THEORY OF ELECTROCHEMICAL LUMINESCENCE AT DOUBLE BAND ELECTRODES - AN EXAMINATION OF STEADY-STATE DIFFUSION AT ULTRAMICROELECTRODES

A theory based on the use of conformal mapping techniques is presented to describe and analyze the behavior of electrochemiluminescence (ECL) generation at double band microelectrodes. Simulations show that when these devices are operated in ECL mode, the current reaches steady state much faster than when they are operated in collector-generator mode, because of the important feedback of the electroactive species in the near vicinity of the electrodes. The limiting current thus achieved is exactly twice that determined in the collector-generator mode, a criterion that can be used to evaluate any possible interference of chemical side reactions depleting the ECL reagent(s). In contrast, the ECL flux reaches steady state at much larger times because it requires the establishment of diffusion layers whose thicknesses greatly exceed the dimensions of the gap and electrode widths. Experiments based on two established systems for ECL, Ru(bpy)3(PF6)2 in acetonitrile and 9,10-diphenylanthracene in acetonitrile-toluene (50:50, v:v) provide verification of the theory and numerical simulations.