The Technology
DESIREE: the technology behind green hydrogen
What is hydrogen?
Hydrogen is the simplest and most abundant chemical element. On Earth, it is typically found bound to oxygen in water or to carbon in fossil fuels.
Hydrogen is an energy carrier, meaning it stores energy produced from other sources. When used, it produces water as a by-product and does not emit carbon dioxide at the point of use.
However, its environmental impact depends entirely on how it is produced.
Why is hydrogen important?
The global energy system has long relied on fossil fuels such as coal, oil and natural gas. Their combustion releases carbon dioxide, contributing to climate change.
Hydrogen offers a pathway to decarbonise sectors that are difficult to electrify, including:
- Steel production
- Chemicals manufacturing
- Oil refining
- Heavy transport
- Aviation and shipping
- Long-duration energy storage
When produced from renewable electricity, hydrogen can significantly reduce greenhouse gas emissions.
What is green hydrogen?
Green hydrogen is produced by splitting water using renewable electricity. It avoids fossil fuels and minimises greenhouse gas emissions.
How does water electrolysis work?
Electrolysis uses electricity to split water into hydrogen and oxygen.
Water + electricity → hydrogen + oxygen
If renewable electricity is used, the resulting hydrogen is considered renewable.
Types of electrolysis technologies
- Alkaline electrolysis
- Proton exchange membrane (PEM) electrolysis
- Solid oxide electrolysis (SOEL)
What is solid oxide electrolysis?
Solid oxide electrolysis (SOEL) is a high-temperature technology that produces hydrogen by splitting steam into hydrogen and oxygen. In contrast with alkaline and PEM electrolysis (which operate at relatively low temperatures, (< 150 ºC) the high operating temperature of SOEL (600-850ºC) makes possible unrivalled energy conversion efficiencies compared to the low-temperature options, thanks to favoured thermodynamics and kinetics. Electrical efficiencies above 85% have been proven already when using steam as fuel in SOELs. Moreover, direct electrochemical conversion of hydrocarbons is also facilitated at high temperatures, which is particularly relevant for the conversion of CO2 into CO (co-electrolysis).
It operates at 600–850°C and uses a solid ceramic electrolyte to conduct oxygen ions. A solid oxide electrolysis cell is constituted by an oxygen electrode (anode) and a hydrogen electrode (cathode) separated by an ionic conducting electrolyte.
As water (steam) is supplied at the cathode side (hydrogen electrode), it is reduced into H2, while O2– ions migrate through the electrolyte to eventually form O2 by oxidation at the anode side (air electrode). So, hydrogen is produced at one side, oxygen at the other.
Since part of the required energy is supplied as heat rather than electricity, SOEL can achieve higher electrical efficiency than low-temperature electrolysis technologies and can integrate with industrial heat sources.
What are the main challenges of solid oxide electrolysis?
Although solid oxide electrolysis offers high efficiency and strong integration potential, several technological challenges still limit its widespread deployment.
These include:
- Accelerated material degradation at high operating temperatures.
- Thermal stress and mechanical instability.
- Long-term durability and lifetime limitations.
- Performance losses under dynamic operation.
- Complex system integration.
- Higher cost and complex manufacturing scalability.
Addressing these challenges is essential for enabling large-scale industrial adoption of high-temperature electrolysis systems.
DESIREE directly targets several of these barriers through improvements at material, stack and system level