Submarine electrode

When a liquid-liquid interface is to be investigated using an electrode in the more dense phase, or for studies at the water-air interface, a submarine electrode can be deployed [18,19,34], depicted schematically in Fig. 3(b). In this case, the electrode is inverted in the cell, such that the tip points upwards, and an insulated connection is made through the solution. Metal electrodes down to the nanometer scale can also be fabricated by sealing an etched Pt or Pt-Ir wire in a suitable insulating material, leaving just the etched end exposed [35-37]. 

Figure 63.8.4 Formation and characterization of the Hg/Pt hemispherical submarine UME. (a) The Pt submarine electrode in phosphate buffer (pH = 7) as it approached the HMDE while poised at —1.1 V vs. Hg/Hg2S04. Upon contact with the HMDE, a hemispherical mercury layer is deposited onto the Pt UME. (b) Hydrogen evolution at Pt and Hg/Pt submarine UME in phosphate buffer, (c) Voltammogram of the 10 M T1(I) at the Hg/Pt submarine electrode in phosphate buffer. Reprinted with permission from reference (2). Copyright the American Chemical Society.

For studies involving air/water interface monolayers or Langmuir-Blodgett techniques, a submarine UME is required. Such an electrode is immersed in the solution and approached to the layer from below (110, 160). The submarine electrode consists simply of a conventional UME of the desired metal and size that is fixed to a glass J tube by Teflon tape or Epoxy (Figure 12.34). 

Submarine ieiecomthunications cables operate at less than 1 A but sub-. marine power cables may operate at several hundreds Of amperes and will require larger spacing between the earth, electrodes and nearby burled or immersed structures. IfpOssible, testsShould be made with trial earth elfec. trOdes at both ends of. the submarine cable and on Off tests made before bringmg the power supply bii the system into permanent Use., ... 

FIG. 3 (a) Block schematic of the typical instrumentation for SECM with an amperometric UME tip. The tip position may be controlled with various micropositioners, as outlined in the text. The tip potential is applied, with respect to a reference electrode, using a potential programmer, and the current is measured with a simple amplifier device. The tip position may be viewed using a video microscope, (b) Schematic of the submarine UME configuration, which facilitates interfacial electrochemical measurements when the phase containing the UME is more dense than the second phase. In this case, the glass capillary is attached to suitable micropositioners and electrical contact is made via the insulated copper wire shown. 

Most separations are done with an agarose gel in a horizontal position, called a submarine gel because it is underneath the buffer in the chamber. However, when DNA sequencing is done (see Section 13.8), a polyacrylamide gel is run in a vertical position. Many different samples can be separated on a single gel. Each sample is loaded at a given place (a distinct well) at the negative-electrode end of the gel, and an electric current flows until the separation is complete (Figure 13.2). 

Raney nickel electrodes prepared in this way were used in many of the fuel cell demonstrations mentioned in the introduction to this chapter. Often Raney nickel was used for the anode and silver for the cathode. This combination was also used for the electrodes of the Siemens alkaline fuel cell used in submarines in the early 1990s (Strasser, 1990). They have also been used more recently, in a ground up form, in the rolled electrodes to be desCTibed in Section 5.4.4 (Gnlzow, 1996). 

The rechargeable silver oxide batteries are noted for their high specific energy and power density. The high cost of the silver electrode, however, has limited their use to applications where high specific energy or power density is a prime requisite, such as lightweight medical and electronic equipment, submarines, torpedoes, and space applications. The characteristics of the silver oxide secondary batteries are summarized in Table 33.1. 

Finally, some limited attention has been given to appUeations other than electric vehicles. A number of years ago, development of sodium/nickel-chloride cells for aerospace applications was undertaken and, more recently, the use of this technology for powering submarines was evaluated. - The aerospace cells are essentially electric-vehicle cells with an optimized positive electrode and wicks for the sodium, and the secondary electrolyte that ensure operation in micro-g space environments. 

Zinc anodes are frequently used for protection of submarine pipelines. They are commercially available in weights from 5 to 60Ib. Prepared backfill should be used for anodes if they are to be installed in the earth. They have a driving potential of-l.lOV compared to a Cu-CuS04 reference electrode. The details of zinc anodes are shown in Fig. 5.19. 

The potential necessary to protect buried steel is —0.85 V, however, in the presence of sulfates, reducing bacteria a minimum potential of-0.95 V with respect to copper sulfate electrode would be necessary. Approximately 15-100 mA/ft current is needed for protection of bare steel in sluggish water. In rapidly moving water, 1-10 mA/ft for bare steel in a soil would be necessary. Current requirements in various environments can be foxmd abundantly in the literature as well as cathodic protection specifications. For submarine pipeline, a current density of 5 mA/ft is required. 

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