Hydrogen: the (sometimes) zero carbon fuel

You’ve probably heard that Hydrogen is ‘fuel of the future’. There are a few reasons for this: it is amazingly energy dense, it’s incredibly light (stemming from it being the lightest element on the periodic table) and doesn’t produce harmful greenhouse gases (GHGs) when burnt. This last one is important in the era of climate change. These GHGs (mainly carbon dioxide and methane) have been linked by the IPCC to an average warming of 1˚C on pre-industrial levels (2018 figure). Burning hydrogen does produces a GHG: water vapour. However it isn’t harmful to the environment in the same way the others are; Carbon Dioxide (CO2) will stay in the atmosphere for around 400 years, while water vapour will come back down in the next shower of rain.

A Hydrogen Fueling Station
A Hydrogen Fuelling Station. Source: GPA Photo Archive via Flickr

Hydrogen also has another advantage going for it: it’s abundant. In fact Hydrogen is the most abundant element in the universe. This abundance extends to Earth, however, the hydrogen we want to use (H2) is virtually non-existent. What we do have is so light it leaks into space. As a result of this we need to break it out of other molecules and convert it this diatomic form to be able to use it.


The hydrogen jail break

There are various processes to make hydrogen, three of the more common ones are: ‘steam reforming’, ‘coal gasification’ and ‘electrolysis’. Both ‘steam reforming’ and ‘coal gasification’ liberate hydrogen from fossil fuels in complex catalyst driven reactions. ‘Electrolysis’ splits water into hydrogen and oxygen gas using electricity. Currently steam reforming is most widely used, but (like other processes) is quite energy intensive. A lot of CO2 is also produced. Coal gasification turns coal into a gas mixture (mainly methane) and also creates large amounts of carbon emissions. The future of using hydrogen as a fuel is dependent on non-fossil fuel sources of hydrogen, electrolysis is the only one of these processes which can be fulfil this. The hydrogen produced from electrolysis is referred to a ‘green’ hydrogen.

Some applications of hydrogen electrolysis. Credit Rh2network on Wikimedia Commons

Green, black, blue… polka dot? What the colours of hydrogen mean

“Wait, isn’t hydrogen colourless?” I hear you say. Yes, it is. The colours of hydrogen are used to help clarify climate impact and help with marketing. Green hydrogen uses renewable energy to provide the energy from the electrolysis. If the renewable energy is wind or solar the production is carbon emission free. Further if the water for the electrolysis is sourced from wastewater, drinking water is not used up which is a further benefit.


The next colours of hydrogen come from fossil fuels and depend on which one. Black or brown hydrogen is generated through coal gasification, whereas grey hydrogen uses steam reforming and is derived from natural gas. Blue hydrogen is another term that has recently surfaced and is used to describe fossil fuel production processes that use Carbon Capture and Storage (CCS) to trap emissions.


Finally polka dot hydrogen: this one doesn’t exist but it would be cool if it did so I could explain it.

Toyota Mirai Hydrogen Fuel Cell Car. Source: M93 on Wikimedia Commons

The rise of hydrogen

Hydrogen has been used for a long time in industry: fertiliser and petroleum production both use large amounts of hydrogen as a feedstock. Now hydrogen fuel cell vehicles are now starting to be released into the market, with the likes of the Toyota Mirai and Hyundai Nexo. Hydrogen trucks, buses, and trains. The success of these vehicles will likely be dictated by the availability of charging facilities, but these are being built with the support of governments and companies.


As humans looks for ways to transition from fossil fuels and electrolysis equipment improves, the price of producing hydrogen will fall. From our current scientific understanding, green hydrogen is the ideal fuel: energy dense, light and no harmful carbon emissions. Now it just seems to be a matter of watching and waiting for it to become a reality



Read More:

IPCC: Global Warming of 1.5˚C

Hydrogen: Royal Society of Chemistry

Featured Image – The Alstom Coradia iLint: the first hydrogen train. Credit Linus Follert via Flickr

2 Responses to “Hydrogen: the (sometimes) zero carbon fuel”

  1. mbalia says:

    Thanks for reading Ruby. I really hope that green hydrogen becomes more common as well. With the energy density, yes it is per kilogram. You are also right with the low volume density with it being a gas. According to the US Department of Energy, 1kg of Hydrogen (compressed) has the same energy content of 2.8 litres of petrol. For a more real life metric, the Toyota Mirai can drive for 500km on a 5kg tank.

    For aviation figures are harder to bring up. Some sites say liquid hydrogen has 3 times the energy of jet fuel, but I can’t verify that properly for you

  2. Ruby Dempsey says:

    I love the explanation of the colours of hydrogen! Hopefully green hydrogen will become more and more common.

    When you say hydrogen is energy dense, what metrics are you using? It might be energy dense by weight but not by volume, seeing as it’s a gas. I also wonder how dense it is compared to petrol or jet fuel?