Catalytic Currents effects

In redox mediation, to have an effective electron exchange, the thermodynamic redox potentials of the enzyme and the mediator have to be accurately matched. For biocatalytic electrodes, efficient mediators must have redox potentials downhill from the redox potential of the enzyme a 50 mV difference is proposed to be optimal [1, 18]. The tuning of these potentials is a compromise between the need to have a high cell voltage and a high catalytic current. Furthermore, an obvious requirement is that the mediator must be stable in the reduced and oxidized states. Finally, for operation of a membraneless miniaturized biocatalytic fuel cell, the mediators for both the anode and the cathode must be immobilized to prevent power dissipation by solution redox reactions between them. 

Cyclic voltammetric responses corresponding to the simple catalytic scheme in Figure 4.1 and to more complex schemes were discussed in detail in Section 2.2.6. The parameters that control the catalytic current have been identified and their effects quantified. Applications of homogeneous redox catalysis to the characterization of short-lived intermediates and the determination of their redox properties have been discussed in Sections 2.3 and 2.6.4. 

Low-valent rhenium complexes are effective in the catalytic reduction of carbon dioxide. The conversion can be accomplished photolytically or electrochemically and is of interest with regard to fuel production and greenhouse gas remediation [9]. Electrocatalytic reduction of CO2 to CO is initiated by the reduction of fac-Re(bpy)(CO)3Cl or a related complex and can be accomplished in homogeneous solution [54, 55] or on a polymer-modified electrode surface [56]. Catalytic current... 

The effects of solution acidity on the polarography of organic compounds have been reviewed, principally in aqueous solution. A thorough discussion of kinetic and catalytic currents that involve hydronium ion has been presented,52 and the irreversible polarographic and voltammetric curves that involve proton transfer in unbuffered and poorly buffered solutions have been discussed.59... 

Effect of pH. The relationship between the catalytic current of a PPy-GOD film (2000 A) and the pH of the solution was recorded in the pH range of 3-11. When the pH was less than 3, no catalytic current was observed, but the current was increased by increasing the pH from 3 to 7. When pH was more than 7.5, the current decreased. The PPy-GOD film electrode showed a good catalytic response to glucose in the solutions of pH ranging between 6 and 8. 

Although its theory is not quite clear, the Brdidka catalytic effect of cysteine or proteins is so typical and sensitive, that it is suitable for use in the analysis. It is not possible to discuss here the whole theory of catalytic currents of sulphydryl compounds (see also [133-141]) but some characteristics must be mentioned. 

In the electrochemical conversion of hydrocarbons the NEMCA (non-faradaic electrochemical modification of catalytic activity) effect has been reported frequently over metal anodes [13] and rarely over metal oxide anodes [14]. The NEMCA effect is known to promote the rate of oxidation and, to the knowledges of the authors, such enhancement in catalytic activity is generally observed over the metal anodes which have original catalytic activity, e.g. Pt, Pd, Rh and Ag, and is also observed as a non-linear function of the electric current. In the present study, we observed an almost linear increase of activity with increase in the electric current. Lacking a reference electrode, it is beyond the scope of this work to elaborate on the work function of the anode material. However, it is likely that the contribution of the NEMCA effect is neglisible and the electrochemically generated ooxygen species operates in the partial oxidation of alkanes. 

The term electrocatalysis will be used in the following for designing electrochemical processes involving the oxidation or reduction of a substrate species, S, whose reaction rate is varied in the presence of a given catalytic species. Cat. The effect of electrocatalysis is an increase of the standard rate constant of the electrode reaction resulting in a shift of the electrode reaction to a lower overpotential at a given current density and a current increase. The faradaic current resulting from the occurrence of a catalytic electrode mechanism is called catalytic current. For a positive electrocatalysis, the current obtained in the presence of the catalyst must exceed the sum of the currents obtained for the catalyst and the substrate, separately, under selected experimental conditions (Bard et al., 2008). Three possible situations can be discerned ... 

Recent studies of the of the stereochemical effect of substituents on the electrocatalytic reduction of CO2 have shown that the complexes RSSR-Ni(2,3, 9,10-tetramethyl-cyclam)2+ (5.11), RRSS-Ni(2,3,9,10-tetramethyl-cyclam) + (5.12) in aqueous KCl solution show increase in the catalytic current by a factor of 50-100, with the current densities of the RRSS-Ni(2,3,9,10-tetra-methyl-cyclam) + and Ni(5,12-dimethyl-cyclam) + complexes being higher than that observed for Ni(cyclam) +. Thus, these complexes appear to be better catalysts than Ni(cyclam) + in terms of their larger catalytic currents and more positive potentials. Hydrogen and formate production is less than 1.5% of CO for each mole of complex . However, the geometric isomer RSSR-Ni(2,3,9,10-tetra-methyl-cyclam) " (5.11) shows a lower catalytic activity because the axial methyl... 

The same stabilization effect was corroborated with another cations (Brpnsted and Lewis acids) . The authors demonstrated that the addition of weak Brpnsted acids such as 1-propanol, 2-pyrolidone, and CF3CH2OH or Lewis acid such as Mg " ", Ca " ,Ba +,Li, and Na" " resulted in a considerable improvement of the catalysis of CO2 by Fe(0) tetraphenylporphyrins . Both the catalytic currents and the lifetime of the catalysts increase without sig-... 

The combination of the enrichment and enhancement effects in CAdSV has been successfully used for reactions involving either a single or a two-electron reduction. As indicated in Table 3, the inclusion of oxidants, such as nitrite, nitrate, peroxide, bromate, chlorite, chlorate, and hydrogen ions, in solutions have been shown to result in (1) considerable amplification of the voltammetric responses obtained with AdSV, (2) a reduction in detection limits, and (3) improved selectivity. This catalytic current generation has been successfully used for the AdSV determination of inorganic substances, such as Co, Cr,... 

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