Global Warming

Technology forthe longer term 311

Fuel cell technology

A fuel cell converts the chemical energy of a fuel

directly into electricity without first burning it to

produce heat. It is similar to a battery in its construc-

tion. Two electrodes (Figure 11.15) are separated

by an electrolyte which transmits ions but not elec-

trons. A fuel cell has a theoretical efficiency of one

hundred per cent. Fuel cells have been constructed

with efficiencies in the range of forty to eighty per

cent.

Hydrogen for fuel cells may be supplied from a

wide variety of sources, from coal or other biomass

(see Note 24), from natural gas,^68 or from the hy-

drolysis of water using electricity generated from

renewable sources such as wind power or solar pho-

tovoltaic (PV) cells (see box onpage 302).

Figure 11.15Schematic of a hydrogen-oxygen fuel cell. Hydrogen is supplied to the porous anode

(negative electrode) where it dissociates into hydrogen ions (H+)and electrons. The H+ions migrate

through the electrolyte (typically an acid) to the cathode (positive electrode) where they combine with

electrons (supplied through the external electrical circuit) and oxygen to form water.

of PV electricityhas been coming down rapidly (Figure 11.13) – a trend
that will continue with technological advances and with increased scale
of production.
Hydrogen is also important for other reasons. It provides a medium
for energy storage and it can easily be transported by pipeline or bulk
transport. The main technical problem to be overcome is to find efficient
and compact ways of storing hydrogen. Present technology (primarily
in cylinders at high pressure) is bulky and heavy, especially for use in
transport vehicles. A number of other possibilities are being explored.
Most of the technology necessary for a solar-hydrogen energy
economy is available now, although the cost of energy supplied this way