Marc De Backer

In situ time-resolved FTIR spectroelectrochemistry: study of the reduction of TCNQ

The efficiency and versatility of time-resolved FTIR spectroscopy has been used to follow concentration profiles of species produced during a cyclic voltammetric scan. It has been tested in situ and in resolved time, by probing the reduction of tetracyanoquinodimethane (TCNQ) on its first and second electrochemical wave. Besides the establishment of the method, the individual concentrations of TCNQ, of the monoanion and of the dianion were monitored at distinct infrared frequencies and the time derivatives of the concentration profiles were compared to the voltammograms.

An infrared study of the complexing ability of manganese phthalocyanine

Abstract The complexing ability of manganese phthalocyanine (MnPhc) in the solid state has been studied in detail using i.r. spectroscopy. It has been shown that in its α modification, MnPhc readily adsorbs phenol, pyridine and formic acid. Nothing happens with the β modification. The results have been compared to previous studies and they are explained in terms of valence bond model and molecular orbital model.

Synthesis, Spectroscopic, and Electrochemical Characterization of a Schiff Base: 4,4′-bis[(4- diethylaminosalicylaldehyde)diphenyl methane]diimine and Its Complexes With Copper(II), Cobalt(II), and Cadmium(II)

The synthesis of a new ligand tetradentate Schiff base: 4,4′-bis[(4-diethyl aminosalicylaldehyde) diphenyl methane] diimine (H2L), obtained by condensation of 4,4′-diaminodiphenyl methane with 4-diethylaminosalicylaldehyde, and its complexes with copper(II), cobalt(II) and cadmium(II), is described. The metal complexes were characterized by elemental analysis, by UV-visible, infrared, and EPR spectroscopy, by cyclic voltammetry, and by thermal analysis (DTA-TG). The coordination of the metal ions to the ligand occurs through the N2O2 system. Thermal studies indicate that the ligand is more stable than the metal complexes (up to 310°C).

A spectroscopic study of the complexing ability of metal phthalocyanines with formic acid

Abstract The behavior of magnesium, iron and zinc phthalocyanines with formic acid has been studied in detail by i.r. spectroscopy. The results show that magnesium and zinc phthalocyanines adsorb formic acid vapors under a dissociated form, while only physisorption occurs with iron phthalocyanine. This latter phthalocyanine does not show any sign of interaction with formic acid in dilute CCl 4 solutions. The results are compared to previous studies and are discussed in terms of a valence bond model and a molecular orbital model.

A spectroelectrochemical study of the reduction of a Schiff base cryptand

The electrochemical reduction of a bicyclic hexaimino Schiff base cryptand 1 (N[(CH2)2N-CH-meta-C6H4-CH=N(CH2)2]3N) and that of one of its strands 2 ((CH3)2CH-N=CH-meta-C6H4-CH=N-CH(CH3)2) has been studied by visible and near infrared in-situ spectroelectrochemical techniques. These results are in good agreement with those obtained using alkali metals, but in this case the effect of the formation of ion pairs is minimized through the use of tetrabutylammonium cations. It is confirmed that 1- and 1= have the same visible and near IR spectrum. The spectrum of the products of the electrochemical reduction of 2 is similar to those of 1- or 1=.

Infrared Spectroelectrochemical Studies of Divided Carbon Electrodes in Acetonitrile-Sodium Tetrafluoroborate Solutions

Electrical energy produced by renewable sources such as wind power or photovoltaic devices is fluctuant by nature. In order to use it reliably, it is necessary to have a means of storing electricity. These storage devices are also of prime importance in systems where surges of power are frequent; e.g. applications such as transportation and regenerative braking. Storage of electrical energy can be accomplished in an elegant way through the use of lightweight capacitors. Recently, devices based on the use of the electrochemical double-layer capacitor ~EDLC! have been developed: the supercapacitors. 1 Supercapacitors are intermediate systems between electrochemical batteries, which can store high energy associated with medium power values, and dielectric capacitors, which can deliver very high power during times of the order of a few milliseconds. Supercapacitors are used for energy storage over time periods ranging from seconds to minutes; their peak power is up to 10-20 times higher than that of batteries, but their energy density is 20-50 times lower. Their principle relies on the use of high specific area electrodes placed in an electrolyte and separated by a thin inert microporous membrane. This work focuses on organic electrolyte capacitors with electrodes manufactured using carbon dispersed in an aqueous solvent. To be useful, these devices must be able to remain charged in open-circuit conditions for great lengths of time. This implies that no irreversible reactions induced by the variation of the potential of each electrode should occur; thus, it is important to understand the mechanisms occurring during charge and spontaneous discharges. During the charge of the EDLC, several phenomena can occur. 2 An increase in the number of ions forming the double layer can be caused by the application of a voltage. A local increase in ionic concentration near the carbon surface, but not directly connected with the double layer, can also be produced if a current flows through the capacitor at or above the electrolyte potential range. Self-discharge processes are complex and involve mechanisms occurring on a short or a long time scale. When the supercapacitor is fully charged, its removal from the power supply induces a fast relaxation phenomenon. This process is reversible at short times. An irreversible process corresponding to faradaic reactions can also be observed on the same time scale. Another reason for self-discharge are the faradaic reactions of various groups at the surface of the carbon during ca. the first 500 h of use of the device. This phenomenon is irreversible. Another cause for voltage drop is the presence of an ‘‘electrochemical shuttle’’ due to electroactive redox couples involving impurities in the carbon layer. To gain some insight into self discharge phenomena, a knowledge of the variations of composition of the electrolyte in the immediate vicinity of the electrode or even modifications of the electrode itself as the potential is swept is of prime importance. In situ spectroelectrochemical measurements are well suited to fulfill this goal. Vibrational spectroscopy yields structural information on all the species present in the solution or on the electrode. Therefore, it appears to be a good method to couple with electrochemistry. Raman spectroscopy associated with confocal microscopy seems ideal because of the spatial resolution that enables one to select which part of the system is studied: electrode or solvent. 3 However, Raman spectroscopy is not very sensitive to the presence of minor components, and the previous studies were not able to detect new species, although variations of the intensities of the major peaks during potential scans were recorded. Rapid scan Fourier transform infrared ~FTIR! spectroscopy associated with electrochemistry in situ was used in this work. Preparation of new electrodes allowed us to keep enough IR light to obtain high-quality spectra. Experimental The spectroelectrochemical cell and its installation in an IR spectrometer have been previously described. 4 The cell was designed to accommodate various electrodes. The distance between the electrode and the optical window could be adjusted by a micrometric screw so that the cell path length was small enough ~ca. 100 mm! to avoid complete absorption of radiation. The window was made of