What is green hydrogen?

Hydrogen is regarded as one of the key building blocks for a climate-friendly energy supply. It can store electricity generated from renewable sources and make it available for use at a later date. But how does this actually work? How is green hydrogen produced? And how can this process be taught in a practical way in the classroom?

What is hydrogen?

Hydrogen is the lightest and most abundant chemical element in the universe. It consists of just one proton and one electron and forms the basis of many natural processes. On Earth, hydrogen rarely occurs in its pure form. Instead, it is usually bound in chemical compounds, for example in water (H₂O) or in organic substances such as natural gas, crude oil and biomass. In order to use hydrogen as an energy carrier, it must first be extracted from these compounds.

How is hydrogen produced?

Not all hydrogen is the same. Depending on how it is extracted from chemical compounds and which energy sources are used in the process, it is assigned different colours. These colour designations indicate how sustainable the production method is and what impact it has on the climate.

The 4 types of hydrogen

Grey hydrogen

  • Main component: methane (CH₄)
  • Steam reforming produces H₂ and CO₂
  • Not very sustainable (emissions)

Blue hydrogen

  • Produced from methane (CH₄), like grey hydrogen
  • CO₂ is stored underground
  • Transitional solution

Turquoise hydrogen

  • Produced from methane (CH₄)
  • Methane pyrolysis splits methane into hydrogen (H₂) and solid carbon (C)
  • More climate-friendly than grey hydrogen

Green hydrogen

  • Produced by electrolysis
  • Water is split into H₂ and O₂
  • No emissions

The most commonly used form of hydrogen today is what is known as ‘grey hydrogen’. It is predominantly produced from natural gas, the main component of which is methane (CH₄). In this process, the methane reacts with water vapour at high temperatures. This process, known as steam reforming, produces hydrogen (H₂) and carbon dioxide (CO₂), which is released into the atmosphere. Because of these emissions, grey hydrogen is therefore considered to be not very sustainable.

Blue hydrogen is produced in the same way as grey hydrogen. The difference is that the carbon dioxide produced is not released into the atmosphere, but is captured and stored deep underground. This results in significantly lower emissions than with grey hydrogen. However, as fossil fuels are still required for its production, blue hydrogen is regarded merely as a transitional solution.

Turquoise hydrogen is also produced from methane (CH₄). Unlike steam reforming, however, the methane is broken down directly into hydrogen (H₂) and solid carbon (C) at high temperatures through methane pyrolysis, without the use of steam or oxygen. As no carbon dioxide is produced in the process, this method is more climate-friendly than the production of grey hydrogen. However, just how sustainable turquoise hydrogen actually is depends on how the required energy is supplied and how the resulting carbon is used or stored.

Green hydrogen is considered to be particularly climate-friendly. It is produced by electrolysis, a process in which water (H₂O) is split into hydrogen (H₂) and oxygen (O₂) using electricity generated from renewable energy sources. As this process produces no emissions, green hydrogen plays a central role in plans for a sustainable and climate-friendly energy supply.

How does hydrogen work as an energy storage medium?

Electricity from solar and wind power is not always generated exactly when it is needed. Hydrogen solves this problem: surplus electricity is used via electrolysis to split water into hydrogen and oxygen. The hydrogen stores the energy chemically, can be transported, and can be converted back into electricity in a fuel cell whenever needed.

Hydrogen is not an energy source, but an energy carrier.

Energy sources such as the sun or wind supply the energy. Hydrogen can absorb this energy, store it, and make it available again at a later point in time. In this way, it helps to balance out fluctuations in electricity generation from renewable sources.

Producing green hydrogen yourself in the classroom

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