Non-electrochemical methods

Industrial electrochemical reduction processes exist for the conversion of 3-hydroxybenzoic acid to 3-hydroxybenzyl alcohol and 4-nitroben-zoic acid to 4-aminobenzoic acid. How may these processes be carried out Compare these processes in terms of the Principles of Green Chemistry with alternative non-electrochemical methods. 

Dr K. Janacek, Dr L. Kavan, Dr K. Micka, Dr P. Novak, Dr Z. Samec and Dr J. Weber read individual chapters of the manuscript and made valuable comments and suggestions for improving the book. Dr L. Kavan is the author of the section on non-electrochemical methods (pages 319 to 329). 

The new edition of Principles of Electrochemistry has been considerably extended by a number of new sections, particularly dealing with electrochemical material science (ion and electron conducting polymers, chemically modified electrodes), photoelectrochemistry, stochastic processes, new aspects of ion transfer across biological membranes, biosensors, etc. In view of this extension of the book we asked Dr Ladislav Kavan (the author of the section on non-electrochemical methods in the first edition) to contribute as a co-author discussing many of these topics. On the other hand it has been necessary to become less concerned with some of the classical topics the details of which are of limited importance for the reader. 

The electrode material and its pretreatment considerably influence the course of the electrode process. The importance of non-electrochemical methods is constantly increasing as a result of the development of experimental techniques. 

Recently, the mechanism of cathodic electrodeposition of ZnO thin films from aqueous Zn(N03)2 baths has been studied using a rotating disc electrode [165]. Non-electrochemical methods of preparation of ZnO were also described, but they are not covered in this review. 

Non-electrochemical methods can and should be used for studying electrode surfaces and the interfacial region structure, particularly in situ in real time where this is possible. 

Barriere, R, and Downard, A.J. 2008. Covalent modification of graphitic carbon substrates by non-electrochemical methods. Journal of Solid State Electrochemistry 12, 1231-1244. 

Other Non-Electrochemical Methods. B. Cahan(56) is examining the passivation of iron and ferrous alloys by a... 

Concrete Bridge Protection and Rehabilitation Chemical and Physical Techniques—Corrosion Inhibitors and Polymers. Discusses the improvement of existing non-electrochemical methods for protecting and rehabilitating chloride-contaminated concrete w ith and without concrete removal and the development of new methods. Five corrosion inhibitors were evaluated and service lives were estimated for the two most effective treatments. Asphalt Portland cement concrete composite (APCCC) was designed and evaluated, and compared with hot-mix asphalts and Portland cement concrete for strength properties, resistance to freeze-thaw and resistance to chloride intrusion. 248 pages. SHRP-S-666... 

Neuroscientists have been interested for many years in being able to make measurements of the concentration of neurotransmitters in extracellular fluid. Two non-electrochemical methods have seen widespread use for these measurements. One is the use of the push-pull cannula. In this experiment, two concentric tubes are placed in the brain region of interest. Fluid is pumped into the brain through the inner tube and removed by the outer tube (Figure 4). This sampling technique, coupled with the use... 

It is clear from this concluding discussion that the theory of simple electrode reactions must be modified considerably to deal with the majority of electrode processes. From the experimental point of view, it is important to measure the anodic and cathodic Tafel slopes as well as the reaction order with respect to all possible reactants (including the supporting electrolyte and the solvent). At the same time, non-electrochemical methods such as infrared and Raman spectroscopy [31,32] can provide direct molecular information which is essential for the proper understanding of electrode processes. 

Corrosion test methods can be divided into electrochemical and non-electrochemical methods. Among the electrochemical techniques that have been used successfully for corrosion prediction are potentiodynamic polarization scans, electrochemical impedance, corrosion current monitoring, controlled potential tests for cathodic and anodic protection, and the rotating cylinder electrode for studies of velocity effects [3i,32]. Though not literally a test, potential-pH (Pourbaix) diagrams have been used as road maps to help understand the results of other tests. 

In a non-electrochemical method with N4 type complexes, Kimura et al. [50] detected volatile organic compounds using a Quartz Crystal Microbalance coated with SAM s of nanostructured macromolecular metal complexes of Co-Pc, Ni-Pc, Cu-Pc or Zn-Pc in the form of polymer brushes. The method was based on the highly hydrophilic character of the brushes and on their good performance as anion exchangers... 

Although on the basis of current-potential relationships important conclusions can be drawn regarding the mechanism of the electrode processes - especially if the experimental parameters are varied over a wide range - the use of combined electrochemical and non-electrochemical methods is inevitable to elucidate the mechanism of the complex electrode processes. As we will see later in this volume, a great variety of advanced electrochemical and in situ probes are available which give different types of information and therefore provide a better insight into the nature of the chemical events that occur during electrochemical reactions. The solid theoretical foundations and the relative simplicity of the final formulae and techniques make electroanalysis an attractive and powerful tool to obtain fast and reliable information on chemical systems. 

As mentioned previously, real surface area (RSA) of a catalyst is one of the most important parameters when it comes to its evaluation. Part of RSA which participates in electrochemical reaction is denoted as electrochemically active surface area (ESA or EASA). However, it should be noted that ESA is usually smaller than RSA (determined by some non-electrochemical method such as gas physisorption analysis, particle size measurement etc.) due to the possibility that entire surface of the electrocatalyst is not available to electrolyte. Hence, the ratio between ESA and RSA gives catalyst utilization. The ration between ESA and geometrical cross section of an electrode gives roughness factor (Rf). There are number of different approaches to determine RSA, both electrochemical and non-electrochemical, however one should note that when electrochemical method is used it is ESA what is determined. These methods are summarized and critically overviewed by Trasatti and Petrii [13], while following section will focus on specific electrochemical methods based on voltammetry. 

Given the absolute and increasing scale of production of nanomaterials allied to their uncertain effects on human health it is important that the presence of nanoparticles in the environment can be measured and monitored along with their chemical identification and concentration. The quantification of environmental nanoparticles represents a significant analytical challenge. In the next section (8.2), we veiy briefly outline existing non-electrochemical methods before considering in detail electrochemical alternatives in Sect. 8.3. 

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