Environmental Engineering Reference
In-Depth Information
O
2
H
2
H
2
O
To Grid
ELECTROLYSER
Heat Exchanger
Nuclear
Reactor
Fig. 2.5
Scheme of a HTE plant based on nuclear power [
89
]
The steam-hydrogen mixture exits from the electrolyser and the water/hydro-
gen gas mixture passes through a separator to obtain pure hydrogen, while a
portion of the electricity produced by the reactor is used to feed the electrolyser.
Electrochemical oxidation of coal has been investigated at the beginning of
1980s [
90
] to evaluate the possibility to limit the high electric power required by
H
2
O electrolysis, simultaneously overcoming the limitations of the conventional
hydrogen production starting from coal (see
Sect. 2.1.1.4
), related to the high costs
due to working temperature and separation units. The electrolysis of coal takes
place according to the following reactions:
C
þ
2H
2
O
!
CO
2
þ
4H
þ
þ
4e
ð
2
:
26a
Þ
4H
þ
þ
4e
!
2H
2
ð
2
:
26b
Þ
Coal is oxidized at the anode, while protons are reduced to form hydrogen
molecule at the cathode. The low current densities achieved in the reaction (about
2.5 mA/cm
2
at 1 V) have discouraged further studies in the successive two dec-
ades, but recent works on the development of noble metal carbon fibre electrodes
have demonstrated the possibility to improve their activity [
91
] justifying further
experimental tests aimed at fabricating a coal electrolytic cell (CEC) operating at
intermediate temperatures (40-108C) [
92
]. Finally, another potential advantage
of the coal electrochemical oxidation is that downstream separation of gases is not
necessary as pure H
2
and CO
2
are generated in different compartments of the cell.
