Solid-State Storage of Hydrogen

In today's energy context, which is essentially focused on sustainable development, hydrogen is attracting a great deal of media attention, as its use has no impact on the carbon footprint if it is green, and its combustion with oxygen produces only water. What's more, as an energy carrier, it can store massive amounts of energy over long periods of time, which can then be used for a wide range of systems, including mobility, heating and industrial processes. It is also ideally suited to compensating for the intermittent nature of renewable energies.

Hydrogen being an energy carrier, it is essential, given the current economic and environmental context, to produce and above all distribute green hydrogen at a "reasonable" cost, i.e. competitive with the current fossil fuel market. In addition to this production and distribution issue, the hydrogen produced can be used for mobile or stationary applications using fuel cells or direct combustion. However, its use essentially depends on its storage, which currently represents a crucial problem for both mobile and stationary applications. Alongside the technical and economic problems inherent in production and use, this storage issue is at the heart of the Hydrogen Stimulus Plan, and forms an integral part of the decarbonized hydrogen research program and priority equipment (PEPR) scheduled for the decade 2020-2030.

At present, chemical storage in the form of organic liquids (Liquid Organic Hydrogen Carriers, LOHC) is used for long-distance transport, while salt cavern storage techniques are used for mass storage (several million cubic meters). However, the most widespread storage techniques are liquid storage at very low temperatures and high-pressure storage. At 20 K, liquid hydrogen has a density of 71 kg·m ^–3 which gives it very interesting volumetric storage properties, especially in restricted environments. High-pressure gaseous storage is currently the technique of choice for automotive mobility, enabling 5 kg of hydrogen to be stored in a 210 L volume at 35 MPa, or in a 125 L volume at 70 MPa. However, these temperature and pressure conditions are extreme (20 K for liquid storage or 70 MPa for pressurized gaseous storage), and an alternative means of storing hydrogen at moderate temperature and pressure needs to be developed. This problem is of major interest, as these extreme temperature and pressure conditions represent a number of major obstacles (in terms of economics, safety, ease of implementation and use) to the deployment of the hydrogen industry. An alternative means of storage at moderate pressure and temperature therefore needs to be considered. Solid-state storage, by absorption in hydride materials or adsorption in porous materials, represents a promising...