Electrochemically assisted modification

Another type of electrochemically-assisted modification reaction that has become popular in recent years for controlling the surface chemistry of sp ... 

There are two categories of covalent modification schemes for carbon electrodes (1) chemical and (2) electrochemically assisted. Common functional groups on carbon electrodes include carboxylic acids, alcohols, and ketones. Most chemical methods employ carboxylic acid or hydroxyl groups, while electrochemically assisted modification can occur by direct reactions with aromatic surface carbon atoms. 

A powerful strategy to covalently derivatize carbon electrodes with monolayers and multilayers utilizes electrochemical reactions (75). Electron transfer is used to activate a heterogeneous chemical reaction. The adlayer is formed after generating the highly reactive species by oxidation or reduction of the solution-based molecule or a surface-based functional group. In most electrochemically assisted modification schemes, the reaction involves a carbon radical. 

Electrochemically assisted modification of carbon electrodes has been accomplished by oxidation of amines (80, 81) and arylacetates (82), reduction of aryl diazonium salts (83), and anodization (oxidation) in a solution with alcohols (75). Of these schemes, reduction of diazonium salts, shown in Figure 8.11, provides a particularly convenient pathway for carbon electrode modification. 

A novel, electrochemically assisted method of obtaining semiconductor quantum dots supported on a surface has been introduced by Penner and his group [123], It comprised a hybrid electrochemical/chemical (E/C) process consisting of electrochemical deposition followed by chemical modification and it was described as a general, rapid, and low-cost solution-phase method for synthesizing supported Q-dots of metal salts. 

Downard AJ (2000) Electrochemically assisted covalent modification of carbon electrodes. Electroanalysis 12 1085-1096. 

One strategy that has become popular in recent years for controlling the chemistry of sp carbon electrodes involves electrochemically-assisted derivati-2ation. This field was recently reviewed by Downard [45], so only a brief synopsis is given herein. This relatively versatile chemical modification strategy involves either the oxidation or reduction of a precursor molecule to form a solution radical species at the electrode-electrolyte interface. This radical species then rapidly reacts at the surface to form a covalently attached admolecule. A wide range of molecules have been... 

This chapter will carefully differentiate situations in which coordination of metal ions assists in the achievement of specific electrochemical aims from experiments designed to study the electrochemistry of coordination compounds. (For information on the latter topic, see, particularly, Chapters 8.1-8.3). Two major areas have been selected for consideration one almost classical, namely the electrodeposition of metals, the other of more recent origin, namely the modification of electrode surfaces. 

Modification of semiconductor electrode response with adsorbed or attached dye molecules is an attractive alternative to other photoelectrochemical systems (7-13). Metal oxides which are stable or have very low corrosion rates but are transparent to visible wavelength light can be used in light-assisted electrochemical reactions when modified with monolayers and multilayers of a wide variety of chromophores interposed between the electrode and electrolyte. With one exception, the initial reports of energy conversion efficiencies of electrodes with adsorbed dyes was disappointingly low. Recently however,... 

The complexity of the reaction rate transients, which consist of one fast and one slow stage, is in agreement with the cyclic voltammetric evidence abont the existence of differently accessible regions for surface charging. The first rapid step (a) is believed to be dne to accumulation of promoting species over the gas-exposed catalyst surface by the mechanism of backspillover, while the second step (b) is due to current-assisted chemical surface modification. Since no correlation between potential transients and reaction rate transients was manifested, a dynamic approach is justified and the applied current —rather than the catalyst overpotential— may be an appropriate parameter to describe the transient behavior of ethylene combustion rate at electrochemically promoted Ir02AfSZ film catalysts. For the interpretation of the fast transient steps (a) and (c), a dynamic model of electrochemical promotion has been developed, as presented in detail in Section 11.3. 

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