Breakthrough Research Achieves High-Density Hydrogen Storage

Abstract

Nanoporous materials have attracted great attention for gas storage, but achieving high volumetric storage capacity remains a challenge. Here, by using neutron powder diffraction, volumetric gas adsorption, inelastic neutron scattering and first-principles calculations, we investigate a magnesium borohydride framework that has small pores and a partially negatively charged non-flat interior for hydrogen and nitrogen uptake. Hydrogen and nitrogen occupy distinctly different adsorption sites in the pores, with very different limiting capacities of 2.33 H2 and 0.66 N2 per Mg(BH4)2. Molecular hydrogen is packed extremely densely, with about twice the density of liquid hydrogen (144 g H2 per litre of pore volume). We found a penta-dihydrogen cluster where H2 molecules in one position have rotational freedom, whereas H2 molecules in another position have a well-defined orientation and a directional interaction with the framework. This study reveals that densely packed hydrogen can be stabilized in small-pore materials at ambient pressures.

Efficient hydrogen storage, a crucial component of future energy systems, has now become a reality. This breakthrough holds immense promise for enhancing the efficiency and economic viability of hydrogen energy utilization, as it enables the storage of hydrogen at high densities.

Professor Hyunchul Oh, from the Department of Chemistry at UNIST, has reported on a groundbreaking development in the field of hydrogen storage. The research focuses on a nanoporous magnesium borohydride structure (Mg(BH4)2), which exhibits the ability to store hydrogen at high densities even under normal atmospheric pressure. By employing advanced high-density adsorption technology, the research team has successfully overcome the challenge of low hydrogen storage capacity, commonly encountered in hydrogen storage and transportation.

Professor Oh explains, "Our developed material has the potential to safely and efficiently store a significant amount of hydrogen, surpassing conventional hydrogen storage methods."

Hydrogen, a promising future fuel, poses difficulties in large-scale storage due to its weak intermolecular interactions. Previous methods relied on either significantly increasing pressure to 700 atmospheres or lowering the temperature to -253 degrees Celsius within the same volume to achieve high-capacity storage. However, these approaches fell short in terms of efficiency.

The research team has successfully synthesized a nanoporous complex hydride, magnesium hydride, by incorporating solid boron hydride (BH4)2 and the metal cation magnesium (Mg+). The developed material allows for the storage of five hydrogen molecules in a three-dimensional arrangement, achieving high-density hydrogen storage.

The reported material exhibits a hydrogen storage capacity of 144 g/L per volume of pores, surpassing alternative methods such as storing hydrogen as a gas in a liquid state (70.8 g/L). Moreover, the density of hydrogen molecules in the material surpasses that of the solid state (density of 86 g/L).

Furthermore, the research team employed various analytical techniques, including neutron scattering, cryogenic volume measurement, and DFT calculations, to precisely determine the molecular locations and understand how such a large quantity of hydrogen can exist within the pores.

Professor Oh remarks, "Our findings present a significant step towards addressing the hydrogen storage challenge, a critical hurdle in the widespread adoption of hydrogen fuel for public transportation. This development offers an opportunity to improve storage density based on volume, a feat that has been elusive with current technologies, while also enhancing the efficiency and economic feasibility of hydrogen energy utilization."

The research findings were published online on February 6 in Nature Chemistry, a prestigious international journal in the field of chemistry. This research was conducted as part of a mid-sized researcher support project supported by the Korea Research Foundation of the Ministry of Science and ICT.

Journal Reference

Hyunchul Oh, Nikolay Tumanov, Voraksmy Ban, et al., "Small-pore hydridic frameworks store densely packed hydrogen," Nature Chemistry, (2024).