Environmental Engineering Reference
In-Depth Information
Other methods are therefore necessary to produce hydrogen so that it is environ-
mentally safe. The ideal way is with electrolysis. The German chemist Johann
Wilhelm Ritter fi rst used electrolysis to produce hydrogen as early as 1800. Using
electric energy, electrolysis decomposes water directly into hydrogen and oxygen.
If the energy comes from a renewable energy power plant, the hydrogen can be
extracted free of carbon dioxide.
Alkaline electrolysis is an example (Figure 13.3). With this method two electrodes
are dipped into a conductive watery electrolyte. This can be a mixture of water and
sulphuric acid or potassium hydroxide (KOH). The anodes and cathodes conduct
direct current into the electrolytes. There they electrolyze water into hydrogen and
oxygen.
Figure 13.3
Principle of alkaline electrolysis.
Although electrolysis has already reached a high state of technical development as
an environmentally compatible option for oxygen production, other alternative
methods are also in development.
Thermo-chemical methods are an example. At temperatures above 1700 °C water
decomposes directly into hydrogen and oxygen. However, these temperatures
require expensive heat-resistant facilities. The required temperature can be reduced
to below 1000 °C through different coupled chemical reactions. For example, con-
centrating solar thermal power plants can produce these temperatures, and this has
already been successfully proven.
Other procedures include the photochemical and photobiological production of
hydrogen. With these procedures, special semiconductors, algae or bioreactors use
light to decompose water or hydrocarbons. These methods are also still at the
research stage. The main problem is developing long-term stable and reasonably
priced facilities.
