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

体积高效的固态氢(H2)储存材料的开发对于运输部门的脱碳至关重要。氢化镁纳米颗粒作为最有前景的储氢材料之一，具有储氢量高(7.6wt.%)、成本低(3美元/公斤)等优点。然而，缓慢的动力学和较高的工作温度(约250℃)限制了其在车载储氢方面的商业应用。为了改善其性能(更高的动力学，更低的温度)，该项目将使用金属纳米团簇(MNC)，与更广泛使用的金属纳米颗粒(直径2 nm)相比，这是根本不同的，后者中的大多数金属原子仍然隐藏在晶格中，被排除在有用的化学参与之外。相比之下，跨国公司中的大多数原子完全可以用于物理化学过程，而由于跨国公司的限制，可能会出现在块状金属或纳米颗粒中无法获得的新功能特性。理论计算表明，纳米级微调可以降低纳米级镁氢化物的脱氢反应能，从而降低催化剂的工作温度[JACS2005.127,16675-80]。这将大大降低车载氢气存储成本，使其能够用于燃料电池汽车的零排放运输。这是诺丁汉大学和钻石光源公司的合作项目。具体步骤将包括：(I)合成石墨碳氮化物(g-C3N4)，这是由于其氮“腔”(诺丁汉)而成为稳定MNC的理想载体，(Ii)在g-C3N4上沉积一系列不同尺寸和组成的MNC(即镁和钯及其纳米合金)及其表征：AC-STEM，包括化学图谱和深度分布，以及钻石中的XPS/NAP-XPS，(Iii)研究在不同温度下氢环境下MNC上的电子变化(AC-STEM和NAP-XPS在钻石中)，(4)评价氢气储存特性，包括容量、动力学、热力学和循环试验(在诺丁汉)。

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).