Electrochemical activity electroplated

Galvanic cells in which stored chemicals can be reacted on demand to produce an electric current are termed primary cells. The discharging reaction is irreversible and the contents, once exhausted, must be replaced or the cell discarded. Examples are the dry cells that activate small appliances. In some galvanic cells (called secondary cells), however, the reaction is reversible that is, application of an electrical potential across the electrodes in the opposite direction will restore the reactants to their high-enthalpy state. Examples are rechargeable batteries for household appliances, automobiles, and many industrial applications. Electrolytic cells are the reactors upon which the electrochemical process, electroplating, and electrowinning industries are based. 

Various methods have been suggested to deposit a thin active layer of material on a support. Those most commonly employed are (i) electroplating (ii) thermal decomposition (iii) in situ formation. Pigmented Ni matrixes have also been proposed [508]. As one can expect, a range of activation has been observed the electrochemical and mechanical stability is also varied. As for the nature of the active material, it seems clear that Ni-Mo based materials show superior qualities. The... 

Ratajewicz and co-workers have also studied the effect of a ultrasonic field on electrode polarization and activation energy in zinc electroplating [96], The conclusion from their work was that the zinc electrochemical reduction reaction was influenced by the presence of organic additives, especially CN ions, and that in the presence of ultrasound the cathode fouling is reduced. 

The thin layer of tin on tin-plated steel cans is less easily oxidized than iron, and it protects the steel underneath from corrosion. It is deposited either by dipping the can into molten tin or by electroplating. Copper is also less active than iron (see Table 21-2). It is sometimes deposited by electroplating to protect metals when food is not involved. Whenever the layer of tin or copper is breached, the iron beneath it corrodes even more rapidly than it would without the coating, because of the adverse electrochemical cell that is set up. 

SECTION 20.9 An electrolysis reaction, which is carried out in an electrolytic cell, employs an external source of electricity to drive a nonspontaneous electrochemical reaction. The current-carrying medium within an electrolytic ceU may be either a molten salt or an electrolyte solution. The products of electrolysis can generaUy be predicted by comparing the reduction potentials associated with possible oxidation and reduction processes. The electrodes in an electrolytic ceU can be active, meaning that the electrode can be involved in the electrolysis reaction. Active electrodes are important in electroplating and in metaUuigical processes. 

Because of the unique properties of lead to exist in three valence states (metal, ion with +2 charge, and ion with a +4 charge), lead is used not only for electrochemical anodes to electroplate other metals from sulfuric acid solution but also to serve as anode, cathode, and active material in lead acid storage batteries. Storage batteries represent over 60% of lead usage worldwide and over 80% of lead usage in the United States. Electrowinning anodes and batteries are two of the unique successes of lead product development efforts. 

For a platinized Pt-based Clark-type NO microsensor (13), the surface of a bare Pt disk electrode is electrochemically platinized by cyclic voltammetry in a platinizing solution (3% chloroplatinic acid in water). As the potential is scanned (from -t-0.6 to -0.35 V vs. Ag/AgCl) using cycUc voltammetry (see Chapter 11), Pt(TV) ions are electroplated on the bare Pt disk electrode to create a porous and roughened electrode surface. The platinized Pt electrode has a larger active surface area as demonstrated by the larger recorded currents and lower detection limits for NO measurements compared with bare Pt electrodes as shown in Figme 6.3.10.1. 

In this two-electrode system, the cardiac tissue behaved electrochemically as the electrolyte in a simple electroplating cell. While stainless steel is passive under recording conditions, it loses its passivity in the chronic, active state (Evans, 1960). Rowley also reported that spectrographic analysis of tissue excised from the positive electrode region showed that metal ions from the electrode had migrated into the myocardial tissue. He showed from a theoretical Faradaic calculation that a 10-mg iron electrode placed in an ionic medium would be electrolyzed in 19 days by a 90-per-min, 1.5-msec-duration, 10-mA unidirectional stimulus. This and other problems associated with electrodes for myocardial and endocardial chronic implantation have been discussed by Greatbach and Chardack (1968). Hallen et al (1965) have also examined the problem. 

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