Discover the different colours of hydrogen

Green, blue, grey – even purple! Although hydrogen is a colourless gas, it seems otherwise, given the numerous names adopted by industry and policymakers to define the different manufacturing methods. Don’t panic – here’s the ultimate guide to understanding the colours of hydrogen. ANEMEL clarifies concepts in hydrogen production, carbon capture, nuclear energy, and more.

“Hydrogen is a clean fuel, the key solution towards a net-zero energy economy”. This statement has almost become a mantra, repeated over and over by experts and policymakers convinced that hydrogen is the cleanest combustible – the cornerstone to control the climate crisis. It makes sense – since hydrogen is harvested from water, burning hydrogen yields only that same substance, clean and crystalline water. However, hydrogen features different denominations, colourful yet confusing. This article is a guide to understanding the so-called “colours of hydrogen” – read on.

Since a few centuries ago, we know how to split water molecules into their basic components – hydrogen and oxygen. In 1806, Humphry Davy famously presented the results of his research on water electrolysis at the Royal Society in London, showcasing that electrical currents could cleave chemical bonds. Even earlier experiments had come to comparable conclusions.

However nowadays, two centuries later, only a frail fraction of the hydrogen we produce comes from splitting water with electricity. Around 99% of the hydrogen our industry consumes comes from fossil fuels, in processes that generate gigantic amounts of carbon dioxide, contributing to the climate crisis. 

Hydrogen is a colourless and odourless gas. However, there’s different types of hydrogen depending on its origin and manufacturing method, hence industry and policymakers created the collection of colour codes. Most hydrogen today is grey hydrogen. Instead of coming from water splitting, grey hydrogen is derived from fossil fuels, including methane and other hydrocarbons. Oil companies carry out a process called “steam reforming”, which combines hydrocarbons with high-temperature, high-pressure water vapour to produce syngas, a mixture of hydrogen and carbon monoxide. The principal purpose of this process is the production of hydrogen – carbon monoxide is usually further oxidised and transformed into carbon dioxide, a greenhouse gas and therefore one of the most contaminant compounds responsible for the current climate crisis. Additionally, steam reforming further contributes to climate change because of the carbon emissions derived from reactors running with remarkable energy demands. Ideally, grey hydrogen should disappear from the current chemical landscape – it’s virtually equivalent to fossil fuels, like coal, oil, and natural gas.

A subtle swift in sustainability comes from capturing the carbon emissions of steam reforming – which yields blue hydrogen. In this case, industries install systems that trap the greenhouse gases emitted during the transformation of hydrocarbons into syngas, and usually stores them underground to avoid the release of contaminants to the atmosphere. This technology, known commonly as carbon capture and storage (CCS), could convey other problems – some derived from the high costs of developing the infrastructure, but most importantly the potential problems associated with carbon dioxide stored underground. Several reports by the European Environment Agency (EEA) point out that carbon capture could contribute to delaying the decommissioning of fossil fuel power plants, as well as lead to an increase of other pollutants in the atmosphere. It’s estimated that blue hydrogen could cut the carbon dioxide emissions of grey hydrogen by up to 90% – but still produces 23% more methane, which has a stronger greenhouse effect than carbon dioxide, and also contributes to the climate crisis. Although the EU considers blue hydrogen as a low-carbon alternative, it still heavily relies on fossil fuels as a feedstock, and therefore is not a completely carbon-free solution.

A graphic that explains the difference between gray and green hydrogen

Green hydrogen is the only real alternative. Green hydrogen is produced splitting water with electricity from renewable sources, mostly solar and wind, but also hydropower and geothermal. Green hydrogen is an important piece of the energy transition to net-zero – really the only “colour” produced in a climate-neutral manner, according to the World Economic Forum. In this case, the meaning of the mantra truly makes sense – when green hydrogen is consumed in a fuel cell, the only product is pure water. And, although nowadays renewable hydrogen is generally more expensive, ANEMEL and other projects work wonders to make it more efficient and even more sustainable. Besides maximising the productivity of electrolysers – the devices that split water into hydrogen and oxygen –, our project produces catalysts with abundant elements, including iron and nickel, instead of scarce and critical raw materials such as iridium and platinum. Additionally, ANEMEL will generate green hydrogen from dirty waters, including seawater, waste water, and other low-grade water sources. This will reduce the reliance on water purification and desalination systems, delocalising and democratising hydrogen production. Green hydrogen could also store the extra energy from intermittent sustainable sources, catapulting the connections between energy abundant and energy hungry areas.

Several companies and policymakers pledged to accelerate the adoption of green hydrogen during the UN’s COP26 Climate Conference in Glasgow, UK, as a means to decarbonise heavy industry, including shipping, and aviation. It’s a further acknowledgment of green hydrogen as an important pillar towards a net-zero economy and energy landscape.

An infographic explaining the different colours of hydrogen based on energy sources and manufacturing processes

Green hydrogen is great – but what about purple then? Because, as it turns out, purple hydrogen is also a thing. And pink, too. Although purple and pink probably the prettiest pigments – this sadly isn’t the case when it comes to the colours of hydrogen generation. In these cases, the energy to split water comes from nuclear power – nuclear electricity for pink hydrogen and nuclear heat (or thermal electrolysis) for purple, although definition vary among the different sources. The rainbow resumes with yellow, red, brown, even turquoise. Since all of these colours are made up by manufacturers, most are misused and mixed-up – partly on purpose, to distract the attention from fossil fuels, the real problem. 

According to the IEA, green hydrogen will help tackle various critical energy challenges, offering innovative ways to decarbonise a range of sectors – including transportation, the chemical industry, and the manufacture of iron and steel. Its versatility could enable renewables to provide an even greater contribution to the net-zero economy, thanks to its unique to help with the intermittency and variable outputs from sustainable sources of energy like solar and wind. Now is the time to scale up green hydrogen technologies, making it an efficient alternative for the energy transition.