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How is green hydrogen produced?

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Quick answer

Green hydrogen is made by electrolysis: renewable electricity from solar or wind passes through water in an electrolyser, splitting each water molecule into hydrogen and oxygen. Hydrogen gathers at the negative electrode and oxygen at the positive one. Because no fossil fuel is involved, producing it releases almost no carbon dioxide, unlike most hydrogen today.

Green hydrogen is produced by splitting water into hydrogen and oxygen in an electrolyser powered by renewable electricity such as solar or wind. Because no fossil fuel is burned and only oxygen is released as a by-product, the process emits almost no carbon dioxide.

Step by step

  1. Solar panels or wind turbines generate electricity, which is converted to direct current for the electrolyser.
  2. Purified water flows into the electrolyser cells, where electrodes sit on either side of a membrane or electrolyte.
  3. Current splits water molecules, releasing oxygen at the positive electrode and hydrogen at the negative electrode.
  4. The two gases are piped out separately, and the oxygen is vented or sold for industrial use.
  5. Hydrogen is dried and compressed, liquefied or turned into ammonia for storage and transport to users.

Key things to understand

  1. Purified water is fed into an electrolyser, a stack of cells each with two electrodes separated by an electrolyte or membrane.
  2. Renewable electricity drives a direct current between the electrodes, supplying the energy needed to break water molecules apart.
  3. Hydrogen gas forms at the negative electrode and oxygen gas at the positive electrode, kept apart by the membrane.
  4. Alkaline and proton exchange membrane electrolysers are the most common types, differing in their electrolyte and how they handle varying power.
  5. The hydrogen is dried, compressed or converted to ammonia for storage, then used in industry, fuel cells or as a fuel.

Labelled diagram

  1. Renewable power

    Solar or wind electricity supplies direct current to the electrolyser stack.

  2. Water feed

    Purified water enters the cells between the two electrodes.

  3. Anode

    The positive electrode releases oxygen gas as water molecules split.

  4. Membrane

    Lets ions pass while keeping the hydrogen and oxygen gases apart.

  5. Cathode

    The negative electrode releases hydrogen gas, which is collected and compressed.

How an electrolyser makes green hydrogen

Real-world examples

  • India's National Green Hydrogen Mission, launched in 2023, supports electrolyser factories and hydrogen hubs on its coasts.
  • Fertiliser makers are testing green hydrogen to make ammonia without the natural gas normally used.
  • A pilot in northern Sweden has made steel using green hydrogen instead of coal to remove oxygen from iron ore.
  • Hydrogen fuel-cell buses in several cities run on hydrogen, emitting only water vapour from their exhaust.

Common mistake

✗ Myth: Hydrogen is an energy source we can dig up or harvest like oil or coal.

✓ Fact: Hydrogen is usually an energy carrier, not a primary source. It must be made using energy from something else, and green hydrogen stores renewable electricity in chemical form, losing some energy along the way.

People also ask

How is green hydrogen made?
It is made by electrolysis. An electrolyser passes direct current from solar or wind power through purified water, splitting it into hydrogen at the negative electrode and oxygen at the positive one. A membrane keeps the gases apart, and the hydrogen is then dried and compressed for storage or use.
Why is it called green hydrogen?
The colour label describes how the hydrogen was made, not its appearance, since hydrogen gas is colourless. Green means renewable electricity powered the electrolysis, so production releases almost no carbon dioxide. Grey hydrogen comes from natural gas with emissions released, and blue hydrogen captures some of those emissions.
Is green hydrogen better than batteries for cars?
For most cars, batteries are more efficient: turning electricity into hydrogen and back in a fuel cell loses far more energy than charging a battery. Hydrogen is more promising where batteries struggle, such as heavy industry, fertiliser production, steelmaking and possibly long-distance shipping.
What is the difference between green, grey and blue hydrogen?
Grey hydrogen is made from natural gas by steam reforming, releasing carbon dioxide. Blue hydrogen uses the same process but captures and stores much of that carbon dioxide. Green hydrogen comes from electrolysis powered by renewable electricity.
How much water does green hydrogen need?
About 9 kilograms of pure water are consumed for every kilogram of hydrogen, set by the chemistry of water. Purification and cooling raise the total, so plants in dry areas often plan desalination or treated wastewater supplies.
Why is green hydrogen expensive?
Electrolysers are costly, and electricity is the biggest running cost: roughly 50 to 55 kilowatt-hours are needed per kilogram of hydrogen. Cheaper solar and wind power and larger factories for electrolysers are expected to bring costs down.
What is green hydrogen used for?
Today's main uses for hydrogen are making ammonia for fertiliser and refining oil, and green hydrogen can replace the fossil-based supply there. It is also being tested for steelmaking, shipping fuels and fuel-cell trucks and buses.

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