Thomas F. Sharpe and Stuart G. Meibuhr
General Motors Corporation Warren, Michigan 48090
A Simple Method for Preparing Spherical Metal Electrodes
In many electrochemical studies it is necessary to use smooth electrodes having a well-defined surface area such as that obtained by preparing a hanging metal drop in an inert a t m o ~ p h e r e . ~Sealed systems have been described2for making such electrodes; however, the technique described i n this note is less cumbersome and inexpensive and still provides electrodes that give reproducible measurements of doublc layer capacity and electrochemical polarization. The electrode shown in the figure was prepared as follows. High purity lead, contained in a porcelain crucible, was heated to its melting point by directing a hydrogen flame into the crucible. After all oxides were reduced, the molten lead was drawn by means of an aspirator into a 7-mm diameter Pyrex tube having a tapered tip. Then the tube was lifted from the crucible, and the molten lead was allowed to flow through the tip where it solidified to form a spherical drop. Prior to drawing the molten lead into the tube, the tube was heated to prevent premature solidification of the lead. Although the drop was allowed to solidify in an air atmosphere, the electrode was spccular in appearance and remained so for several hours. For electrical contact,. a small oxygen-gas flame was used to weld a platiDELAHAY, P., "Double Layer and Electrode Kinetics," Interscience (division of John Wiley & Sons, Inc.), New York, 1965, p. 129. BORISHOVA, T. I., .4ND E R S H LB. ~ ,V., Zhur. Fiz. Khim., 24, 337 (1950). BOCKRIS, J. OIM., CONIVAY, B. E . , AND M E n ~W., , Jour. Sci. Inslr., 33, 400 (1956).
num wire to the lead remaining inside the tube. A microscope or 10X eyepiece was used to obtain the exact dimensions of the electrodes for area calculat,ions. Tubes having a tapered tip similar to that found on a 10-ml pipet gave lead electrodes ranging in area from 0.02 to 0.05 cm2. I n addition to lead electrodes, the method has been used for making tin and zinc electrodes and would appear to apply to other metals which have a melting point lower than that of Pyrex. A similar technique was performed in a dry box for making electrodes of sodium.
Lead electrode: lo) mognifled view of electrode tip and complete electrode.
lbl
drawing of
Volume 46, Number 2, February 7 969
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