Studying electron transfer through alkanethiol self-assembled monolayers on a hanging mercury drop electrode using potentiometric measurements

Abstract

A new approach based on measuring the change of the open-circuit potential (OCP) of a hanging mercury drop electrode (HMDE), modified with alkanethiols of different chain length conducted in a solution containing a mixture of Ru(NH3)6(2+) and Ru(NH3)6(3+) is used for studying electron transfer across the monolayer. Following the time dependence of the OCP allowed the extraction of the kinetic parameters, such as the charge transfer resistance (R(ct)) and the electron transfer rate constant (k(et)), for different alkanethiol monolayers. An electron tunneling coefficient, beta, of 0.9 A(-1) was calculated for the monolayers on Hg.

Potential-assisted assembly of 1-dodecanethiol on polycrystalline gold

“…The k app values found by us agree well with those reported for DT SAMs coated Au(111) and Au(210) in 1 mM RuðNH 3 Þ 3þ=2þ 6 and 0.1 M NaClO 4 [51]. One order of magnitude greater k app was reported for DT SAMs on a hanging Hg electrode in 0.1 M KNO 3 containing RuðNH 3 Þ 3þ=2þ 6 [52]. The higher value of k app on Hg is probably influenced by its surface properties.…”

Electron tunneling through monolayers of alkanethiols self-assembled on a hanging mercury drop electrode in the presence of aliphatic alcohols

“…1.0-1.3 lF/ cm 2 essentially independent of the electrode potential within the potential window of at least 0 to À0.8 V vs. SSCE as reported earlier by several groups [45,52,61,64]. The electron transfer between the hydrophilic redox probes, such as RuðNH 3 Þ 3þ 6 , and the Hg electrode occurs via electron tunneling with the apparent rate constant decaying exponentially with the monolayer thickness (see Eq.…”

“…Recently, Mandler used impedance spectroscopy and potentiometric measurements to characterize SAMs on mercury [64,65]. They found that while RuðNH 3 Þ 3þ 6 cannot freely penetrate into the monolayer, the more hydrophobic species, such as CoðbpyÞ 2þ 3 penetrate into the film causing the Fermi level of the Hg surface to attain the Nernst potential of the solution.…”

Potential dependence of the structure of water at the hydrophobic liquid interface

“…In this model, the alkanethiol monolayer stores charge supplied by the electrochemical potential which imposes a voltage drop across its thickness. The relatively slow electron transfer kinetics attendant electron transfer along the C-C bonded backbone of the alkane chain [10,[43][44][45][46] helps to maintain the potential drop. This effect has been described in detail for several related systems with results varying from nearly complete loss of applied potential to losses of only a few tens of millivolts [43,44,46,47].…”