The Energy Challenge: Why We Need New Materials

As you already know, in recent years there has been an accelerated race to find alternatives to fossil fuels. Hydrogen has emerged as an interesting option because its combustion produces large amounts of energy and water. Leaving aside the challenges of producing H₂ in a clean, cost-effective, and efficient way, the fundamental problem lies in its storage. Its low weight and high diffusivity mean that storing H₂ requires either very low temperatures or extremely high pressures. This makes it difficult to handle and poses certain safety risks.

The “fuel of the future” is light, takes up a lot of space, and leaks easily.

In the post Small spheres, big impact: sustainable materials for hydrogen storage, we introduced the need to develop new materials for hydrogen storage and explained how MAST3RBoost is working on it.

Today, however, we would like to focus more on what the scientific community is investigating, what the different options to improve H₂ storage are, and what role nanotechnology plays.

How can we store hydrogen?

Before going into technical details, it is important to have a general overview of hydrogen storage methods. Broadly speaking, we can classify them into three main categories (leaving aside large-scale solutions such as underground storage):

1. Physical storage. This mainly consists of reducing the volume occupied by H₂, in other words, increasing its density. This is achieved through changes in pressure or temperature. These are the most well-known methods and probably sound familiar. Examples include compressed gas, using very high pressures; liquid hydrogen, which is obtained at temperatures of −253 °C; and cold/cryogenic compression, which combines both high pressure and low temperatures.
2. Solid-state storage. This approach uses materials that interact with hydrogen and act as containers. It is a wide category that includes many different types of materials. We can find adsorbents (physisorption) such as zeolites, activated carbon, or the MOFs studied in MAST3RBoost, where hydrogen is stored in the pores of the material. It also includes absorption methods (chemisorption), where hydrogen forms chemical bonds with compounds. One example is hydrides such as NaBH₄ or LiBH₄, which release hydrogen when reacting with water (hydrolysis), producing NaBO₂ as a by-product.
3. Liquid organic hydrogen carriers (LOHCs). This is similar to chemisorption but uses liquid compounds. Once again, hydrogen reacts with molecules, such as toluene, forming stable but reversible compounds that act as a storage method.

How do we currently store hydrogen?

Once we understand the main storage methods, or at least the basic concept behind each one, we can review the current state of hydrogen storage technologies to understand their advantages and drawbacks.

The most widely used method today is Compressed Gas Storage (CGS). As mentioned earlier, it falls under physical storage, where pressure is applied to increase the amount of stored hydrogen. Its main advantage is that it is a mature technology; however, it requires large tanks and extremely high pressures, which raises safety concerns.

Liquid hydrogen and cryogenic storage allow for smaller tanks than CGS, but they are very costly. Liquefying the gas requires a large amount of energy, equivalent to 30-40%[1] of the energy content of the stored hydrogen. In other words, storing 100 kJ of hydrogen consumes 30-40 kJ.

Solid-state storage methods, as mentioned earlier, are diverse. In general, their main advantage is increased safety, as they use fewer extreme pressures and temperatures while storing larger amounts of hydrogen.

Liquid organic hydrogen carriers allow H₂ to be stored at ambient pressure and temperature, making them very safe. Existing infrastructure such as gas stations and pipelines could even be used, taking advantage of current facilities. The drawback is that releasing the hydrogen requires additional steps, which are costly.

So, what is the best option for storing hydrogen?

Many researchers (including all the partners of MAST3RBoost) agree that solid-state storage methods stand out as having the greatest potential to store hydrogen in a technologically simple and safe way.

This is where nanomaterials come into play, offering a significant advantage over other materials such as hydrides or zeolites.

Specifically, nanomaterials, materials whose particles have dimensions between 1 and 100 nm, play a key role and promise to transform the future of H₂ storage.

• Storage at more “normal” temperatures and pressures, reducing the risk of explosions and leaks.
• More hydrogen stored in a smaller container. Capacities of up to 6.78¹ wt % have been achieved.
• Versatile materials. Nanotechnology enables the design of tailor-made materials. In our latest post, A circular future for gas storage materials: the Metal-Organic Frameworks (MOFs) developed in MAST3RBoost, we explain why MOFs and MDCs represent a circular approach to gas storage.

To make this easier to visualize, a nanomaterial is composed of pores that are on a scale one million times smaller than a millimetre. These pores allow H₂ molecules (as mentioned, the smallest element) to fit into each cavity. This makes it possible to store much more hydrogen in less space by taking advantage of the internal pores of the material.

What are the current challenges? What is MAST3RBoost working on?

Significant progress has been made in recent years in the design of nanomaterials, although safety and technical and economic efficiency barriers remain. In other words, we need to develop materials that are safe, technically efficient, and competitive in the market.

For this reason, MAST3RBoost adopts a broad approach. On the one hand, it focuses on developing new adsorbent materials, sustainably improving adsorption capacity. At the same time, storage tanks are being designed, as well as the metallic materials that will make up these tanks. As a result, eight scientific review papers have been published within the framework of the project, summarizing the different advances achieved. If you are curious, you can find open-access links to all these scientific publications on our website.

[1] Advances in hydrogen storage materials for physical H2 adsorption – ScienceDirect

Author: Noemi Alonso