Promising materials for hydrogen storage
Hydrogen is a near-zero emission energy carrier that could play an important role in the future low-carbon energy and transport sectors in Europe. It can be oxidised electrochemically to produce electric power and water, which is the only by-product of this process. Despite hydrogen's high-energy density, usage of hydrogen fuel cells for mobile applications is a challenge since storage systems are ineffective and difficult in their handling. Cooperation between the EU and India addressed the problem of hydrogen storage by computational modelling of different materials in the EU-funded project HYPOMAP (New materials for hydrogen powered mobile applications). The focus was on the interactions and reactions of hydrogen molecules with solid surfaces. Hydrogen storage can be achieved by chemisorption and physisorption. In chemisorption, hydrogen is split and the hydrogen atoms are chemically absorbed into the host material through chemical bonds. In physisorption, hydrogen is physically absorbed into the host material. Storage of hydrogen in a bulk material, either by chemisorption or physisorption, offers the possibility to store hydrogen gas safely and at higher density. Scientists increased the hydrogen adsorption enthalpy by introducing cations to metal hydrides and metal-organic frameworks. Another approach was to introduce defects into nanostructures that should strongly interact with the adsorbed hydrogen molecules. Scientists also determined the gravimetric and volumetric hydrogen storage capacity of ammonia boranes – another bulk storage material. Due to the low mass of boron and nitrogen atoms, they showed very high gravimetric storage capacity. Hydrogen can thus be released easily using thermolysis. Scientists also studied suitable catalysts that control hydrogen release from ammonia boranes. The project shed focus on spillover – a way of storing dissociated molecular hydrogen by chemisorption – on single-wall carbon nanotubes. Such materials represented the best possible gravimetric and volumetric hydrogen storage capacities. Furthermore, the project identified moieties serving as new construction elements for liquid or solid-state storage materials that showed exceptional affinity to molecular hydrogen. HYPOMAP organised a summer school, several workshops and conferences, and findings were published in 48 articles in international peer-reviewed journals.
Keywords
Materials, hydrogen storage, mobile applications, metal-organic frameworks, ammonia boranes
