The Size Dependence of Hydrogen Mobility and Sorption Kinetics for Carbon‐Supported MgH₂ Particles

Abstract

MgH 2 is a promising material for reversible solid-state hydrogen storage. It is known that particle size can have a strong impact on hydrogen dynamics and sorption characteristics, but more detailed insight has been hampered by the great challenge to prepare small and well-defi ned particles and study their hydrogen storage properties upon cycling. The preparation of MgH 2 nanoparticles supported on high surface area carbon aerogels with pore sizes varying from 6-20 nm is reported. Two distinctly different MgH 2 particle populations are observed: X-ray diffraction invisible nanoparticles with sizes below 20 nm, and larger, crystalline, MgH 2 particles. They release hydrogen at temperatures 140 °C lower than bulk MgH 2 . The size-dependent hydrogen kinetics is for the fi rst time corroborated by intrinsic hydrogen dynamics data obtained by solid state 1 H NMR. Fast cycling is possible (80% of the capacity absorbed within 15 min at 18 bar and 300 °C), without a change in the hydrogen sorption properties, showing that the growth of the nanoparticles is effectively prevented by the carbon support. A clear correlation is found between the hydrogen desorption temperature and the size of the MgH 2 nanoparticles. This illustrates the potential of the use of supported nanoparticles for fast, reversible, and stable hydrogen cycling.

Catalytic effects of different Ti-based materials on dehydrogenation performances of MgH2

“…Obviously, ball-milling can effectively decrease the size of powders and create more fresh surfaces. Previous reports had demonstrated that the reaction kinetics of MgH 2 was enhanced with its decreasing particle size, caused by a larger surface to volume ratio and decreased diffusion distance for hydrogen [19]. Due to the agglomeration, the pure MgH 2 sample had some visible large clusters existed.…”

Review of magnesium hydride-based materials: development and optimisation

“…The first systematic study of the kinetics of hydrogen sorption as a function of particle size was conducted by Au et al [67], using 6-20 nm MgH 2 particles in carbon aerogels. As shown in Fig.…”

Experimental Challenges in Studying Hydrogen Absorption in Ultrasmall Metal Nanoparticles

“…(Wilcoxon and Abrams, 2006;Roesler and Fischer, 2015). Another interesting technique is the melt infiltration of low temperature melting metals, such as Mg, into different porous carbon hosts (de Jongh and Eggenhuisen, 2013;Au et al, 2014). For both synthetic method many experimental parameters are plying a crucial role to ensure the stability toward coalescence and the high dispersion of such nanoparticles on the support: the porosity/surface chemistry of the support, the nature of metal precursor, the metal loading, and the synthesis conditions: temperature, reducing agent, etc.…”