Types of hydrogen and technologies

Hydrogen – Types and Technologies

There is an entire rainbow of hydrogen, not all of it “clean”.

Green HydrogenElectrolysis, using renewable energy (wind, solar etc.) to split water into its component parts (H2 + O2).No carbon emissions, ability to “store” surplus electricity from renewable sources.
Yellow HydrogenAs above, using nuclear power instead of renewable energy.Low carbon emissions, ability to “store” surplus electricity.
Brown HydrogenGasification, using coal/biomass/waste to heat water and break it down. Also known as “town gas”.Along with the component parts of water, other harmful elements are produced: carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), and ethylene (C2H4).
Grey HydrogenSteam Methane Reforming (SMR), using methane to heat water and break it down.As above, produces other harmful elements: CH4 and CO2.
Blue HydrogenSMR and carbon capture, use and storage (CCUS).Grey hydrogen but with carbon capture so it is seen as a lower carbon option.
Turquoise HydrogenUsing Molten Metal Pyrolysis, natural gas is passed through a molten metal that releases hydrogen and solid carbon.Solid carbon can be used for industrial applications, so it is seen as a lower carbon option.

Electrolysing technology

Electrolysis of water is the process of using electricity to split water into hydrogen and oxygen. This reaction takes place in electrolysers, devices which can range in size up to large-scale production facilities that can be linked to wind and solar farms.

As pure water is not a particularly good conductor, electrolysers use substances that are able to conduct electricity when dissolved in water which are known as electrolytes. There are different types of electrolysers depending on the (i) electrolyte materials they use and (ii) temperature at which they are operated.

Low-temperature electrolysis technologies are the most developed. High-temperature electrolysis is also possible but is still in development stage and not yet commercially available. The hope is that, in due course, it will increase conversion efficiency (efficiency being measured as the amount of electricity required to produce a certain amount of hydrogen) and produce synthetic gas for use in synthetic liquid fuels.

Alkaline Electrolysis (AE)Low-temperature electrolysis that uses a solution composed of water and a liquid electrolyte. This method has been in commercial use since the middle of the 20th century. With a liquid electrolyte, more peripheral equipment such as pumps for the electrolyte, solution washing and preparation are required. So, although it is the cheapest to purchase, it has relatively high maintenance costs.
Proton Exchange Membrane (PEM) electrolysisLow-temperature electrolysis that uses a conductive solid membrane and requires no liquid electrolyte. Compared to alkaline electrolysis, PEM electrolysis can react more quickly to fluctuations in generation. It is often used for distributed systems because the equipment is low-maintenance and delivers high-quality gas. However, precious metals such as platinum are often required so it is expensive up front.
Anion exchange membrane (AEM) electrolysis, also known as alkaline PEMNewer variant of low-temperature electrolysis, which does not use precious metals, currently only manufactured by Enapter.
Solid Oxide Electrolysis (SOE)Some studies posit that H2 production by high temperature steam electrolysis using SOEs is competitive to H2 production from fossil fuels at electricity prices below €0.02–0.03/kWh, while recognising that “substantial R&D is still required to obtain inexpensive, high performing and long-term stable electrolysis cells”.

This list is by no means exhaustive, but we hope it will serve as a helpful introduction to the language of hydrogen technology. It is also worth noting that many of the electrolysis processes above do not need to operate solely in large industrial installations. Electrolysers can be large scale, or they can use the modular approach favoured by Enapter.

Finally, a word about fuel cells. A fuel cell generates electricity from an electrochemical reaction just like a battery but the ‘fuel’ often being referred to is hydrogen, e.g. the hydrogen produced from electrolysis. The fuel cell converts the chemical energy of hydrogen into electricity by reacting hydrogen with oxygen to form water and as by-product, releasing electrons through an external circuit as an electric current. Fuel cells can produce electricity indefinitely as long as the hydrogen and oxygen are supplied. For our more technically minded readers, further information about how fuel cells operate can be found here.

“As part of their commitment to reaching net zero emissions, many governments around the world are looking to ban vehicles with internal combustion engines in the run up to 2050.”


There are many existing applications for hydrogen technologies, and many more industries with vast potential. It is an exciting time for stakeholders in these industries, whether they are transforming and revitalising existing businesses, building new business models or deploying new hydrogen technologies.

Current and potential applications for hydrogen include:

  • as a replacement fuel for oil and gas in transport, heat and generation
  • storage of “excess” renewable energy, e.g. from offshore wind.
  • making use of existing gas pipelines
  • a potential export via pipeline and ships to boost economies
  • revitalising industrial ports
  • fuel for ships, heavy goods vehicles and freight
  • marine transport, both shipping and cruise lines
  • aviation, and
  • submarine transport.

Drivers of growth

There are many factors that are driving interest in and growth of green hydrogen. Many countries have signed up to the Paris Agreement and are therefore seeking to reduce carbon emissions. Their goal is to limit the impact of climate change and, more specifically, limit global temperature increase to 1.5 degrees Celsius. Some countries have gone even further, with the United Kingdom being the first major economy to enshrine a net zero emissions target into law in June 2019. As the United Nations reported in September 2020, the “number of commitments to reach net zero emissions from local governments and businesses has roughly doubled in less than a year”.

As part of this commitment, many governments around the world are looking to ban vehicles with internal combustion engines in the run up to 2050. In its Global EV Outlook 2020, published in June 2020, the IEA noted that “17 countries have announced 100% zero-emission vehicle targets or the phase-out of internal combustion engine vehicles through 2050.” The report cited France as the first country to put this into law in December 2019, with a target date of 2040. The UK recently (November 2020) increased its ambition, bringing forward the target date to 2030.  As set out by the BBC, “the UK is now in second place after Norway, which has a fossil fuel vehicle abolition date of 2025”.

Reducing carbon emissions in electricity production is, in some ways, the easiest part of the puzzle.  Work has clearly started toward reducing emissions in road transportation, as set out above.  However, reductions are also needed in long haul transportation, heating and industry.