How Is Green Hydrogen Actually Made?

The short version

Green hydrogen is made by running an electric current through water to split it into hydrogen and oxygen — a process called electrolysis. What makes it "green" isn't the chemistry, which is the same regardless of color-code: it's that the electricity powering the reaction comes from renewables like wind or solar, so no fossil fuel is burned anywhere in the process.

Why the color matters

Hydrogen itself is colorless — the color labels describe how it was produced, not the gas.

• Grey hydrogen — made from natural gas via steam methane reforming. This is how the vast majority of hydrogen produced today is made, and it releases significant CO₂ in the process.
• Blue hydrogen — the same natural-gas process as grey, but paired with carbon capture to reduce (not eliminate) the emissions.
• Green hydrogen — made by electrolysis using renewable electricity. No fossil fuel input, and the only byproduct of the reaction itself is oxygen.

The color-coding exists because "hydrogen" alone tells you nothing about its carbon footprint — two hydrogen molecules can be chemically identical while one required drilling and combustion and the other required only water and sunlight.

What actually happens inside an electrolyzer

An electrolyzer has two electrodes — an anode and a cathode — submerged in water, separated by a membrane, with an electric current running between them.

1. Water molecules at the cathode gain electrons and split into hydrogen gas and hydroxide ions.
2. The hydroxide ions migrate across the membrane to the anode, where they lose electrons and combine into oxygen gas and more water.
3. The membrane keeps the hydrogen and oxygen gas physically separated as they form, which matters — mixed together, they're explosive.

The two dominant electrolyzer designs are PEM (proton exchange membrane) and alkaline. PEM units respond faster to fluctuating power input, which matters when the electricity source is wind or solar rather than a steady grid draw — a genuine engineering reason renewable-powered electrolysis leans PEM more than older alkaline designs do.

The efficiency problem nobody skips past

Electrolyzer efficiency typically runs 60-80%, meaning a real share of the input electricity is lost as heat rather than ending up in the hydrogen. That's before accounting for compression or liquefaction, both of which cost additional energy if the hydrogen needs to be transported or stored densely. This is the core economic tension in green hydrogen: it's a genuinely clean energy carrier, but converting electricity to hydrogen and back is less efficient than just using that electricity directly — which is why green hydrogen makes the most sense for use cases electricity can't easily reach, like steelmaking, shipping fuel, or long-duration storage, rather than as a general substitute for the grid.

The takeaway

Green hydrogen isn't a different chemical from grey or blue hydrogen — it's the same molecule made without fossil fuel input. The real story is efficiency and cost: electrolysis works today, but scaling it affordably is the actual bottleneck the industry is working through, not the underlying science.