Electrodes electrocatalytic properties

Intensive research on the electrocatalytic properties of polymer-modified electrodes has been going on for many years Until recently, most known coatings were redox polymers. Combining redox polymers with conducting polymers should, in principle, further improve the electrocatalytic activity of such systems, as the conducting polymers are, in addition, electron carriers and reservoirs. One possibility of intercalating electroactive redox centres in the conducting polymer is to incorporate redoxactive anions — which act as dopants — into the polymer. Most research has been done on PPy, doped with inter alia Co 96) RyQ- 297) (--q. and Fe-phthalocyanines 298,299) Co-porphyrines Evidently, in these... 

The Effect of Structurally Well-Defined Pt Modification on the Electrochemical and Electrocatalytic Properties of Ru(0001) Electrodes... 

The influence of Pt modihcations on the electrochemical and electrocatalytic properties of Ru(OOOl) electrodes has been investigated on structurally well-defined bimetallic PtRu surfaces. Two types of brmetalhc surfaces were considered Ru(OOOl) electrodes covered by monolayer Pt islands and monolayer PtRu/Ru(0001) surface alloys with a highly dispersed and almost random distribution of the respective surface atoms, with different Pt surface contents for both types of structures. The morphology of these surfaces differs significantly from that of brmetaUic PtRu surfaces prepared by electrochemical deposition of Pt on Ru(0001), where Pt predominantly exists in small multilayer islands. The electrochemical and electrocatal5d ic measurements, base CVs, and CO bulk oxidation under continuous electrolyte flow, led to the following conclusions ... 

Another type of model electrode uses multilayer electrolytic deposits, which attracted the interest of electrochemists long before physical methods for their structural characterization were introduced. These electrodes were usually characterized by their roughness factors rather than particle size, the former being of the order of 10 -10 (for original references, see the review [Petrii and Tsirhna, 2001]). Multilayer electrolytic deposits have very complex stmctures [Plyasova et al., 2006] consisting of nanometer-sized crystallites joined together via grain boundaries, and hence have very pecuhar electrocatalytic properties [Cherstiouk et al., 2008] they will not be considered further in this chapter. 

Takasu Y, Eujii Y, Yasuda K, Iwanaga Y, Matsuda Y. 1989. Electrocatalytic properties of ultra-fine platinum particles for hydrogen electrode reaction in an aqueous solution of sulfuric acid. Electrochim Acta 34 453-458. 

The first CNT-modified electrode was reported by Britto et al. in 1996 to study the oxidation of dopamine [16]. The CNT-composite electrode was constructed with bro-moform as the binder. The cyclic voltammetry showed a high degree of reversibility in the redox reaction of dopamine (see Fig. 15.3). Valentini and Rubianes have reported another type of CNT paste electrode by mixing CNTs with mineral oil. This kind of electrode shows excellent electrocatalytic activity toward many materials such as dopamine, ascorbic acid, uric acid, 3,4-dihydroxyphenylacetic acid [39], hydrogen peroxide, and NADH [7], Wang and Musameh have fabricated the CNT/Teflon composite electrodes with attractive electrochemical performance, based on the dispersion of CNTs within a Teflon binder. It has been demonstrated that the electrocatalytic properties of CNTs are not impaired by their association with the Teflon binder [15]. 

Clays are usually cation-exchangeable aluminosilicates, and exfoliated clay particles have a platelet shape with nanoscopic size. Cast protein-clay films on electrodes have been used to immobilize proteins. The Clay/Mb electrode has good electrocatalytic properties for the reduction of oxygen and hydrogen peroxide [236] and the biosensors can also be made based on these properties. 

A. Salimi, E. Sharifi, A. Noorbakhsh, and S. Soltanian. Direct voltammetry and electrocatalytic properties of haemoglobin immobilized on a glassy carbon electrode modified with nickel oxide nanoparticles. Electrochem. Commun. 8, 1499-1508 (2005). 

Rosalbino F., Maccio D., Angelini E., Saccone A., Delfino S., Electrocatalytic properties of Fe-R (R = rare earth metal) crystalline alloys as hydrogen electrodes in alkaline water electrolysis, ]. Alloys Compd., 403(1-2), 275-282,2005. 

The formation of Au-OHad or surface oxides on gold in alkaline electrolyte was in fact proposed to explain some of the electrocatalytic properties observed for a gold electrode (e.g., incipient hydrous oxide/adatom mediator model ). Our previous measurement of the interfacial mass change also indicated the formation of Au oxides (AU2O3, AuOHorAu(OH)3) on gold nanoparticle surfaces. A detailed delineation of the catalytic mechanism is part of our on-going work. 

Phthalocyanine complexes are organic macrocycles with 18 7t-electrons, structurally resembling the naturally-occuring porphyrins complexes [1-3], Electrodes modified with transition metal (notably Fe, Co, Mn, Ni) phthalocyanine (MPc, Fig.l) complexes have continued to generate immense research interests because of their well-established electrocatalytic properties [3-6],... 

The adsorption and oxidation of hydrazine on electrodispersed and electro-faceted Pt electrodes [27] furnish another interesting example for the influence of crystalline surface composition on the electrocatalytic properties of the electrode. 

In the present chapter devoted to the electrochemistry of POMs, our purpose is not to provide an exhaustive review of all the papers in which some electrochemical aspects of POMs intervene, but rather to emphasize the fundamental principles that govern the vast majority, if not all, of the electron transfer behaviors of these chemicals at electrodes and help to explain their electrocatalytic properties. As... 

Pb Lead, and particularly underpotentially deposited Pb, exhibits electrocatalytic properties in numerous electrode processes. The model reaction can be oxygen reduction with slow step of peroxide reduction ]374-376] or reduction of nitrobenzene and other nitrocompounds [377, 378]. In the case of... 

According to the presented model of oxides formation on Au, the outer surface of the thick oxide film exposed to the solution is either AU2O3 or Au(OH)3. The type of oxide determines the surface electronic structure and electrocatalytic properties. Electrocatalytic properties of gold oxide-covered electrodes have been discussed by Burke and Nugent [366, 368]. 

There are certain combinations of electrode materials, solvents and operating conditions, which allow the reduction of C02 to afford hydrocarbons. It was concluded in a comparative study using many different metal electrodes in aqueous KHCO3 solution that either CO (Ag, Au) or formic acid (In, Sn, Hg, Pb) are produced as a result of the reduction of C02, and Cu has the highest electrocatalytic activity for the production of hydrocarbons, alcohols, and other valuable products.137 Most of the studies, since the mid-1990s, consequently, have focused on the further elucidation of electrocatalytic properties of copper. 

At the equilibrium potential, both anodic and cathodic processes of a single electron transfer reaction take place at the same exchange rate (exchange current density) and no net current is observed through the external circuit. The exchange rate reflects the kinetics of the overall reaction and, in many cases, the electrocatalytic properties of the electrode surface. The open circuit potential, in this case, is the equilibrium potential and is therefore a thermodynamic quantity independent of kinetic factors and is related to the activities in solution through the Nemst law. 

The selective facilitation of the charge transfer of the species of interest is called electrocatalysis. In such a case, the species of interest are transformed at energies substantially lower than those of the interferants. The higher selectivity therefore implies a lower applied potential at the modified working electrode, which exhibits such selective electrocatalytic properties. In such a situation, the choice of the... 

Raney Ni with additives is also used [77, 276]. In particular, valve metals are added to stabilize the catalyst structure [102,410, 411], thus decreasing the recrystallization and sintering which always takes place as the solution temperature is raised [412] (which points to the high energy state of such an electrode structure). In this respect, potential cycling has also been observed to be detrimental since it can induce recrystallization [407]. This is probably the reason why surface oxidation may be deleterious with Raney structures [390] while it normally results in improved electrocatalytic properties with bulk Ni electrodes [386]. However, after prolonged cathodic load resulting in deactivation, Raney Ni electrodes can be reactivated (temporarily) by means of anodic sweeps [405]. 

The surface area is a function of the temperature of preparation of the oxides [169, 486]. Thus, the apparent electrocatalytic activity decreases with increasing temperature of calcination (which is usually in the range 350°-500 °C) [227, 475]. However, if the calcination is carried out at too high temperature, the electrode surface is deactivated probably as a consequence of some dehydration, and the observed Tafel slope can be very high [487], The important relationship between the acid-base properties of an oxide surface in solution and its electrocatalytic properties has been pointed out by the present author [488]. 

A common observation in most cases is that the surface of amorphous alloys, especially those containing Ti, Zr and Mo, is largely covered with inactive oxides which impart low electrocatalytic properties to the material as prepared [562, 569, 575], Activation is achieved by removing these oxides either by prepolarization or, more commonly and most efficiently, by leaching in HF [89, 152, 576]. Removal of the passive layer results in a striking enhancement of the electrocatalytic activity [89], but surface analysis has shown [89, 577] that this is due to the formation of a very porous layer of fine particles on the surface (Fig. 32). A Raney type electrode is thus obtained which explains the high electrocatalytic activity. Therefore, it has been suggested [562, 578] that some amorphous alloys are better as catalyst precursors than as catalysts themselves. However, it has been pointed out that the amorphous state appears to favor the formation of such a porous layer which is not effectively formed if the alloy is in the crystalline state [575]. 

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