Insights on metal nanoclusters (MNCs) (de)hydrogenation for on-board hydrogen storage application using electron microscopy and spectroscopy technique

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The development of volumetric efficient solid-state hydrogen (H2) storage materials is crucial for decarbonisation in the transport sector. As one of the most promising H2 storage materials, the advantages of magnesium hydride nanoparticles includes their high H2 storage capacity (7.6 wt.%) and low cost ($3/kg). However, slow kinetics and a high working temperature (ca. 250 C) limit its commercial application for on-board H2 storage. In order to improve its properties (higher kinetics, lower temperature), this project will utilise metal nanoclusters (MNCs), which are fundamentally different compared to more widely used metal nanoparticles (diameters >2 nm), where the majority of metal atoms remain 'hidden' within the lattice and are excluded from participation in useful chemistry. In contrast, the majority of the atoms in MNCs are fully accessible for physicochemical processes, while new functional properties, inaccessible in bulk metals or in nanoparticles, can emerge as a result of confinement in MNCs. Theoretical calculations predict that nano-tuning could reduce the (de)hydrogenation reaction energy when NCs of Mg/MgH2 are used, therefore reducing the working temperature [JACS, 2005, 127, 16675-80]. This would substantially reduce the on-board H2 storage cost enabling their use in fuel cell vehicles for zero-emission transport. This is a collaboration project between University of Nottingham and Diamond Light Source. The specific steps will involve (i) synthesis of graphitic carbon nitride (g-C3N4), which is an ideal support for stabilisation of MNCs due to its nitrogen "cavity" (Nottingham), (ii) depositing a series of MNCs with different sizes and composition (i.e. Mg and Pd, and their nano-alloys) on g-C3N4 and their characterisation: AC-STEM including chemical mapping and depth profile, and XPS / NAP-XPS in Diamond, (iii) Investigating the electronic changes on MNCs under H2 environment at different temperatures (AC-STEM and NAP-XPS in Diamond), (iv) evaluation of H2 storage properties including capacity, kinetics, thermodynamics and cycling test (in Nottingham).