Heterogeneous versus homogeneous electron transfer reactions at liquid–liquid interfaces: The wrong question?

Abstract

The exact mechanism of the electron transfer reactions at liquid-liquid interfaces still remains a source of interrogation. The purpose of this paper is to revisit this topic using a finite element simulation approach to analyze cyclic voltammograms for some previously published systems. Also, we compare the current obtained in the absence or presence of an adsorbed gold nanoparticle film. The current results indicate that the electron transfer between ferrocene in the organic phase and hexacyanoferrate(III) in the aqueous phase takes place by potential independent homogeneous reaction in the aqueous phase, while the observed potential dependence stems from that of the concomitant ion transfer reaction of ferrocenium. In the presence of the interfacial gold nanofilm the electron transfer takes place by a bipolar mechanism where the electrons are shuttled through the metallic nanofilm.

Gold Nanofilms at Liquid–Liquid Interfaces: An Emerging Platform for Redox Electrocatalysis, Nanoplasmonic Sensors, and Electrovariable Optics

“…Finite-element method simulations have also been used to study this process. 174,175 Moreover, the AuNPs provide a catalytic surface to further negate the kinetic barriers to IET at bare liquid−liquid interfaces. Additional thermodynamic driving force can then be provided by adjusting Δ o w ϕ to establish further control over both the rate of a reaction and the direction of electron transfer across the interface.…”

Electrovariable gold nanoparticle films at liquid–liquid interfaces: from redox electrocatalysis to Marangoni-shutters

“…The parameter a et is the charge transfer coefficient of the Butler-Volmer equation, 14,17 reecting the fraction of the potential difference that is effectively felt by the donor-acceptor couple.…”

“…For example, the Fermi level of nanoparticle assemblies can be tuned and manipulated with an external electric eld [13][14][15][16] to perform various electrochemical and electron transfer reactions. 17,18 On the other hand, the physical position of the nanoparticles at the ITIES can be controlled by the electric eld, anticipating the fabrication of "smart" plasmonic mirrors and lters in the near future. 7,8,10 Therefore, to set the canvas of the current article, we shall present here the recent progress in both of the above mentioned topics.…”

“…Thus, it opened up a new homogenous ET mechanism with associated ion transfer (IT) reactions (so called, ET-IT mechanism). However, in several recent papers 14,17 we extensively showed both experimentally and with computer modelling that ET reactions occurring at the ITIES took place in two steps, where the rst reaction was potential independent. The rst step can be (i) the partition of one reactant into the adjunct phase, (ii) a truly heterogeneous ET reaction at the interface with the charge transfer coefficient close to 0, or a combination of (i) and (ii).…”

“…Thus, the potential dependence of the ET reaction stems either from the concomitant ion transfer reaction, or a truly heterogeneous back electron transfer reaction at the interface with the charge transfer coefficient close to 1, or a mixture of both. 17 Furthermore, we developed an in-depth theoretical explanation of interfacial redox electrocatalysis to describe the ET reaction at a gold NP functionalized ITIES.…”