Atomic Hydrogen Diffusion in Novel Magnesium Nanostructures: The Impact of Incorporated Subsurface Carbon Atoms

Effects of carbon on hydrogen storage performances of hydrides

“…It is worth noting that, although the presence of monolayer C atoms leads to no significant reduction in the energy barrier for H 2 dissociation on Mg (0001), the hydrogen diffusion barrier may be reduced by adding carbon because experimental results have proved that carbon is a more effective additive than metallic catalyst in the capacity increment of Mg under identical conditions. 70 This speculation agrees well with other DFT calculations by Du et al 67 The calculated variation of diffusion barriers with and without incorporated C atoms indicates that the diffusion barrier is significantly decreased by C-Mg interactions. They found that subsurface C atoms not only facilitate the preferred positioning of H atoms on the surface after dissociation, but also promote a ''funnelling'' effect, thus enhancing the diffusion of atomic H into the subsurface by lowering the activation barriers to transport downward the encircled fcc channels.…”

First-Principle Study of Adsorption of Hydrogen on Ti-Doped Mg(0001) Surface

“…Further studies exploring various possible pathways for H diffusion from the Ti site into the bulk material will be required in order to probe for possible low-energy diffusion pathways that might then provide a robust theoretical explanation of the catalytic role. In a related context, we note that our recent studies 22,23 have revealed a potential catalytic role that incorporated atomic carbon may play in facilitating hydrogen diffusion into the Mg bulk. Such synergetic effects have been also observed in recent ball-milling experiments for mixing Ti, graphite, or carbon nanotubes (5%) with Mg materials.…”

“…[17][18][19] We have recently carried out a preliminary investigation of the effect of incorporated titanium or carbon on the dissociative chemisorption of a single hydrogen molecule 20,21 and the diffusion of atomic H on a Mg(0001) surface and into the first sublayer. 22,23 Two theoretical groups have shown recently that transition metal atoms such as Sc and Ti coated on carbon fullerenes and nanotubes can bind molecular hydrogen with a binding energy of the order of 0.5 eV/H 2 molecule and with gravimetric density of up to 8 wt %. 24,25 This can be understood by the facts that (i) Ti or Sc is first ionized due to charge transfer between carbon and Ti (Sc) and (ii) the transition metal cation then polarizes molecular H 2 .…”

Advances in the application of nanotechnology in enabling a ‘hydrogen economy’

“…Yao and colleagues [98,99] tried to develop Mg-based nanocomposites with nanoscale catalysts such as Fe and Ti that could enhance the kinetics of hydrogen absorption and desorption, and CNTs that could improve ambient hydrogen storage capacity. The results obtained for hydrogen absorption at 300°C are summarized in Fig.…”