WIND ENERGY SYSTEMS - Cd3wd

Chapter 7—Asynchronous Loads 7–41
The plates are mild steel, solid nickel, or nickel-plated steel. There is a diaphragm in
the middle of each cell to prevent the mixing of the oxygen and hydrogen produced. The
diaphragm is made of asbestos cloth in the older, low pressure systems.
When a direct current is applied, oxygen gas is evolved at the positive terminal of each
cell and hydrogen gas at the negative terminal. Only the water is used up in this reaction so
additional water must be continually added to maintain the same alkaline concentration.
A simplified version of the chemical process is shown in Fig. 15 for a single cell with
a potassium hydroxide electrolyte. Initially, the two plates in the cell are surrounded by
a solution of water, positive potassium ions, and negative hydroxal ions. When a voltage
difference is applied to the electrodes, the negative ions migrate to the positive plate and the
positive ions to the negative plate. If the applied voltage is large enough, four hydroxal ions at
the positive electrode will give up one electron each and form one molecule of oxygen and two
molecules of water. At the same time, four water molecules at the negative electrode accept
one electron each, forming two molecules of hydrogen and four hydroxal ions. Current flow
in the electrolyte is carried by the hydroxal ions migrating from the negative to the positive
plate.
Figure 15: Chemical action in a simple electrolysis cell: (a) no voltage applied; (b) Limited
voltage applied; (c) more voltage applied.
Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001