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 µm gap sizes and variable trench depths by controlling assembly parameters. Non‐ideal behaviour is observed for three aqueous redox systems: Ru(bpy) 3+/2+ 3 , 1,1′‐ferrocenedimethanol and Ru(NH 3 ) 3+/2+ 6 . Under fast mass transport conditions, the former two systems exhibit slower oxidation features. For Ru(NH 3 ) 3+/2+ 6 , non‐steady‐state behaviour is observed due to irreversible (EC irrev ′) consumption of oxygen in the microtrench. A mechanism leading to hydrogen peroxide formation via superoxide in Ru(NH 3 ) 2+ 6 solution is proposed. Under optimised conditions all three redox systems provide reliable trench depth calibration information.