Carbon-paced electrodes

Garberoglio B, Inguaggiato B, Chinaglia B, Cerise O (1983) Initial results with an activated pyrolytic carbon tip electrode. Pacing Clin Electrophysiol 6(2 Pt 2) 440-448... 

IV. VOLTAMMETRY OF POWDERED ACTIVE CARBON ELECTRODES (PACE)... 

FIG. 7 (a) Overall view of the electrochemical cell 1, PACE 2, SCE 3, Pt reference, (b) Cross-section of the powdered acuve carbon electrode 1, carbon powder 2, Pt contact. (From Refs. 27 and 194.)... 

Thus the potential in the macropores is directly affected by transport and charging phenomena in the micropores accessible to electrolyte. These properties of active carbon render it a difficult material to use as an electrode. The large electrochemically active surface area leads to considerable double-layer charging currents, which tend to ob.scure faradic current features. The network of micropores in the electrode material might be expected to result in a significant ohmic effect, which would further impair the potential resolution (IR drop on electrode material) obtainable by PACE voltammetry. CV curves recorded with different masses (and sediment layer thicknesses) of powdered samples of selected carbons in various electrolyte solutions are presented in Fig. 8 as an example [194]. Where amounts of material were greater than 20 mg, the CVs recorded were of the same shape. 

It is expected that practical problems in using PACEs could arise as a result of electrical contacts between the sediment layer and the current collector, and with the mechanical durability of the electrode bed. The comparison of CVs for a Pt electrode and selected PACE (with the same current scale) is shown in Fig. 9 to illustrate the influence of Pt contact on the voltammograms recorded. Similar results were obtained using graphite, glassy carbon, or Au as contact materials... 

Variations in cathodic peak current with the square of the sweep rate [/p,.. = /(v -)] for. selected PACE/electrolyte systems are shown in Figs. 13a and 13b [194]. In all ca.ses the relation is linear and the correlation coefficient tends to unity, especially in the lower ranges of the potential sweep rates. In agreement with numerous researchers [7,9,14,16,24,26,132], we also suggest that the cathodic peak is due to the reduction of quinonelike groups, whereas the anodic wave is due to the oxidation of hydroquinonelike groups in different environments on the active carbon surface of the electrode. These reactions are faradic... 

Therefore the electrochemical response with porous electrodes prepared from powdered active carbons is much increased over that obtained when solid electrodes are used. Cyclic voltammetry used with PACE is a sensitive tool for investigating surface chemistry and solid-electrolyte solution interface phenomena. The large electrochemically active surface area enhances double layer charging currents, which tend to obscure faradic current features. For small sweep rates the CV results confirmed the presence of electroactive oxygen functional groups on the active carbon surface. With peak potentials linearly dependent on the pH of aqueous electrolyte solutions and the Nernst slope close to the theoretical value, it seems that equal numbers of electrons and protons are transferred. 

O2 also can be detected by cyt c-modified electrode [214], When cyt c was covalently attached to the modified electrode, the immobilized cyt c was used as an integral part of an amperometric O2 sensor. Superoxide generated by xanthine/XOD caused the one-electron reduction of cytochrome c to cytochrome c. The reduced protein was then reoxidized at the electrode surface. McNeil used this immobilization procedure to detect O2 production by stimulated human neutrophils [215]. The neutrophils that stimulated with phorbol-12 myristate-13 acetate (PMA) produced current changes that were cell number dependent. Fabian [216] used a platinized activated carbon electrode (PACE) to... 

As with pacing leads, the ICD lead cathode is a platinum, iridium, and titanium combination the electrode structure depends on whether fixation mechanism is passive with tines or active with a screw. In an active-fixation lead, the platinum-iridium screw is usually electrically active, but there are also models with both electrically active collar and helix or others with electrically silent helix and active carbon cathode collar. A platinum-iridium anode lies immediately behind the cathode in a true bipolar system. All models now elute steroids to reduce chronic threshold and prevent pacing threshold rise or exit block. 

Thuesen L, Jensen PJ, Vejby-Christensen H et al (1989) Lower chronic stimulation threshold in the carbon-tip than in the platinum-tip endocardial electrode a randomized study. Pacing Clin Electrophysiol 12(10) 1592-1595... 

Carbon monofluoride (CFx) is one such fluoride compound that today is used as a positive electrode material in Li batteries for a number of different applications. For example, they are used in certain types of heart failure devices - implantable cardiac resynchronization therapy pacemakers (CRT-P). CRT-P devices can pace the right atrium and right ventricle, but they are also capable of pacing the left ventricle. Pacing three chambers requires more power than a cell can deliver, so a different battery type is needed. Li/CFx cells were developed in response to the increased power required by CRT-P devices. Vagal nerve stimulator devices also use a Li/CFx cells. 

The activated carbon plays the role of an electrolyte supplier to provide sufficient H2SO4 in the inner plate when the diffusion of H2SO4 from plate surface cannot keep pace with the electrode reaction. 

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