Glassy carbon electrode surfaces films

Other Substrates Deposition of cadmium was also studied on Bi, Sn and Pb [303], Ni [304], reticulated vitreous carbon [305], Ti [306], and indium tin oxide [307]. UPD of Cd on tellurium results in CdTe formation [270, 308]. Electrodes coated with conducting polymers were also used to deposit cadmium electrochemi-cally. In the case of polyaniline, the metal reduction potential corresponds to the neutral (nonconducting) state of the polymer, therefore cadmium was found to deposit on the substrate-glassy carbon electrode surface, in the open pores of the polymer film [309, 310]. 

Cyclic voltammetry was carried out in the presence of penta- and hexacyano-ferrate complexes in order to probe the homogeneity and conductivity of the TRPyPz/CuTSPc films (125), (Fig. 36). When the potentials are scanned from 0.40 to 1.2 V in the presence of [Fe (CN)6] and [Fe CN)5(NH3)] complexes, no electrochemical response was observed at their normal redox potentials (i.e., 0.42 and 0.33 V), respectively. However, a rather sharp and intense anodic peak appears at the onset of the broad oxidation wave, 0.70 V. The current intensity of this electrochemical process is proportional to the square root of the scan rate, as expected for a diffusion-controlled oxidation reaction at the modified electrode surface. The results are consistent with an electrochemical process mediated by the porphyrazine film, which act as a physical barrier for the approach of the cyanoferrate complexes from the glassy carbon electrode surface. 

Silica sol-gel glass-coated ferricyanide-doped Tosflex-modified screen-printed electrode used for the mediated oxidation of AA (neutral pH).The electrochemical mediation of AA is found to follow the Michaelis-Menten kinetic pathway A polymer film of N,N-dimethylaniline having a positive charge on the quaternary ammonium group in its backbone is electrochemical deposited on a glassy carbon electrode surface resulting a film-coated GC electrode... 

Since model compounds reveal well-defined cyclic voltammograms for the Cr(CNR)g and Ni(CNR)g complexes (21) the origin of the electroinactivity of the polymers is not obvious. A possible explanation (12) is that the ohmic resistance across the interface between the electrode and polymer, due to the absence of ions within the polymer, renders the potentially electroactive groups electrochemically inert, assuming the absence of an electronic conduction path. It is also important to consider that the nature of the electrode surface may influence the type of polymer film obtained. A recent observation which bears on these points is that when one starts with the chromium polymer in the [Cr(CN-[P])6] + state, an electroactive polymer film may be obtained on a glassy carbon electrode. This will constitute the subject of a future paper. 

Formate production has also been reported for electropolymerized films of [Co(4-vinylterpyridine)2] " on glassy carbon electrodes in dimethylformamide solutions [63]. Interestingly, the product of this same catalytic system in aqueous solutions is formaldehyde [81]. Other heterogeneous systems that produce formate include Cd, Sn, Pb, In, and Zn electrodes in aqueous media [12] (see also Vol VII 5.2.3). It is likely that the pathway to formate formation on metal electrodes follows the sequence of M—H bond formation followed by CO2 insertion to form a M—0C(0)H species followed by desorption from the electrode surface. 

Lead and mercury are deposited as micron-sized clusters, predominantly at intercrystallite boundaries [105] so does lithium from the polyethylene oxide solid electrolyte. What is more, Li intercalates into the sp2-carbon [22, 138], Thus, observations on the Li intercalation and deintercalation enable one to detect non-diamond carbon on the diamond film surface. Copper is difficult to plate on diamond [139], There is indirect evidence that Cu electrodeposition, whose early stages proceed as underpotential deposition, also involves the intercrystallite boundaries [140], We note that diamond electrodes seem to be an appropriate tool for use in the well-known electroanalytical method of detection of traces of metal ions in solutions by their cathodic accumulation followed by anodic stripping. The same holds for anodic deposition, e.g. of, Pb as PbCh with subsequent cathodic reduction [141, 142], Figure 30 shows the voltammograms of anodic dissolution of Cd and Pb cathodically predeposited from their salt mixtures on diamond and glassy carbon electrodes. We see that the dissolution peaks are clearly resolved. The detection limit for Zn, Cd, and Pb is as low as a few ppb [143]. 

Fig. 2.28. Case diagram for NADH oxidation at a glassy carbon electrode coated with a poly(aniline)/poly(vinylsulfonate) film. The points are the experimental data. The surface and case boundaries have been determined from the inhibited fit parameters given in Table 2.8. The residuals are shown as a function of the concentration of NADH below the plot.

In fact, the film formed on the GC electrode surface by the ssDNA acts purely as a conducting path such as in a conducting polymer. Alternatively, if we only use the dsDNA adsorbed on the glassy carbon electrode without conditioning by the ssDNA to investigate an electron-transfer process it is not possible to obtain reproducible results. 

Due to their small size and high surface area, nanoparticles can be applied to modify electrode surface property. Convenient and sensitive electrochemical sensors to various targets have been set up by using nanoparticle modification. The determination of acetaminophen in a commercial paracetamol oral solution was reported using a multiwall CNTs composite film-modified glassy carbon electrode with a detection limit of 50 nM (Li etal. 2006a). Heavy metal ions, such as ar-senite (Dai and Compton 2006 Majid et al. 2006) and lead ion (Cui et al. 2005),... 

Figure 41. Spectroelectrochemistry of a film of Co(4-TCPyP) on a glassy carbon surface, in aqueous solution, showing (a) the Ru(III)Ru(III)Ru(III)/Ru(III)Ru(III)Ru(II) in the range from 0.12 to 0.42 V. (b) The Co(III/II) reduction in the range from —0.06 to 0.12 V. (c) Cyclic voltammograms of a Co(4-TCPyP) modified glassy carbon electrode in 0.5 M KNO3 aqueous solution. Inset. Plot of the peak current intensities as a function of the scan rate.

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