ITO-ITO Dual-Plate Microgap Electrodes: E and EC' Generator-Collector Processes

Tin-doped indium oxide electrodes are fabricated and employed in a dual-plate microtrench geometry with the inter-electrode gap controlling the mass transport conditions in generator-collector mode. Electrodes are fabricated with 2-50 mm gap sizes and variable trench depths by controlling assembly parameters. Non-ideal behaviour is observed for three aqueous redox systems: Ru(bpy)(3)(3+/2+), 1,1'-ferrocenedimethanol and Ru(NH3)(6)(3+/2+). Under fast mass transport conditions, the former two systems exhibit slower oxidation features. For Ru(NH3)(6)(3+/2+), non-steady-state behaviour is observed due to irreversible (ECirrev') consumption of oxygen in the microtrench. A mechanism leading to hydrogen peroxide formation via superoxide in Ru(NH3)(6)(2-) solution is proposed. Under optimised conditions all three redox systems provide reliable trench depth calibration information.