Hydrogen production from nano-porous Si powder formed by stain etching

Hydrogen reservoirs based on porous silicon (PS) nanostructures are considered. Silicon-based hydrogen tanks are believed to be applicable for portable device energy supply and compatible with micro-sources of energy of new generation. Stain etching of silicon powder to produce PS is studied as a technology alternative to conventional electrochemical etching and application of the PS powder for hydrogen production is also described. Size selection of initial Si micro-particles constituting the powders was carried out by sedimentation technique. Hydrogen content in PS was investigated by FTIR spectroscopy. Extraction of hydrogen in water environment in presence of small amount of NH₃ as catalyst was shown to have advantages such as safety and tunability, additional production of hydrogen from water dissociation, and a possibility to characterize PS as a hydrogen source material in terms of hydrogen effective shell and crystalline core conception.     

DFT study of H2 adsorption on Pd-decorated single walled carbon nanotubes with C-vacancies

Carbon nanotubes are considered important materials for hydrogen storage. Although the C–H interaction is very weak at room temperature, the incorporation of highly dispersed Pd nanoparticles increases the H₂ adsorption on carbon surfaces. In this work we performed density functional theory studies of H₂ adsorption on single walled carbon nanotubes (SWCNTs) with C-vacancies and a Pd decoration. We used the VASP and SIESTA codes. Our calculations show that Pd adsorption is favored on the C-vacancies of the (5,5) SWCNT, while H₂ adsorption also occurs preferentially on C-defective sites.     

Bonding in PdH2 and Pd2H2 systems adsorbed on carbon nanotubes: Implications for hydrogen storage

This work presents a bonding study of hydrogen adsorption processes on palladium decorated carbon nanotubes by using the density functional theory (DFT). First, we considered simple decoration models involving single palladium atoms or palladium dimers, and then we analyzed the adsorption of several molecular and dissociated hydrogen coordination structures, including Kubas-type complexes. In all cases we computed the energy, bonding and electronic structure for the different nanotube-supported hydrogen–palladium systems. Our results show that Pd(H₂) and Pd₂(H₂) complexes with relaxed but not dissociated H–H bonds are the most stable adsorbed systems. The role of s, p and d orbitals on the bonding mechanism for all adsorbates and substrates was also addressed. We found intermolecular donor–acceptor C–Pd and Pd–H delocalizations after adsorption. We also studied the palladium clustering effect on the hydrogen uptake based on Kubas-type bonding.     

Mechanochemical modification of LiAlH4 with Fe2O3 - A combined DFT and experimental study

LiAlH₄ is a promising material for hydrogen storage, having the theoretical gravimetric density of 10.6 wt% H₂. In order to decrease the temperature where hydrogen is released, we investigated the catalytic influence of Fe₂O₃ on LiAlH₄ dehydrogenation, as a model case for understanding the effects transition oxide additives have in the catalysis process. Quick mechanochemical synthesis of LiAlH₄ + 5 wt% Fe₂O₃ led to the significant decrease of the hydrogen desorption temperature, and desorption of over 7 wt%H₂ in the temperature range 143–154 °C. Density functional theory (DFT)-based calculations with Tran-Blaha modified Becke-Johnson functional (TBmBJ) address the electronic structure of LiAlH₄ and Li₃AlH₆. ⁵⁷Fe Mössbauer study shows the change in the oxidational state of iron during hydrogen desorption, while the ¹H NMR study reveals the presence of paramagnetic species that affect relaxation. The electron transfer from hydrides is discussed as the proposed mechanism of destabilization of LiAlH₄ + 5 wt% Fe₂O₃.     

Lithium decoration characteristics for hydrogen storage enhancement in novel periodic porous graphene frameworks

Hydrogen storage in porous materials by physical adsorption is being discussed to provide widespread usage of hydrogen energy systems. One of the recent hydrogen storage media that store hydrogen physically is Porous Graphene Frameworks (PGFs). In the study, three different PGFs were constructed by using Benzene-1,3,5-tricarboxylic acid (BTC), 4,40,400-Benzene-1,3,5-triyltribenzoate (BTB) and 4,40,400-(benzene-1,3,5triyl-tris (benzene-4,1-diyl))tribenzoate (BBC) organic linkers. The geometries of the structures were optimized and lithium atoms were dispersed inside. Then, thirty-three different structures were derived. Finally, hydrogen storage capacities and surface areas of each structure were computed. It was found out that 160 lithium dispersed Graphene-BBC structure has the highest hydrogen storage capacity with 4.26 wt % at 298K and 100 bars while 70 lithium dispersed graphene-BTB structure store 9.81 wt % hydrogen at 77K and 4 bars, and lithium free graphene-BBC structure store 20,68 wt % hydrogen at 77K and 100 bars. Lithium dispersion enabled extra surfaces for Graphene-BTB and Graphene-BBC structures to the limits. But surface area of Graphene-BTC structure decreased with lithium dispersion. The number of limits for Graphene-BTB and Graphene-BBC named structures were 70 and 200 lithium atoms, respectively. At the final it is pointed out that constructed novel PGFs could store comparable and relatively high hydrogen in various conditions. The existence of lithium atoms played a minor role to enhance hydrogen storage capacity but the limits are critically important to reach maximum capacity.     

Light and stable LinB14(n=1–5) clusters for high capacity hydrogen storage at room temperature: A DFT study

In this article, we have explored the hydrogen (H₂) storage capacity of the Li doped B clusters Li_nB₁₄(n = 1–5) using density functional theory (DFT). The geometrical and Bader's topological parameters indicate that the clusters adsorb H₂ in the molecular form. The Li atom polarises the H₂ molecules for their effective adsorption on the clusters. The Li_nB₁₄ (n = 1–5) clusters are found to be stable even after H₂ adsorption at room temperature. The average adsorption energy is found to be in the range of 0.12–0.14 eV/H₂. Among the various clusters, the Li₅B₁₄ shows maximum H₂ storage capacity (13.89 wt%) at room temperature. The ADMP simulation reveals that within few femtoseconds (fs), the H₂ molecules begin to move away from the clusters and within 400 fs most of the H₂ molecules moved away from the clusters.     

X-ray diffraction and H-storage in ultra-small palladium particles

In situ X-ray diffraction (XRD) and gravimetric hydrogen uptake measurements of d ∼ 2–3 nm spherical PdH_x particles have been studied in the temperature and pressure range of 323 < T < 428 K and 0 < P < 10 bar. The Pd particles were protected from sintering with a hydrogen-permeable carbon coating. While only containing ∼300–1000 atoms, the Pd particles were found to exhibit the same fcc structure and lattice constant as the bulk. Our isothermal studies show that, with increasing x, these highly crystalline PdH_x nanoparticles also exhibit a complete transformation from the dilute α solid solution phase to the more concentrated β hydride phase. However, we observed that the character of the α–β phase transition in these nanoparticles is very different from that in the bulk. Indeed, the hydrogen uptake isotherm exhibits a noticeable positive slope in the α + β co-existence region. Furthermore, we also observed a noticeable narrowing of the α + β co-existence region (δx) in the nanoparticles. Also, a significant suppression of the critical temperature T_c for the phase boundary was observed: T_c(nano) ≈ 430 K while T_c(bulk) ≈ 570 K. These results signal a significant change in the thermodynamic behavior of very small hydride nanoparticles that may be common to many other nano-scale metal hydride systems as well.     

Recent advances in catalyst-enhanced LiAlH4 for solid-state hydrogen storage: A review

LiAlH₄ is regarded as a potential material for solid-state hydrogen storage because of its high hydrogen content (10.5 wt%). However, its high decomposition temperature, slow dehydrogenation kinetics and irreversibility under moderate condition hamper its wider applications. Mechanical milling treatment and doping with a catalyst or additive has drawn significant ways to improve hydrogen storage properties of LiAlH₄. Microstructure or nanostructure materials were developed by using a ball milling technique and doping with various types of catalysts or additives which had dramatically improved the efficiency of LiAlH₄. However, the state-of-the-art technologies is still far from meeting the expected goal for the applications. In this paper, the overview of the recent advances in catalyst-enhanced LiAlH₄ for solid-state hydrogen storage is detailed. The remaining challenges and the future prospect of LiAlH₄–catalyst system is also discussed. This paper is the first systematic review that focuses on catalyst-enhanced LiAlH₄ for solid-state hydrogen storage.     

Hydrogen storage behaviour of Li3N doped with Li2O and Na2O

Mixtures of Li₂O/Li₃N and Na₂O/Li₃N have been investigated for hydrogen storage. When Li₃N is doped with ca. 5 mol% Li₂O and annealed, both binary compounds exist as separate phases as evident from powder X-ray diffraction. Li₂O acts as a spectator in the hydrogen storage reactions and there is no evidence of enhanced Li⁺ or H⁺ mobility. Na₂O (5 mol%) interacts more strongly with Li₃N, leading to the generation of an unidentified phase, which also appears to play no part in the hydrogen storage reactions of the composite system. We conclude that addition of these levels of Li₂O or Na₂O to Li₃N followed by annealing does not improve the hydrogen storage properties of Li₃N.     

Computational exploration of magnesium-decorated carbon nitride (g-C3N4) monolayer as advanced energy storage materials

Density functional theory (DFT) computational studies were conducted to explore the hydrogen storage performance of a monolayer material that is built on the base of carbon nitride (g-C₃N₄, heptazine structure) with decoration by magnesium (Mg). We found that a 2 × 2 supercell can bind with four Mg atoms. The electronic charges of Mg atoms were transferred to the g-C₃N₄ monolayer, and thus a partial electropositivity on each adsorbed Mg atom was formed, indicating a potential improvement in conductivity. This subsequently causes the hydrogen molecules’ polarization, so that these hydrogen molecules can be efficiently adsorbed via both van der Waals and electrostatic interactions. To note, the configurations of the adsorbed hydrogen molecules were also elucidated, and we found that most adsorbed hydrogen molecules tend to be vertical to the sheet plane. Such a phenomenon is due to the electronic potential distribution. In average, each adsorbed Mg atom can adsorb 1–9 hydrogen molecules with adsorption energies that are ranged from ?0.25 eV to ?0.1 eV. Moreover, we realised that the nitrogen atom can also serve as an active site for hydrogen adsorption. The hydrogen storage capacity of this Mg-decorated g-C₃N₄ is close to 7.96 wt %, which is much higher than the target value of 5.5 wt % proposed by the U.S. department of energy (DOE) in 2020 [1]. The finding in this study indicates a promising carbon-based material for energy storage, and in the future, we hope to develop more advanced materials along this direction.     

π-Stacked organic molecular crystals under electric fields as viable storage media for molecular hydrogen

The goal of efficient storage of molecular hydrogen at room temperature and reasonable pressures has not been achieved so far. This requires a model system with sufficient H₂ binding energy and low H₂ internal pressure. Here, via theoretical investigations, we show that the two requirements can be satisfied simultaneously by using a π-stacked organic semiconductor as the physisorption substrate in the presence of an electric field.