Not all hydrogen is created equally. One is clean and renewable, but others are made from dirty fuels. So what separates green, blue, brown and black hydrogen? 

Hydrogen is the smallest and most abundant element in the universe, and it’s poised to be one of the key solutions to the world’s transition to clean energy.

Soon, hydrogen will be used for energy storage, and to power cars, trucks and ships. 

Burning pure hydrogen releases no climate pollution, so if it’s done right, it’s a great climate solution. 

But not all hydrogen is created equally. 

In January 2022, Australia exported liquefied hydrogen overseas.

But while this was hailed as an important moment in Australia’s energy transition, the hydrogen was produced with polluting coal.

So what are the differences between the way hydrogen is manufactured, and which methods are truly clean?

Hydrogen colour codes explained

The first thing we learn in high school chemistry is that hydrogen is the most abundant element in the universe.

We also learn that it’s a completely colourless gas in its natural state.

But a range of colours are used to describe the type of hydrogen produced by a range of chemical and physical processes - some using renewable energy, others using fossil fuels like coal and gas. 

So which hydrogens are clean, and which are dirty?

Green hydrogen is clean hydrogen

Green hydrogen is produced using renewable energy in a process called electrolysis, which involves channeling an electric current through water. 

The energy from this current breaks the bonds in the water molecules, releasing separate hydrogen and oxygen atoms.

And because the electricity used in this process is generated by a renewable power source (such as a solar array or wind turbine), no climate pollution is released.

Methane gas creates ‘dirty’ hydrogen

Hydrogen production using coal or gas results in the creation of climate pollution.

‘Grey’ and ‘blue’ hydrogen are made through a process called steam methane reforming

In a nutshell, this involves separating hydrogen atoms from methane gas.

However this process also releases the main climate pollutant carbon dioxide.

When carbon dioxide escapes the process and enters the atmosphere, it contributes to the continued heating of the planet and exacerbates the effects of climate change.

Grey hydrogen is the term given when carbon dioxide is released in steam methane reforming.

Blue hydrogen is used when this carbon is captured and stored.

So is blue hydrogen clean or dirty?

Blue hydrogen is ‘dirty’ because it involves the use of methane during production.

Blue hydrogen is distinguished from grey hydrogen because carbon capture projects are meant to capture the pollution created.

But in reality, expensive climate capture projects have been unsuccessful and delay the shift to clean energy projects.

This was recently highlighted by failures at the world’s most expensive carbon capture project in Western Australia.

This Chevron-led project is also the only CCS initiative operating in Australia.

This project was required by the WA government to safely store 80% of the gas field’s carbon dioxide beneath Barrow Island.

Chevron captured just 45% of its target.

Even if Chevron purchases millions of dollars in carbon offsets (some of which may not represent carbon abatement) to compensate for this failure, it won’t take the 5.23 million tonnes of carbon it failed to store out of the atmosphere.

What about black and brown hydrogen?

These are some of the dirtiest forms of hydrogen possible.

Why? Simply because brown or black thermal coal must be heated in the gasification process used to make brown or black hydrogen. 

As with other forms of energy production using coal, this results in the creation and release of carbon dioxide pollution. 

Colours are confusing, can we make it simple?

Hydrogen production is exciting for consumers wanting to see a rapid transition to renewable energy around the world. 

And as one of the sunniest and windiest countries in the world, Australia is well placed to be a leader in clean, renewable hydrogen.

If no climate pollutants – carbon dioxide, methane or other hydrocarbons – are released in the process, then the hydrogen product can be described as clean.

Right now, clean hydrogen is green hydrogen.

If it creates climate pollution, the hydrogen is not clean.

And that means all blue, grey, brown and black hydrogen is dirty.

Matt Agius

Australian Conservation Foundation