Carbon supported lithium hydride nanoparticles: Impact of preparation conditions on particle size and hydrogen sorption

Nanosizing of light metal hydrides has yielded significant improvements to their hydrogen storage properties. We explored for the first time a procedure for preparing supported LiH nanoparticles. Impregnation of a carbon framework with a butyllithium solution, followed by reaction with gaseous hydrogen yielded LiH particles ranging in size from 2 nm to the micrometer scale. Reducing the reaction temperature from 300 C to 100 C, as well as the use of a t-butyllithium precursor instead of an n-butyllithium precursor, gave significant improvements on the degree of confinement of the LiH particles. The particle size of the LiH has a significant impact on the hydrogen release profile, 11 nm crystallites begin to release hydrogen as low as 100 C under argon flow, a reduction of roughly 400 C on the macrocrystalline system. The hydrogen release is reversible, with hydrogen uptake after desorption as high as 7.0 wt% w.r.t. LiH (0.8 wt% w.r.t the sample) under 0.1 bar of hydrogen at 200 C and full uptake takes place within 5 min at 26 bar. This new preparation procedure for supported light metal hydrides is particularly relevant for the field of hydrogen storage

All-solid-state lithium-sulfur battery based on a nanoconfined LiBH₄ electrolyte

In this work we characterize all-solid-state lithium-sulfur batteries based on nano-confined LiBH4in mesoporous silica as solid electrolytes. The nano-confined LiBH4has fast ionic lithium conductivity at room temperature, 0.1 mScm-1, negligible electronic conductivity and its cationic transport number (t+= 0.96), close to unity, demonstrates a purely cationic conductor. The electrolyte has an excellent stability against lithium metal. The behavior of the batteries is studied by cyclic voltammetry and repeated charge/discharge cycles in galvanostatic conditions. The batteries show very good performance, delivering high capacities versus sulfur mass, typically 1220 mAhg-1after 40 cycles at moderate temperature (55°C), 0.03 C rates and working voltage of 2 V. © The Author(s) 2016

Surface-modified carbon materials for CO2 electroreduction

The electrochemical reduction of CO2 to produce sustainable fuels and chemicals has attracted great attention in recent years. It is shown that surface-modified carbons catalyze the CO2RR. This study reports a strategy to modify the surface of commercially available carbon materials by adding oxygen and nitrogen surface groups without modifying its graphitic structure. Clear differences in CO2RR activity, selectivity and the turnover frequency between the surface-modified carbons were observed, and these differences were ascribed to the nature of the surface groups chemistry and the point of zero charge (PZC). The results show that nitrogen-containing surface groups are highly selective towards the formation of CO from the electroreduction of CO2 in comparison with the oxygen-containing surface groups, and the carbon without surface groups. This demonstrates that the selectivity of carbon for CO2RR can be rationally tuned by simply altering the surface chemistry via surface functionalization

Effects of LiBF4 Addition on the Lithium-Ion Conductivity of LiBH4

Complex hydrides, such as LiBH4, are a promising class of ion conductors for all-solid-state batteries, but their application is constrained by low ion mobility at room temperature. Mixing with halides or complex hydride anions, i.e., other complex hydrides, is an effective approach to improving the ionic conductivity. In the present study, we report on the reaction of LiBH4 with LiBF4, resulting in the formation of conductive composites consisting of LiBH4, LiF and lithium closo-borates. It is believed that the in-situ formation of closo-borate related species gives rise to highly conductive interfaces in the decomposed LiBH4 matrix. As a result, the ionic conductivity is improved by orders of magnitude with respect to the Li-ion conductivity of the LiBH4, up to 0.9 × 10−5 S cm−1 at 30◦C. The insights gained in this work show that the incorporation of a second compound is a versatile method to improve the ionic conductivity of complex metal hydrides, opening novel synthesis pathways not limited to conventional substituents

Combined Effect of Halogenation and SiO2 Addition on the Li-Ion Conductivity of LiBH4

In this work, the combined effects of anion substitution (with Br− and I−) and SiO2 addition on the Li-ion conductivity in LiBH4 have been investigated. Hexagonal solid solutions with different compositions, h-Li(BH4)1−α(X)α (X = Br, I), were prepared by ball milling and fully characterized. The most conductive composition for each system was then mixed with different amounts of SiO2 nanoparticles. If the amount of added complex hydride fully fills the original pore volume of the added silica, in both LiBH4-LiBr/SiO2 and LiBH4-LiI/SiO2 systems, the Li-ion conductivity was further increased compared to the h-Li(BH4)1−α(X)α solid solutions alone. The use of LiBH4-LiX instead of LiBH4 in composites with SiO2 enabled the development of an optimal conductive pathway for the Li ions, since the h-Li(BH4)1−α(X)α possesses a higher conductivity than LiBH4. In fact, the Li conductivity of the silica containing h-Li(BH4)1−α(X)α is higher than the maximum reached in LiBH4-SiO2 alone. Therefore, a synergetic effect of combining halogenation and interface engineering is demonstrated in this work

The Nature of Interface Interactions Leading to High Ionic Conductivity in LiBH4/SiO2Nanocomposites

Complex metal hydride/oxide nanocomposites are a promising class of solid-state electrolytes. They exhibit high ionic conductivities due to an interaction of the metal hydride with the surface of the oxide. The exact nature of this interaction and composition of the hydride/oxide interface is not yet known. Using 1H, 7Li, 11B, and 29Si NMR spectroscopy and lithium borohydride confined in nanoporous silica as a model system, we now elucidate the chemistry and dynamics occurring at the interface between the scaffold and the complex metal hydride. We observed that the structure of the oxide scaffold has a significant effect on the ionic conductivity. A previously unknown silicon site was observed in the nanocomposites and correlated to the LiBH4 at the interface with silica. We provide a model for the origin of this silicon site which reveals that siloxane bonds are broken and highly dynamic silicon-hydride-borohydride and silicon-oxide-lithium bonds are formed at the interface between LiBH4 and silica. Additionally, we discovered a strong correlation between the thickness of the silica pore walls and the fraction of the LiBH4 that displays fast dynamics. Our findings provide insights on the role of the local scaffold structure and the chemistry of the interaction at the interface between complex metal hydrides and oxide hosts. These findings are relevant for other complex hydride/metal oxide systems where interface effects leads to a high ionic conductivity

Thermochemical Treatment of Nigerian Raw Clays for Oil and Gas Drilling Operations

Sodium-based bentonite is used for drilling operations because of its high swelling capacity. This type of bentonite clay is not sourced locally in many oil- and gas-producing nations. However, low-swelling clays (calcium- and potassium-based) are in abundant quantities in most of these countries. Hence, there is a need to convert low-swelling bentonite clays to sodium-based bentonite. The method used to convert low-swelling clays is more applicable to calcium-based bentonite. This research investigated a thermochemical treatment method that converted potassium-based bentonite to sodium-based bentonite. The raw clay materials were sourced from Pindinga (P) and Ubakala (U) clay deposits in Nigeria. An X-ray diffractometer (XRD), an energy dispersive X-ray (EDX), and a scanning electron microscope (SEM) were used to characterize the raw clay samples. Mud slurry was prepared by mixing 22 g of the local raw clays, 3 wt.% soda ash, and MgO at concentrations between 1 and 3 wt.% and heating at 90 °C. The result showed that the viscosities of samples P and U increased from 6 to 26 and 8 to 35.5 cP before and after thermochemical treatment, respectively. Also, due to the thermochemical treatment, the samples’ yield point, consistency factor, consistency index, and thixotropy behavior were all significantly improved

Improving the Cycle Life of Solid-State Batteries by Addition of Oxide Nanoparticles to a Complex Hydride Solid Electrolyte

We report that the addition of silica nanoparticles to the iodide-substituted LiBH4 (h-Li(BH4)0.8(I)0.2) improves the ion conductivity and, remarkably, the cycle life of the all-solid state batteries. The h-Li(BH4)0.8(I)0.2-SiO2 was synthesized by mechanochemical treatment and possesses a Li+ conductivity of 9.3 × 10-5 S cm-1 at RT. It has an electrochemical stability window of about 2.5 V vs Li+/Li and an improved stability against Li-metal, compared to h-Li(BH4)0.8(I)0.2, owing to the addition of oxide nanoparticles, which we ascribed to a greater mechanical stability of the solid-state electrolyte. The all-solid state battery Li|h-Li(BH4)0.8(I)0.2-SiO2|TiS2 demonstrated a good long-term cyclability, i.e., over 200 cycles at C/20 and even including a C-rate of C/5, demonstrating that the addition of oxide nanoparticles improves the cycling stability of the electrolyte

Ionic conductivity in complex metal hydride-based nanocomposite materials: The impact of nanostructuring and nanocomposite formation

Complex metal hydrides have recently gained interest as solid electrolytes for all-solid-state batteries due to their light weight, easy deformability, and fast ion mobility at elevated temperatures. However, increasing their low conductivity at room temperature is a prerequisite for application. In this review, two strategies to enhance room temperature conductivity in complex metal hydrides, nanostructuring and nanocomposite formation, are highlighted. First, the recent achievements in nanostructured complex metal hydride-based ion conductors and complex metal hydride/metal oxide nanocomposite ion conductors are summarized, and the trends and challenges in their preparation are discussed. Then, the reported all-solid-state batteries based on complex metal hydride nanocomposite electrolytes are highlighted. Finally, future research directions and perspectives are proposed, both for the preparation of improved metal hydride ion conductors, as well as metal hydride-based all-solid-state batteries