1.3 Electrolyzer technologies 13
1.3 Electrolyzer technologies
An electrolyzer is a device made for splitting water into hydrogen and oxygen
by electrochemical means. Water splitting is an endothermic reaction so energy
is required for it to proceed. In an electrolyzer this energy is supplied as an
electrical current passed through the electrochemical cell. A simple schematic
of an electrolyzer cell can be seen in gure 1.13. The electrolyzer as a device
is then a series of these cells connected to deliver the rate of hydrogen needed.
In acidic electrolyte, water is oxidised into oxygen and solvated protons at the
anode. The protons are then conducted through the electrolyte (can be an ion
conducting membrane) and reduced to form hydrogen gas at the cathode. The
necessary inputs are therefore water and electricity. The potential applied per
cell determines the eciency.
Figure 1.13: In a Polymer Exchange Membrane cell, the electrolyte is a proton
conducting membrane. In electrolysis mode water is oxidised at the anode, generating
oxygen gas and protons. The protons are then transferred through the electrolyte to
the cathode where they are reduced to form hydrogen gas.
The existing electrolyzer technologies are divided by the type of electrolyte being
used. The electrolyte is a key component, providing ionic conductivity while
being electronically insulating. Traditionally, alkaline electrolytes have been
used for this purpose and in particular concentrated potassium hydroxide. This
type of electrolyzer was the rst to be commercially available and can deliver
stable performance up to 15 years with eciencies in the range of 40-80 % 32,35.
The advantages of this technology lie in their technological maturity and the