Electrodes, cleaning preparation

A modified immersion method has been used by Hamm et al.140 to obtain electrochemical cell by a closed-transfer system, and immersed in 0.1 M HCIO4 solution at various . was derived from the charge flowing during the contact with the electrolyte under potential control. For the reconstructed Au(l 11M22 X Vayo.l M HCIO4interface, =0.31 0.04V (SCE) (Table 9). Using the impedance method, = 0.34 V (SCE) for recon-... 

Experimental. Uranium oxide electrodes were prepared from sintered UC>2 and reduced to the correct stoichiometry in a vacuum furnace. After cleaning, samples were exposed to a 0.5 M Na2S0 solution of pH 7 and electrochemically oxidized at a potential of +300 mVgcg. After various times, samples were removed from the solution within the inert gas chamber. They were rinsed in deoxy-genated water and transferred into the UHV chamber within 60 seconds. XPS peaks were taken using an Al Ka X-ray source. 

In one case [50] the electrode was prepared by casting a polished and clean glassy carbon electrode GCE with 10 pL of a solution obtained by dispersion of MWCNTs in concentrated sulfuric acid (1 mg/mL) followed by drying at 200 °C for 3h and careful rinsing. 

Metalhc or electrically conductive samples, such as sheets, wires, or rods of alloys or pure metals, may be used directly as one or both of the electrodes. Some preparation may be required, such as milling the metal into the desired shape or melting the metal and casting it into a mold. The end of the electrode is either pohshed flat or tapered at one end. The formed electrode must be cleaned to remove any surface contamination before analysis. The most common approach used in modem spark instmments is to have a polished flat metal sample serve as the cathode and a tungsten electrode as the anode, shown schematically in Fig. 7.11. 

Polycrystalline gold and platinum electrodes can be converted into clean, well-ordered single-crystal electrodes by heating the respective wires in an Hj h- O2 flame. This is the so-called Clavilier method (134-137). Such electrodes are prepared by melting one end of a pure wire (1 mm diameter)—a zone-refining process. The crystallinity of the bead is usually... 

Our spectroelectrochemical cell consisted of a quartz glass cylinder with a diameter ca. 1 cm and a capacity of ca. 1 cm of solution. The working electrode was a polycrystalline Ag metal disk, ca. 2 nun in diameter, enclosed in a Teflon holder. This metal electrode was prepared before each experiment by mechanical polishing, ultrasonic treatment and electrochemical cleaning by evolution. 

The differential capacitance method cannot be used for reactive metals, such as transition metals in aqueous solutions, on which the formation of a surface oxide occurs over a wide potential re ion. An immersion method was thus developed by Jakuszewski et al. 3 With this technique the current transient during the first contact of a freshly prepared electrode surface with the electrolyte is measured for various immersion potentials. The electrode surface must be absolutely clean and discharged prior to immersion.182-18 A modification of this method has been described by Sokolowski et al. The values of obtained by this method have been found to be in reasonable agreement with those obtained by other methods, although for reactive metals this may not be a sufficient condition for reliability. 

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. 

The chemisorption of species occurs at specific sites on the electrode, for example on top of certain atoms, or in the bridge position between two atoms. Therefore, most adsorption studies are performed on well-defined surfaces, which means either on the surface of a liquid electrode or on a particular surface plane of a single crystal. Only fairly recently have electrochemists learned to prepare clean single crystal electrode surfaces, and much of the older work was done on mercury or on amalgams. 

Aniline. Aniline black is a well known polymer of aniline formed by electrophilic additionf3.41. Numerous investigators have formed poly(aniline) films by anodic deposition of Pt and other electrode materials. We have examined the interaction of aniline with clean Ni(lll) and Ni(100) surfaces in ultrahigh vacuum and found aniline to form an orientationally ordered, thermally stable polymer film. Electrochemically prepared poly(aniline) films also show the high degree of orientational ordering. 

To implement this program of measurements on well-defined electrodes, the method of preparation of clean and well-ordered single crystal surfaces is essential. Such surfaces can be obtained either by the use of ultra-high vacuum or "atmospheric" procedures, the latter methods will briefly be described below. 

---