Hydrogen generation via hydrolysis with magnesium

Geopolitical issues, scarcity of resources, environmental impacts and climate change are all sources of growing tension when it comes to energy supply and management. In this context, the diversification of energy production, storage and distribution processes is essential. The research, development and implementation of processes that perform these functions are therefore booming, particularly in the "hydrogen sector". The dihydrogen molecule (H ₂ ) is a highly attractive energy carrier, since its production and consumption cycle can be carried out without greenhouse gas emissions. Among dihydrogen synthesis methods, those based on the decomposition of water molecules H ₂ O into H ₂ and O ₂ have long been known. The energy enabling this dissociation is provided by an electric current in the case of electrolysis. In the case of hydrolysis, there is no energy input other than the chemical energy contained in the material used for the reaction. This second method is the subject of this article. The hydrolysis reaction is carried out with materials that can be easily oxidized (reducing agents, such as most metals) or release the hydrogen contained in their structure (hydrides) on contact with water.

Among these different materials, magnesium has several major interests: i) it is abundant in the earth's crust, ii) it is inexpensive, iii) it is highly reactive with water, iv) it can form the hydride MgH ₂ , doubling the amount of H ₂ produced and therefore the energy density, and v) it is safe for health and the environment. Controlling the hydrolysis reaction in the presence of magnesium also enables hydrogen to be produced on demand, under controlled pressure and without energy input.

After setting the scene for the hydrolysis process using magnesium-based materials, a description of the types of reagents used and the work involved in optimizing the reaction are presented. In a second section, the methods used to characterize the reagents used for hydrolysis are discussed. Finally, an overview of process applications is presented, before concluding.