High Energy Density Materials Research Articles

Manganese(II) Porphyrin and Cumyl Hydroperoxide: An Efficient Catalyst for Aryl-Pentazole C-N Bond Cleavage.

The selective cleavage of C-N bonds in N-containing compounds holds significant research value in organic synthesis, particularly for the synthesis of promising polynitrogen species. For instance, the discovery of the cyclo-pentazolate (cyclo-N5 -) anion in 2017 as a result of cleavage of the C-N bond has sparked interest within the field of high energy density materials. However, previous methods using ferrous glycinate and m-chloroperoxybenzoic acid generated the cyclo-N5 - anion in a low yield of 19.5 % after 24 hours, and the mechanism remained unclear. In this study, we developed an efficient catalytic system comprising Mn (II) tetraphenylporphyrin and cumyl hydroperoxide. This system enables the cyclo-N5 - anion to be produced from 3,5-dimethyl-4-hydroxyphenylpentazole in 35.4 % yield in 4 hours. Characterization of Mn(IV)-oxo porphyrins, ⋅CH3, and ⋅C8H8ON5 radicals provides evidence for the mechanism whereby the cyclo-N5 - anion forms. Our study underscores the competitive potential of radical-initiated selective C-N bonds cleavage in N-arylazoles and opens avenues for further exploration in this field.

DECOMPOSITION MECHANISM OF ALKYLIDENE BRIDGED TETRAZOLES WITH DIFFERENT CARBON CHAIN LENGTHS.

Nitrogen-rich heterocycles, particularly tetrazole-based high-energy density materials (HEDMs) offer high performance, low sensitivity, and are eco-friendly. Despite the diversity of nitrogen-rich energetic heterocycles, many are sensitive to external stimuli, and the introduction of a methylene, ethylene, or C-C linkage between nitrogen-rich heterocycles is a successful strategy to improve mechanical sensitivity and thermal stability. Understanding the potential anomalous thermal or kinetic behavior of such molecules is crucial for the design of new HEDMs and practical applications of these molecules. We have investigated the influence of introducing an alkylidene bridge between the energetic nitrogen heterocycles on the decomposition mechanism and pathway of different bridged tetrazoles, namely 5,5'-Bis-1H-tetrazole, 1,2-Bis(5-tetrazolo)methane, and 1,2-Bis(5-tetrazolo)ethane, using thermal experiments, mass spectrometry, and computational analysis. Kinetic parameters were evaluated using a non-linear integral method, and decomposition pathways were proposed based on mass fragmentation data. Stability comparisons were made using HOMO-LUMO gap and electrostatic potential (ESP) values from computational calculations.

Engaging Two Anions with Single Cation in Energetic Salts: Approach for Optimization of Oxygen Balance in Energetic Materials.

The field of high energy density materials faces a long-standing challenge to achieve an optimum balance between energy and stability. While energetic salt formation via a combination of oxygen- and nitrogen-rich anions (providing energy) with nitrogen-containing cations (providing stability) has been a proven approach for improving physical stability, constraints such as lowering density and energetic performance remain unresolved. This can be addressed by utilizing oxygen-containing cations for salt formation. However, this approach is rarely explored because its synthesis is challenging. In this work, we have designed an oxygen-rich cationic precursor 2 by incorporating 4-amino-3,5-dinitropyrazole with 3,4-diaminotriazole via an N-methylene-C bridge. Further combination with energetic acids resulted in the formation of high-performing, physically stable energetic salts 3-10. The salts were found to be generally more energetic than the salts of respective energetic acids with previously reported cations and showed prominent improvement in physical stability with respect to their anionic precursors. All the compounds were thoroughly characterized through IR, NMR spectroscopy, HRMS, and elemental analysis. Salt 9 was confirmed through 15N NMR analysis, and salts 2 and 8 were confirmed through single-crystal X-ray diffraction. Additional analyses such as Hirshfeld surface analysis, noncovalent interaction (NCI) analysis, and electrostatic potential studies were also carried out to correlate the structure-property relationship.

Benzofuroxan‐Based Energetic Materials with Alternating Nitro and Hydroxyl Groups: Synthesis, Characterization, and Energetic Properties

AbstractDue to its good stability, density and oxygen balance, the benzofuroxan fused ring framework has attracted particular attention in the field of high energy density materials. The planar structure of the benzofuroxan facilitates the straightforward derivatization with explosophores and contributes to molecular stability. In this work, a benzofuroxan scaffold was utilized to develop a highly dense energetic material, namely 5,7‐dihydroxy‐4,6‐dinitrobenzo[c][1,2,5]oxadiazole 1‐oxide (DHDNBF). The successive inclusion of explosophores like nitro (−NO2) and oxidative functionality like hydroxyl (−OH) on benzofuroxan resulted in an impressive density (ρ=1.91 g cm−3) and a positive oxygen balance (6.20 %) in DHDNBF (2). Furthermore, the hydroxy groups on DHDNBF enable the formation of dicationic energetic salts 3–7, contributing to additional modifications in the overall performance. Energetic salts 3, 4, and 5 exhibit significantly higher densities ranging from 1.84 (5) to 1.87 (3) g cm−3 and possess a favorable oxygen balance approaching zero or equal to zero. A marked improvement in thermal stabilities was observed in all the energetic salts (3–7) compared to their neutral counterparts, DHDNBF. Energetic salts 4 (Dv=8459 m s−1, P=32.10 GPa) and 5 (Dv=8539 m s−1, P=30.37 GPa) possess good energetic performance, comparable to that of well‐known explosives such as LLM‐105 (Dv=8560 m s−1, P=33.4 GPa). Overall, the favorable characteristics of energetic salts 4 and 5 make them potential candidates for use as benzofuroxan‐based secondary and primary explosives, respectively, in various military and civilian applications.

Nanotechnology in Lithium-Sulfur Batteries: Addressing the Challenges in Battery Cycle Life and Safety

Lithium-sulfur (Li-S) batteries, with their high energy density and affordable material prices, are a viable alternative to ordinary lithium-ion batteries, especially for electric cars. Their actual application is limited by challenges such as substantial volume expansion, low electrical conductivity, and the polysulfide shuttle effect, despite their advantages. This research investigates how incorporating nanomaterials into Li-S battery cathodes, anodes, and electrolytes might improve battery performance and analyzes the potential of nanotechnology to address these problems. The application of metal oxides, graphene oxide, and carbon nanofibers to improve the stability and conductivity of sulfur cathodes is covered. Additionally, it examines anode protection strategies using nanocoating and protective layers to inhibit dendrite growth and improve safety. The incorporation of nanoparticles in electrolytes to improve ionic conductivity and reduce side reactions is also analyzed. Despite the progress, challenges such as the polysulfide shuttle effect and volume changes remain. The paper concludes with recommendations for future research to develop commercially viable Li-S batteries with higher capacity, longer lifespan, and improved safety.

Thinking Outside the Energetic Box: Stabilizing and Greening High-Energy Materials with Reticular Chemistry.

ConspectusReticular chemistry has provided intriguing opportunities for systematically designing porous materials with different pores by adjusting the building blocks. Among them, framework materials have demonstrated outstanding performance for the design of new functional materials used in a broad range of fields, including energetic materials. Energetic materials are widely used for rockets, satellites, mining, and tunneling. In terms of energetic materials, explosophores and nitrogen-rich heterocycles are fundamental building blocks for high-energy compounds. However, the traditional strategy of synthesizing HEDMs (high energy density materials) at the molecular level has faced the long-term challenge of balancing energy and stability. Inspired by reticular chemistry, nitrogen-rich heterocycles offer diverse nitrogen sites for designing diversified coordination interactions. Ionic bond interactions exist in a wide range of energetic salts. Furthermore, most metastable explosophores, e.g., nitro, nitramino, and amino groups, can form strong hydrogen-bonding networks. Based on these noncovalent interactions (such as coordination, ionic, and/or hydrogen bonds (HBs)) and/or covalent interactions can determine intermolecular packing/linkage of the energetic fuel and oxidizer components, reticular chemistry provides a new platform evolving from single-molecular design to various energetic frameworks (E of the energetic frameworks with superior comprehensive properties. For example, to achieve coordination with metals or introduce sufficient hydrogen bond donor/acceptor structural units, the host structure of energetic framework materials usually contains less oxygen-rich substituents such as nitro, so the host molecules of the framework, F) at the crystal level, which can enhance the integrated stabilities of EFs.Along with growing concerns about the environment and safety issues, considerable effort has been devoted to pursuing environmentally friendly and insensitive energetic materials. The newly emerging EFs are conducive to introducing explosophores into a green chemical pathway. Benefiting from these cross-disciplinary achievements, taming metastable energetic molecules in specific porous frameworks is a green strategy to desensitize energetic materials while concomitantly retaining excellent energetic properties, which has become one of the most forward and promising investigations. In the past decade, EFs have achieved further results in stabilizing and greening energetic materials using HBs, covalent bonds, and alkaline earth metal-involving coordination bonds to avoid heavy metal toxicity and to employ halogen-free oxidizers. Because this field is still expanding rapidly, it is of great value for researchers and possible users of the work to be able to view all the progress.Through this Account, we intend that more readers will become knowledgeable about EFs, including their definition, history, synthesis, properties, and possible applications. The aim of this Account is to present the latest advances in EFs in recent years and to offer a perspective on the future direction of this field.

N18 ring: A building block for constructing 1D and 2D polymeric nitrogen frameworks

Exploring the fundamental building block is essential for constructing functional materials with extended topological configurations. In the polymeric nitrogen system, no fundamental building blocks have been reported so far. Here, we successfully synthesize the buckled 1-dimensional (1D) band-shaped and 2-dimensional (2D) layered polymeric nitrogen frameworks with N18 ring as a fundamental building block for the first time. Furthermore, the dimensions of the polymeric nitrogen frameworks can be regulated by pressure conditions. Bader charge analyses indicate that the charge transfer from the La atom to the low-order bonded nitrogen atom plays a crucial role in stabilizing these two low-dimensional polymeric frameworks. Both LaN16 and LaN8 are promising high-energy-density materials (HEDMs). This study reveals that the N18 ring can serve as a fundamental building block, analogous to thesix-membered ring in carbon-based materials, enabling the construction of novel polymeric nitrogen materials with extended frameworks.

Three stable nitrogen-rich Ce-N compounds predicted from first-principles calculations at high pressure

As a new type of environmentally friendly high energy density material, metal-doped nitrogen-rich compounds have drawn much attention in recent years in the field of scientific research due to their unique high pressure properties. In this paper, a first principle computational approach has been used to conduct an extensive structural search for energetically favorable structures in the Ce-N system. We finally discovered three new structures: Ce2N3 in the P21/m phase, CeN3 in the C2/m phase, CeN5 in the P phase. Among them, the C2/m-CeN3 structure remains kinetically stable at 0 GPa and can be quenched to ambient conditions after synthesis at high temperatures and pressures. The C2/m-CeN3 and P1¯-CeN5 compounds, which have significantly higher detonation velocities and pressures than TNT and HMX, can be used as potential energy materials. Their structures of P21/m-Ce2N3, C2/m-CeN3 and P1¯-CeN5 were successfully predicted, providing valuable references for synthesizing and exploring novel stable cerium-nitrogen compounds.

Synthesis, crystal structure, and thermal properties of energetic complex Cu(II) and Ag(I) based on 3-amino-4-(4,5-diamino-1,2,4-triazole-3yl)-furazan

High nitrogen compounds have received much attention due to their great potential as high energy density materials, and the selection of high nitrogen heterocyclic rings as ligands for energetic coordination compounds (ECCs) play a leading role in regulating the energy properties of ECCs. Furazan is rarely used as a building block for the development of high-energy metal ligands. In this study, a new type of high nitrogen ligand 3-amino-4-(4,5-diamino-1,2,4-triazole-3yl)-furazan (ATF) was selected and four kinds of high energy coordination polymers [Cu(II)(ATF)2·4H2O](NO3)2·2H2O (1), [Cu(II)(ATF)2·4H2O](ClO4)2·2H2O (2), [Ag(I)(ATF)2]ClO4·H2O (3) and [Ag(I)(ATF)2NO3] (4) were prepared by water solvent volatilization method and characterized for the first time. The single crystal XRD confirmed that there were abundant hydrogen bond interactions in the four complexes, resulting in dense aggregation with densities of 1.680 ∼ 2.089 g·cm−3. Meanwhile, theoretical calculations show that the detonation velocities of the four ECCs, 7578 ∼ 8192 m·s−1. In terms of thermal stability, the decomposition temperatures of the four ECCs (Td: 253 ∼ 288 °C) showed higher thermal stability during the rapid heating process than the reported ECCs (Cu(PZCA)2(ClO4)2, [Ag+(daf)NO3−]n and CHHP). Both shock and friction sensitivities are greater than 20 J and 300 N. This new structural motif is a promising high-energy material. Moreover, they can promote the combustion decomposition of ammonium perchlorate (AP) well, and the promotion effect of 1 and 2 is better than that of 3 and 4. In the field of explosives and propellants, four ECCs can be attractive candidates.

Fabrication, Characterization, and Performance Evaluation of Thermally Stable [5,6]-Fused Bicyclic Energetic Materials.

In recent decades, there has been considerable interest in investigating advanced energetic materials characterized by high stability and favorable energetic properties. Nevertheless, reconciling the conflicting balance between high energy and the insensitivity of such materials through traditional approaches, which involve integrating fuel frameworks and oxidizing groups into an organic molecule, presents significant challenges. In this study, we employed a promising method to fabricate high-energy-density materials (HEDMs) through the intermolecular assembly of variously substituted purines with a high-energy oxidant. Purines are abundant in nature and are readily available. A series of advanced energetic materials with a good balance between energy and sensitivity were prepared by the simple and effective self-assembly of purines with high-energy oxidants. Notably, these compounds exhibit incredibly improved crystal densities (1.80-2.00 g·cm-3) and good detonation performance (D: 7072-8358 m·s-1; P: 19.82-34.56 GPa). In comparison to RDX, these self-assembled energetic materials exhibit reduced mechanical sensitivities and enhanced thermal stabilities. Compounds 1-5 demonstrate both high energy and low sensitivity, indicating that self-assembly represents a straightforward and effective approach for developing advanced energetic materials with a balanced combination of energy and safety. Moreover, this study offers an avenue for synthesizing energetic materials based on naturally occurring compounds assembled through intermolecular attractions, thereby achieving a balance between energy and sensitivity along with versatile functionality.

Recoverable Zigzag N4 Chains in High‐Pressure Synthesized Cerium Polynitride

AbstractMetal polynitrides have raised significant interest for their applications as potential high‐energy‐density materials (HEDMs). Despite extensive research on energetic polynitrogen species, reducing synthesis pressures and realizing their recovery at ambient conditions remain challenging. Here, for the first time, the zigzag N4 chains are successfully stabilized in the new polynitride Ce2N6 and recovered to ambient pressure and temperature by introducing cerium nitride as a precursor. The stable mechanism of the recoverable N4 chain originates from the large quantity of charge captured, the favorable bonding environment, and low structural enthalpy. This study reveals the crucial role of precursors in stabilizing and recovering polynitrogen species, providing an alternative route to design and prepare novel HEDMs.

Structure, Bonding, and Vibrational Dynamics of a Triamine High Energy Density Material under Pressure

Structure, Bonding, and Vibrational Dynamics of a Triamine High Energy Density Material under Pressure

Graph neural network coarse-grain force field for the molecular crystal RDX

Condense phase molecular systems organize in wide range of distinct molecular configurations, including amorphous melt and glass as well as crystals often exhibiting polymorphism, that originate from their intricate intra- and intermolecular forces. While accurate coarse-grain (CG) models for these materials are critical to understand phenomena beyond the reach of all-atom simulations, current models cannot capture the diversity of molecular structures. We introduce a generally applicable approach to develop CG force fields for molecular crystals combining graph neural networks (GNN) and data from an all-atom simulations and apply it to the high-energy density material RDX. We address the challenge of expanding the training data with relevant configurations via an iterative procedure that performs CG molecular dynamics of processes of interest and reconstructs the atomistic configurations using a pre-trained neural network decoder. The multi-site CG model uses a GNN architecture constructed to satisfy translational invariance and rotational covariance for forces. The resulting model captures both crystalline and amorphous states for a wide range of temperatures and densities.

Thermodynamic and propulsive characterization of nitro-substituted quadricyclane

This investigation delves into the potential of Octa-nitro Quadricyclane (ONQC), a nitro-substituted quadricyclane, as a next-generation energetic material. Employing a robust B3LYP-gCP-D3/6-31G(d) computational approach, the study evaluates key material properties of ONQC, including strain energy (700.2 kJ/mol), enthalpy of formation (668.6 kJ/mol), and density (2.08 g/cm³). These enhanced properties result in predicted increases of 124 % in detonation pressure and 49.5 % in detonation velocity compared to TNT, significantly surpassing the performance of conventional high-energy density materials. Additionally, ONQC's suitability as an energetic additive in bipropellant formulations was evaluated with NASA's Chemical Equilibrium with Applications (CEA) software. The primary focus was on bipropellant formulations employing kerosene-based fuels (RP-1, JP-10, JP-5, etc.) and liquid oxygen (LOX) as the oxidizer. Incorporating ONQC into propellant formulations provides substantial improvements in specific impulse and reduces oxidizer requirements. This makes ONQC a promising candidate for advancing propulsion technology.

Sodium chloride induced nitrogen salt with cyclo- N5 anions at high pressure

The energy landscape of sodium chloride-nitrogen mixtures has been comprehensively explored to examine the ability of the formation of unknown compounds under pressures of up to 100 GPa, using swarm-intelligence structure prediction methodology and first-principles calculations. We identified a thermodynamically stable NaN5ClN5 compound containing two cyclo-N5 species under pressures exceeding 53 GPa, representing milder conditions in comparison to those requisite for pure solid nitrogen. In NaN5ClN5, the high electron affinity of the cyclo-N5 motif allows it to oxidize the chlorine atoms, resulting in the formation of two cyclo-N5 anions. Additionally, the weak covalent interactions between Cl and nearby N atoms plays a key role in stabilization of structure. It has been demonstrated that simple NaN5 salt was a suitable precursor for the synthesis of NaN5ClN5 at high pressure. molecular dynamics simulations demonstrated the recoverability of NaN5ClN5 as a metastable phase at ambient pressure-temperature conditions. Additionally, NaN5ClN5 exhibits a higher energy density of 3.86 kJ/g and a lower mass density of 1.67 g/cm3 in comparison to metal pentazolate salts, highlighting its potential as a high energy-density material. Published by the American Physical Society 2024

Damage analysis of solid propellants with default defects based on macro-microscopic approach

Solid Rocket Motors (SRMs) rely on solid propellants, directly impacting the energy capacity of launch vehicles. High energy density material (HEDM) propellant exhibits superior energy density owing to the incorporation of a substantial quantity of energetic particles. However, the elevated particle fill ratio makes the formation of pores more prevalent during the manufacturing process of propellants. These pores, representing default defects, are indispensable factors in the investigation of mechanical properties of propellants. This study investigated default defects effects on HEDM propellants, analyzing both microscopic and macroscopic perspectives. Utilizing micro-CT imaging, the microstructure and default defects were characterized. Subsequently, using the cohesive zone model (CZM), microscopic damage evolution was depicted with the representative volume element (RVE) model, allowing in-depth analysis. Furthermore, a damage constitutive model, based on microscopic damage, was developed, with its softening function calibrated using microscopic damage evolution characteristics. Implemented into ABAQUS via user-defined material subroutine (UMAT), this model enabled the prediction of the mechanical response of HEDM propellants with different defects. The results demonstrate that the developed model accurately predicts the mechanical responses of HEDM propellants with different defects, showcasing the potential of macro-microscopic approaches in analyzing propellants with default defects.

New compound XeN14 with high energy density

As a high-energy density material, polymeric nitrogen has attracted considerable attention, while the exceptionally high synthesis pressure hinders its studies and applications. A significant discovery indicates that the insertion of noble gas elements can effectively reduce the synthesis pressure of polymeric nitrogen compounds. This work utilized the particle swarm optimization algorithm and first-principles calculations to extensively explore the stoichiometry of Xe–N compounds under high pressures. Two phases of XeN14, P6mm and P-62m, have been discovered, which are energetically more stable than the basic mixture of Xe and N2. Evidence of charge transfer between Xe and N was found, verifying that Xe plays a crucial role in forming polymeric nitrogen compounds. These two compounds are kinetically stable at pressures ranging from 50 to 200 GPa and exhibit semiconductor properties. A unique channel-like structure was discovered in the P6mm phase. The energy densities of P6mm and P-62m phases are 7.39 and 7.59 kJ/g, respectively, significantly exceeding those of TNT (Trinitrotoluene) and HMX (Octogen), indicating their potential as high-energy density materials.

Pressure-Induced High-Energy-Density BeN6 Materials: First-Principles study

Recently, the use of polymeric nitrogen in the search for high-energy–density materials (HEDMs) has attracted widespread attention. However, synthesizing polymeric nitrogen materials is quite challenging; for instance, the synthesis of cubic gauche nitrogen requires a high pressure of 110 GPa. Previous theoretical predictions and experiments have shown that adding alkaline earth metals as cationic ligands can stabilize polymeric nitrogen and reduce the synthesis pressure. Using the USPEX structural prediction code and first-principles calculations, this study predicted 2 new nitrogen salt with nitrogen contents up to 89.80 %, namely α-BeN6 and β-BeN6, with their unique nitrogen chain structures, have energy densities as high as 3.32 and 3.59 kJ/g, respectively. The exceptional explosive properties reveal these two BeN6 are potential HEDMs. In addition, α-BeN6 is a direct bandgap semiconductor.

2,2'-Bisdinitromethyl-5,5'-bistetrazole: A High-Performance, Multi-Nitro Energetic Material with Excellent Oxygen Balance.

Bistetrazoles are highly sought after for developing innovative high-energy density materials. The 1,1'-substituted bistetrazoles, exemplified by TKX-50, have outstanding performance. However, the research of high-perfomance 2,2'-substituted bistetrazoles remains limited. In this work, dinitromethyl groups were introduced into bistetrazole structures as 2,2'-substituted bistetrazoles (BDBTZ), which was extensively characterized through NMR, thermal analysis, and single crystal X-ray diffraction, exhibiting excellent oxygen balance, moderate sensitivity, acceptable thermal stability, high crystal density, and excellent detonation performance.

Exploring the Explosive Potential: Synthesis and Characterization of Ring-Fused Oxadiazolo[3,4-b]pyrazine 1-Oxide Polymorphs with Balanced Energetic Properties.

A novel fused-ring compound, 5-azido-6-oxo-6,7-dihydro-[1,2,5]oxadiazolo[3,4-b]pyrazine 1-oxide (3a), was synthesized for the first time with simple two-step process and characterized using various spectroscopic techniques such NMR, IR, EA and HRMS. Two polymorphs (α-3a and β-3a) identified by SCXRD differ in crystal packing and noncovalent interactions, demonstrating high density, substantial heat of formation, and superior detonation properties with reduced mechanical sensitivity compared to TNT, TATB, and close to RDX, suggesting their potential as environmentally friendly high energy density materials.