Electrodes PIGE

As shown in Fig. 2.5, the cyclic voltammograms for Prussian blue attached to paraffin-impregnated graphite electrodes (PIGEs) in contact with aqueous electrolytes exhibit two well-defined one-electron couples. Prussian blue crystals possess a cubic structure, with carbon-coordinated Fe + ions and nitrogen-coordinated Fe + ions, in which potassium ions, and eventually some Fe + ions, are placed in the holes of the cubes as interstitial ions. The redox couple at more positive potentials can be described as a solid-state process involving the oxidation of Fe + ions. Charge conservation requires the parallel expulsion of K+ ions [77] ... 

Paraffin impregnated graphite electrode (PIGE) - electrode prepared from graphite rods by impregnation with melted paraffin under vacuum. These electrodes are not permeated by aqueous solutions and can be used for solution studies, as well as for immobilizing microparticles and microdroplets to study their electrochemistry. See also - carbon, - voltammetry of immobilized microparticles. 

The hardness of an electrode often limits the ability of a solid compound to adhere to an electrode surface. For example, fairly soft, flake-like materials, such as many organic compounds, will preferably adhere to a hard surface, e.g., that of a glassy carbon (GC) electrode, while hard solids such as oxides or minerals will adhere to a soft surface such as that of a paraffin-impregnated graphite electrode (PIGE). 

Rao, Jayalakshmi and coworkers have prepared NPs of SnO, SnS and ZnS in order to study their capacitance behavior [88-90]. The metal oxide and metal sulfide NPs were prepared using hydrothermal methods. After immobilization in PIGE electrodes, their electrochemical properties were examined. Capacitance values in the 4—15 Fg were reported for SnS. Comparable values were reported for ZnS. 

Fig. 12 ECL intensity-time curves obtained from continuous potential scanning over 10 cycles between 0 and 1.50 V versMS Ag/AgClinO.lO M TPrA-0.10 M PBS (pH 7.40) with a scan rate of 50mV/s at different electrodes (a) Au/MUA-Rul, (b) PIGE/4-ABSA-Rul without PCI5 activation, and (c) PIGE/4-ABSA-Rul with PCI5 activation. The PMT was biased at - 900 V. Reprinted with permission from Ref 94. Copyright (2010) American Chemical Society.

Usually, this is the case within a time span of 2 h. After ambient pressure has been established, the rods are removed from the melt before the paraffin solidifies. The warm electrodes are placed onto filter paper to allow them to cool and dry. The lower end of the electrode is carefully polished on smooth paper. This surface will later accommodate the solid particles to be studied. The electrodes are now ready for use. For easy cleaning, the PIGE is used without an insulation of its cylindrical surface, as will be described below. The upper end of the electrode is connected to the electrochemical instrument with an alligator clip. 

Fig. 4.8a-c Consecutive cyclic voltammetric curves obtained for 3-methylthiophene droplets attached to a paraffin-impregnated graphite electrode in the presence of an aqueous solution containing 0.5 moldm LiC104. Cycles a 1 to 4 (curves 2-5) b 5-14 c 15-24 and 25-34. Curve 7 shows the background current ofthe uncoated PIGE. Scan rate 100 mVs . (Reproduced from [131] with the permission of Elsevier Ltd.)... 

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