Electrochemical activity, enhanced

Xu, L., Ding, Y., Chen, C., Zhao, L., Rimkus, C., Joesten, R. and Suib, S.L. (2008) 3D flowerlike a-nickel hydroxide with enhanced electrochemical activity synthesized by microwave-assisted hydrothermal method. Chemistry of Materials, 20, 308-316. 

Polymeric ion-radicals are usually formed as a result of one-electron redox modifications of uncharged polymers containing electrochemically active groups. They attract an enhanced attention in the sense of possible practical applications. Because polymeric ion-radicals contain many spin-bearing groups, a similarity emerges between polymeric ion-radicals and poly(ion-radicals). 

Marken, F., Tsai, Y.-C., Saterlay, A.J., Coles, B.A., Tibbetts, D., Holt, K., Goeting, C.H., Foord, J.S. and Compton, R.G., Microwave activation of electrochemical processes enhanced PbCh electrodeposition, stripping and electrocatalysis, J. Solid State Electrochem., 2001, 5, 313. 

All electrodes react with their environment via the surfaces in ways which will determine their electrochemical performance. Properly selected surface modification can effectively enhance the electrode heterogeneous catalysis property, especially selectivity and activity. The bulk materials can be chosen to provide mechanical, chemical, electrical, and structural integrity. In this part, several surface modification methods will be introduced in terms of metal film deposition, metal ion implantation, electrochemical activation, organic surface coating, nanoparticle deposition, glucose oxidase (GOx) enzyme-modified electrode, and DNA-modified electrode. 

Besides activity, durability of metal electrode nano-catalysts in acid medium has become one of the most important challenges of low-temperature fuel cell technologies. It has been reported that platinum electrode surface area loss significantly shortens the lifetime of fuel cells. In recent years, platinum-based alloys, used as cathode electrocatalysts, have been found to possess enhanced stability compared to pure Pt. The phenomenon is quite unusual, because alloy metals, such as Fe, Co and Ni, generally exhibit greater chemical and electrochemical activities than pure Pt. Some studies have revealed that the surface stmcture of these alloys differs considerably from that in the bulk A pure Pt-skin is formed in the outmost layer of the alloys due to surface segrega-... 

On the other hand, detection difficulties are often experienced with basic drugs because their therapeutic levels are in the low ng ml" range. Some of the problems can be alleviated by employing either an electrochemical or fluorescence detector, since it is possible to achieve detection levels of sub-nanogram with these instruments, if operated under favourable conditions. Furthermore, both of these detection methods can enhance selectivity because analytes will only be detected if they contain an electrochemically active group or fluoresce. 

Some anions can also be electrochemically active and an oxidative electrochemical detector is often coupled together in series with either the ion chromatograph conductivity detector or the UV detector when using the IPD technique. This dual detection technique can enhance anion identification or discrimination and provide increased sensitivity. 

The CV curves obtained for carbons with preadsorbed copper shown in Figs. 45 (curves b, b, c, c ) and 46 (a-a")) exhibit only slight peaks of the Cu(II)/Cu(I) couple and broad waves due to the redox reaction of surface carbon functionalities (.see Section IV). However, preadsorbed copper enhances the peaks of the redox process in bulk solution (especially the anodic peaks for D—H and D—Ox samples), as can be seen in Fig. 46 (curves c-c"). The low electrochemical activity of samples with preadsorbed copper species observed in neutral solution is the result of partial desorption (ion exchange with Na ) of copper as well as the formation of an imperfect metalic layer (microcrystallites). Deactivation of the carbon electrode as a result of spontaneous reduction of metal ions (silver) was observed earlier [279,280]. The increase in anodic peaks for D—H and D—Ox modified samples with preadsorbed copper suggests that in spite of electrochemical inactivity, the surface copper species facilitate electron transfer reactions between the carbon electrode and the ionic form at the electrode-solution interface. The fact that the electrochemical activity of the D—N sample is lowest indicates the formation of strong complexes between ad.sorbed cations and surface nitrogen-containing functionalities (similar to porphyrin) [281]. Between —0.35 V and -1-0.80 V, copper (II) in the porphyrin complex (carbon electrode modifier) is not reduced, so there can be no reoxidation peak of copper (0) [281]. 

Therefore the electrochemical response with porous electrodes prepared from powdered active carbons is much increased over that obtained when solid electrodes are used. Cyclic voltammetry used with PACE is a sensitive tool for investigating surface chemistry and solid-electrolyte solution interface phenomena. The large electrochemically active surface area enhances double layer charging currents, which tend to obscure faradic current features. For small sweep rates the CV results confirmed the presence of electroactive oxygen functional groups on the active carbon surface. With peak potentials linearly dependent on the pH of aqueous electrolyte solutions and the Nernst slope close to the theoretical value, it seems that equal numbers of electrons and protons are transferred. 

If no derivatization takes place, detection is preferably accomplished by UV at a low wavelength (200-210 nm) in order to enhance detection sensitivity. However, detection selectivity is sacrificed at such low wavelengths. Electrochemical detection, when applied to the analysis of free amino acids, offers higher selectivity but suffers from a small linearity range. Furthermore, most amino acids (with the exception of tryptophan, tyrosine, and cysteine) are not intrinsically electrochemically active within the current useful potential range [5]. Lately, the development of the evaporative light-scattering detector (ELSD) offers an attractive alternative for the determination of nonderivatized amino acids (see Fig. 1). 

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