Sequential cyclic voltammetry

Smooth polycrystalline Au, Pt and Ir thin-layer electrodes were utilized (10-11). Electrodes were cleaned between trials by sequential electrochemical oxidation above 1.2 V [Ag/AgCl (1 M Cl-) reference] and reduction below -0.2 V in 1 M H2SO4 surface cleanliness was verified with the aid of cyclic voltammetry in the same molar sulfuric acid solution. Experiments were carried out in 1 M H2SO4, 1 M NaC104 buffered at pH 7 and 10, and in 1 M NaOH solutions were prepared with pyrolytically triply distilled water (12). Surface reagents employed were iodide, hydroquinone (HQ), 2,5-dihydroxythiophenol [DHT (13)1. and 3,6-dihydroxypyridazine (DHPz). 

With stringent precautions to avoid the presence of water, polycyclic aromatic hydrocarbons show two one-electron reversible waves on cyclic voltammetry in dimethylformamide (Table 7.1). These are due to sequential one-electron additions to the lowest unoccupied molecular n-orbital [1]. Hydrocarbons with a single benzene ring are reduced at very negative potentials outside the accessible range in this solvent. Radical-anions of polycyclic aromatic hydrocarbons [2] and also alkyl benzenes [3] were first obtained by the action of alkali metals on a solution of the hydrocarbon in tetrahydrofuran. They have been well characterised by esr spectroscopy. The radical-anions form coloured solutions with absorption bands at longer wavelength than the parent hydrocarbon [4,5]. 

Bioprocesses incorporating more than one redox enzyme in an oxidative reaction system might involve, in the simplest case, two oxidizing enzymes coupled so that they act sequentially to effect two oxidation steps. A key issue in the development of such oxidative biocatalytic systems would be the determination of the values, for each enzyme involved, of the redox potentials. These can be determined by potentiometric titration using redox mediators (such as NADH) and techniques such as cyclic voltammetry or electrophoresis [44]. Knowledge of the redox potentials would facilitate the design and engineering of a process in which the two... 

Another evolution from the linear sweep mode is cyclic voltammetry, namely, a sequential combination of two (or more) linear sweep potential scans in the opposite direction for this reason, the current versus potential response supplies information about the reversibility of redox systems. 

Nitrenium ions can be viewed as products from two-electron oxidation of amines (Fig. 13.13) followed by loss of a proton. Thus they need to be considered as intermediates in the oxidation of amines. In two early studies, diarylnitrenium ions were shown to have formed in the oxidation of diarylamines. Svanholm and Parker carried out cyclic voltammetry on A,A-di-(2,4-methoxyphenyl)amine (25) in acetonitrile with alumina added to suppress any adventitious nucleophiles. The voltam-mogram revealed two sequential oxidation processes (1) formation of the cation radical 26, and (2) either the nitrenium ion 27 or its conjugate acid. In strongly acidic solution the latter was sufficiently stable that its absorption spectrum could be recorded. 

Fig. 3.10 Cyclic voltammetry using a electrochemical quartz crystal microbalance of formic acid electrooxidation on a polycrystalline Pt surface in 0.2 M formic acid and 0.2 M HCIO4 at 50 mV s (a) current and (b) frequency (corresponding to negative mass changes) response. The upper potential limit is sequentially increased with each subsequent cycle [66]...

The activity and the stability of the added OER catalysts were evaluated via quasisteady state polarization measurements. Slow scan cyclic voltammetry (CV) was performed from 0.7 V to the upper voltage limit which was sequentially increased in increments of 0.05 V from 1.45 to 1.65 V. Three consecutive scans for each upper potential limit were recorded. In Fig. 22.8, some of the characteristic polarization scans that best illustrate the OER on Ru and Ir overcoated on Pt-NSTF are presented. Up to the first voltage limit of 1.45 V, only the added Ru produced a substantial... 

Polyaromatic ethers coordinated to CpFe+ moieties have also been prepared via sequential S Ar reactions of chloroarene complexes with hydroquinone (189). The electrochemical behavior of cationic aromatic ether, thioether, and sul-fone complexes of cyclopentadienyliron has been studied using cyclic voltammetry and coulometry (190). Reaction of the aromatic ether complexes with sodium cyanide resulted in the formation of neutral adducts which imder-went oxidative demetallation to give the corresponding organic aromatic nitriles (191). 

Once power production has been maximized and the system is at steady state, we generate a polarization curve with sequential load changes as described [17,18]. Additional electrochemical tests such as linear scan voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy can be performed to further characterize each electrode. Samples can also be collected for analysis of the microbial community and microscopy. 

If a chemical reaction follows an electrochemical step, the cyclic voltam-mogram is typically irreversible and i jip 1 and/or A p 59/n mV. Cyclic voltammetry can be used to estimate the relative energy of the frontier orbitals of a series of complexes for each coordination site. A cyclic voltammogram for [Os(bpy)3] shows a reversible oxidation with 1/2= 0.81 V and three reversible reductions starting at —1.29 V. The oxidation is representative of Os , while the reduction represents sequential bpy for each coordinated ligand. The electrochemistry shows that frontier orbitals of [Os(bpy)3] involve an osmium-based HOMO and a bpy-based LUMO. This is consistent with the photochemical properties of [Os(bpy)3] in which the lowest energy... 

Reiter et al. [15] have reported a multielectrode system that is compatible with the format of standard 96-well microplates. The system, housed in a Faraday cage, is capable of sequentially monitoring, by cyclic or differential pulse voltammetry, the contents of 16 wells, using three-electrode cells with Pt working electrodes. The authors used this system to optimize conditions for redox modification of pyrroquinolinequinone-dependent glucose dehydrogenase with a ruthenium complex for enhanced electrochemical properties. 

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