Redox electrochemical behavior

Ravindranath and co-workers studied the electrochemical behavior of 5-amino-2-phenyl-4-arylazo-l,2-dihydro-3//-pyrazol-3-one (90UC864) and 5-methyl-4-arylazo-2-(pyridin-2-ylcarbonyl)-2,4-dihydro-3//-pyrazol-3-(Mie (90IJC895). Similar studies were undertaken by Jain and Damodharan of pyrazol-3-ones 408a-f (95CJC176) (Scheme 94). The underlying rationale for this study on the electrochemical reduction of these biologically important pyrazol-3-ones is that it can lead to information on the reaction routes and mechanisms of biological redox reactions. 

Sodium dodecyl sulfate has been used to modify polypyrrole film electrodes. Electrodes synthesized in the presence of sodium dodecyl sulfate have improved redox processes which are faster and more reversible than those prepared without this surfactant. The electrochemical behavior of these electrodes was investigated by cyclic voltametry and frequence response analysis. The electrodes used in lithium/organic electrolyte batteries show improved performance [195]. 

The electrochemical behavior of heterometallic clusters has been reviewed clsewbcre."" The interest in examining clusters stems from their potential to act as "electron sinks " in principle, an aggregate of several metal atoms may be capable of multiple redox state changes. The incorporation of heterometals provides the opportunity to tune the electrochemical response, effects which should be maximized in very mixed"-metal clusters. Few very mixed -metal clusters have been subjected to detailed electrochemical studies the majority of reports deal with cyclic voltammetry only. Table XII contains a summary of electrochemical investigations of "very mixed"-metal clusters. 

The coordination of redox-active ligands such as 1,2-bis-dithiolates, to the M03Q7 cluster unit, results in oxidation-active complexes in sharp contrast with the electrochemical behavior found for the [Mo3S7Br6] di-anion for which no oxidation process is observed by cyclic voltammetry in acetonitrile within the allowed solvent window [38]. The oxidation potentials are easily accessible and this property can be used to obtain a new family of single-component molecular conductors as will be presented in the next section. Upon reduction, [M03S7 (dithiolate)3] type-11 complexes transform into [Mo3S4(dithiolate)3] type-I dianions, as represented in Eq. (7). 

PBE dendrons bearing a focal bipyridine moiety have been demonstrated to coordinate to Ru + cations, exhibiting luminescence from the metal cation core by the excitation of the dendron subunits [28-30]. The terminal peripheral unit was examined (e.g., phenyl, naphthyl, 4-f-butylphenyl) to control the luminescence. The Ru +-cored dendrimer complexes are thought to be photo/redox-active, and photophysical properties, electrochemical behavior, and excited-state electron-transfer reactions are reported. 

MV /MV " (HV is heptyl viologen and MV is methyl viologen). The specific effects of iodide on the electrochemical behavior of the layer-type compounds were compared, and the characteristics of several PEC cells were described. The interface energies for n-MoSe2 in contact with various redox couples were given as in Fig. 5.9. 

Dong et al. have reported on crown ether-bound biferrocene, 21, in which the redox potentials are shifted by the capture of metal ions within the crown ether (55). For example, the electrochemical behavior observed for the biferrocene derivative with Ba2+ ion is fundamentally different, as new redox couples are observed for 9 with Ba2+ concentrations within the range 0 < [Ba2+] < 2 eq. The peak currents for the two new redox couples increase with concentrations of the Ba2+ ion until a full equivalent is added at this point, the original redox couples disappear and the new redox couples reach full development. 

There are a number of informative reviews on anodes for SOFCs [1-5], providing details on processing, fabrication, characterization, and electrochemical behavior of anode materials, especially the nickel-yttria stabilized zirconia (Ni-YSZ) cermet anodes. There are also several reviews dedicated to specific topics such as oxide anode materials [6], carbon-tolerant anode materials [7-9], sulfur-tolerant anode materials [10], and the redox cycling behavior of Ni-YSZ cermet anodes [11], In this chapter, we do not attempt to offer a comprehensive survey of the literature on SOFC anode research instead, we focus primarily on some critical issues in the preparation and testing of SOFC anodes, including the processing-property relationships that are well accepted in the SOFC community as well as some apparently contradictory observations reported in the literature. We will also briefly review some recent advancement in the development of alternative anode materials for improved tolerance to sulfur poisoning and carbon deposition. 

Charge transfer reactions represent an important category of electrochemical behavior. As already pointed out above, an appropriate investigation of kinetic parameters of electrochemical reactions in aqueous electrolytes suffers from the small temperature range experimentally accessible. In the following, some preliminary results using the FREECE technique are presented for the Fe2+/Fe3+ redox reaction and for hydrogen evolution at various metal electrodes. 

The redox reaction Fe2+/Fe + was the first reaction for which it could be demonstrated that the investigation of electrochemical behavior in frozen aqueous electrolytes is possible (9). The electrolyte was 1M HCIO4 which has the... 

Electrochemistry. The redox processes for porphyrazines 21, 25, 28, 29, the heteroleptic Zr (pz/porphyrin) 30 and 31 have been measured by cyclic voltammetry and the formal potentials are given in Table VII. The potentials are compared to the available data for the analogous porphyrin and pc complexes. In general, the electrochemical behavior of the pz sandwiches more closely mirror that observed for the phthalocyanines than the porphyrins. In particular, all of the porphyrazines have at least one ring-based oxidation, attributable to the formation of the bis Jt-radical cation for Lu(III) sandwiches and the formation of the 7T-radical cation for the Zr(IV) and Ce(IV) sandwiches. Additionally, all of the porphyrazines exhibit at least one ring-based reduction. 

The tetracation 312+ exhibited the idealized electrochemical behavior upon CV and DPV, although the redox interaction among the cation units was still small. Additionally, tetracation 314+, synthesized as a representative for the cyanine-cyanine hybrid, also did not exhibit the presumed multiple-color change during electrochemical reduction. 

The bimetallic complex [Re(CO)3Cl]jtbpq synthesized in this work showed the typical spectroscopic and electrochemical behavior based on analogous polypyridyl complexes of rhenium(l). Re(l) dn tpbq n charge transfer transition and ligand-field n- n transitions are observed. Typical redox behavior of this system consists of Re /Re oxidation and tpbq/tpbq reduction. Such electrochemical activity, particularly in the reductive region, is found ideal for catalytic processes such as CO reduction. IR-SEC studies have shown that the reduction process occurring at -0.50... 

We have studied the electrochemical behavior and redox-driven mass changes for PAH-Os/PVS films immersed in solutions of salts with a common anion and different cations and a common cation and different anions [148]. The electrochemical and... 

It is important to clarify that there have been, in the literature, some examples of electrochemical processes on CNT-modified electrodes on which an apparent electrocatalytic process associated to the CNTs seems to take place (that is from the edge-plane-like sites) where in fact that was not the case. An example is the apparent electrocatalytic oxidation ofhydrazine at MWNTelectrodes [64,65]. Such electrochemical behavior has been demonstrated to be a consequence of iron impurities contained in the CNTs that were responsible for the observed electrocatalytic effects (Figure 3.7). Therefore, caution is needed when reporting catalytic effects of CNTs under a given redox system and a careful comparison vdth, for instance, edge HOPG is mandatory to make sure that the CNTs are the responsible for the electrochemical enhancement. 

Chen and coworkers were the first to describe the electrochemical behavior of PB NPs [41]. They prepared solutions of PB NPs by reaction of Fe(III) with Fe(CN)6 in the presence of H2O2, giving 30-50-nm diameter NPs. These were then immobilized at cysteine-modified Au electrodes with pendant amine groups by prolonged (10 h) exposure of the modified electrode to a solution of the NPs. This produced a monolayer of immobilized NPs that was subsequently examined using cyclic voltammetry. Interestingly, they observed two redox processes near 0.25 V vs. 

J.-M. Zen, A. S. Kumar and J.-C. Chen, Electrochemical Behavior of Lead-Ruthenium Oxide Pyrochlore Catalyst Redox Characteristics in Comparison with that of Ruthenium Dioxide, J. Mol. Catal. A Chem. 165 (2001) 177-188. 

Although the hybridization of single-stranded DNA to its complement results in detectable changes in electrochemical properties, particularly in support of non-Faradaic current, the DNA bases may also demonstrate redox behavior that gives rise to Faradaic currents. The electrochemical behavior of DNA has been studied over the past few decades. Differential pulse voltammograms show clearly defined peaks for the reduction of cytosine and adenosine. Electrochemical characterization of guanine by cyclic voltammetry has shown... 

Rhenium(III) tris-chelates are formed by the reaction of 2-(diphenylphosphinomethyl)-4-methylphenol, PpOH (258a), or 2-diphenylphosphinophenol, P2-OH (258b) with [ReCl3(PPh3)2(CH3CN)] in a 1 3 ratio. [Re(Pi-0)3] is stable as solid and in solutions while [Re(P2-0)3] is easily oxidized in air giving the rhenium(V) 0x0 complex [Re0(P2-0)2(0P2-0]. This behavior is also reflected in the electrochemical behavior of the compounds, where each one well-defined redox couple for one-electron oxidation and reduction steps are observed for both compounds. A second oxidative wave (Re /Re ) is only reversible for [Re(Pi-0)3]. 

The corrosion inhibitor can also be a redox couple presenting a reversible and fast electrochemical behavior that is able to react in place of the metal. This is obtained when its redox couple potential is lower than that of the considered metal. The reversible behavior allows the continuous regeneration of the corrosion inhibitor. These reducing agents are often organic compounds soluble in aqueous solutions. A nonexhaustive list is given in Ref. [5]. 

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