All colours of hydrogen

If it were easy to achieve a 'hydrogen economy', it would have been done long ago. It has been talked about for at least 20 years, with little result (at least until now). And yet all sorts of things are said about hydrogen, from grey to blue, from purple to green. Here are a few insights.

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© Luz Calor Som on Pexels - Stars are made of hydrogen, as is 75% of all matter.

Let’s start with the basics: hydrogen, which chemists like to identify with the letter H, is the most common element in the universe: almost 75% of all matter is made up of hydrogen. It may sound poetic, and perhaps it really is, but to paraphrase Dante, one could say that it is hydrogen that moves the sun and other stars, because it is precisely hydrogen that makes up the sun, just as planets such as Jupiter and Saturn are largely made up of hydrogen. On Earth, however, this element does not like to be alone, it is as sociable as it is abundant: when it bonds with oxygen we get water, if it bonds with carbon we get hydrocarbons (from methane to coal), when it bonds with both oxygen and carbon we get the various organic compounds. Finding it on its own is virtually impossible: there are no hydrogen mines on Earth! And yet we need it, and lots of it: before we even imagine green transition uses, we need to be aware that hydrogen is used a lot in agriculture today: we need hydrogen to make ammonia, and therefore ammonium salts, and fertilisers. We literally eat hydrogen.

The colours of hydrogen: a question of production

On earth, hydrogen has to be produced, and here’s where the problems start, because to get it, you literally have to detach it from the molecules in which it is combined. And doing this requires energy, sometimes a lot of energy. In order to quickly describe how hydrogen is produced, people have started to use ‘colours’, although this is not the actual colour of the element, which is completely transparent and, in its gaseous state, invisible to the human eye.

Black. The first molecule from which hydrogen can be ‘detached’ is water. We all know, more or less from primary schools, that the water molecule is in fact made up of two hydrogen atoms (H) and one oxygen atom (O): the famous H2O. By running a very powerful flow of electric current through the water, i.e. using a process called electrolysis, I can detach the individual atoms from each other and obtain hydrogen on one side and oxygen on the other. The question is: how do I generate the (much) electricity needed for electrolysis? If I get it from coal- or oil-fired power stations, I pollute. And a lot of it: to make 1 kg of hydrogen with this technology requires an amount of energy equal to the needs of an average Italian family for a whole week. Since it is very polluting, the hydrogen produced in this way is identified as black.

Grey. Most of the hydrogen produced, 97% to be precise, is grey. The technological process used is known as reforming, i.e. starting not from water but from methane – consisting of one carbon atom and four hydrogen atoms (CH4) – or other hydrocarbons. During this operation a lot of carbon dioxide is released into the atmosphere, the infamous CO2 which, being odourless and colourless, was never a problem until a few years ago: we have always released it into the atmosphere without great concern, creating the climatic disaster that we are now beginning to perceive.

Brown. Hydrogen extracted through the gasification process of hard coal (lignite) is brown, again producing a large amount of CO2 which is released into the atmosphere.

© Publlic Domain Pictures on Pixabay – Lignite. It is used to produce so-called ‘brown’ hydrogen.

Blue. Hydrogen produced in the same way as grey hydrogen is called blue, but the process does not throw the CO2 produced directly into the atmosphere, but captures and stores it. In practice, however, it is not so simple: storing CO2 has a very high cost, not only in energy terms. To date, the only use is by the oil industry, which uses this carbon dioxide for secondary oil recovery: CO2 is pushed into the reservoirs with the aim of bringing to the surface the residual oil from the wells which otherwise would not have been extracted. But this means not releasing CO2 – generated to produce hydrogen – into the atmosphere in order to obtain oil, which then burns and generates more CO2 that is released into the atmosphere. A nonsense (from a green transition perspective, certainly not from an economic point of view for the oil industry). And then: to pump carbon dioxide into wells 1,000 metres deep requires energy: a power plant, and how is it powered? If I use fossil fuels, there is a double nonsense. If I use renewables, well, then I could have used them directly and polluted less. So, blue is a beautiful colour, but for hydrogen it is just a beautiful idea that in practice generates more problems than it solves.

Green. Green hydrogen is generated from water, like black hydrogen. Only in this case, the electricity needed for electrolysis is not obtained from fossil fuels, but from renewable energy such as hydroelectric, solar or photovoltaic power. To produce hydrogen in this way, therefore, a surplus of renewable energy is needed. At present, Italy – which is among the top European producers of renewable energy – produces 40% of its needs. This means that we consume all of it for ordinary purposes and have none left over to produce green hydrogen.

Violet. Violet hydrogen is generated from water, like black hydrogen. Only in this case, the electricity needed for electrolysis is obtained not from fossil fuels, but from nuclear energy. And so it is necessary to envisage the construction of nuclear power plants which, as we know, are very efficient, technologically advanced, do not produce carbon dioxide, but radioactive processing waste which is very difficult to dispose of and treat, and has a high social impact.

And once hydrogen is produced, how is it distributed?

Whatever technology is used to produce hydrogen, with the pros and cons we have tried to summarise, hydrogen has another very serious problem: it is difficult to store and transport. Hydrogen is the lightest element in nature, and is the smallest molecule in the universe. To try and store it, I can currently do mainly two things:

  • I could compress it, but I’d have to take it to very high pressures and that’s not at all trivial (about 700 bar) and put it in tanks;
  • I could liquefy it, but to do that I’d have to be able to bring it to – and maintain – minus 253 degrees below zero, so I’d have to use a lot of energy. It’s no coincidence that to date you can only do that for the space shuttle.
© NASA Imagery – The Space Shuttle’s External Tank contains liquid hydrogen and oxygen used during take-off.

There are other ways of storing it (in the form of ammonia, metal hydrides, using highly porous solids, and so on), but in many cases we are still talking about basic research that cannot be used on the market. It would quickly corrode the existing pipes, and the valves and compressors would have to be changed; they would have to be different from those used for methane, and would need to be at least three times more powerful. This would require very sophisticated tests to devise a hydrogen distribution network and very expensive investments in infrastructure.

Temporary conclusions

The path to energy transition is not trivial and is fraught with technological, social and economic obstacles and difficulties. It is easy to be misled by “coloured” simplifications, which often conceal pitfalls or markedly partisan interests, and this is what decision-makers must avoid at all costs. As yet, there is no clear path to follow: they all need to be explored with patience and common sense to identify the best one and achieve the decarbonisation targets that have been set. So, a few thoughts and questions:

  • Research in the field of hydrogen storage and distribution is crucial and should be funded: it makes no sense for our country or Europe not to invest in research and then buy technology from third parties: what are we doing in this regard?
  • We need to focus strongly on the electrification of end-use consumption, on energy efficiency and energy recovery, so that we all become energy prosumers. Today, conventional thermal power stations convert about 30% of the fuel’s energy into electricity and the remaining 70% is lost in heat. If we add to this the heat loss downstream (buildings, cars, appliances, etc.) we realise the enormous absurdity we are experiencing. Efficiency. Efficient. Efficient. What is being done in this regard?

To conclude: the end of the oil age and the advent of a society where energy for a large part of mankind will be derived from hydrogen is a rather dated intuition. Cesare Marchetti, a researcher at the International Institute for Applied Systems Analysis in Luxemburg, spoke about it for the first time in the 1970s. The economist Jeremy Rifkin also described all the positive aspects in a book about twenty years ago entitled ‘The Hydrogen Economy’. But if it were as easy as Rifkin claimed, we would have done it already. But it is not easy. That is why we must commit ourselves, as usual, starting from the awareness that the future can only come from courageous political choices based on data, evidence, science and technology. Letting ourselves be swayed, saying all sorts of things, especially about hydrogen, distances us from what should be our real goal.

A few insights

National hydrogen strategy:

https://www.mise.gov.it/images/stories/documenti/Strategia_Nazionale_Idrogeno_Linee_guida_preliminari_nov20.pdf

Towards a hydrogen market for Europe:

https://www.consilium.europa.eu/it/press/press-releases/2020/12/11/towards-a-hydrogen-market-for-europe-council-adopts-conclusions/#

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