Comparative Electrochemical Investigations in Ionic Liquids and Molecular Solvents of a Carbon Surface Modified by a Redox Monolayer

Abstract

International audienceElectrochemical properties of carbon surfaces modified by a covalently attached redox monolayer (alkyl-ferrocenyl) have been investigated in three different classical room temperature ionic liquids (RTILs): BMIPF6, BMINTf2, Me3BuNNTf2, and in two common molecular solvents (ethanol and CH2Cl2) for evidencing special aspects of the electronic transfer in RTILs. If the redox activity and the stability of the layer are globally preserved in the RTILs, a considerable decrease of the amount of active redox groups is observed when the layer is examined in the RTILs. The oxidation potentials are only slightly higher in the RTILs contrarily to the charge transfer kinetics that decrease by a factor of 10–20 as measured for the rates between the attached redox moieties and the substrate. These behaviors that appear as possible limitations for practical applications of such systems in RTILs could be ascribed to specific ionic associations and a large reorganization of the layer during its charging process

Aggregation Behavior of Several Ionic Liquids in Molecular Solvents of Low Polarity—Indication of a Bimodal Distribution

“…Increasingly, there are also applications using ILs not as the main medium but as additives in traditional nonaqueous solvents. For example, ILs are being evaluated as supporting electrolytes in solutions of nonaqueous organic solvents as possible replacement options for water in electrochemical applications such as redox flow batteries . ILs have been shown to homogenize and thus activate rhodium catalysts in the hydrogenation of liquid organic reactants in which they were dissolved at dilute concentrations .…”

“…For example, ILs are being evaluated as supporting electrolytes in solutions of nonaqueous organic solvents as possible replacement options for water in electrochemical applicationss uch as redox flow batteries. [13][14][15] ILs have been shown to homogenizea nd thus activate rhodium catalysts in the hydrogenationo fl iquid organic reactants in which they were dissolved at dilutec oncentrations. [16] Low-dielectric solvents such as chloroform (CHCl 3 )a re being used with ILs, for example, for morphologys tudies on the pores of hybrid organic-inorganic materials, [17] as co-solvents for chemical reactions, [18] and for liquid-liquidm icroextraction.…”

A post-functionalization toolbox for diazonium (electro)-grafted surfaces: review of the coupling methods

“…114,129,136,141,156 In these studies, ferrocene, which gives a reversible and stable redox signal, is commercially available, inexpensive and easily chemically functionalizable, was chosen as model molecule. These reasons also motivated the use of this redox probe to validate and better understand different concepts including functionalization of non-conventional electrodes, 132,135,140,157,158 electron transfer, 125,127,128,159 formation of more or less compact monolayers, 105,115,123,124,130,137,139 fabrication of mixed (mono)layers, 105,116,120,122,138 surface structuring, 117,126,131,133 building of dendrimer modified surfaces. 119 Immobilization of this molecule on a reactive platform is also a good way to compare the effectiveness of different functionalization methods.…”

“…Whether they are carried out in one direction or another (azide surface and alkyne in solution, or the opposite), the couplings are made under similar operating conditions. Cupper(I) is always used as a reaction catalyst (directly added, 134,148,162,173,175 or formed in situ from cupper(II) and a reducing agent 85,105,[113][114][115]119,[121][122][123][124]127,128,132,135,139,140,142,147,149,157,158,160,[163][164][165][166]168,177,178 or electrochemically generated 137,176 ). The most common option relies on the combined use of copper(II) sulfate and ascorbic acid (or sodium ascorbate, usually in excess) as reducing agent.…”

Self-assembly of catecholic ferrocene and electrochemical behavior of its monolayer

“…Ferrocene-terminated self-assembled monolayers (Fc-SAMs) are one of the most studied molecular aggregates on metal substrates 8 and have attracted considerable interest over the past decade due to the attractive electrochemical characteristics of ferrocene (fast electron-transfer rate, low oxidation potential, and stability). [13][14][15] Generally, SAM molecules consist of a head group, tail group and functional end group. 11,12 Fc-SAMs have been used extensively as convenient, robust, and well-reproducible surfaces to study the kinetics and thermodynamics of electron transfer processes, the properties of the electrical double layer, and the mechanisms of electron transfer.…”