Hydrogen bears a fantastic promise: a fuel that, when used, only releases … water. Even better: you only need, to produce it, electricity and … water. The perfect circular economy! It is, however, an extremely reductive view of reality.

First of all, this is nothing new, electrolysis being known since 1800. We already talked about hydrogen economy (= based on hydrogen as a fuel) in the 1970s! Second, even if hydrogen is hardly used for mobility today, we still use around 90 million tonnes of it every year! It is used for essential productions: the synthesis of fertilizers and the refining of petroleum products.

This is one of the most complex and interesting subjects of the energy transition. It lies at the heart of two central subjects: ecomobility (hydrogen-energy) and agriculture (hydrogen-raw material).

The hydrogen atom

To understand the issues surrounding hydrogen, you must first know the characteristics of this atom and of the dihydrogen molecule. The fact that H2 is the smallest molecule is, for example, central to understand the difficulties surrounding its storage. Likewise, it is a gas with a very low density, which complicates its transport: it must be transformed to make it more dense, which poses many challenges.

To go further, you can read our articles on the hydrogen atom.

Hydrogen production

Hydrogen production is a less straightforward subject than you might think. We sometimes think to ourselves that we just need to use electrolysis, plug it into renewable energies and that’s it. In reality, even in this case, you have to think about which electrolysis: alkaline, Proton-Exchange-Membran (PEM), solid oxide (SOEC)…? For example, the problem with alkaline electrolysis is that it isn’t compatible with irregularity. The one with PEM is the cost of its materials.

In addition, most of the production of dihydrogen is currently the co-product of other productions, such as coke, or is part of an industrial production cycle around the refinery, and therefore cannot be replaced in the short term. term. Finally, it is entirely conceivable that methods of producing hydrogen considered to be “fossil” or “dirty” may in fact be low carbon, such as biomass gasification.

To go further, you can read our articles on hydrogen production.

Storage of hydrogen

To store hydrogen, it’s not enough to put it in a tank – it’s the smallest molecule and it has a ridiculous density. To store it, you must therefore transform it chemically or physically. The main mode of “chemical” transport envisaged is transformation into ammonia. Nevertheless, it is the physical transformations which are currently privileged: compression, liquefaction or adsorption. There is also the question of the risks, especially for compression, hydrogen being a very explosive gas.

To go further, you can read our articles on hydrogen storage.

The uses of H2

Hydrogen is already a widely used product: 90 million tonnes each year (2020). It is mainly used in the refinery of petroleum products (46%) and in the production of ammonia, which is then used to make fertilizers (45%). There are also plans to use it to decarbonize steel production and, of course, to decarbonize heavy transport.

To learn more, you can read our articles on the practical applications of hydrogen.