The relevance of energy storages for an autarky of electricity supply ...

Oxygen
Hydroxidions
O2
OH -
OH -
+
Figure 4.2: Hofmann Voltameter (schematic illustration from author)
(3) Cathode: H + + 1e - à H
H + H à H2
(4) Anode: OH - - 1e - à OH
4 OH à 2 H2O + O2
(5) Overall: 2 H2O à 2 H2 + O2
–
2H2
Anode (+) Cathode (-)
H +
H +
Hydrogen
Hydrogenions
Alkaline water electrolysis is a mature technique and widely used. 20 – 40 %
potassium hydroxide aqueous solution is most commonly used as electrolyte.
Electrolytes increase the efficiency of the facility to about 75 %. Typical operating
temperatures are between 80°C and 100°C. Most industrial electrolysers have a
bipolar connection of the cells where one electrode serves as anode and cathode at
the same time. This is called a stack, where currents are low but high voltages have
to be handled. Solid-polimer Electrolysis (SPE) names a technology, which replaces
liquid alkaline or acidic solutions with solid electrolytes. Reduced corrosion, a
constant electrolyte concentration and the ability to use the electrolyte
simultaneously as a diaphragm are advantages of this technology. Possible materials
are ion exchange membranes. Compared to alkaline electrolysis, material costs are
high for SPE electrolysers. On the other hand, a higher gas quality can be produced
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