Search results for "Cyclic voltammetry"
showing 10 items of 238 documents
Electrochemical study of intramolecular charge transfer complexes derived from 1,4-naphthoquinone Part 1. Electroreduction
1995
Abstract Electrochemical investigations (polarography, cyclic voltammetry, rotating ring-disk electrode voltammetry) of intramolecular charge transfer complexes (AC) derived from 1,4-naphthoquinone were performed in acetonitrile. It is concluded that in the first one-electron stage of its electrochemical reduction the AC is in a complexed form. At the same time the amino moiety, which shows a marked inductive (−I) effect, acts as an electron donor in the donor-acceptor (D-A) interaction. Facilitation of the reduction of the quinone part by the aryl amine residue is compensated by the D-A interaction, which makes the electroreduction more difficult. By using ultramicroelectrodes it was shown…
Water-soluble and redox-responsive hyperbranched polyether copolymers based on ferrocenyl glycidyl ether
2015
Water-soluble copolymers of ferrocenyl glycidyl ether (fcGE) and glycidol were prepared via anionic ring-opening multibranching polymerization (ROMBP). The resulting hyperbranched materials with molecular weights (Mn) of 3500 to 12 300 g mol−1 and relatively narrow molecular weight distributions (Mw/Mn = 1.40–1.69) exhibit both temperature- as well as redox-responsive behavior, which was studied via turbidity measurements. The cloud point temperatures (Tc) were adjusted between 45 and 60 °C through variation of the fcGE comonomer content. Additionally, these Tcs can be increased by the addition of an oxidizing agent. The extent of oxidation of the materials was quantified by Mosbauer spectr…
Clarification of the oxidation state of cobalt corroles inheterogeneous and homogeneous catalytic reduction of dioxygen
2008
Co(III) corroles were investigated as efficient catalysts for the reduction of dioxygen in the presence of perchloric acid in both heterogeneous and homogeneous systems. The investigated compounds are (5,10,15-tris(pentafluorophenyl)corrole)cobalt (TPFCor)Co, (10-pentafluorophenyl-5,15-dimesitylcorrole)cobalt (F 5PhMes 2Cor)Co, and (5,10,15-trismesitylcorrole)cobalt (Mes 3Cor)Co, all of which contain bulky substituents at the three meso positions of the corrole macrocycle. Cyclic voltammetry and rotating ring-disk electrode voltammetry were used to examine the catalytic activity of the compounds when adsorbed on the surface of a graphite electrode in the presence of 1.0 M perchloric acid, a…
Identification of Processes Associated with Different Iron Sites in the Prussian Blue Structure by in Situ Electrochemical, Gravimetric, and Spectros…
2012
The physicochemical properties of Prussian blue films are strongly dependent on the ratio Fe3+/Fe2+ in the structure. This ratio can be modulated by electrochemical techniques such as cyclic voltammetry, and some information about physicochemical properties can be extracted from in situ auxiliary techniques. Prussian blue films have been studied by the use of in situ vis–NIR spectroscopy, quartz crystal microbalance, and electrochemical techniques (cyclic voltammetry and electrochemical impedance spectroscopy). By cyclic voltammetry + absorbance derivative curves + mass derivative curves, it has been possible to identify at least three different processes during the reduction of Prussian bl…
Prussian blue films deposited on graphite+epoxy composite electrodes: electrochemical detection of the second percolation threshold
2000
Abstract The electrochemical behavior of Prussian blue films galvanostatically electrodeposited on graphite+epoxy-resin composite electrodes was studied. The composite electrodes were prepared with different graphite proportions and their effect on electrochemical reduction of the Prussian blue was analyzed by means of the uncompensated resistance approximation and the electrical percolation theory. The results suggest that the electrode with 60% graphite reaches the second percolation threshold and its internal structure changes from a compact to a porous one. Mechanical tensile tests were performed in order to confirm the critical behavior of this material at the percolation thresholds. T…
Improving the onset potential and Tafel slope determination of earth-abundant water oxidation electrocatalysts
2021
To date, a plethora of electrocatalysts for the Oxygen Evolution Reaction (OER) have been proposed. For evaluating their electrocatalytic behavior the determination of the onset potential in each studied electrolyte is a key parameter. Nevertheless, this evaluation becomes particularly problematic for first- transition metal catalysts as well as by the use of electroactive collectors ( e.g. Ni foams) whose redox peaks overlap the onset potential. A usual solution to detect the onset potential requires the availabil- ity of in-situ mass spectrometric determination of the generated oxygen. In this work, we present fast and easier available cyclic voltammetry and coulovoltammetric responses to…
ESR, electrochemical and cyclodextrin-inclusion studies of triazolopyridyl pyridyl ketones and dipyridyl ketones derivatives.
2008
Abstract The electron spin resonance (ESR) spectra of free radicals obtained by electrolytic reduction of triazolopyridyl pyridyl ketones and dipyridyl ketones derivatives were measured in dimethylsulfoxide (DMSO). The hyperfine patterns indicate that the spin density delocalization is dependent of the rings presented in the molecule. The electrochemistry of these compounds was characterized using cyclic voltammetry, in DMSO as solvent. When one carbonyl is present in the molecule one step in the reduction mechanism was observed while two carbonyl are present two steps were detected. The first wave was assigned to the generation of the correspondent free radical species, and the second wave…
Effect of axially bound anions on the electroreduction of tin(IV) porphyrins in tetrahydrofuran
1989
The spectroscopic characterization and electrochemistry of SnL(X)2 is presented where L is the dianion of tetra-p-tolylporphyrin or tetra-m-tolylporphyrin and X is ClO4–, Br–, Cl–, F–, or OH–. In all cases, electroreduction leads to porphyrin π anion radicals and dianions which were characterized in tetrahydrofuran by spectroelectrochemistry and e.s.r. spectroscopy. Dissociation of one ClO4– ion from SnL(ClO4)2 occurs before electroreduction of the complex but no dissociation is observed either before or after electroreduction of SnL(F)2 or SnL(OH)2. In contrast, one Br– ion dissociates after the first electron addition to SnL(Br)2 while one Cl– ion dissociates from SnL(Cl)2 after the secon…
In situ spectroelectrochemical study of the reductive coupling of benzaldehyde catalyzed by Ti(III) complexes in the presence of Mg(II)
2003
Abstract The UV–vis spectroelectrochemical technique has been used to visualize for the first time, the formation of a trimetallic intermediate Ti(III)Mg(II)Ti(III) during the reductive coupling of benzaldehyde in the presence of electrogenerated Ti(III) and MgCl 2 . This intermediate is supposed to induce the high diastereoselectivity of the reaction. We have built a special thin layer cell adapted from the scheme proposed by A. Neudeck and L. Dunsch [‘J. Electroanal. Chem. 370 (1994) 17; J. Electroanal. Chem. 386 (1995) 135’] which allows the simultaneous recording of the cyclic voltammogram and of a great quantity of UV–vis spectra at a frequency of 1 spectrum per second by means of a …
Mechanism of the palladium-catalysed electrosynthesis of diethyl carbonate from carbon monoxide and ethanol
2004
Abstract A mechanism is proposed for the PdBr2(PPh3)2-catalysed electrosynthesis of diethyl carbonate from carbon monoxide and ethanol, proceeding at room temperature and atmospheric CO pressure. The mechanism is investigated by cyclic voltammetry and 31P NMR spectroscopy. The active Pd0 complex able to coordinate CO is generated by the chemical reduction of PdBr2(PPh3)2 by EtO– ions generated from EtOH at the cathode. After reaction of EtO– ions with Pd0(PPh3)2(CO), the ensuing anionic complex [(PPh3)2Pd0–COOEt]– is oxidized at the anode in a key step leading to BrPdII–COOEt(PPh3)2. A nucleophilic attack of ethoxide on the latter generates diethyl carbonate and the Pd0 complex active in th…