Reducing the Energy Carbon Content - Energy and Climate: How to Achieve a Successful Energy Transition - page 83

Hydrogen is capable of playing this role, provided that a number of
major obstacles can be overcome (cost, the need to set up transport and
distribution infrastructures, storage). Hydrogen can in fact be used to
store energy, but to reach sufficient storage densities, relatively expensive
devices must be implemented: storage under very high pressure (600 bar),
liquid at very low temperature or solid ('hydride' type inclusion

compounds).
Hydrogen is also the most suitable fuel for fuel cells. Fuel cells convert
the chemical energy of combustion directly into electricity with very high
conversion efficiency, which is why they are often considered as the energy
converter of the future. A distinction is made between the low-tempera-
ture cells, including the proton exchange membrane fuel cell (PEMFC)
and its variants based on methanol or ethanol (DMFC and DEFC), and
cells operating at a higher temperature, the alkaline fuel cell (AFC),
molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC)
[71]. Despite significant progress, the fuel cells, in particular the low-
temperature fuel cells, which are intended for large-scale distribution, are
still faced with lifetime and cost problems. The high cost is due in
particular to the use of a platinum catalyst.
For the time being, therefore, their application is restricted to niche
markets (military applications, emergency generator sets and portable
electronics, developing market for miniature cells, hydrogen PEMFC or
methanol DMFC).
Hydrogen can either be produced from fossil fuels or by electrolysis:

Initially, hydrogen will be produced from natural gas, coal or
biomass, via a synthesis gas. Synthesis gas is obtained from natural
gas by an endothermic steam reforming reaction, in the presence of
steam and from coal or biomass by an exothermic partial oxidation
reaction in the presence of oxygen 4 . The synthesis gas is then con-
verted in the presence of steam into amixture of hydrogen and carbon
dioxide ('shift conversion' reaction).
Provided that the CO 2 is captured and stored, the hydrogen
obtained can be used to produce electricity from coal or possibly
natural gas without CO 2 emission.
Consequently, production of hydrogen from fossil fuels is only of
any interest if combined with CO 2 capture and storage. Centralised
production facilities are therefore preferred, since CO 2 capture for

.

4 Exothermic reaction: reaction occurring with production of heat.