Modelling of adsorption and intercalation of hydrogen on/into tungsten disulphide multilayers and multiwall nanotubes

Abstract

Understanding the interaction of hydrogen with layered materials is crucial in the fields of sensors, catalysis, fuel cells and hydrogen storage, among others. Density functional theory, improved by the introduction of van der Waals dispersion forces, provides an efficient and practical workbench to investigate the interaction of molecular and atomic hydrogen with WS multilayers and nanotubes. We find that H physisorbs on the surface of those materials on top of W atoms, while atomic H chemisorbs on top of S atoms. In the case of nanotubes, the chemisorption strength is sensitive to the nanotube diameter. Diffusion of H on the surface of WS encounters quite small activation barriers whose magnitude helps to explain previous and new experimental results for the observed dependence of the hydrogen concentration with temperature. Intercalation of H between adjacent planar WS layers reveals an endothermic character. Intercalating H atoms is energetically favorable, but the intercalation energy does not compensate for the cost of dissociating the molecules. When H molecules are intercalated between the walls of a double wall nanotube, the rigid confinement induces the dissociation of the confined molecules. A remarkable result is that the presence of a full H monolayer adsorbed on top of the first WS layer of a WS multilayer system strongly facilitates the intercalation of H between WS layers underneath. This opens up an additional gate to intercalation processes.

WS2 Nanotubes as a 1D Functional Filler for Melt Mixing with Poly(lactic acid):Implications for Composites Manufacture

“…A small mass loss of 1.7% was detected below 400 °C, which can be attributed to evaporation of physisorbed water from the surface, inner core, or in between the layers of the NTs. 40 A further mass loss of 6.1% was measured between 400 and 550 °C. This weight loss progression as the temperature increased corresponds to the WS 2 oxidation accompanied by a color change of the WS 2 NTs powder from an original black (20 °C) to dark gray (500 °C) and then to a yellow/pale green (800 °C) (see Figure 3a-top).…”

“…Thermal analysis of the WS 2 NTs was performed by TGA in an air atmosphere, Figure a), where a total mass loss of ∼8% was detected when the sample was heated to 550 °C, with no further mass loss at higher temperatures, up to 1000 °C. A small mass loss of 1.7% was detected below 400 °C, which can be attributed to evaporation of physisorbed water from the surface, inner core, or in between the layers of the NTs …”

Cathodoluminescence in single and multiwall WS2 nanotubes: Evidence for quantum confinement and strain effect

“…A detailed description and explanation of the fundamental structural aspects of these systems, as given by the DFT computations, can be found in previous works by some of the present authors. 49,50 The calculated electronic gaps between occupied and unoccupied states of armchair and zigzag single wall WS 2 nanotubes are shown as a function of the nanotube diameter in Fig. 11(a); and Tables II and III of the supplementary material give the numerical values of diameters and gaps for armchair and zigzag nanotubes, respectively.…”

Implantation of Gallium into Layered WS2 Nanostructures is Facilitated by Hydrogenation

“…[5][6][7] The availability of these nanomaterials led to the investigation of their properties, and stimulated numerous applications in photoelectronics and nano-optics, [8][9][10] tribology, [11,12] and hydrogen storage. [13][14][15] Implantation of atoms into solid materials provides a way to modify their properties. [16] Doping of silicon by ion implantation is an important step in the process of semiconductor fabrication for classical and quantum devices.…”

“…We decided to apply this hydrogen plasma pretreatment based on the previously observed effect of interlayer expansion in the WS 2 nanoparticles due to hydrogenation, [14] which was confirmed and explained by density functional theory (DFT) calculations. [14,15] In the present work, DFT calculations relevant to the implantation process have been performed to complement the FIB experiments. These calculations successfully explain the decisive effect of hydrogenation in facilitating Ga implantation.…”