Electrodeposited Magnesium Nanoparticles Linking Particle Size to Activation Energy

Abstract

Abstract:The kinetics of hydrogen absorption/desorption can be improved by decreasing particle size down to a few nanometres. However, the associated evolution of activation energy remains unclear. In an attempt to clarify such an evolution with respect to particle size, we electrochemically deposited Mg nanoparticles on a catalytic nickel and noncatalytic titanium substrate. At a short deposition time of 1 h, magnesium particles with a size of 68 ± 11 nm could be formed on the nickel substrate, whereas longer deposition times led to much larger particles of 421 ± 70 nm. Evaluation of the hydrogen desorption properties of the deposited magnesium nanoparticles confirmed the effectiveness of the nickel substrate in facilitating the recombination of hydrogen, but also a significant decrease in activation energy from 56.1 to 37.8 kJ·mol −1 H 2 as particle size decreased from 421 ± 70 to 68 ± 11 nm. Hence, the activation energy was found to be intrinsically linked to magnesium particle size. Such a reduction in activation energy was associated with the decrease of path lengths for hydrogen diffusion at the desorbing MgH 2 /Mg interface. Further reduction in particle size to a few nanometres to remove any barrier for hydrogen diffusion would then leave the single nucleation and growth of the magnesium phase as the only remaining rate-limiting step, assuming that the magnesium surface can effectively catalyse the dissociation/recombination of hydrogen.

Heat Modeling and Material Development of Mg-Based Nanomaterials Combined with Solid Oxide Fuel Cell for Stationary Energy Storage

“…The hydrogen absorption process is one step in forming a MgH 2 layer based on the reaction between Mg and hydrogen on the surface of Mg particles. The significant kinetics difference between the Mg nanoparticles and the 325 mesh Mg is because the Mg nanomaterials show a large surface area and a small particle/grain size [6,25,45], meaning that Mg nanomaterials have a much greater contact area for the hydrogen reaction, and a much shorter diffusion distance for hydrogen diffusion during the hydrogen absorption reaction [1,6,46,47]. For real storage application, both absorption and desorption properties, including the hydrogen capacity and kinetics, are essential for hydrogen intake and subsequent supply to the SOFC component.…”

Nanosized Magnesium Electrochemically Deposited on a Carbon Nanotubes Suspension: Synthesis and Hydrogen Storage

“…We previously reported on the electrochemistry of MgBu2 and at a current of 0.5 mA cm −2 , this Mg precursor is readily reduced into metallic Mg (Shen and Aguey-Zinsou, 2016). The XRD pattern of the pristine CNTs ( Figure 1A) shows the (002) peak around 26 corresponding to the inter-planar spacing of 0.34 nm (Kawasaki et al, 2005).…”

How to Design Hydrogen Storage Materials? Fundamentals, Synthesis, and Storage Tanks

“…Nanocrystalline materials, characterised by a crystal size < 100 nm, can be formed by techniques including vapour condensation, [179] sputtering, [180] thermal decomposition, [181] chemical precipitation [182] and so on. [183] But the advantage of mechanical milling is in the possibility of producing bulk quantities of material. However, from a commercial perspective, mechanical milling remains an expensive production method and alternatives in the forms of high pressure torsions, equal channel angular pressing, and cold rolling have been proposed.…”

“…(a) Size dependence E a for Mg synthesised by chemical reduction [53a, 311a] and electrochemical deposition; [183] (b) correlation between A and E a for Mg nanoparticles. Values were extracted from the literature.…”