Platinum electrodes conductivity

To measure the conductivity of a solution it is placed in a cell carrying a pair of platinum electrodes which are firmly fixed in position. It is usually very difficult to measure precisely the area of the electrodes and their distance apart, and so if accurate conductivity values are to be determined, the cell constant must be evaluated by calibration with a solution of accurately known conductivity,... 

Figure 4. Log intensity vs. potential plots (Tafel plots) obtained from the voltammograms of a platinum electrode submitted to a 2 mV s l potential sweep polarized in a 0.1 M LiC104 acetonitrile solution having different thiophene concentrations. (Reprinted from T. F. Otero and J. Rodriguez, Parallel kinetic studies of the electrogeneration of conducting polymers mixed materials, composition, and kinetic control. Electrochim, Acta 39, 245, 1994, Figs. 2, 7. Copyright 1997. Reprinted with permission from Elsevier Science.)...

The existence of materials now included among the conducting polymers has long been known. The first electrochemical syntheses and their characterization as insoluble systems took place well over a century ago. In 1862 Letheby reported the anodic oxidation of aniline in a solution of diluted sulphuric acid, and that the blue-black, shiny powder deposited on a platinum electrode was insoluble in HjO, alcohol, and other organic solvents. Further experiments, including analytical studies, led Goppelsroeder to postulate in 1876 that oligomers were formed by the oxidation of aniline. 

The first reported electroorganic synthesis of a sizeable amount of material at a modified electrode, in 1982, was the reduction of 1,2-dihaloalkanes at p-nitrostyrene coated platinum electrodes to give alkenes. The preparation of stilbene was conducted on a 20 pmol scale with reported turnover numbers approaching 1 x 10. The idea of mediated electrochemistry has more frequently been pursued for inorganic electrode reactions, notably the reduction of oxygen which is of eminent importance for fuel cell cathodes Almost 20 contributions on oxygen reduction at modified... 

In contrast with these active electrodes, a passive electrode conducts electrons to and from the external circuit but does not participate chemically in the half-reactions. Figure 19-8 shows a redox setup that contains passive electrodes. One compartment contains an aqueous solution of iron(III) chloride in contact with a platinum electrode. Electron transfer at this electrode reduces Fe " (a q) to Fe " ((2 q) ... 

The glass tubes contain mercury and are firmly fixed in the ebonite cover of the cell so that the distance between the electrodes may not change during the experiment. Contact with the platinum electrodes is made by dipping the copper wires of the circuit in the mercury contained in the tubes. The coating of the electrodes with platinum black is carried out in order to inhibit polarization. When examining certain electrolytes, platinized electrodes cannot be used since platinum black may catalyze the decomposition or the oxidation of the electrolyte. The cell is maintained at constant temperature thermostatically, as conductivity increases rather significantly with temperature. 

Let the electrolysis of dilute sulfuric acid (so-called electrolysis of water) with a platinum cathode and a platinum anode be considered next. Pure water is a very weak electrolyte and consequently a very poor conductor of electricity. It dissociates very slightly into H+ ions (it may be recalled that in fact, H+ ions does not remain as such but forms hydronium in H30+ by combining with a molecule of water, H+ + H20 H30+) and OFT ions. In the presence of little sulfuric acid (or for that matter any other strong electrolyte) the conductivity, i.e., ionization is greatly increased. The acidified water now contains H+ ions, OFT and SC3 ions. During electrolysis with platinum electrodes, H+ ions are attracted to the cathode, where each ion gains an electron and becomes a hydrogen atom ... 

During measurement, the conductivity cell is filled with an electrolyte solution this cell is usually made of glass with sealed platinum electrodes. Various shapes are used, depending on the purpose that it is to serve. Figure 2.9 depicts examples of suitable cell arrangements. The electrodes are covered with platinum black, to avoid electrode polarization. The electrodes are placed close to one another in poorly conductive solutions and further apart in more conductive solutions. 

The reduction of [Pt(bipy)2]2+ in water by metallic iron or at a platinum electrode gives monomeric [Pt(bipy)2]N03-2I I20 that forms as black-green needles. 25The needles have a relatively high electrical conductivity and a Pt - Pt separation of 3.563(1) A.125 In contrast, reduction in aprotic solvents such as DMF or DMSO results in the formation of dimeric [Pt2(bipy)2(/x-bipy)]21 (bipy = 2,2 -bipyridine) with a Pt- -Pt separation of 2.527,2(5) A.126... 

CE, another high performance separation technique, was also proved to be a powerful tool and an alternative for HPLC in the analysis of natural dyestuffs, even if its application in this field is still considerably limited. It could play an important role especially in the analysis of artworks, as it requires a very small volume of a sample solution (a few dozen nanolitres). In CE[ 10 14] separation of charged species is based on their different migration properties along the capillary tube which is in a constant electric field. Two platinum electrodes and both ends of a narrow bore (i.d. 25 100 pm) flexible fused silica capillary (usually 60 100 cm long) filled with a suitable conducting buffer are immersed in two... 

Conductometric transducers, as the oldest electrochemical devices, seem not to enjoy wide applications due to their poor selectivity. For example, Yagiuda et al. proposed a conductometric immunosensor for the determination of methamphetamine (MA) in urine [89], The decrease in the conductivity between a pair of platinum electrodes might result from the direct attachment of MA onto the anti-MA antibodies immobilized on the electrode surface. The system was claimed to be a useful detection technique of MA in comparison with a gas chromatography-mass spectrometry method. 

Kiguchi M, Tal O, Wohlthat S, Pauly F, Krieger M, Djukic D, Cuevas JC, van Ruitenbeek JM (2008) Highly conductive molecular junctions based on direct binding of benzene to platinum electrodes. Phys Rev Lett 101(4) 046801... 

In general Zr02 oxygen sensors consist of a tube-like solid-state Zr02 electrolyte where the electronic conductivity is based on oxygen ion charge carrier transport. The inner and outer surface of the yttrium-doped and stabilized zirconia tube is covered by porous platinum electrodes. 

Platinum electrodes low-potential ac source conductance bridge. 

The amperometric dehydrogenase sensor for ethanol consists of a platinum electrode on the surface of which alcohol dehydrogenase (ADH), Meldra blue (MB) and NAD are immobilized with a conductive polypyrrole membrane as schematically illustrated in Fig.24. 

A platinum disk electrode was electrolytically platinized in a platinum chloride solution to increase the surface area and enhance the adsorption power. The platinized platinum electrode was then immersed in a solution containing 10 mg ml l ADH. 0.75 mM and 6.2 mM NAD. After sufficient adsorption of these molecules on the electrode surface, the electrode was transferred into a solution containing 0.1 M pyrrole and 1 M KC1. Electrochemical polymerization of pyrrole was conducted at +0.7 V vs. Ag/AgCl. The electrolysis was stopped at a total charge of 1 C cm 2. An enzyme-entrapped polypyrrole membrane was deposited on the electrode surface. 

The conductance of a solution is the inverse of its resistance, and conductance has units of ohms 1 or mohs. The higher the conductance of a solution, the lower is its electrical resistance. A conductivity meter and conductivity cell are used to determine the effective resistance of a solution. The conductivity cell consists of a pair of platinized platinum electrodes with an area of approximately 1.0 cm2 with spacers designed to hold the electrodes rigidly parallel and at a fixed distance from each other. The cell can be standardized with solutions of known conductivity to obtain the cell constant, k so that the instrument response R... 

Electrical conductance The conductance measurements were made in a glass cell consisting ot two equivalent electrode sections. Circular platinized platinum electrodes parallel to the plane of the membrane were embedded in each section. The membrane area was 0.98 cm2. Resistance measurements were made with and without the membrane in O.IN NaCl solution. 

Polypyrrol is a polymeric support that can be used in immobilization of ONDs to surfaces. The generation of polypyrrol films can be by electrochemical co-polymerization of pyrrole and pyrrole-modified ONDs onto platinum electrodes. The polymer forms a black and insoluble film that is electrically conducting and whose thickness depends on the current used during the polymerization process (Fig. 14). The final surface density of the OND can be controlled by the ratio of pyrrole/OND being polymerized [53-55]. 

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