Electrocatalysis/electrocatalytic

Like other ion-exchange polymers, conducting polymers have been used to immobilize electroactive ions at electrode surfaces. Often the goal is electrocatalysis, and conducting polymers have the potential advantage of providing a fast mechanism for electron transport to and from the electrocatalytic ions. 

As shown in Figure 9.31, butane is formed electrocatalytically (Ab t < 1) since no gaseous H2 is supplied, thus Abutis restricted to its electrocatalysis limits (tA negative potential region of electrocatalysis, electrochemically promoted formation of isomerization products continues with large A and p values (Fig. 9.31). 

Electrocatalysis refers to acceleration of a charge transfer reaction and is thus restricted to Faradaic efficiency, A, values between -1 and 1. Electrochemical promotion (NEMCA) refers to electrocatalytically assisted acceleration of a catalytic (no net charge-transfer) reaction, so that the apparent Faradaic efficiency A is not limited between -1 and 1. 

In electrocatalysis, the major subject are redox reactions occurring on inert, nonconsumable electrodes and involving substances dissolved in the electrolyte while there is no stoichiometric involvement of the electrode material. Electrocatalytic processes and phenomena are basically studied in aqueous solutions at temperatures not exceeding 120 to 150°C. Yet electrocatalytic problems sometimes emerge as well in high-temperature systems at interfaces with solid or molten electrolytes. 

Electrocatalytic reactions have much in common with ordinary (chemical) heterogeneous catalytic reactions, but electrocatalysis has certain characteristic special features ... 

Jarvi TD, Stuve EM. 1998. Fundamental aspects of vacuum and electrocatalytic reactions of methanol and formic acid on platinum surfaces. In Lipkowski J, Ross PN, eds. Electrocatalysis. New York Wiley-VCH. pp. 75-153. 

Figure 17.7 Electrocatalysis of O2 reduction by Pycnoporus cinnabarinus laccase on a 2-aminoanthracene-modified pyrolytic graphite edge (PGE) electrode and an unmodified PGE electrode at 25 °C in sodium citrate buffer (200 mM, pH 4). Red curves were recorded immediately after spotting laccase solution onto the electrode, while black curves were recorded after exchanging the electrochemical cell solution for enzyme-fiiee buffer solution. Insets show the long-term percentage change in limiting current (at 0.44 V vs. SHE) for electrocatalytic O2 reduction by laccase on an unmodified PGE electrode ( ) or a 2-aminoanthracene modified electrode ( ) after storage at 4 °C, and a cartoon representation of the probable route for electron transfer through the anthracene (shown in blue) to the blue Cu center of laccase. Reproduced by permission of The Royal Society of Chemistry fi om Blanford et al., 2007. (See color insert.)...

There have been a number of reports of electrocatalysis of alcohol oxidation using immobilized PQQ-dependent alcohol dehydrogenases or flavin-containing alcohol dehydrogenases or oxidases with dissolved mediators in solution. Co-immobihzing the mediator with the enzyme is advantageous, as set out in Section 17.1, and several such strategies have been employed for electrocatalytic alcohol oxidation. 

As mentioned in Section 5.1, adsorption of components of the electrolysed solution plays an essential role in electrode processes. Adsorption of reagents or products or of the intermediates of the electrode reaction or other components of the solution that do not participate directly in the electrode reaction can sometimes lead to acceleration of the electrode reaction or to a change in its mechanism. This phenomenon is termed electrocatalysis. It is typical of electrocatalytic electrode reactions that they depend strongly on the electrode material, on the composition of the electrode-solution interphase, and, in the case of single-crystal electrodes, on the crystallographic index of the face in contact with the solution. 

Dloxygen reduction electrocatalysis by metal macrocycles adsorbed on or bound to electrodes has been an Important area of Investigation (23 ) and has achieved a substantial molecular sophistication in terms of structured design of the macrocyclic catalysts (2A). Since there have been few other electrochemical studies of polymeric porphyrin films, we elected to inspect the dloxygen electrocatalytic efficacy of films of electropolymerized cobalt tetraphenylporphyrins. All the films exhibited some activity, to differing extents, with films of the cobalt tetra(o-aminophenylporphyrin) being the most active (2-4). Curiously, this compound, both as a monomer In solution and as an electropolymerized film, also exhibited two electrochemical waves... 

Efremov B.N., Tarasievich M.R. Electrocatalysis and Electrocatalytic Processes (in Russian). In Sbornik Nauchnykh Trudov (Collection of Sci. Transactions), Kiev Naukova Dumka, 1986 44-71. 

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. 

A remarkable progress has been made in the last several years in electrocatalysis on single crystal surfaces. This parallels the progress in surface science and it has been partly stimulated by developments in that field, mostly regarding the preparation and characterization of surfaces. New advances in preparation of surfaces outside of high vacuum, achieved in electrocatalytic studies, also helped this trend. 

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