Electrolysis - what and how?

The green hydrogen world often regards Jules Verne as a prophet. In his book, the Mysterious Island, written 146 years ago, he wrote,

"I believe that water will one day be employed as fuel, that hydrogen and oxygen, which constitute it… will furnish an inexhaustible source of heat and light."

BUT electrolysis was first used to split water by two English scientists William Nicholson and Anthony Carlisle in 1800; so perhaps Monsieur Verne is less of a prophet and more of a technocrat with a keen eye for a good idea.

By Étienne Carjat - This file comes from Gallica Digital Library and is available under the digital ID btv1b84497879/f1, Public Domain, https://commons.wikimedia.org/w/index.php?curid=83065220 

Since the discovery of electrolysis there have been compounding advancements over the last 200 years that have produced an electrolyser unit that is now commercially deployable, enabling the spatially disparate unleashing of the energy stored in the hydrogen contained in water molecules.

The electrolyser is one of the key components to the HydroGenesis solution. Electrolysers use electricity to split water (H₂O) into hydrogen (H₂) and oxygen (O) through an electrochemical reaction. When a voltage is applied and a DC current passes between two electrodes in contact with an ionic conducting medium, hydrogen and oxygen is produced by water decomposition:

 

H₂O +electric energy→ H₂+½ O₂

Electrolysis operates with aqueous electrolytes containing approximately 30% KOH (potassium hydroxide); which gives the maximum ionic conductivity, though there are different types electrolysers that function in slightly different ways, mainly due to the different electrolyte materials involved.

There have been some interesting developments recently (last 5 years) in PEM and AEM electrolyser space.

PEM (proton exchange membrane): H₂O reacts at the anode to form oxygen and positively charged hydrogen ions (protons). The electrons flow through an external circuit and the hydrogen ions selectively move across the PEM to the cathode. At the cathode, hydrogen ions combine with electrons from the external circuit to form hydrogen gas

Source: Wood Mackenzie, U.S. Department of Energy

AEM (or Anion Exchange Membrane): operate via transport of hydroxide ions (OH-) through the electrolyte from the cathode to the anode with hydrogen being generated on the cathode side. Electrolysers using a liquid alkaline solution of sodium or potassium hydroxide as the electrolyte have been commercially available for many years but the newer approaches using solid alkaline exchange membranes as the electrolyte are now providing the ability to deploy at small scale.

Source: Enapter

AEM electrolysers are well suited for the smaller installations largely due to the lower cost and green credentials of the materials required to achieve good lifetimes and performance. The PEM Electrolyser cells call for more expensive noble metal catalyst materials (iridium, platinum) and large amounts of titanium, so these are better suited to larger applications to enable value and efficiency gains of working with them.

The AEM Electrolyser builds on advantages from traditional Electrolysers:

• Works in a highly diluted alkaline environment and is therefore much safer to handle.
• The AEM Electrolyser can use similarly cost-efficient materials while making much purer hydrogen at higher efficiency.
• The AEM Electrolyser can fully ramp and is ideal to link up with variable renewable energy sources such as wind and solar that HydroGenesis will be deploying and integrating alongside our systems.
• Finally, the AEM electrolyser can tolerate a lower degree of water purity and de-ionized water is not required. This reduces the complexity of the input water and enables the integration of filtered rain and tap water, providing the dual benefits of easier deployment in non-expert, end-user locations. This is also more in harmony with an off-grid solution and more favourable to the environment.

Hydrogen can also be created in a number of different ways, but that topic will be covered in a future discussion around the colours of hydrogen.