Square-wave treatment

Chen et al. [95], very recently, prepared Au thin-film electrodes made by electroless deposition for in situ electrochemical attenuated total-reflection surface-enhanced infrared adsorption spectroscopy (ATR-SEIRAS) which consisted of 46 nm Au nanoparticles deposited on a Si infrared window. Very interestingly, they observed that a square-wave treatment of the Au film led to a much enhanced ORR activity (02-saturated 0.1 M HCIO4) as a consequence of the surface reconstruction of the nanoparticle film. Thus, whereas the ORR activity of the initial Au... 

Some other less important types of AC polarography may also be considered as sinusoidal ac techniques, as their theoretical treatment can be based on signals from a complex Fourier function in this context we confine ourselves to mentioning sawtooth or triangular wave48 superimposed on the dc ramp. Square-wave polarography is also of that type, but in view of its greater importance we shall treat it separately. 

Extension of this treatment to pulse techniques can, in principle, be made for several cases. In the case of square-wave voltammetry, theoretical current-potential curves for reversible electron transfer between species in solution are given by [184, 185]... 

This chapter analyzes the subtractive techniques Differential Multipulse Voltammetry (DMPV), Differential Staircase Voltammetry (DSCVC), and Square Wave Voltammetry (SWV). Of these, the most employed SWV will be analyzed in more detail. Interesting alternatives to DSCVC and SWV are Differential Staircase Voltcoulometry (DSCVC) and Square Wave Voltcoulometry (SWVC), which are based on the analysis of the difference of converted faradaic charge signals obtained between two successive potential pulses when a staircase potential or a square wave potential is applied [4, 5], which is very useful for the study of surface-confined redox species. There exists, however, a book in this series devoted entirely to the theory and application of SWV [6], so in some of the reaction mechanisms analyzed, the reader will be directed to this title for a more thorough treatment of the SWV response. 

Activation (of noble metal electrodes) — Noble metal electrodes never work well without appropriate pretreatment. Polycrystalline electrodes are polished with diamond or alumina particles of size from 10 pm to a fraction of 1 pm to obtain the mirror-like surface. The suspensions of polishing microparticles are available in aqueous and oil media. The medium employed determines the final hydrophobicity of the electrode. The mechanical treatment is often followed by electrochemical cleaning. There is no common electrochemical procedure and hundreds of papers on the electrochemical activation of -> gold and platinum (- electrode materials) aimed at a particular problem have been published in the literature. Most often, -> cyclic and - square-wave voltammetry and a sequence of potential - pulses are used. For platinum electrodes, it is important that during this prepolarization step the electrode is covered consecutively by a layer of platinum oxide and a layer of adsorbed hydrogen. In the work with single-crystal (- monocrystal) electrodes the preliminary polishing of the surface can not be done. 

It is usual to compare the infrared spectra of the electrochemically treated amorphous alloys to those of the chemically or thermally (at 380°C) prepared spinels to ascertain the nature and composition of the compound. With this methodology, it can be demonstrated that the hydrous oxide coating acts as a precursor of a spinel structure either from the electrolessly deposited amorphous alloys or after the square-wave potential treatment. 

Pothakamury et al. (1996) subjected E. coli to 35 and 36 kV ctir EF strengths using exponential decay and square wave pulses, the treatment temperature was varied from 3°C to 30°C. They reported greater inactivation above 20°C. For exponential decay pulses, an additional 1.5-log reduction of E. coli was achieved at 30°C than at 3°C. For a sqnare wave pulse, an additional l-log reduction was achieved at 33°C than at 7°C. 

The above treatment assumes that the measured reduction potentials are thermodynamically meaningful. Although redox potentials can be measured by a variety of electrochemical techniques, cyclic voltammetry, differential pulse polarography, and more recently, square wave voltammetry have found the greatest use because of the ability of these techniques to reveal the dynamics of the associated chemical processes, and hence access the chemical and electrochemical reversibility of the couple. Chemical and electrochemical reversibility have been defined and problems associated with the distinction between these terms have been covered in Chapter 2.15 (2.15.2.2.1), however, for the purpose of this discussion it is useful to treat these behaviors separately. 

The breakthrough of shape-controlled synthesis of Pt nanoparticles of high-energy surface has been made by Tian et al. at Xiamen University in 2007. They have developed a two-step synthesis process as illustrated in Fig. 5A. The first step is electrodeposition of polycrystalline Pt nanospheres 750nm in diameter on glassy carbon (GC) substrate. The Pt nanospheres are then subjected to a square-wave potential treatment in a solution containing 0.1 M H2SO4 and 30 mM ascorbic acid, where they become partially... 

Lamari et al. [15], in a recent work, studied the electrochemical detection of ascorbic acid (AA) by square wave voltammetry using a carbon paste electrode modified with a polymer of eugenol by voltammetric synthesis. Ascorbic acid, vitamin C, is an organic compound involved in several biological processes and has various applications [16-18]. To electropolymerizes eugenol by CV used a working electrode of stainless steel covered with carbon paste after anodic treatment, SCE reference electrode, platinum counter electrode, 0.1 mol L KOH as electrolyte and 4 rrrmol L eugenol. 

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