Fact sheet n°2 : How does an electrolyser work?

 As of today, hydrogen is mostly produced from natural gas which leads to tremendous CO2 emissions. Another way of producing hydrogen is coming into being: electrolysis, a process through which hydrogen can be produced from decarbonised or renewable electricity. But…

What is electrolysis?

The principle of electrolysis is quite simple. A direct current is injected into an electrolytic solution, in order to separate the water molecules into hydrogen and oxygen. 


Let’s see what electrolysers are made of, the most widespread for instance: the alkaline electrolyser.

An alkaline electrolyser cell consists of two electrodes immersed in a bath of electrolytic solution. Strong direct currents are injected, and that’s it!

Hydrogen will appear at the cathode and oxygen will appear at the anode.

However alkaline electrolysis is not the only technology used. The three great families are: 


Proton Exchange Membrane electrolysers


Alkaline electrolysers


High-temperature Solid Oxide Electrolyser Cell.

different types of electrolysers

The general principle of these different technologies is the same, but there are some differences:


The electrolyte solution is replaced by a solid polymer membrane. The protons (H+) pass through it and form the H2 at the cathode.


These are the electrolysers described above. The electrolyte is an aqueous liquid solution. The hydroxide ions (OH-) flow through the membrane to form O2 at the anode.


Here the electrolyte is in the form of a solid ceramic. At the cathode, the hydrogen is separated from the oxygen ions (O2-), which pass through the ceramic membrane and form O2 at the anode.

Each technology has its advantages and disadvantages. PEM electrolysers are highly compatible with renewable energy sources. They are responsive, compact, and have good prospects regarding mass production and efficiency.

Alkaline electrolysers is the most mature and deployed solution. They are slightly cheaper than PEMs and are more suitable for mass production. 

High-temperature electrolysers (SOEC) have excellent efficiency, but require high temperatures and they still suffer from teething problems. They have a very promising future in industrial applications.

Our latest articles