Electrode porous graphite

The H2/O2 fuel cell uses inert electrodes (porous graphite containing platinum as a catalyst, for example). A solution of phosphoric acid, or some other acid, serves as electrolyte. The reaction between oxygen and hydrogen is spontaneous and the fuel cell therefore provides electric power. The current is directly proportional to the number of moles of H2 and O2 that react at the electrodes, with n = 4 and n = 2 for oxygen and hydrogen, respectively ... 

Working electrodes made of other materials such as the ultratrace graphite electrode (porous graphite structure impregnated with epoxy resin, produced by Metrohm, Switzerland), have much shorter lead-in times. The relatively rapid response of this kind of electrode arises from its semimicro electrode properties [48]. 

Webb et al. [56] determined free penicillamine in the plasma of rheumatoid arthritis patients. Plasma ultrafiltrate was mixed with trichloroacetic acid and 4-aminobenzoic acid as internal standards, and HPLC mobile phase to determine total reduced penicillamine. Plasma was vortexed with trichloroacetic acid, the precipitated protein was removed after 15 min by centrifuging, and the supernatant solution was filtered and mixed with 4-aminobenzoic acid. In each instance, a 50-pL portion of solution was analyzed on a 25-cm column of Spherisorb-NH2 (5 pm) at 25 °C, with an electrochemical detector having dual porous graphite electrodes set at... 

Figure 2. The concept of using additives of Si (or Sn) in the negative electrode a) the beginning of charge b) the end of charge. 1 and 3 - elastic porous graphite (or alloy) matrix with Li+ ions the particle of Si (or Sn) before (2) and after Lt ions intercalations.

Porous catalytic pellets, 25 271-272 Porous electrodes, 3 428-429 Porous glass, 22 394 Porous graphite, 12 747 Porous hydrogels, for tissue engineering, 13 750-751... 

In coulometric detectors, the eluent flows through a porous graphite electrode such that, in theory, 100% of any electroactive species will undergo electrolytic conversion. As a result, this significantly increases the detection sensitivity, as the surface area is relatively large. 

Figure 19.5—Amperometric detection in HPLC and CE. a) Two models of amperometric detection are shown. The working electrode, made of porous graphite with a large surface area, operates under coulometric conditions. The flow of the mobile phase at the working electrode ensures renewal of electroactive species b) expanded diagram of the end of the capillary in CE. Ions exiting the capillary impinge on the working electrode, which is placed on the cathodic side of the instrument. The complete detection cell is not shown.

Development of chlorine electrode materials has benefited from the experience of chlor-alkali electrolysis cell technology. The main problem is to find the best compromise between cycle life and cost. Porous graphite, subjected to certain proprietary treatments, has been considered a preferable alternative to ruthenium-treated titanium substrates. The graphite electrode may undergo slow oxidative degradation, but this does not seem to be a significant process. 

Fig. 14 Analytical HPLC of the phylloquinone fraction from an extracted sample of brown rice isolated by semipreparative HPLC. Column, Spherisorb C8 (octyl) mobile phase, methanol/50 mM acetate buffer pH 3.0 (97 3) containing 0.1 mM EDTA, dual-electrode coulometric detection (redox mode), porous graphite electrodes, — 1.5 V (generator electrode), +0.05 V (detector electrode). The arrows signify the fraction containing tritiated phylloquinone 2,3-epoxide (internal standard) and phylloquinone (analyte) that is collected for quantitation by radioisotopic dilution. (Courtesy of M. J. Shearer.)...

MeOH/50 mM acetate buffer pH 3.0, 97 3 containing 0.1 mM EDTA Dual-electrode coulometric detection (redox mode), porous graphite electrodes,... 

Dual-electrode coulometric detection (redox mode), porous graphite electrodes ... 

The porous graphitic carbon electrode also facilitates the construction of electrode arrays. In use, the porous electrode offers such a large surface area to the solute that 100% of the material is reacted. 

The Coulometric Electrode System Employing Porous Graphitic Carbon Electrodes Courtesy ESA Inc. 

The absence of a chromophore for sensitive detection is a problem which is met with HPLC determination of these thiol analytes. However, two approaches are possible to resolve this point 1) direct detection using electrochemistry, either amperometry on gold/mercury amalgamated electrodes or coulometry on porous graphite electrodes ... 

The kinetics of the hydrogen electrode reaction on dense porous graphite electrodes in molten KHSO4 from 245° C to 280°C [88-90] showed that the cathodic and anodic reactions are not strictly conjugated processes. The cathodic reaction was discussed in terms of conventional mechanisms, but the anodic reaction involves the simultaneous oxidation of hydrogen and graphite surface. The reaction exhibits a one-half power dependence on hydrogen pressure. 

Balskus, E.J., Triaca, W.E., and Arvia, A.J. (1972). Hydrogen evolution and dissolution on graphite electrodes in molten potassium bisulphate. II. Kinetics and mechanism of the reactions on porous graphite. Electrochim. Acta, 17, 45-62. 

For preparation of the GOD electrode a highly porous graphite foil of 1 mm thickness (Union Carbide, USA) is oxidized in air at 100°C. A 0.1 mol/1 l,l -dimethylferrocene solution in toluene is dropped onto the electrode and the solvent allowed to evaporate. GOD is covalently bound to the oxidized carbon surface by carbodiimide coupling and the surface is covered by a polycarbonate membrane of 0.03 pm thickness. Before use, the electrode is conditioned in 7 mmol/1 glucose solution for 10 h with an applied potential of + 160 mV. 

Extensive testing of metal sulfide electrode materials was performed in cells of the type shown in Figure 1. The metal sulfide electrode case and current take-off rod were made of dense graphite to avoid any contact and possible contamination of the active material by metallic constituents. The active material (metal sulfide powder in a porous graphite matrix or a mixture of metal sulfide and graphite powder) was contained in the cavity (2.5 cm in diameter X 0.6 cm deep) of the dense graphite electrode case. A porous ceramic separator was placed over the active material and secured with high purity alumina pins. 

Detector E, ESA Coulochem model 5100 A, two porous graphite working electrodes and associated palladium reference electrodes, +0.55 V for first electrode, +0.70 V for second (monitoring) electrode... 

Detector E, Environmental Sciences Associates Model 5100, porous graphite electrode W1 900 mV W2 400 mV, difference in electrolysis current monitored... 

Detector E, ESA Coulochem 5100-A, guard cell 1.0 V, dual porous graphite electrode 0.85 and 0.95 V... 

The most popular electrode materials are glassy carbon and porous graphite, since they have a large potential range (about — l.OV to +1.2V vs. Ag/ AgCl) with good chemical and mechanical resistance. 

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