Small spheres, big impact: Sustainable materials for hydrogen storage
The demand for fuel, vehicles, machinery, and energy has only increased in the last few decades, and projections say it will keep growing. How, then, are we supposed to meet this demand? Fossil fuel supplies, like petroleum oil and natural gas, are dwindling, extraction costs are rising, and economic uncertainty drives consumer prices even further.
This is why renewable energy and alternative fuels are increasingly relevant in modern society. Electric vehicles (EVs) are often more sustainable alternatives than regular cars. But the rare metal requirements for batteries make them imperfect solutions. Alternative fuels like biogas are great options but still contaminate the environment. Few alternatives remain, but one of the most interesting is hydrogen.
Avoiding past pitfalls for hydrogen vehicles
Hydrogen as a fuel and energy source is not new, but there are many technical hurdles to overcome before its use becomes widespread. While this might seem like a drawback in comparison to other alternatives, it may also be an advantage. Biogas works similarly to diesel or gas, but it is made from waste. Still, when burnt, it pollutes the environment. EVs require large batteries with an unknown fate, as recycling is challenging, and many rare metals must be used in their manufacture.
It is clear then that the energy sources of the future must do better. We must design implementation strategies that sustainably cover hydrogen sourcing and production, use fuel without polluting, and develop engine and material designs based on sustainable materials.
Transition to hydrogen fuel requires a transition in storage systems
You might be wondering, if hydrogen can be a good alternative fuel, why is it not widespread already? A crucial reason is storage. While most fuels are liquid, hydrogen is a gas, and as such it takes very large volumes, needing huge spaces for storage. There are ways to make it better, such as compression and cooling, but even then, the storage vessel size is usually quite big. So, what can we do? The EU-funded project MAST3RBoost is working on new solutions.
Developing materials for the absorption of hydrogen
Hydrogen is already used as fuel in some applications, but usually industrial scale. Some commercial vehicles also run on hydrogen. However, both require extremely high-pressure hydrogen storage tanks, with up to 700 times the atmospheric pressure. And even then, these tanks hold little amounts of hydrogen for the space they take.
MST3RBoost is pioneering the use of carbon materials for storage. How does that work? Hydrogen molecules are small and far between. Solid materials could be used to bind the molecules for storage and release them when needed. The storage vessel would then carry more hydrogen, absorbed into the material inside. In the proposed method, the material has a high amount of the element carbon, like coal.
The hydrogen tank imagined by MAST3RBoost would still require cooling to low temperatures, and moderate pressures, but much lower ones than current hydrogen tanks use.
Spheres, the ideal shape
New research published by scientists working on the MAST3RBoost project shines a light on how to store hydrogen using carbon materials. The scientists working on the project analysed several materials and shapes. They concluded that spheres were ideal for the material shape. This is because they have a high surface, and the more surface the more hydrogen is absorbed into the material.
To make them have a higher surface, the researchers used a process called activation. The goal was to make spheres with high surface and high porosity. The pores would also increase the surface area and hydrogen binding capabilities.
Microspheres from sustainable carbon polymers
To make the spheres, they used a polymer-rich in carbon, with other elements like oxygen and nitrogen. The polymer is made from components extracted from wood and fermentation processes, so it is sustainable. A microwave process is used to form the microspheres from the polymer. However, the microspheres were unideal for hydrogen storage, as they have a lot of other elements other than carbon. To fix this, they were heated at 850 ºC, in a process known as carbonisation. This released most elements other than carbon, and the microspheres had plenty of pores. But to make them even more porous, the activation process uses similar temperatures with CO2 gas. This results in microspheres of about 2 µm, or 50 times smaller than a micrometre, and with plenty of pores.
The microparticles are so small that to the eye look like a fine powder of black, carbon material.
And what can these do? They are relatively lightweight, because of their porosity, and a single gram has a combined surface of up to 3.3 kilometres. You read that right, kilometres. That is why they can absorb up to 9% of their weight in hydrogen at low temperatures and medium pressure, making them an excellent storage material. Current hydrogen tanks for cars can fit 5 kg of hydrogen at most, and that is enough to drive for hundreds of kilometres. MAST3RBoost’s microspheres are also made of sustainable materials and show great performance at low temperatures and high pressures.
The next steps in building a hydrogen tank for vehicles
From designing a material to a finished prototype, the road is still long, and the goal is far away. However, this is a very promising milestone for MAST3RBoost, as the technology for making microparticles with a sustainable material is now validated and works well on a small scale.
We might need to make further improvements in the particles and the system that will work with them as well. Other parts of the project are working in parallel to develop lightweight materials for the hydrogen tank that are still safe at the pressures and temperatures needed.
Lastly, the aim is to have a finished working prototype by the end of the 4 years of the project timeline, which can store 1 kg of hydrogen safely. If we can do so, we will not be far from scaling up to the ideal market-entry tank of 5 kg of hydrogen storage, which can be used for many road vehicles. This will allow Europe to decarbonise the transportation industry by 2030 with hydrogen-fuel vehicles.
Author: Darío Sánchez