aqueous−Glycerol Electrolyte Media

Microwave activation, when applied to metal disk electrodes immersed in aqueous electrolyte media, causes highly localized heating of the liquid dielectric at the tip of the electrode. This is usually resulting in vapor bubble nucleation, cavitation, liquid jet formation, and boiling close to the electrode surface. However, when conducted in the presence of glycerol, boiling and vapor bubble formation appear to be suppressed and considerable superheating effects can be observed locally at the electrode surface. At a 50 μm diameter platinum disk electrode immersed in aqueous solution containing 0.1 M KCl supporting electrolyte, 5 mM Fe(CN) 6 3−, and 5 mM Fe(CN) 6 4− as a temperature-sensitive redox probe, and a 40 vol % glycerol content, apparent electrode temperature of up to ca. 480 K (estimated) can be reached under conditions of continuous microwave irradiation (in steady state mode). The effects of viscosity and temperature on the mass transport controlled limiting current are investigated. The use of glycerol−aqueous media (or other similar boiling suppressing mixtures) makes feasible the study of chemical and electrochemical processes under hydrothermal and superheating conditions.