Study of dehydrogenation properties of metallic borohydrides for hydrogen storage

Ce travail de thèse a été consacré à l'exploration des composés à base de borohydrures métalliques et de leurs dérivés en tant que matériaux prometteurs pour le stockage de l’hydrogène à l’état solide, avec des capacités massiques théoriques élevées (> 10 wt%) et des températures de désorption modérées (10wt%) and moderate desorption temperatures (<150°C). The candidate materials are ammine metal borohydrides, AxM(BH4)m+x(NH3)n where A is alkali metal, M any other metal (for example Zn, Al, Mg) , m is the oxidation state of M, n is the number of neutral ammonia adducts and x=0-2. These materials contain positively (N-Hδ+) and negatively (B-Hδ-) charged hydrogens in their structure, upon heating the electrostatic attraction between these oppositely charged hydrogens, their combination and release as a hydrogen molecule is the main dehydrogenation process. The major challenges preventing the application of these materials are the lack of straight-forward synthesis process to obtain desired composition, precise control of dehydrogenation properties based on the chemical formula and the rehydrogenation of spent fuel.High electronegativity metal borohydrides are stabilized by combining them with alkali metal borohydrides. By adhering to the same logic, we explored the potential of ammonium cation [NH4]+ as pseudo-alkali cation that can also participate in decomposition of Zn(BH4)2 and increase its theoretical hydrogen capacity. So, we synthesized ammonium zinc borohydride (NH4)Zn(BH4)3 for the first time. However, the compound was not stable at room temperature and its thermal decomposition released a lot of diborane and borazine gases.In literature, the typical synthesis process involves salt metathesis reaction using ball-milling or solvothermal approaches to obtain metal borohydride, followed by exposure to ammonia gas. To bypass this multi-step approach we developed liquid ammonia synthesis process that directly enables the formation of AZn(BH4)3(NH3)2. The technique allowed us to synthesize LiZn(BH4)3(NH3)2 and KZn(BH4)3(NH3)2 for the first time. By combining the known compounds from literature Zn(BH4)2(NH3)2 and NaZn(BH4)3(NH3)2, we obtained a unique set of compounds that have zinc cation sharing its coordination sphere with two borohydride and two ammonia molecules. We determined that monometallic and bimetallic compounds have different dehydrogenation reactions. The presence of an alkali cation with lower polarizing power than zinc cation in the structure is more detrimental to the purity of released hydrogen. Use of zinc chloride precursors results in chloride anion substitution of borohydride sites in AZn(BH4)3(NH3)2 which also increases ammonia impurity. Chloride anion substitution is eliminated by using ZnF2 precursor which also enables the filtration of the main phase from ammonia insoluble alkali fluoride byproduct. Hydrogen capacity and the purity can be improved by adding ammonia borane (NH3BH3). ZnCl2―8NaZn(BH4)3(NH3)2―20NH3BH3 mixture releases 10 wt% pure hydrogen, which is highest performance for Zn-B-N-H system. This performance comes at the cost of thermal stability which lower the dehydrogenation temperature too much making the mixture essentially unstable at room temperature. Therefore, we explored Mg-B-N-H system instead which have higher thermal stability. We observed that magnesium metal (or magnesium hydride) in liquid ammonia can react with ammonia borane to form magnesium amidoboranes Mg(NH2BH3)2(NH3)3 type compounds. This reaction even under 67 bar hydrogen pressure cannot be forced to form borohydride phases. Since magnesium amidoboranes is a type destabilized ammonia borane we continued our efforts for synthesis of Mg(BH4)2(NH3)6 phase. Synthesis of these compounds with MgF2 precursors were not possible; instead, the reaction of MgH2 with L·BH3 (L= triethylamine) in liquid ammonia was successful. The hydrogen storage properties of amorphous Li2Mg(BH4)4(NH3)2 was the most attractive with at least 10 wt% hydrogen capacity and high hydrogen purity

Etude des propriétés de déshydrogénation des borohydrures métalliques pour le stockage de l'hydrogène

This thesis work is dedicated to the exploration of metal borohydride compounds and their derivatives as a family of materials that can potentially enable solid-state storage of hydrogen, with high gravimetric capacity (>10wt%) and moderate desorption temperatures ( 10 wt%) et des températures de désorption modérées (< 150 °C). Les candidats potentiels sont les borohydrures métalliques complexés avec l’ammoniac, AxM(BH4)m+x(NH3)n où A ― métal alcalin, M tout autre métal (par exemple Zn, Al, Mg), m ― le degré d’oxydation de M, n ― nombre de molécules d’ammoniac et x = 0-2. Ces composés contiennent des atomes d'hydrogène chargés positivement (N-Hδ+) et négativement (B-Hδ-). Le processus de déshydrogénation est basé principalement sur l'attraction électrostatique entre ces atomes d'hydrogène à charge opposée, leur combinaison et libération sous forme de molécule d'hydrogène.Les borohydrures métalliques à haute électronégativité sont stabilisés en les combinant avec des cations métalliques alcalins. En suivant la même approche, nous avons exploré le potentiel du cation ammonium [NH4]+ en tant que cation pseudo-alcalin pouvant également participer à la décomposition du Zn(BH4)2 et augmenter sa capacité théorique en hydrogène. Nous avons donc synthétisé pour la première fois le borohydrure d'ammonium et de zinc (NH4)Zn(BH4)3. Cependant, le composé n’est pas stable à la température ambiante et sa décomposition thermique libère beaucoup de gaz tels que le diborane ou la borazine.Dans la littérature, le processus de synthèse typique implique une réaction de métathèse de sels utilisant des techniques de broyage à billes ou la méthode solvothermale pour obtenir d’abord le borohydrure métallique, suivi par à une exposition à l'ammoniac gazeux. Pour contourner cette approche en plusieurs étapes, nous avons développé un procédé de synthèse d'ammoniac liquide qui permet directement la formation de AZn(BH4)3(NH3)2. La technique nous a permis de synthétiser les composés LiZn(BH4)3(NH3)2 et KZn(BH4)3(NH3)2 pour la première fois. Avec les composés déjà connus, Zn(BH4)2(NH3)2 et NaZn(BH4)3(NH3)2, nous avons obtenu un ensemble unique de composés dont le cation zinc partage sa sphère de coordination avec deux BH4 et deux NH3. Nous avons déterminé ainsi que les composés monométalliques et bimétalliques ont des réactions de déshydrogénation différentes. La présence d'un cation alcalin avec un pouvoir polarisant inférieur à celui du zinc dans la structure nuit davantage à la pureté de l'hydrogène libéré. L'utilisation de précurseurs de chlorure de zinc entraîne la substitution par l'anion chlorure de sites borohydrures dans AZn(BH4)3(NH3)2, ce qui augmente également les impuretés d'ammoniac. La substitution par l’anion chlorure est éliminée en utilisant un précurseur de ZnF2 qui permet également la filtration de la phase principale à partir du sous-produit de fluorure alcalin, insoluble dans l’ammoniac. La capacité en hydrogène et la pureté peuvent être améliorées en ajoutant du borazane (NH3BH3). Le mélange ZnCl2―8NaZn(BH4)3(NH3)2-20NH3BH3 libère 10 wt% d'hydrogène pur, ce qui représente la meilleure performance pour le système Zn-B-N-H.Nous avons également exploré le système Mg-B-N-H, qui présente une stabilité thermique supérieure. Nous avons observé que le magnésium métallique (ou l'hydrure de magnésium) dans l'ammoniac liquide peut réagir avec le borazane pour former des composés de type amidoboranes de magnésium Mg(NH2BH3)2(NH3)3. Même sous une pression d'hydrogène de 67bar, la formation des phases borohydrure n’a pas été possible. Comme l’amidoborane de magnésium est une sorte de borazane déstabilisé, nous avons poursuivi nos efforts afin de synthétiser le composé Mg(BH4)2(NH3)6. La réaction de MgH2 avec le L·BH3 (L= triéthylamine) dans l’ammoniac liquide a réussi. Parmi ces composés, les propriétés de stockage d'hydrogène de Li2Mg(BH4)4(NH3)2 amorphe sont les plus attractives, avec une capacité en hydrogène d'au moins 10 wt% et une pureté élevée

Spin injection and detection in Fe/GaAs hybrid lateral spin-valve structure

Spintronics devices are the future of the electronics industry. One of the most attractive proposed spintronics devices is Spin field effect transistor by Datta and Das, which has not been fabricated yet due to the fundamental three problems of spintronics: spin injection, manipulation of spin degree of freedom of electron and spin detection. In this thesis, electrical injection and detection of spin in lateral Fe/GaAs structures has been demonstrated. Spin polarization in GaAs is created by spin injection at reverse biased Fe/GaAs Schottky tunneling barrier. Using the advanced device fabrication techniques, lateral Fe/GaAs devices are fabricated. Interface between layer of Fe and GaAs is Schottky tunnel barrier created by heavily doping GaAs surface.Bachelor of Science in Physic

Electrochemical Regeneration of LiAlH4

International audienceHydrogen, a promising clean energy vector, surpasses traditional fuels in energy content (140 MJ/kg) but faces storage challenges. Aluminum-based complex metal hydrides like LiAlH4 offer solutions with high volumetric (>80g H2/L) and gravimetric (>8 wt %) energy densities, along with low decomposition temperatures (1 kbar). Consequently, a significant interest is in cost-effective approaches for regenerating LiAlH4 from its spent (hydrogen-depleted) material and H2.Graetz[1] proposed its first chemical regeneration, examining dehydrogenated LiH and Al with a Ti catalyst in THF under high H2 pressure (50 bar). Humphries[2] explored sub-ambient regeneration (<0°C) using Me2O and 95 bar H2. However, their practicality is hindered by reliance on high H2 pressure. Our research group investigates the viability of an electrochemical approach for its regeneration and potential elimination on the use of high H2 pressure, a novel concept not previously reported in the literature..Electrochemical properties were studied in THF-based electrolyte and Ar atmosphere at RT. Figure 1 shows a cyclic voltammogram of 1M LiAlH4 in THF to which we identified essential reactions, including Li and Al deposition, and irreversible anodic polarization of [AlH4-] associated with H2 release[3]. Applying a constant reduction potential ( -3.10 V vs. standard hydrogen electrode) resulted in dehydrogenated LiAlH4 (Li-Al alloy formation) and H2 release, demonstrating room-temperature electrochemical dehydrogenation with a Faradaic efficiency of 69%. We explore the effect of H2 pressure on these electrochemical reactions using our custom electrochemical pressure cell. The next step involves regenerating the deposited Li-Al alloy under moderate H2 pressures (<10 bar) and applying oxidative potentials to induce [AlH4-] reformation using Pd, Pt, Ti, or Ni electrocatalysts. Reformed LiAlH4 is quantified using 27Al NMR coupled with ICP-MS. Fundamental parameters will be investigated, including its kinetics, diffusion coefficients, and regeneration mechanisms, using various electroanalytical techniques like chronoamperometry, voltammetry, rotating disk electrode, and electrochemical-impedance spectroscopy

The LUAA Gundeti Technique for Bilateral Robotic Ureteral Reimplantation: Lessons Learned over a Decade for Optimal (Resolution, Urinary Retention, and Perioperative Complications) Trifecta Outcomes

Background: Ureteral reimplantation is the gold standard treatment for high-grade vesicoureteral reflux (VUR) in pediatric patients. Robot-assisted laparoscopic extravesical ureteral reimplantation (RALUR-EV) using the LUAA technique has emerged as a viable alternative to traditional open and laparoscopic surgical correction. Objective: To evaluate the outcomes, reflux resolution, urinary retention, and complications associated with bilateral RALUR-EV for primary VUR using the LUAA Gundeti technique in pediatric patients. Design, setting, and participants: A retrospective study was conducted at a single academic center, involving 34 consecutive pediatric patients who underwent RALUR-EV for bilateral VUR management between December 2008 and December 2022. The study included only patients who were evaluated with postoperative voiding cystourethrogram (VCUG). Surgical procedure: The LUAA extravesical ureteral reimplantation technique was performed, involving the identification and mobilization of the ureter, creation of a peritoneal window, dissection close to the neurovascular bundle, Y dissection at the ureterovesical junction, detrusorotomy, detrusorrhaphy with advential inclusion, and apical alignment suture. Measurements: The primary outcome was radiographic resolution of VUR on VCUG. The secondary outcomes included urinary retention and Clavien-Dindo grade III complications. Results and limitations: The overall radiographic resolution rate was 85.2%, with success rates of 76.7%, 75%, and 96.7% across the three distinct patient cohorts. The overall Clavien-Dindo grade III complication rate was 5.8%, and transient urinary retention was 8.8%. Resolution of urinary retention occurred within 7–28 d. The study's limitations include the small sample size, single-center design, and retrospective nature. Conclusions: The LUAA technique demonstrates sustainable outcomes for VUR resolution with a low incidence of transient urinary retention and complications. A thorough understanding of pelvic anatomy is essential for successful dissection and minimization of the risk of complications. Further studies are needed to evaluate the effectiveness of different approaches in reducing the incidence of transient urinary retention following bilateral extravesical reimplantation. Patient summary: In this study, we examined the results of the Gundeti LUAA surgical technique for treating primary vesicoureteral reflux in children. We identified various essential modifications that increase the likelihood of achieving favorable outcomes

A novel ammine lithium aluminum borohydride material for hydrogen storage: synthesis and regeneration

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Electrochemical Regeneration of LiAlH4

International audienceHydrogen, a promising clean energy vector, surpasses traditional fuels in energy content (140 MJ/kg) but faces storage challenges. Aluminum-based complex metal hydrides like LiAlH4 offer solutions with high volumetric (>80g H2/L) and gravimetric (>8 wt %) energy densities, along with low decomposition temperatures (1 kbar). Consequently, a significant interest is in cost-effective approaches for regenerating LiAlH4 from its spent (hydrogen-depleted) material and H2.Graetz[1] proposed its first chemical regeneration, examining dehydrogenated LiH and Al with a Ti catalyst in THF under high H2 pressure (50 bar). Humphries[2] explored sub-ambient regeneration (<0°C) using Me2O and 95 bar H2. However, their practicality is hindered by reliance on high H2 pressure. Our research group investigates the viability of an electrochemical approach for its regeneration and potential elimination on the use of high H2 pressure, a novel concept not previously reported in the literature..Electrochemical properties were studied in THF-based electrolyte and Ar atmosphere at RT. Figure 1 shows a cyclic voltammogram of 1M LiAlH4 in THF to which we identified essential reactions, including Li and Al deposition, and irreversible anodic polarization of [AlH4-] associated with H2 release[3]. Applying a constant reduction potential ( -3.10 V vs. standard hydrogen electrode) resulted in dehydrogenated LiAlH4 (Li-Al alloy formation) and H2 release, demonstrating room-temperature electrochemical dehydrogenation with a Faradaic efficiency of 69%. We explore the effect of H2 pressure on these electrochemical reactions using our custom electrochemical pressure cell. The next step involves regenerating the deposited Li-Al alloy under moderate H2 pressures (<10 bar) and applying oxidative potentials to induce [AlH4-] reformation using Pd, Pt, Ti, or Ni electrocatalysts. Reformed LiAlH4 is quantified using 27Al NMR coupled with ICP-MS. Fundamental parameters will be investigated, including its kinetics, diffusion coefficients, and regeneration mechanisms, using various electroanalytical techniques like chronoamperometry, voltammetry, rotating disk electrode, and electrochemical-impedance spectroscopy

A novel ammine lithium aluminum borohydride material for hydrogen storage: synthesis and regeneration

International audienc

Unravelling the effect of alkali cations and halide anions on the de-hydrogenation properties of ammine zinc borohydrides

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