Platinum electrodes polishing

The nature and the physical state of the metal employed for the electrodes. The fact that reactions involving gas evolution usually require less overpotential at platinised than at polished platinum electrodes is due to the much larger effective area of the platinised electrode and thus the smaller current density at a given electrolysis current. 

Glassy carbon electrodes polished with alumina and sonicated under clean conditions show activation for the ferrl-/ ferro-cyanlde couple and the oxidation of ascorbic acid. Heterogeneous rate constants for the ferrl-/ ferro-cyanlde couple are dependent on the quality of the water used to prepare the electrolyte solutions. For the highest purity solutions, the rate constants approach those measured on platinum. The linear scan voltammetrlc peak potential for ascorbic acid shifts 390 mV when electrodes are activated. 

Methanol Oxidation at a Smooth Polished Polycrystalline Platinum Electrode d 3.3—The Electrochemical Reduction of CO[sub(2)]... 

Methanol oxidation at a smooth polished polycrystalline platinum electrode... 

Figure 2. Diagram of electrode in adsorption position and "squeezed" position for adsorbate measurement (1) smooth, polycrystalline platinum electrode (2) polished glass scintillator detector (3) Macor ceramic disk, which forms cell bottom ( )) resin (5) electrode shaft.

The polycrystalline platinum electrode was mounted in Kel>F resin and polished with a scries of alumina powders down to 0.05, resulting mirror finish. The apparent surface area was 1.85 cm. The electrode was washed with fuming sulfuric add and rinsed with ultra pure water prior to each measurement. 

Figure 8.7 shows such a flow plot for the radical cation of the viologen species, l,l -bis(p-cyanophenyl)-4,4 -bipyridilium ( CPQ ), as the bis(tetrafluoroborate) salt in propylene carbonate solution, with the radical having been formed at a polished platinum electrode. The plot is seen to be linear, implying that, once formed, the CPQ radical cation is chemically stable. 

The electrical conductivity was measured by W. H. Ross, who found that in all cases the conductivity of the salt soln. was increased with time, especially with the more dil. soln. This is due to the decomposition of the salts under the influence of the platinum-black of the electrodes with polished electrodes, the effect is considerably smaller. The base itself is oxidized even more rapidly than the salts. The soln. are in all cases decomposed by the platinum electrodes, and G. M. J. MacKay showed that tin does not decompose the soln. at all, while copper decomposes the soln. completely. The order in which the metals were found to decompose the soln. is tin, platinum, silver, nickel, mercury, and copper. The electrical conductivity of hydroxylamine, using tin electrodes, in terms of mercury at 18°, with v vols. of soln. per mol, is as follows ... 

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. 

It is often recommended by manufacturers or others that working electrodes be polished prior to the measurements. We cannot recommend this as a general procedure. In our experience platinum electrodes, for example, improve in quality by being used and, after a measurement or a series of measurements, they should only be rinsed by an organic solvent and wiped to dryness by a soft paper tissue. Only when this gentle treatment is not sufficient to remove material from the surface, for instance a deposit, should the electrode be re-polished. 

Elbs and Brunner electrolyzed an aqueous solution containing 5 g.-molecule equivalents of alcohol and 0.5-1 g.-rnole-cule equivalent of sulphuric acid. They obtained acetaldehyde, acetic acid, and carbon dioxide, but no carbon monoxide. Acetic acid is the principal product at a bright (polished) platinum electrode. It is formed with a current yield of over 80%, the yield of aldehyde amounting to about only one twentieth of the weight of the acetic acid. 

They find that the anode potential determines the effect. The first reaction which occurs predominatingly at iron and palladium electrodes, requires the lowest potential. With platinized platinum electrodes the potential lies higher the oxidation action can exceed the evolution of oxygon and with a particularly high potential, which is obtained by prepolarizing the platinized anode,1 ethane is produced. With polished platinum and iridium anodes the potential is still higher than with prepolarized platinized platinum anodes. Thus the production of ethane predominates over the oxidation of acetic ester. 

The application of a typical train of pulses, when using stainless steel electrodes, resulted in small polarization of the electrodes and the appearance of a residual low DC component (<2 V). To avoid polarization, it is recommended to switch electrode polarity after each treatment and to clean and polish electrodes after each experiment. When employing stainless steel electrodes one observes, in some culture media, the formation of precipitates. It is, therefore, recommended to employ platinum electrodes, which do not lead to precipitation. 

Activation (of noble metal electrodes) — Noble metal electrodes never work well without appropriate pretreatment. Polycrystalline electrodes are polished with diamond or alumina particles of size from 10 pm to a fraction of 1 pm to obtain the mirror-like surface. The suspensions of polishing microparticles are available in aqueous and oil media. The medium employed determines the final hydrophobicity of the electrode. The mechanical treatment is often followed by electrochemical cleaning. There is no common electrochemical procedure and hundreds of papers on the electrochemical activation of -> gold and platinum (- electrode materials) aimed at a particular problem have been published in the literature. Most often, -> cyclic and - square-wave voltammetry and a sequence of potential - pulses are used. For platinum electrodes, it is important that during this prepolarization step the electrode is covered consecutively by a layer of platinum oxide and a layer of adsorbed hydrogen. In the work with single-crystal (- monocrystal) electrodes the preliminary polishing of the surface can not be done. 

Figure 23-24 shows the current response when a solution that is 6 mM in K3Fe(CN)6 and 1 M in KNO3 is subjected to the cyclic excitation signal shown in Figure 23-23. The working electrode was a carefully polished stationary platinum electrode, and the reference electrode was a saturated calomel electrode. At the initial potential of +0.8 V, a tiny anodic current is observed, which immediately...

FIGURE 1.2 Tafel plots as electrode potential, E, versus the logarithm of the current density, logy, for mercury ( - ), platinized mercury to 1% (o-o), platinized mercury as thin film (a-a), fresh etched silver ( - ), aged etched silver (O-O), polished silver ( - ), bright platinum (H—h), and spongy platinum electrodes (c-c). 

This research evaluates the measurement of the "master" Eh of solutions in terms of heterogeneous electron-transfer kinetics between aqueous species and the surface of a polished platinum electrode. A preliminary model is proposed in which the electrode/solution interface is assumed to behave as a fixed-value capacitor, and the rate of equilibration depends on the net current at the interface. Heterogeneous kinetics at bright platinum in 0.1 m KCl were measured for the redox couples Fe(III)/Fe(II), Fe(CN)53-/Fe(CN)6, Se(VI)/Se(IV), and As(V)/As(Iin. Of the couples considered, only Fe(III)/Fe(II) at pH 3 and Fe(CN)g37Fe(CN)g at pH 6.0 were capable of imposing a Nemstian potential on the platinum electrode. 

The intersection of the tangents of the two branches of the potential curve is taken as the end point of the titration. A levelling off of the potential jump may occasionally be observed this phenomenon may be eliminated by careful polishing of the platinum electrode with emery. 

P. H. Bottelberghs and G. H. J. Broers [1976] Interfacial Impedance Behavior of Polished and Paint Platinum Electrodes at Na2W04-Na2Mo04 Solid Electrolytes,... 

---