WIND ENERGY SYSTEMS - Cd3wd

Chapter 7—Asynchronous Loads 7–44
Figure 16: Plot showing the effect of pressure on electrolysis cell characteristics at 400 o F.
cells.
The Oklahoma State cell used asbestos sheets to separate the gases between the electrodes.
Asbestos is also a standard separator for the low pressure cells. It is chemically an excellent
choice since it is not attacked by the hot KOH. It is not such a good separator from a mechanical
standpoint, however, since pressure differentials can blow holes in it. The electrolysis
unit must then be torn down and rebuilt. The pressure controlling valves on the oxygen and
hydrogen lines are difficult to build and operate in such a way as to maintain the very low
differential pressures required by the asbestos cloth. These problems indicated the need for a
high pressure cell which would not require the use of asbestos.
One recent design solution to this problem is the solid polymer electrolyte (SPE) cell. The
basic construction of such a cell is shown in Fig. 18.
At the center of the cell is the SPE sheet. This sheet is perhaps 250 µm thick and is made
of a perfluoronated linear polymer with sulfuric acid groups integrally linked to the polymeric
structure to provide ionic conductivity[14]. This material is essentially a form of teflon which
has excellent physical strength and forms a rugged barrier between the generated hydrogen
and oxygen gases. When saturated with water the polymer is an excellent ionic conductor
and it is the only electrolyte required. Ionic conductivity is provided by the mobility of
the hydrated hydrogen ions (H + · xH 2 O). These ions move through the sheet of electrolyte
by passing from one sulfonic acid group to another. The sulfonic acid groups are fixed,
Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001