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17 October 2003

An Electrochemical Cell

by C. L. Stong
Excerpted from "Scientific American's The Amateur Scientist", first published November, 1967.

If all the electrical energy that is locked in the chemical bonds of gasoline could be transformed into useful work, an automobile of average size would run at least 100 miles on a gallon of fuel. The vehicle could be set in motion at the touch of a switch. It would operate silently and discharge no noxious fumes.

 

Figure 1: Elements of an electrochemical cell. Click image to enlarge.

Experimenters, both professional and amateur, have long dreamed of developing an inexpensive, compact and durable electrochemical cell that would make the transformation in a single step.

IF ALL THE ELECTRICAL ENERGY that is locked in the chemical bonds of gasoline could be transformed into useful work, an automobile of average size would run at least 100 miles on a gallon of fuel. The vehicle could be set in motion at the touch of a switch. It would operate silently and discharge no noxious fumes.

Substantial progress toward meeting these objectives has been made in recent years. Some of the resulting cells are simple enough for amateur construction. For example, Sol M. Gruner of Elmer, N.J., has made working models of two types. One uses ... alcohol.

He writes: ""The alcohol cell is based on a demonstration cell that was first described by the Esso Research and Engineering Company. It is more convenient to use than the hydrogen-oxygen cell and appears to operate at higher efficiency... Each cell consists of a glass container that can be a large test tube, a beaker or a similar vessel; a cover made of an insulating material such as plastic or rubber, and a pair of electrodes, which are suspended from the cover.

The electrodes consist of 150-mesh nickel screening. They are two inches wide and five inches long. (Nickel screening of this mesh can be obtained from the Newark Wire Cloth Company, 351 Verona Avenue, Newark, N.J. 07104. A sheet six inches square is currently priced at $1.75.)

Figure 2: Sol M Gruner's fuel cell. Click image to enlarge.

"One end of each electrode is bent to a right angle and pierced for a nickel-plated machine screw that attaches the screening to the cover of the cell [see Figure 2]. The electrodes must also be coated with catalysts of platinum and silver. The fuel electrode, which is the negative terminal of the cell, is prepared by immersion for one hour in a solution of chloroplatinic acid dissolved in 100 milliliters of distilled water. During immersion the electrode is turned over several times to ensure a uniform coating. Platinum ions in the solution deposit on the nickel in the form of platinum black. Some nickel goes into solution as nickel ions. The oxygen electrode is similarly coated with silver by immersing the second piece of screening for an hour in a solution consisting of five grams of silver nitrate dissolved in 100 milliliters of distilled water. Avoid touching the surfaces of the coated electrodes.

"Both cells use the same electrolyte: a 5.5-molar solution of potassium hydroxide. Any glass vessel that will accommodate the electrodes can be used as the container. I prefer a beaker with a volume of one liter. The container should be filled so that the electrodes will be immersed almost up to the heads of the machine screws. The fuel consists of 35 milliliters of methyl alcohol, which is mixed with the electrolyte. (My experiments indicate that denatured ethyl alcohol works about as well.) A sheet of white filter paper or blotting paper should be inserted between the electrodes to prevent the screens from making accidental contact, which would short-circuit the cell.

"After the fuel has been added a potential of .5 volt will appear across the electrodes. A milliammeter connected to the terminals will indicate an initial current of about 20 milliamperes. At this current the terminal voltage will fall almost to zero because the oxygen electrode will quickly accumulate a coating of fine bubbles that are released by the reaction. Most of the voltage will appear between the electrolyte and the oxygen electrode, across the layer of bubbles."