Investigation of comproprotionation and association reactions on EE type mechanisms using scanning electrochemical microscopy and microelectrodes

Scanning Electrochemical Microscopy (SECM) is a powerful technique in probing fast homogenous and heterogeneous kinetics due to mass transport enhancement at small tip-substrate separations. The association and comproportionation homogeneous reactions coupled with two electron transfer electrochemical reactions are investigated using SECM. A SECM setup consisted of Ultra-Micro Electrode (UME) tip of radius a and RG = 3 (RG refers to the ratio of the radius of the tip including the metallic disk and the glass insulating sheath (rg), to the radius of the metallic disk (a); i.e., RG = rg/a.) is positioned above either a very large conductive substrate relative to the size of the tip, or above a conductive substrate of UME with a same metal diameter with RG >10.;A comprehensive electrochemical study of tetracyanoquinodimethane (TCNQ) and anthrarufin and their radical anions including comproportionation and association reactions was performed. A reliable set of diffusion coefficients, electron transfer rate, and formal standard potentials were found using independent SECM experiments. SECM with two finite size conducting electrodes were used appropriately in the determination of electrochemical parameters associate with second reduction reaction of TCNQ. SECM pulse technique was successfully applied to obtain a reliable value for the comproportionation rate constant of TCNQ. The association reaction rate for anthrarufin was determined using positive feedback approach curves recorded with a SECM setup consisted of two finite size conducting electrodes. SECM pulse technique was successfully extended to investigate the rate of comproportionation reaction for anthrarufin in the presence of association reaction. The theoretical treatment of experimental data was based on Comsol Multiphysics simulations.