Platinum-disc electrodes

In a typical study of conductivity. Cook (1982) used a cell consisting of two platinum disc electrodes, 12 mm in diameter and 1-5 mm apart. The setting AB cement was examined in this cell which had been calibrated using a standard solution of0 02 M potassium chloride. Plots were recorded of spedfic conductance against time for each of the setting cements. For zinc polycarboxylate there was found to be a rapid drop in spedfic conductance about 10 minutes after the start of mixing. This behaviour was consistent with the replacement of relatively mobile protons by significantly less mobile zinc ions in the polycarboxylate chain. Con-... 

The electrodes consist of platinum discs, slightly platinized and mounted in glass tubes which are placed in the glass vessels. The types of Wheatstone bridge commercially available for conductometry and known as conductivity bridges can be used in either the resistance mode or the conductance mode the choice between these modes depends on the character of the solution under investigation and on the performance of the conductance cell. 

Chronopotentiometry has also been used to determine chloride ions in seawater [31]. The chloride in the solution containing an inert electrolyte was deposited on a silver electrode (1.1 cm2) by the passage of an anodic current. The cell comprised a silver disc as working electrode, a symmetrical platinum-disc counter-electrode and a Ag-AgCl reference electrode to monitor the potential of the working electrode. This potential was displayed on one channel of a two-channel recorder, and its derivative was displayed on the other channel. The chronopotentiometric constant was determined over the chloride concentration range 0.5 to 10 mM, and the concentration of the unknown solution was determined by altering the value of the impressed current until the observed transition time was about equal to that used for the standard solution. 

None of the set-ups discussed so far provides stirring of the electrolyte for bubble removal or for enhancement of the reaction rates. A standard set-up developed to study kinetic electrode processes is the rotating disc electrode [11]. The electrode is a small flat disc set in a vertical axle. The hydrodynamic flow pattern at the disc depends on rotation speed and can be calculated. An additional ring electrode set at a different potential provides information about reaction products such as, for example, hydrogen. However, because this set-up is designed to study kinetic processes and is usually equipped with a platinum disc, it becomes inconvenient if silicon samples of different geometries have to be mounted. 

Table 1 Typical tabulation of cyclic voltammetric data. [Fe(f-C5H )2)] solution (1.0 X 10 3 mol dm 3) in CH2CI2. Supporting electrolyte [NBu4][PF6] (0.2 mol dm 3). Platinum disc electrode radius = 1 mm. Potential values are referred to SCE...

The membranes, of thickness usually about 40 pm, were mounted in a Perspex cell in which all measurements were carried out. The membrane faces were not obstructed by supports as zero pressure difference was maintained in the cell. A.C. conductances at 1400 Hz were measured with platinum disc electrodes parallel to the... 

In a first set of experiments, the voltammetric behaviour of sodium dithionite was investigated in alkaline solution (pH around 12.5), by variation of the rotation rate of the platinum-disc electrode for different concentrations of sodium dithionite. In Fig. 6.1, current-potential curves are shown, obtained at different rotation rates of the electrode in a solution with constant sodium dithionite concentration. Two anodic waves are observed. In principle, sodium dithionite is the only electroactive species in solution, therefore it is supposed that both well-separated waves can be attributed to the oxidation of sodium dithionite with formation of a relatively stable intermediate product in the first wave. 

Logarithmic plot of the relationship between rotation rate of the electrode and limiting current for the first wave of the oxidation of sodium dithionite in alkaline solution at a platinum-disc electrode as a function of sodium dithionite concentration (1) 2.9x10 3, (2) 5.8x10 3 and (3) 1.2x10 2mol I1. 

Relationship between potential and logarithm of the kinetic current for the oxidation of sodium dithionite at the surface of a platinum-disc electrode in alkaline solution (pH = 12.5) at a rotation rate of 1000rpm. Sodium dithionite concentrations are (1)... 

Table 6.1 Values for ana calculated from the difference between peak and half-wave potential for the oxidation of sodium dithionite at a platinum-disc electrode...

The amperometric detection of sucrose was performed with a conventional three-electrode potentiostatic system. With an LC-3D voltammo-graph (Bioanalytical Systems). The working electrode was a 2-mm diameter platinum disc, polished with alumina down to 0.05 pm particle size and rinsed thoroughly with distilled water, the reference electrode was an Ag/AgCl (3M KC1) electrode and the auxiliary electrode was a stainless-steel rod. 

Fig. 3.20 Normal Pulse Voltammograms for the reduction of 6.9 x 10 4 M tetracyanoquino-dimethane (TCNQ) in acetonitrile with 0.10 NBu4NPF6 at 293 K (platinum disc electrode with diameter 0.31 cm). Pulse duration 0.050 s. Lines are simulations with the following input parameters Ef = —0.107 V, t Ef = —0.551 V, kJ = 104 cm s-1, a = 0.5, a% = 0.35, k = 6.5 x 10-3 cm s-1, diffusion coefficients of neutral, anion, and di-anion are 1.44 x 10 5, 1.35 x 10 5, and 9.1 x 10 6 cm2 s-1, respectively. Reproduced from reference [38] with permission...

As species Wall jet cell and micro sized platinum disc electrodes [290]... 

Fig. 8.4. A wall-jet cell with ring-disc electrode. A, disc electrode contact B, ring electrode contact C, Ag/AgCl reference electrode D, platinum tube auxiliary electrode E, solution entry F, cell body in Kel-F (from Ref. 1 with...

Fig. 34 Voltammograms (with background correction) for the reduction of 2,6-diphenylpyrylium perchlorate at a 10 fim platinum disc electrode. The following scan rates were used (a) 250, (b) 150 and (c) 75 kV s . The substrate concentration was 10 mM. Data adapted from Amatore and Lefrou (1991).

Fig. 36 Voltammograms obtained at 25°C for the oxidation of 2 mM ferrocene in acetonitrile/0.1 M (C4H9)4NC104 at a 2-mm diameter platinum disc electrode using a scan rate of 20mVs" recorded either (a) under silent conditions, or (b) under insonation (20 kHz, 50 mW cm ) using the experimental arrangement of Fig. 35 with...

Fig. 43 (a) Cyclic voltammogram measured at a scan rate of 200 mV s for the reduction of 1 mM Ru(NH3)g in aqueous 0.1 M KCl. (b) Sonovoltammogram obtained in the presence of 33 W cm ultrasound with a 1 mm platinum disc electrode in a face-on geometry with a horn-to-electrode distance of 7 mm. (c) Time-resolved current signal recorded as for (b) at potentials of 0.1 and -0.5 V (vs. SCE). Data adapted from Marken el al. (1996a). 

The working electrode consisted of a mirror pohshed platinum disc, or a gold disc or glassy carbon (GC) disk (diameter 8 nun) glued to a glass tube as the holder. For nanoparticle powders the catalyst suspension was deposited on the GC disk and the solvent was evaporated under a pure nitrogen stream. 

O ) polarography uses a dropping mercury cathode and the current is measured 00 the rotating-disc method uses a spinning platinum disc as the cathode and the current in the steady state situation at a series of rotation speeds is measured Hi) the potentiostatic method uses fixed electrodes and the fall of current with time is measured. 

Besides screening, the robotic system allows detailed investigation of sensor parameters and quality control measurements. A Ni-porphyrin of the library was electrochemically deposited on a platinum disc electrode (d = 250 pm), dip coated with Nafion, and evaluated in the robotic system. Each well can be used for calibration... 

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