Effect of the Metal on Electron Transfer across Self-Assembled Monolayers

Abstract

Electron-transfer kinetic measurements are made on one type of self-assembled monolayer {HS(CH2)15COOH with attached [RuII(NH3)5(4-aminomethylpyridine)]} on gold, platinum, and silver polycrystalline electrodes in one electrolyte at room temperature. Cyclic voltammograms over a wide range of scan rates are analyzed to extract the rate constants as a function of overpotential. Tafel plots are fitted to theoretical curves based on the Marcus DOS theory to obtain the standard rate constants and the reorganization energies. A reorganization energy of 0.8 ± 0.1 eV is obtained on all three metals. The standard rate constants for Au, Pt, and Ag are 1.0 ± 0.3, 1.7 ± 0.4, and 0.6 ± 0.2 s-1. The results confirm the theoretical prediction that the electronic coupling of “d” band states in the metal to remote redox centers is weak.