Platinum film electrodes

Sandwich casting permits one to prepare an MIP film with uniform thickness [28, 106, 108, 109]. In this procedure, a drop of the solution containing a monomer, cross-linker, template and initiator is dispensed on the surface of a PZ transducer and covered with a microscope quartz slide. Then this assembly is exposed to UV light in order to initiate polymerization that results in a thin MIP film. The polymerization can be performed either on the activated immobilized initiator PZ transducer surface or on the bare transducer surface. For example, sialic acid has been determined with an MIP film immobilized on a platinum-film electrode of the quartz resonator using the former procedure [57]. That is, 1-butanethiol has been used for modification of the Pt surface. An indole-3-acetic acid plant hormone served as the template. An MIP-PZ chemosensor prepared that way operated reproducibly. That is, the coefficient of variation of the chemosensor performance was 9% for three different sensors. 

The observation of luminescence from laser dyes by ECL methods offers the possibility of using this approach to create dye lasers. A laser operating by ECL would not require an additional pump laser, and enhanced power, tunability, and wavelength selection are additional factors. While the pumping rate achieved by ECL previously has been two orders of magnitude lower than the optimal, Horiuchi et al. have reported a device structure designed to enhance the ECL efficiency and realize laser action driven by ECL [67], This experiment is illustrated in Fig. 14. A pair of sputter-deposited platinum film electrodes were positioned facing each other 2 to 7 microns apart. One electrode functioned... 

A thin-film electrode is relatively dense, as the metallic film does not have the electrocatalytic properties that a porous electrode has. Therefore, in many instances, the surface of the thin film is chemically or electrochemically modified to enhance its electrocatalytic activity. For instance, thin platinum film electrodes can be platinized electrochemically forming a porous platinum black layer. This platinum black layer is electrocatalytically more active than the thin platinum film. Thin-film processes are more capital and labor intensive and the process is more complicated than thick-film processes. Thin-film deposition is also a batch process which may produce sensors of limited numbers of silicon substrates. This is very desirable in prototype development, for it allows modification on prototypes with minimum cost. 

Instrumentation. An STM is equipped with suitable additional electronics to generate the desired bias modulation and to detect the modulation of the tunneling current [72]. Differential Conductance Tunneling Spectroscopy data that was obtained for a platinum film electrode have been interpreted in terms of step density and... 

Zhu Y, Uchida H, Watanabe M. Oxidation of carbon monoxide at a platinum film electrode studied by Fourier transform infrared spectroscopy with attenuated total reflection technique. Langmuir 1999 15 8757-64. 

Of recent years the use of mercury film electrodes based on substrates other than platinum has been explored, and increased sensitivity is claimed for electrodes based on wax-impregnated graphite, on carbon paste and on vitreous carbon a technique of simultaneous deposition of mercury and of the metals to be determined has also been developed. 

Figure 9. Chronoamperometric curves for the growth of a polythiophene film on a stationary platinum disk electrode, from 0.1 M thiophene and 0.1 M LiC104 acetonitrile solutions, at different water contents (---) 0.04%, (--------) 0.14%,...

The apparatus used for studying the photoelectrochemical behavior (11) of the Ti02 film electrode is shown in Figure 5- Platinum plate of 35x25 mm and saturated calomel electrode (S.C.E.) were employed as a counter and a reference electrode, respectively. A 500 W Xenon lamp was used for illuminating the Ti02 electrode. 

In this type of DSSCs, once the dye is photoexcited, charge separation drives electrons from the valence band (vb) of the semiconductor to the photoexcited dye. Common to both types of DSSCs is the regeneration of the oxidized or reduced dye by a redox mediating electrolyte. The latter is mainly in the form of a liquid and/or a solid. Platinum films deposited onto ITO or FTO are the most utilized counter-electrodes and are required to close the electronic circuit. 

Figure 6.14 Cyclic voltammogram obtained for a multiple-electron-transfer system, where a thin film of sputtered V2O5 on a platinum working electrode has been immersed in an electrolyte solution of propylene carbonate containing LiCI04 (1.0 mol dm ). From Cogan, S. F., Nguyen, N. M Perrotti, S. J. and Rauh, R. D Electroctromism in sputtered vanadium pentoxide , SPIE, 1016, 57-62 (1989). Reproduced by permission of the International Society for Optical Engineering (SPIE).

Figure 6. Cyclic voltammograms of a platinum disk-electrode modified with a film of the octanuclear dendrimer 2, measured in 0.1 M Bu NPFj/CHjClj. The surface coverage of electroactive ferrocenyl sites in the film is determined to be T = 2.01 x 10" mol cm . inset, scan rate dependence of the anodic peak current.

Figure 7. Scanning electron micrograph of a film of 2 electrochemically deposited on a platinum wire electrode (0.25 mm of diameter).

The preparation of film electrodes Prussian blue films are usually prepared by cycling an electrode in a freshly prepared solution containing iron(III) and hexacyanoferrate(III) ions [70-72]. As substrate, mostly platinum is used, sometimes glassy carbon [73] is used, and very frequently ITO electrodes [74] are used because the latter are very useful for electrochromism studies. Similar procedures using solutions containing metal ions and hexacyanoferrate(III) have been used to deposit cobalt hexacyanoferrate [75] and chromium hexacyanoferrate [76, 77]. Crumbliss et al. reported a plasma deposition of iron species from a plasma containing iron pentacarbonyl and ethane, followed by electrochemical derivatization of the deposited iron sites with the help of hexacyanoferrate solutions [78]. 

The enhancement of electrochemical reactions usually occurs at modified electrode surfaces. The large NP surface area facilitates oxidation or reduction of small molecules at the electrode. For example, Niwa et al. modified a carbon film electrode with electrocatalytic platinum NPs to create a sensitive H2C>2 sensor.62 Co-sputtering of carbon and platinum produces platinum NPs of 2.5 nm diameter embedded in a carbon matrix. The platinum NPs catalyze the oxidation of H2O2 at the electrode... 

Note particularly that film electrodes make it economically practical to use very expensive materials as electrodes because of the very small quantities required to form the film. For example, a platinum film of 300 nm thickness and 1 cm2 cross-sectional area contains 640 pg of platinum. A macroscopic wire electrode of the same surface area constructed with 26-gauge platinum wire (0.4 mm diameter, 7.9 cm long) contains 210 mg of platinum, or 330 times as much platinum. At a price of 60/g, the cost of the platinum in the film ( 0.04) is much lower than the cost of the wire ( 12.80). Despite the great reduction in raw materials cost, the resulting electrode may not actually be proportionally less expensive than bulk platinum for small numbers of film electrodes, due to significantly greater fabrication costs. However, when produced on a large scale, costs of film electrodes may be dramatically lower. 

An optically transparent, porous platinum film has been produced by photoelectrodeposition on an InP semiconductor substrate [15], Polyester sheet covered with a thin film of sputtered gold has also proved suitable as an OTE [71]. When overcoated with a layer of Ti02, these electrodes exhibited electrochemical behavior consistent with a microelectrode array, including cyclic voltammetric current plateaus instead of clearly defined peaks, although this feature was not recognized at the time [71]. 

In recent years, mercury film ultramicroelectrodes have received wider application in electroanalytical practice [51,54,55]. Such electrodes are especially useful in analytical determinations, since they combine the features of ultramicroelectrodes (Chap. 12) with those of mercury film electrodes. In this case, the mercury can be deposited on carbon fibers, but many prefer a metallic support which is wetted by mercury. The solubility of the supporting metal in mercury should be low. Iridium [54] and silver [55], as well as platinum and nickel, have been used as supporting metals. Surprisingly, even gold fibers wetted by mercury have been very successfully used as electrodes in microchromatography and capillary electrophoresis detectors (Chap. 27). 

A molecularly imprinted polypyrrole film coating a quartz resonator of a QCM transducer was used for determination of sodium dodecyl sulphate (SDS) [147], Preparation of this film involved galvanostatic polymerization of pyrrole, in the presence of SDS, on the platinum-film-sputtered electrode of a quartz resonator. Typically, a 1-mA current was passed for 1 min through the solution, which was 0.1 mM in pyrrole, 1 mM in SDS and 0.1 M in the TRIS buffer (pH = 9.0). A carbon rod and the Pt-film electrode was used as the cathode and anode, respectively. The SDS template was then removed by rinsing the MlP-film coated Pt electrode with water. The chemosensor response was measured in a differential flow mode, at a flow rate of 1.2 mL min-1, with the TRIS buffer (pH = 9.0) as the reference solution. This response was affected by electropolymerization parameters, such as solution pH, electropolymerization time and monomer concentration. Apparently, electropolymerization of pyrrole at pH = 9.0 resulted in an MIP film featuring high sensitivity of 283.78 Hz per log(conc.) and a very wide linear concentration range of 10 pM to 0.1 mM SDS. 

Platinum films [27,88], microwires [19,84] and microdisks [12,103] were also employed. Characterisation of electrode fouling and surface regeneration for platinum electrode on an electrophoresis microchip was reported [104], The platinum tip of a scanning electron microscope has also been used for carrying out EC measurements combined in an end-configuration to a CE microchip [76]. 

A gold film was also evaluated using pAP as analyte model. The theoretical plate number (AO was 5990 m-1 with a half-peak width (wy2) of 4.1s for pAP. Peak current at gold-film electrode was lower than at SPEs but higher than at gold and platinum wire. 

C. -C. Wu, R.-G. Wu, H.-G. Huang, Y.-C. Lin and H.-C. Chang, Three-electrode electrochemical detector and platinum film decoupler integrated with a capillary electrophoresis microchip for amperometric detection., Anal. Chem., 75 (2003) 947-952. 

For reductions, hanging mercury drop electrodes or mercuryfilm electrodes are frequently used owing to their microscopic smoothness and because of the large overpotential for hydrogen evolution characteristic for this electrode material. Mercury film electrodes are conveniently prepared by the electrochemical deposition of mercury on a platinum electrode from an acidic solution of an Hg2+ salt, e.g. the nitrate. However, the oxidation of mercury metal to mercury salts or organomercurials at a low potential, 0.3-0.4 V versus the saturated calomel electrode (SCE), prevents the use of these electrodes for oxidations. 

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