Pt cathode

In electrogravimetry the analyte is deposited as a solid film on one electrode in an electrochemical cell. The oxidation of Pb +, and its deposition as Pb02 on a Pt anode is one example of electrogravimetry. Reduction also may be used in electrogravimetry. The electrodeposition of Cu on a Pt cathode, for example, provides a direct analysis for Cu +. 

Note that the Pt cathode is an inert electrode that carries electrons to the reduction half-reaction. The electrode itself does not undergo oxidation or reduction. 

Redox Electrodes Electrodes of the first and second kind develop a potential as the result of a redox reaction in which the metallic electrode undergoes a change in its oxidation state. Metallic electrodes also can serve simply as a source of, or a sink for, electrons in other redox reactions. Such electrodes are called redox electrodes. The Pt cathode in Example 11.1 is an example of a redox electrode because its potential is determined by the concentrations of Ee + and Ee + in the indicator half-cell. Note that the potential of a redox electrode generally responds to the concentration of more than one ion, limiting their usefulness for direct potentiometry. 

Selecting a Constant Potential In controlled-potential coulometry, the potential is selected so that the desired oxidation or reduction reaction goes to completion without interference from redox reactions involving other components of the sample matrix. To see how an appropriate potential for the working electrode is selected, let s develop a constant-potential coulometric method for Cu + based on its reduction to copper metal at a Pt cathode working electrode. 

By changing the enzyme and mediator, the amperometric sensor in Figure 11.39 is easily extended to the analysis of other substrates. Other bioselective materials may be incorporated into amperometric sensors. For example, a CO2 sensor has been developed using an amperometric O2 sensor with a two-layer membrane, one of which contains an immobilized preparation of autotrophic bacteria. As CO2 diffuses through the membranes, it is converted to O2 by the bacteria, increasing the concentration of O2 at the Pt cathode. 

Preparation of Memfield resin-bound nitro acetates, which is a suitable bndding block for the development of combinatorial solid phase synthesis, is repotted. The anion of ethyl nitro acetate is generated in DMF by an electrochemical method using Pt cathode, magnesium rod anode, and tetrabutylairunonium bromide as an electrolyte. Alkylaton of this anion with alkyl hahdes gives mono-alkylated products in 80% yield." ... 

Potassium Nitride. K3N, mw 131.31, N 10.67%, gm-blk cryst, mp 343°. ignites spontaneously in air. Effervesces violently with w quantitatively evolving ammonia. Prepd by heating K amide to redness in a closed vessel or by striking an arc between a Pt cathode and a K anode under liq nitrogen (Refs 1—3)... 

The electrochemical results suggested to explore the possibility of creating a C-C bond between the electrogenerated a-carbanion fi and carbon nucleophiles. Results of practical importance have hitherto been obtained upon electroreduction of 2-bromoisobutyramides in acetonitrile at Hg or Pt cathodes, in the presence of carbon dioxide and an alkylating agent. The enolate-amide fi undergoes quantitative carboxy-alkylation, to yield ester amides of 2,2-dimethylmalonic acid (ref. 16). 

Bouroushian M, Kosanovic T, Loizos Z, SpyreUis N (2000) On a thermodynamic description of Se(IV) electroreduction and CdSe electrolytic formation on Ni, Ti and Pt cathodes in acidic aqueous solution. Electrochem Commun 2 281-285... 

Hg cathode, undivided cell MeOH solvent + LiC104 Pt cathode, divided cell... 

One must realize that once complete metal deposition has been attained, the emf across the electrodes cannot be switched off before the cathode has been taken out of the solution and rinsed with water, otherwise the metal deposit may start to redissolv e in the solution as a consequence of internal electrolysis by the counter emf. After disconnection the electrode is rinsed with acetone and dried at 100-110° C for 3-4 min. The analytical result is usually obtained from difference in weight of the dry cathode before and after electrolysis. In a few instances a copper- or silver-plated Pt cathode or even an Ag cathode is used, e.g., Zn and Bi are difficult to remove entirely from Pt, as they leave black stains and on heating form an alloy with the noble metal for this and other reasons (see below) the experimenter should consult the prescriptions in handbooks149. 

Similar results of photoelectrolysis of water in cells with n-type SrTi03 single-crystal anode and platinized Pt cathode were reported around the same time in a preliminary communication by Mavroides et al. [53] who measured the maximum quantum efficiency... 

Radhakrishnan R, Virkar AV, and Singhal SC. Estimation of charge-transfer resistivity of Pt cathode on YSZ electrolyte using patterned electrodes. J. Electrochem. Soc. 2005 152 A927-A936. 

Pt cathode graphite or Pt anode NaOMe in MeOH -20°C, 75% yield... 

MeOH—Et4NOTs—NH4CI Divided ceii-constant current (Pt cathode)... 

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