Electronic Structure and Initial Dehydrogenation Mechanism of M(BH₄)₂·2NH₃ (M = Mg, Ca, and Zn): A First-Principles Investigation

The electronic structure and initial dehydrogenation mechanism of M­(BH₄)₂·2NH₃ (M = Mg, Ca, and Zn) have been systematically studied using first-principles calculations. A detailed study of the electronic structure reveals that the metal cations in M­(BH₄)₂·2NH₃ play a crucial role in both suppressing ammonia emission and destabilizing the N–H/B–H bonds. The calculation results of hydrogen removal energies are in agreement with the tendency of dehydrogenation temperatures of these ammoniates, i.e., Zn­(BH₄)₂·2NH₃ < Mg­(BH₄)₂·2NH₃ < Ca­(BH₄)₂·2NH₃. The initial dehydrogenation of M­(BH₄)₂·2NH₃ is achieved by the dissociation of (N)­H^δ+ from NH₃ and (B)­H^δ− atoms from BH₄ groups, resulting in the formation of N–B dative bonds and the reduction of the neighboring (N)­H^δ+···(B)­H^δ− dihydrogen bonds, which accelerate the subsequent dehydrogenation

Magnesium Hydride Nanoparticles Self-Assembled on Graphene as Anode Material for High-Performance Lithium-Ion Batteries

MgH₂ nanoparticles (NPs) uniformly anchored on graphene (GR) are fabricated based on a bottom-up self-assembly strategy as anode materials for lithium-ion batteries (LIBs). Monodisperse MgH₂ NPs with an average particle size of ∼13.8 nm are self-assembled on the flexible GR, forming interleaved MgH₂/GR (GMH) composite architectures. Such nanoarchitecture could effectively constrain the aggregation of active materials, buffer the strain of volume changes, and facilitate the electron/lithium ion transfer of the whole electrode, leading to a significant enhancement of the lithium storage capacity of the GMH composite. Furthermore, the performances of GMH composite as anode materials for LIBs are enabled largely through robust interfacial interactions with poly­(methyl methacrylate) (PMMA) binder, which plays multifunctional roles in forming a favorable solid-electrolyte interphase (SEI) film, alleviating the volume expansion and detachment of active materials, and maintaining the structural integrity of the whole electrode. As a result, these synergistic effects endow the obtained GMH composite with a significantly enhanced reversible capacity and cyclability as well as a good rate capability. The GMH composite with 50 wt % MgH₂ delivers a high reversible capacity of 946 mA h g^–1 at 100 mA g ^–1 after 100 cycles and a capacity of 395 mAh g^–1 at a high current density of 2000 mA g^–1 after 1000 cycles

Graphene Oxide Based Recyclable Dehydrogenation of Ammonia Borane within a Hybrid Nanostructure

The recyclable dehydrogenation of ammonia borane (AB) is achievable within a graphene oxide (GO)-based hybrid nanostructure, in which a combined modification strategy of acid activation and nanoconfinement by GO allows AB to release more than 2 equiv of pure H₂ at temperatures below 100 °C. This process yields polyborazylene (PB) as a single product and, thus, promotes the chemical regeneration of AB via reaction of PB with hydrazine in liquid ammonia

Decomposition Mechanism of Zinc Ammine Borohydride: A First-Principles Calculation

The decomposition mechanism of zinc ammine borohydride ([Zn­(NH₃)₂]­[BH₄]₂) has been studied by density functional theory calculation. The release of B₂H₆ and BH₃ is predicted to be kinetically and/or thermodynamically unfavorable for [Zn­(NH₃)₂]­[BH₄]₂, in agreement with experimental results that no boranes were detected during decomposition. The climbing image nudged elastic band calculation and ab initio molecular dynamics simulations indicate the formation of NH₃BH₃ and B₂H₇^– intermediates during decomposition of [Zn­(NH₃)₂]­[BH₄]₂, which is different from that observed for other reported ammine metal borohydrides. The dehydrogenation occurs through reaction pathways involving transfer of hydrides from the Zn cation to BH₄^– or transfer of protons from NH₃BH₃ to NH₃

Complex Ammine Titanium(III) Borohydrides as Advanced Solid Hydrogen-Storage Materials with Favorable Dehydrogenation Properties

Ammine metal borohydrides (AMBs), with high hydrogen contents and favorable dehydrogenation properties, are receiving intensive research efforts for their potential as hydrogen storage materials. In this work, we report the successful synthesis of three ammine titanium borohydrides (denoted as ATBs), Ti­(BH₄)₃·5NH₃, Li₂Ti­(BH₄)₅·5NH₃, and Ti­(BH₄)₃·3NH₃ via metathesis reaction of metal chloride ammoniates (TiCl₃·5NH₃ and TiCl₃·3NH₃) and lithium borohydride. These ATBs present favorable stability, owing to the coordination with NH₃ groups, compared to the unstable Ti­(BH₄)₃ at room temperature. Dehydrogenation results revealed that Ti­(BH₄)₃·5NH₃, which theoretically contains 15.1 wt % hydrogen, is able to release ∼13.4 wt % H₂ plus a small amount of ammonia. This occurred via a single-stage decomposition process with a dehydrogenation peak at 130 °C upon heating to 200 °C. For Li₂Ti­(BH₄)₅·5NH₃, a three-step decomposition process with a total of 15.8 wt % pure hydrogen evolution peaked at 105, 120, and 215 °C was observed until 300 °C. In the case of Ti­(BH₄)₃·3NH₃, a release of 14 wt % pure hydrogen via a two-step decomposition process with peaks at 109 and 152 °C can be achieved in the temperature range of 60–300 °C. Isothermal TPD results showed that over 9 wt % pure hydrogen was liberated from Ti­(BH₄)₃·3NH₃ and Li₂Ti­(BH₄)₅·5NH₃ within 400 min at 100 °C. Preliminary research on the reversibility of this process showed that dehydrogenated ATBs could be partly recharged by reacting with N₂H₄ in liquid ammonia. These aforementioned preeminent dehydrogenation performances make ATBs very promising candidates as solid hydrogen storage materials. Finally, analysis of the decomposition mechanism demonstrated that the hydrogen emission from ATBs is based on the combination reaction of B–H and N–H groups as in other reported AMBs

Intrinsically Coupled 3D nGs@CNTs Frameworks as Anode Materials for Lithium-Ion Batteries

Acquiring high-quality integrated nanographene sheets (nGs) and mitigating their self-aggregation are highly essential to achieving their full potential in energy related applications. The insertion of enthetic spacers into nGs layers can relieve the stacking problems but always results in a change in the intrinsic properties of the nGs and/or the introduction of complexity at the interfaces. In this work, a facile and scalable strategy is used to construct highly integrated, intrinsically coupled, N, S-doped 3D nanographene sheets trapped within carbon nanotubes (nGs@CNTs) through a modified counterion intercalation. The as-obtained nGs@CNTs are composed of two building blocks, in which large amounts of integrated unzipped nanoscale graphene sheets are tightly attached to the intact inner walls of the CNTs. The remaining CNTs serve as inherent spacers to prevent the self-stacking of nGs. Benefiting from the permanent and robust column bracing frameworks, the resultant 3D aerogels are expected to act as effective electrode materials for lithium-ion batteries with superior cyclic performance, delivering a reversible capacity as high as 1089 mAh g^–1 at a current density of 2 A g^–1 even after 300 cycles. The good lithium-ion storage performance is attributed to the hierarchical porous feature, the intrinsically unstacked bridged structure, and the synergistic effects between the N and S. This promising strategy represents a new concept for mitigating the self-aggregation of nGs by using autologous spacers

In Situ Fabrication of CoS and NiS Nanomaterials Anchored on Reduced Graphene Oxide for Reversible Lithium Storage

CoS and NiS nanomaterials anchored on reduced graphene oxide (rGO) sheets, synthesized via combination of hydrothermal with sulfidation process, are studied as high-capacity anode materials for the reversible lithium storage. The obtained CoS nanofibers and NiS nanoparticles are uniformly dispersed on rGO sheets without aggregation, forming the sheet-on-sheet composite structure. Such nanoarchitecture can not only facilitate ion/electron transport along the interfaces, but also effectively prevent metal-sulfide nanomaterials aggregation during the lithium reactions. Both the rGO-supported CoS nanofibers (NFs) and NiS nanoparticles (NPs) show superior lithium storage performance. In particular, the CoS NFs-rGO electrodes deliver the discharge capacity as high as 939 mA h g^–1 after the 100th cycle at 100 mA g^–1 with Coulombic efficiency above 98%. This strategy for construction of such composite structure can also synthesize other metal-sulfide-rGO nanomaterials for high-capacity lithium-ion batteries

LC-MS-MS quantitative analysis reveals the association between FTO and DNA methylation

<div><p>Fat mass and obesity-associated protein (FTO) is α-ketoglutarate-dependent dioxygenase and responsible for demethylating N6-methyladenosine (m6A) in mRNA, 3-methylthymine (m3T) in single-stranded DNA (ssDNA) and 3-methyluracil (m3U) in single-stranded RNA (ssRNA). Its other function remains unknown but thousands of mammalian DNA show 5-methyl-2'-deoxycytidine (5mdC) modification and 5mdC demethylases are required for mammalian energy homeostasis and fertility. Here, we aimed to confirm whether FTO proteins can demethylate 5mdC in DNA. However, we found that FTO exhibits no potent demethylation activity against 5mdC in vitro and in vivo by using liquid chromatography-tandem mass spectrometry (LC-MS-MS). The result showed FTO demethylase has the characteristics of high substrates specificity and selectivity. In addition, we also used immunofluorescence technique to demonstrate overexpression of wild type TET2, but not FTO and mutant TET2 in Hela cells results in higher levels of 5-hydroxymethyl-2'-deoxycytidine (5hmdC) generated from 5mdC. In conclusion, our results not only reveal the enzymatic activity of FTO, but also may facilitate the future discovery of proteins involved in epigenetic modification function.</p></div

Aluminum Borohydride Complex with Ethylenediamine: Crystal Structure and Dehydrogenation Mechanism Studies

We report the structure of an aluminum borohydride ethylenediamine complex, Al­(EDA)₃·3BH₄·EDA. This structure was successfully determined using X-ray powder diffraction and was supported by first-principles calculations. The complex can be described as a mononuclear complex exhibiting three-dimensional supramolecular structure, built from units of Al­[C₂N₂H₈]₃, BH₄, and ethylenediamine (EDA) molecules. Examination of the chemical bonding indicates that this arrangement is stabilized via dihydrogen bonding between the NH₂ ligand in EDA and the surrounding BH₄. The partial ionic bonding between the Al and N atoms in EDA forms a five-member ring (5MR), an Al­[NCCN] unit. The calculated H₂ removal energies confirm that it is energetically favorable to remove the loosely bonded EDA and H atoms with N–H···H–B dihydrogen bonds upon heating. Our results suggest that the NH₂ terminal ligand in the EDA molecule combines with a H atom in the BH₄ group to release H₂ at elevated temperature, and our results confirm that the experimental result Al­(EDA)₃·3BH₄·EDA can release 8.4 wt % hydrogen above 149 °C with detectable EDA molecules. This work provides insights into the dehydrogenation behavior of Al­(EDA)₃·3BH₄·EDA and has implications for future development of promising high-performance metal borohydride ethylenediamine complexes

Hydrogen Generation from Hydrolysis and Methanolysis of Guanidinium Borohydride

Metal-catalyzed hydrolysis and methanolysis of guanidinium borohydride (C­(NH₂)₃BH₄ or GBH) for hydrogen generation are reported. GBH is comparatively stable in water with only 0.3 equiv of H₂ liberated in 24 h at 25 °C while it reacts vigorously with methanol, releasing more than 3.2 equiv of H₂ within only 17 min. Even at 0 °C, there was still nearly 2.0 equiv of H₂ released after 2 h, but no H₂ liberation was observed for hydrolysis under the same conditions. Various metal chlorides were adopted to enhance the reaction kinetics of the hydrolysis and methanolysis, of which CoCl₂ exhibits the highest activity in both cases. With the addition of 2.0 mol % CoCl₂ at 25 °C, the methanolysis of GBH could generate 4 equiv of H₂ within 10 min with a maximum hydrogen generation rate of 9961.5 mL·min^<b>–</b>1·g^<b>–</b>1 while only 1.8 equiv of H₂ was obtained under the same conditions at a maximum hydrogen generation rate of 692.3 mL·min^<b>–</b>1·g^<b>–</b>1 for hydrolysis. Compared with hydrolysis, methanolysis of GBH possesses much faster reaction kinetics, rendering it an advantage for hydrogen generation, especially at subzero areas. It was proposed that the faster reaction kinetics of methanolysis of BH₄^– containing compounds is ascribed to the more electron donating methoxy group than that of hydroxyl group. Moreover, a comparison between hydrolysis and methanolysis of GBH indicates that the loss of the first H from BH₄^– controls the hydrolysis kinetics instead of the cleavage of the O–H bond