Nanostructured Mg-Based Hydrogen Storage Materials: Synthesis and Properties

A hydrogen economy is thought to be one of the ultimate carbon-neutral energy solutions. For a future scenario, one may obtain hydrogen from renewable power, for instance, wind or solar energy; this hydrogen can be provided to fuel cell component to supply electricity and heat. For this energy storage and utilization route, one enabling technology is hydrogen storage because hydrogen as energy carrier is a gas state at normal temperature and atmosphere conditions and the energy density of hydrogen gas is low. Therefore, a critical step is to find one hydrogen storage technology with low cost and high energy density. Mg-based materials are very promising candidates for hydrogen storage due to the great abundance of Mg in earth’s crust, high hydrogen storage capacity (7.7 wt% for MgH₂) and low cost (2–3 USD/kg). Mg-based materials have been investigated as possible onboard applications for decades. The challenges in Mg-based materials for onboard development are the poor kinetics and unsuitable thermodynamics. Nanostructured materials have attracted great attention in the last decades. Downsizing from millimeter or micrometer scale to a nanometer one brings a lot of novel physical and chemical properties to the materials. Numerous nanoprocessing techniques have been adopted by researchers to fabricate Mg-based materials in nanoscale in order to enhance the sorption kinetics and alter the thermodynamics. The author and his colleagues applied a novel nano-processing strategy—hydrogen plasma metal reaction (HPMR)—to synthesize metal nanoparticles and further produce nanostructured Mg-based hydrogen storage materials from these nanoparticles. Here in this chapter, the author will summarize the synthesis results under different conditions and morphology and microstructure information of the obtained samples, and especially focus on how downsizing could affect the sorption kinetics and the thermodynamics, including desorption enthalpy and entropy, in Mg-based hydrogen storage materials.