Adsorption dynamics and interfacial properties of thiol-based cobalt terpyridine monolayers

Research output: Contribution to journalArticlepeer-review

Authors

  • E Campagnoli
  • J Hjelm
  • CJ Milios
  • M Sjodin
  • RJ Forster

Colleges, School and Institutes

Abstract

Spontaneously adsorbed monolayers of [Co(ttp-CH2-SH)2](PF6)2 have been formed on platinum microelectrodes by exposure to micromolar solutions of the complex in 0.1 M TBABF4 in acetonitrile, ttp-CH2-SH is 4'-(p-(thiolmethyl)-phenyl)-2,2':6',2 ''-terpyridine. Resonance Raman spectroscopy on roughened polycrystalline platinum macro electrodes show that the molecule undergoes adsorption through the sulphur atom onto the platinum surface. The monolayers show reversible and well defined cyclic voltammetry when switched between Co2+ and Co3+ forms, with a peak to peak splitting of 0.040 ± 0.005 V up to 200 V s-1 and an FWHM of 0.138 ± 0.010 V. Adsorption is irreversible leading to the maximum surface coverage, 6.3 ± 0.3 x 10-11 Mol cm-2 for 2.5  ≤ [Co(ttp-CH2-SH)2] ≤ 10 μM. The rate of monolayer formation appears to be controlled not by mass transport or interfacial binding but by surface diffusion of the complex. The surface diffusion coefficient is 5.5 ± 1.1 × 10−7 cm2 s−1 indicating that prior to formation of an equilibrated monolayer, the adsorbates have significant mobility on the surface. The electron transfer process across the monolayer–electrode interface has been probed by high speed chronoamperometry and the standard heterogeneous electron transfer rate constant, k°, is approximately 3.06 ± 0.03 × 104 s−1. The reorganization energy is at least 18.5 kJ mol−1.

Details

Original languageEnglish
Pages (from-to)6692-6699
Number of pages8
JournalElectrochimica Acta
Volume52
Issue number24
Early online date3 May 2007
Publication statusPublished - 1 Aug 2007

Keywords

  • Spontaneously adsorbed monolayer, Electron transfer, Adsorption kinetics, Microelectrode, Chronoamperometry