Ever wondered how one element can come in so many colours? From green and blue to turquoise and purple, and everything in between, here’s what all the colours on the hydrogen spectrum actually mean.

Hydrogen has emerged as an energy source with a key role to play in decarbonising the global economy, according to both CSIRO and the International Energy Agency. It’s the simplest and most common element in the universe, and the first on the periodic table, but here on Earth, it almost never occurs naturally in its pure form.

Instead, it forms part of other materials, such as water, fossil fuels and minerals. Releasing it from those forms requires energy, which is where the hydrogen colour wheel comes into play.

In reality, hydrogen is an invisible gas – it doesn’t actually come in different colours. But it’s assigned a colour-coded name based on the source it was produced from and the process used to separate it, in order to differentiate between the various methods that have been invented to harness its power.

As a general rule, lighter and brighter colours are assigned to methods of production that are lower in greenhouse gas emissions, while darker colours are assigned to methods that are higher in emissions.

Here are the main hydrogen colours you need to be aware of – and a few that are lurking on the edges of the rainbow.

The hydrogen colour spectrum

Green hydrogen

Green hydrogen – also known as renewable hydrogen – is produced from water, using a process called electrolysis.

This involves a strong electrical current – generated from renewable sources like solar or wind energy – being passed through purified water. The apparatus used to do this is called an electrolyser. The electrochemical reaction splits the water into its constituent elements, hydrogen and oxygen.

Because the electricity that powers the electrolyser comes from renewable sources, and the only by-product of the process is oxygen, the production of green hydrogen releases no greenhouse gas emissions. It’s a sustainable and environmentally friendly means of hydrogen production.

Hydrogen can be stored for long periods of time. This means that green hydrogen production can use the excess solar and wind energy generated on sunny and windy days, and then convert the energy produced by these intermittent resources back into electricity when the market needs it, helping to firm the electricity grid.

Green hydrogen is relatively expensive to produce, which is why it currently makes up a small percentage of overall hydrogen production. But as renewable energy prices fall and electrolysers become cheaper and more efficient, it’s expected to become increasingly common.

Blue hydrogen

Blue hydrogen is produced through a process known as steam reformation, which uses steam to separate hydrogen from natural gas.

Natural gas is a fossil fuel, and this process does produce greenhouse gas emissions, which is why it’s sometimes referred to as ‘low-carbon hydrogen’. But in blue hydrogen production, those emissions are neutralised through the use of carbon capture and storage technology, which captures carbon dioxide emissions and stores them to prevent them from affecting the atmosphere.

Grey hydrogen

Grey hydrogen is also extracted from natural gas via steam reformation in the same way as blue hydrogen. The difference is that none of the carbon is captured – instead, the emissions are released into the atmosphere, hence its gloomy ‘grey’ moniker.

Brown and black hydrogen

This is hydrogen extracted from brown (lignite) or black (bituminious) coal. This is done via gasification, a process that uses heat to turn carbon-rich coal into gas.

This releases the hydrogen contained within, but it also releases carbon emissions. As with grey hydrogen, none of these emissions are captured or stored, but are instead released into the atmosphere.

The hydrogen discussion tends to be dominated by the colours we’ve described so far – but these aren’t the only methods of hydrogen production.

Turquoise hydrogen

Still in the experimental phase, this is hydrogen that’s produced via pyrolysis. This is a method that sees natural gas heated to such high temperatures that it breaks down into hydrogen and solid carbon.

Because the carbon is in solid form, it isn’t being released into the atmosphere, and can either be buried underground or used for other purposes, like tyre manufacturing.

The hydrogen production process itself doesn’t produce any greenhouse gases, but it wouldn’t be accurate to call it a ‘zero emissions’ method, because the extraction and transport of natural gas still results in fugitive emissions.

Fugitive emissions make up about 10 per cent of Australia’s greenhouse gas inventory, and are classified as losses, leaks and other releases of gas that occur during the production, processing, transport, storage, transmission and distribution of fossil fuels.

Yellow hydrogen

Essentially just a more specific form of green hydrogen, this is hydrogen that’s produced through electrolysis powered purely by solar energy, as opposed to any other form of renewable energy.

Confusingly, because hydrogen naming conventions aren’t necessarily agreed upon universally, you may also see ‘yellow hydrogen’ used to describe hydrogen produced through electrolysis using a mix of renewables and fossil fuels – i.e. whatever power is available through the grid at the time.

Pink hydrogen

Sometimes referred to as purple hydrogen, this is also produced using the electrolysis method – but in this case, the electrolyser is powered by nuclear energy.

Nuclear power stations continue to be banned in every state and territory of Australia, which means you’re unlikely to hear about pink hydrogen in the context of Australia’s hydrogen future.

White hydrogen

White hydrogen is said to be a naturally occurring version of hydrogen in its pure form that can be found underground. At present, however, it isn’t viable to extract it, and there is little known about this type of hydrogen.

Green is gold

Green hydrogen, as a zero emissions fuel that can be used to help stabilise the electricity grid by soaking up and storing excess solar and wind energy, is increasingly being seen as the gold standard of hydrogen production for the future.

There are a range of applications for green hydrogen that can help to decarbonise Australia’s economy, including powering heavy transport and industrial facilities and processes, and replacing or partially substituting natural gas for cooking and heating in homes.

But the greatest potential for green hydrogen is likely to be in international trade, as Australia can export hydrogen to countries that aren’t as rich in renewable resources.

With abundant solar and wind resources, world-class infrastructure, export-ready ports and close proximity to Asia, Queensland is particularly strongly positioned to become the green hydrogen supplier of choice for countries such as Japan and South Korea.

To that end, there are significant green hydrogen projects planned or under development across the state, including Stanwell’s Central Queensland Project (CQ-H2).

Stanwell is working with domestic and international partners from across the hydrogen supply chain to develop Queensland’s global-scale renewable hydrogen project, with the view to exporting renewable hydrogen via its different carriers, to Japan and Singapore, as well as supplying large industrial customers in Central Queensland.

The CQ-H2 Project consortium comprises Japanese foundation companies Iwatani Corporation and Marubeni Corporation, Stanwell Corporation, and Singapore’s Keppel Limited.

The CQ-H2 Project involves the development of a hydrogen production facility at Aldoga, near Gladstone, the development of a hydrogen gas pipeline to transport hydrogen to Gladstone Port, the development of a hydrogen liquefaction facility and ship loading facilities at Gladstone Port, and the supply of hydrogen to an ammonia production facility at Gladstone Port.

The CQ-H2 Project could become the largest renewable hydrogen project in Queensland, eventually scaling up to produce 800 tonnes per day of clean, green hydrogen by the early 2030s.

CQ-H2 is at an advanced stage, with the CQ-H2 consortium, nearing completion of a Front-End Engineering Design (FEED) study for the project. The FEED study includes a commitment of AU$117 million from government and consortium partners. 

The Australian Government, via its Clean Hydrogen Industrial Hubs program, has also announced $69.2 million in funding to Stanwell to support the development of the Central Queensland Hydrogen Hub.