Ph modulated heterogeneous electron transfer across metal/monolayer interfaces

TLDR: In this article, the authors used Chronoamperometry to measure the heterogeneous electron transfer rate constant k for the Os2+/3+ redox reaction, which is consistent with electron transfer occurring via a through-space tunneling mechanism.

Abstract: Dense monolayers of [Os(bpy)2(p3p)2]2+, where bpy is 2,2‘-bipyridyl and p3p is 4,4‘-trimethylenedipyridine, have been formed by spontaneous adsorption onto clean platinum microelectrodes. Cyclic voltammetry of these monolayers is nearly ideal, and the area occupied per molecule suggests that only one of the p3p ligands binds to the electrode surface, the other being available for protonation. Chronoamperometry conducted on a microsecond time scale has been used to measure the heterogeneous electron transfer rate constant k for the Os2+/3+ redox reaction. For electrolyte concentrations above 0.1 M, heterogeneous electron transfer is characterized by a single unimolecular rate constant (k/s-1). Tafel plots of the dependence of ln k on the overpotential η show curvature, and larger cathodic than anodic rate constants are observed for a given absolute value of η. This response is consistent with electron transfer occurring via a through-space tunneling mechanism. Plots of k vs pH are sigmoidal, and the standa...