Electrocatalysis application

Conducting polymers have found applications in a wide variety of areas,44 45 and many more have been proposed. From an electrochemical perspective, the most important applications46 appear to be in batteries and supercapacitors 47,48 electroanalysis and sensors49-51 electrocatalysis,12,1, 52 display and electrochromic devices,46 and electromechanical actuators.53... 

Detailed and shorter39 45 reviews of the electrochemical promotion literature prior to 1996 have been published, mainly addressed either to the catalytic or to the electrochemical community. Earlier applications of solid electrolytes in catalysis, including solid electrolyte potentiometry and electrocatalysis have been reviewed previously. The present book is the first on the electrochemical activation of catalytic reactions and is addressed both to the electrochemical and catalytic communities. We stress both the electrochemical and catalytic aspects of electrochemical promotion and hope that the text will be found useful and easy to follow by all readers, including those not frequently using electrochemical, catalytic and surface science methodology and terminology. 

In the first part of the present review, new techniques of preparation of modified electrodes and their electrochemical properties are presented. The second part is devoted to applications based on electrochemical reactions of solute species at modified electrodes. Special focus is given to the general requirements for the use of modified electrodes in synthetic and analytical organic electrochemistry. The subject has been reviewed several times Besides the latest general review by Murray a number of more recent overview articles have specialized on certain aspects macro-molecular electronics theoretical aspects of electrocatalysis organic applicationssensor electrodes and applications in biological and medicinal chemistry. 

These conclusions from the infrared reflectance spectra recorded with Pt and Pt-Ru bulk alloys were confirmed in electrocatalysis studies on small bimetallic particles dispersed on high surface area carbon powders.Concerning the structure of bimetallic Pt-Ru particles, in situ Extended X-Ray Absorption Fine Structure (EXAFS>XANES experiments showed that the particle is a true alloy. For practical application, it is very important to determine the optimum composition of the R-Ru alloys. Even if there are still some discrepancies, several recent studies have concluded that an optimum composition about 15 to 20 at.% in ruthenium gives the best results for the oxidation of methanol. This composition is different from that for the oxidation of dissolved CO (about 50 at.% Ru), confirming a different spatial distribution of the adsorbed species. 

At present, most workers hold a more realistic view of the promises and difficulties of work in electrocatalysis. Starting in the 1980s, new lines of research into the state of catalyst surfaces and into the adsorption of reactants and foreign species on these surfaces have been developed. Techniques have been developed that can be used for studies at the atomic and molecular level. These techniques include the tunneling microscope, versions of Fourier transform infrared spectroscopy and of photoelectron spectroscopy, differential electrochemical mass spectroscopy, and others. The broad application of these techniques has considerably improved our understanding of the mechanism of catalytic effects in electrochemical reactions. 

Apart from the study of physicochemical aspects such as ion solvation, and bio-mimetic aspects such as photosynthesis or carrier-mediated ion transfer (Volkov et al., 1996, 1998), there are several areas of potential applications of electrochemical IBTILE measurements comprising electroanalysis, lipophilicity assessment of drugs, phase transfer catalysis, electro-assisted extraction, and electrocatalysis. 

Chang SC, Ho Y, Weaver MJ. 1992. Applications of real-time infrared spectroscopy to electrocatalysis at bimetallic surfaces. I. Electrooxidation of formic acid and methanol on bismuth-modified platinum (111) and platinum (100). Surf Sci 265 81-94. 

Nevertheless, in applications relevant for electrocatalysis and reactions that occur at solid-liquid interfaces, it has been essential to develop a methodology that can provide detailed insight into the surface and near-surface stmcture during the course of reaction. For that purpose, the in sim SXS diffraction technique, depicted in... 

Summing up this section, we would like to note that understanding size effects in electrocatalysis requires the application of appropriate model systems that on the one hand represent the intrinsic properties of supported metal nanoparticles, such as small size and interaction with their support, and on the other allow straightforward separation between kinetic, ohmic, and mass transport (internal and external) losses and control of readsorption effects. This requirement is met, for example, by metal particles and nanoparticle arrays on flat nonporous supports. Their investigation allows unambiguous access to reaction kinetics and control of catalyst structure. However, in order to understand how catalysts will behave in the fuel cell environment, these studies must be complemented with GDE and MEA tests to account for the presence of aqueous electrolyte in model experiments. 

As we demonstrate in this chapter, enzymes can be extremely active electrocatalysts at ambient temperatures and mild pH, and have significantly higher reaction selectivity than precious metals. The main disadvantage in applying redox enzymes for electrocatalysis arises from their large size, which means that the catalytic active site density is low. Enzymes also have a relatively short hfetime (usually not more than a few months), making them more suited to disposable applications. 

The choice of immobilization strategy obviously depends on the enzyme, electrode surface, and fuel properties, and on whether a mediator is required, and a wide range of strategies have been employed. Some general examples are represented in Fig. 17.4. Key goals are to stabilize the enzyme under fuel cell operating conditions and to optimize both electron transfer and the efficiency of fuel/oxidant mass transport. Here, we highlight a few approaches that have been particularly useful in electrocatalysis directed towards fuel cell applications. 

Fuel cells based on unmediated electrocatalysis by heme-containing sugar dehydrogenases have not yet been tested in biological fluids, but may be useful for implantable applications, as they avoid the need for toxic or expensive mediators and have minimal design constraints. Realistically, the lifetime of biofuel cells is still insufficient for biomedical applications requiring surgical installation. 

Modification of electrodes by electroactive polymers has several practical applications. The mediated electron transfer to solution species can be used in electrocatalysis (e.g. oxygen reduction) or electrochemical synthesis. For electroanalysis, preconcentration of analysed species in an ion-exchange film may remarkably increase the sensitivity (cf. Section 2.6.4). Various... 

The mechanism of the cocatalytic effect is still a matter of investigation. For most of the systems of interest in electrocatalysis, data for characterization of the surface by means of spectroscopic UHV methods are still missing. Also measurements of changes in the electronic properties of the metal in the presence of adatoms in addition to more intensive application of in situ and on-line methods are desirable for a systematic search of new catalytic materials. 

Trasatti, S. (ed.) (2003) Electrocatalysis from theory to industrial applications. Electrochim. Acta, 48, 3727-3974. 

Guo, L., Huang, Q., Li, X. and Yang, S. (2001) Iron nanoparticles synthesis and applications in surface enhanced Raman scattering and electrocatalysis. Physical Chemistry Chemical Physics, 3, 1661-1665. 

The aim of this overview is first to present the general principles of electrocatalysis by metal complexes, followed by a series of selected examples published over the last 20 years illustrating the major electrochemical reactions catalyzed by metal complexes and their potential applications in synthetic and biomimetic processes, and also in the development of sensory devices. The area of metal complex catalysts in electrochemical reactions was reviewed in 1990.1... 

Electrocatalysis with nickel-bpy complexes has been shown useful for synthetic applications,202,211 especially when used in combination with the sacrificial anode process in an undivided cell (Equation (45)).207,211 Under these very simple experimental conditions, efficient nickel catalysts can be also generated in the presence of the cheap pyridine ligand.212... 

Electrocatalysis in oxidation has apparently first been shown for ascorbic acid oxidation by Prussian blue [60] and later by nickel hexacyanoferrate [61]. More valuable for analytical applications was the discovery in the early 1990s of the oxidation of sulfite [62] and thiosulfate [18, 63] at nickel [62, 63] and also ferric, indium, and cobalt [18] hexacyanoferrates. More recently electrocatalytic activity in thiosulfate oxidation was shown also for zinc [23] hexacyanoferrate. Prussian blue-modified electrodes allowed sulfite determination in wine products [64], which is important for the wine industry. 

J. H. Zagal, in Handbook of Fuel Cells—Fundamentals, Technology and Applications , eds. W. Vielstich, H. Gasteiger and A. Lamm, John Wiley Sons, Ltd, 2003, vol. 2 Electrocatalysis. 

---