Scanning Electrochemical Microscopy. 49. Gas-Phase Scanning Electrochemical Microscopy Measurements with a Clark Oxygen Ultramicroelectrode

Abstract

The use of an ultramicroelectrode tip as a basis for a Clark membrane electrode allows the sensing of oxygen concentration using the oxygen reduction signal and the application of scanning electrochemical microscopy (SECM) to pure gas-phase measurements. A 25-μm-diameter Pt wire was sealed in glass and the glass coated with silver paint near the tip to produce a Ag ring, Pt disk electrode. A drop of electrolyte provided the contact between the Pt cathode indicator electrode and the Ag anode counter/reference electrode, while the liquid phase was maintained by a high-density polyethylene membrane pulled over the tip and fastened with an O-ring. The membrane isolated the electrode both electrically and chemically from the sample environment. The electrode was tested with both solution- and gas-phase samples, and SECM approach curves were recorded. The presence of a membrane caused a deviation in electrode behavior from theory in both solution and gas phases, due in part to an increase in the electrode respo...