Two-dimensional material has potential as hydrogen store

One of the long-term stumbling blocks to the so-called hydrogen economy – where hydrogen replaces fossil fuels as the basis for much energy applications, either through combustion or by its use in a fuel cell to generate electricity – is the difficulty in storing the gas. The very lightweight and small size of the H₂ molecule makes it likely to leak from many forms of containment, and it is potentially explosive. Moreover, the very high pressures needed to store useful volumes of hydrogen gives pause to automotive designers, as some drivers may be nervous about driving a vehicle with a high-pressure explosive gas on board.

One solution to this problem which is being investigated intensively springs from hydrogen’s tendency to absorb into solid materials: another artefact of the small size of the molecule, which allows it to tuck into the lattice atomic or molecular structure of its host. The question has generally been, which material? A team of researchers from Tokyo Institute of Technology, the University of Tsukuba and Kochi University of Technology report in Nature Communications that the answer may be one of the family of two-dimensional materials similar to graphene.

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Further reading

• How the hydrogen economy could make a comeback
• Wax and microwaves could unlock storage roadblock to hydrogen economy
• Nuclear generator links up with hydrogen specialist

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Hydrogen boride (also known as borophane) was discovered in 2017, and quickly became the focus of research into its potential for applications in energy and catalysis. However, a method for making the material has been lacking until now. In the Nature paper, Masahiro Miyauchi and colleagues explain their method for making hydrogen boride nanosheets by an ion exchange treatment of magnesium diboride in acetonitrile solution. “Interestingly,” they say, “our HB sheets produced gaseous H₂ under heat treatment at 150 to 1200°C and exhibited a semi-conductive photo absorption property.” Moreover, they add, previous theoretical experiment will studies suggest that the H₂ storage capacity of HB is about 8.5% of the weight of its boron content. “The HB sheet has more advantages than conventional H₂-storage systems such as metal-based materials and high-pressure containers owing to its high H₂ capacity and safe operation,” they claim.

The Nature paper also describes how illuminating the HB sheets with ultraviolet light under ambient room temperature and pressure can release significant amounts of hydrogen. Miyauchi’s team is now investigating whether the light sensitivity of HB can be tuned so that visible light could be used to release hydrogen, with the material can be recharged with the gas after release, and how durable the material might be for such application. "Cost reduction of the starting materials - magnesium diboride - for HB sheets will be another important factor," he adds.