A prospect for LiBH4 as on-board hydrogen storage

Spatial Confinement of Lithium Borohydride in Bimetallic CoNi-Doped Hollow Carbon Frameworks for Stable Hydrogen Storage

While lithium borohydride is one of the most promising hydrogen storage materials due to its ultrahigh hydrogen storage density, high thermodynamic stability, kinetic barriers, and poor reversibility, it is far from being used in practical applications. Herein, we prepare a cubic hollow carbon dodecahedron uniformly modified with a bimetallic CoNi alloy (CoNi/NC) for preserving the stable catalytic effect of CoNi alloys toward reversible hydrogen storage. It is theoretically confirmed that bimetallic CoNi alloys effectively weaken the B-H bonds of LiBH4 by extending their average length to 1.33, 0.09 and 0.04 Å longer than that of LiBH4 and LiBH4 under metallic Co, respectively. More importantly, the alloying of Co with Ni avoids the reattachment of H from LiBH4 to the Co surface, which prevents LiBH4 from dehydrogenation for the formation of H2 on the Co surface, thus resulting in an ultralow hydrogen desorption energy of 0.1, 1.85 and 0.52 eV lower than that of LiBH4 and LiBH4 under metallic Co. Therefore, the onset and peak hydrogen desorption temperatures decrease to 130 and 355 °C, respectively, 170 and 97 °C lower than that of bulk LiBH4. More importantly, a reversible H2 capacity of 9.4 wt % is achieved even after 10 cycles.

From Iron to Copper: The Effect of Transition Metal Catalysts on the Hydrogen Storage Properties of Nanoconfined LiBH4 in a Graphene-Rich N-Doped Matrix

Incipient wetness impregnation was employed to decorate two N-doped graphene-rich matrixes with iron, nickel, cobalt, and copper nanoparticles. The N-doped matrix was wetted with methanol solutions of the corresponding nitrates. After agitation and solvent evaporation, reduction at 800 °C over the carbon matrix promoted the formation of nanoparticles. The mass of the metal fraction was limited to 5 wt. % to determine if limited quantities of metallic nanoparticles catalyze the hydrogen capture/release of nanoconfined LiBH₄. Isotherms of nitrogen adsorption afforded the textural characterization of the matrixes. Electronic microscopy displayed particles of definite size, evenly distributed on the matrixes, as confirmed by X-ray diffraction. The same techniques assessed the impact of LiBH₄ 50 vol. % impregnation on nanoparticle distribution and size. The hydrogen storage properties of these materials were evaluated by differential scanning calorimetry and two cycles of volumetric studies. X-ray diffraction allowed us to follow the evolution of the material after two cycles of hydrogen capture-release. We discuss if limited quantities of coordination metals can improve the hydrogen storage properties of nanoconfined LiBH₄, and which critical parameters might restrain the synergies between nanoconfinement and the presence of metal catalysts.

High pressure polymorphism of LiBH4 and of NaBH4

The pressure-induced structural changes in LiBH4 and in NaBH4 have been investigated experimentally up to 290 GPa by coupling Raman spectroscopy, infrared absorption spectroscopy and synchrotron X-ray diffraction. This data set is also analysed in the light of Density Functional Theory calculations performed up to 600 GPa. The [BH4]- unit appears to be remarkably resistant under pressure. NaBH4 remains stable in the known Pnma γ-phase up to 200 GPa and calculations predict a transition to a metallic polymeric C2/c phase at about 480 GPa. LiBH4 is confirmed to exhibit a richer polymorphism. A new Pnma orthorhombic phase VI is found to be stable above 60 GPa and there are hints of a possible phase VII above 160 GPa. DFT calculations predict that two other high pressure LiBH4 phases should appear at about 290 and 428 GPa. A very slight solubility of H2 inside phases II, III and V of LiBH4 is observed. A NaBH4(H2)0.5 complex is predicted to be stable above 150 GPa.

Enhancement Effect of Bimetallic Amide K2Mn(NH2)4 and In-Situ Formed KH and Mn4N on the Dehydrogenation/Hydrogenation Properties of Li–Mg–N–H System

In this work, we investigated the influence of the K2Mn(NH2)4 additive on the hydrogen sorption properties of the Mg(NH2)2 + 2LiH (Li–Mg–N–H) system. The addition of 5 mol% of K2Mn(NH2)4 to the Li–Mg–N–H system leads to a decrease of the dehydrogenation peak temperature from 200 °C to 172 °C compared to the pristine sample. This sample exhibits a constant hydrogen storage capacity of 4.2 wt.% over 25 dehydrogenation/rehydrogenation cycles. Besides that, the in-situ synchrotron powder X-ray diffraction analysis performed on the as prepared Mg(NH2)2 + 2LiH containing K2Mn(NH2)4 indicates the presence of Mn4N. However, no crystalline K-containing phases were detected. Upon dehydrogenation, the formation of KH is observed. The presence of KH and Mn4N positively influences the hydrogen sorption properties of this system, especially at the later stage of rehydrogenation. Under the applied conditions, hydrogenation of the last 1 wt.% takes place in only 2 min. This feature is preserved in the following three cycles.

Nanoparticle shapes by using Wulff constructions and first-principles calculations

BACKGROUND

The majority of complex and advanced materials contain nanoparticles. The properties of these materials depend crucially on the size and shape of these nanoparticles. Wulff construction offers a simple method of predicting the equilibrium shape of nanoparticles given the surface energies of the material.

RESULTS

We review the mathematical formulation and the main applications of Wulff construction during the last two decades. We then focus to three recent extensions: active sites of metal nanoparticles for heterogeneous catalysis, ligand-protected nanoparticles generated as colloidal suspensions and nanoparticles of complex metal hydrides for hydrogen storage.

CONCLUSION

Wulff construction, in particular when linked to first-principles calculations, is a powerful tool for the analysis and prediction of the shapes of nanoparticles and tailor the properties of shape-inducing species.