Large Dissociation Energy Research Articles

Metal nitrides as electrocatalysts in green ammonia synthesis

Green ammonia is assumed to be an important part of the European hydrogen economy and one of the most important substrates of chemical industry. The future development of its manufacturing processes can be related to the electrocatalytic studies yielding in the development of the catalytic materials that would effectively break the nitrogen-nitrogen bond to successfully drive the N2RR—a process of molecular nitrogen electroreduction to ammonia. Molecular nitrogen is characterized with strong triple bond energies (942 kJ/mol) which leading into large dissociation energy of N2 (9,76 eV) and also large energy barrier of the first step of triple bond dissociation 410 kJ/mol (4,25 eV). Those large energies makes reduction to ammonia an extremely difficult task. Metal nitrides of d and f block became in interest due to their activity in ammonia production from molecular nitrogen and hydrogen. Practically all the transition elements occurs in one of the four types of crystalline structures: regular, regular face cantered, hexagonal and hexagonal close packed. The reactions of these metals with nitrogen (or ammonia) typically yields in nitride compounds of an identical type of crystalline structure as the initial metal. Dealing with single metal systems, their ternary counterparts and metal–metal nitride heterostructures, the presented review shows that nitrides are promising groups of electrocatalytic materials. Being property-prone to their internal structural features such as non-stoichiometry and correlated concentration of nitrogen vacancies, metal nitrides are a good candidate for joined investigations spanned between electrochemistry, inorganic chemistry and material engineering.

Yttria substitution effect of tantalate aluminosilicate glasses with ultra‐high Young's modulus

AbstractWe report novel oxide glasses that are compatible with ultra‐high Young's modulus (∼150 GPa) and a small coefficient of thermal expansion (∼5.0 ppm/K). These glasses were prepared using a conventional melt‐quenching technique. The viscosity–temperature relation provides the reshaping temperature for the stiff and less dilated oxide glasses. The origin of the ultra‐high Young's modulus is the inclusion of Y2O3 as well as five‐ and six‐coordinated alumina oxide and Ta2O5, which has a large ionic packing ratio due to higher oxygen coordination numbers. On the other hand, the small thermal expansion coefficient originates from including Ta2O5 and SiO2 with large dissociation energy due to strong bonds.

Deficient Tin oxide nanofibers with regulated valence for efficient nitrate reduction to ammonia

Electrocatalytic nitrate reduction emerges as a promising process for removal of nitrate and simultaneous production of value-added ammonia, but robust electrocatalysts with high selectivity are required due to the large dissociation energy of N≡O in nitrate. Herein, we propose oxygen deficient Tin oxide nanofibers with regulated bivalence (SnO) and tetravalency (SnO2-δ) as efficient catalysts for nitrate reduction reaction (NitRR). Such quadrivalent catalyst achieves a large NH3 yield of 17.27 mg h−1 mgcat.−1 and an extremely high Faradaic Efficiency (FE) of 95.67 % in 0.1 M PBS with 0.1 M NO3−, which also exhibits excellent electrochemical stability. Material calculations reveal that SnO2-δ exhibits a direct band gap of 0.79 eV, smaller than 1.17 eV for SnO with an indirect band gap, and the potential determining step (*NO2 → *NO) hits a free energy change of only 0.1 eV.

Superalkali halide perovskites with suitable direct band gaps for photovoltaic applications.

The construction of superalkali halide perovskites has attracted attention for the development of new photovoltaic materials, but stable superalkalis have not been found until now. Herein, to construct new three-dimensional superalkali halide perovskites with a MI3 frame (M = Sn and Pb), a new Li(H2O)3+ superalkali cation is designed and selected based on low vertical ionization potential, suitable tolerance factor, small ionic radius and large dissociation energy. High-throughput first-principles calculations show that superalkalis with lower vertical ionization potentials exhibit stronger interactions with the MI3 frame. The normal and cubic Li(H2O)3MI3 perovskites and cubic Li(H2O)4PbI3 perovskites have direct band gaps, s-p and p-p electron transitions, effective carrier masses of less than 0.45me and exciton binding energies of less than 291 meV. Moreover, the cubic Li(H2O)3PbI3 perovskite with a direct band gap of 1.40 eV can in theory show a power conversion efficiency of 33.49%. These results strongly suggest that superalkali cations with large dissociation energy can be used to develop stable superalkali perovskites for photovoltaic applications.

Screening seven-electron boron-centered radicals for dinitrogen activation.

The activation of dinitrogen is significant as nitrogen-containing compounds play an important role in industries. However, the inert NN triple bond caused by its large HOMO-LUMO gap (10.8 eV) and high bond dissociation energy (945 kJ mol-1 ) renders its activation under mild conditions particularly challenging. Recent progress shows that a few main group species can mimic transition metal complexes to activate dinitrogen. Here, we demonstrate that a series of seven-electron (7e) boron-centered radical can be used to activate N2 via density functional theory calculations. It is found that boron-centered radicals containing amine ligand perform best on the thermodynamics of dinitrogen activation. In addition, when electron-donating groups are introduced at the boron atom, these radicals can be used to activate N2 with low reaction barriers. Further analysis suggests that the electron transfer from the boron atom to the π* orbitals of dinitrogen is essential for its activation. Our findings suggest great potential of 7e boron radicals in the field of dinitrogen activation.

Cr3C2 nanoparticles decorated carbon nanofibers for efficient nitrate reduction to ammonia at ambient conditions

Electrochemical nitrate (NO3−) reduction is a promising approach to relieve nitrate pollution and produce value-added ammonia (NH3), but efficient and durable catalysts are required due to the large bond dissociation energy of nitrate and low selectivity. Herein, we propose chromium carbide (Cr3C2) nanoparticles loaded carbon nanofibers (Cr3C2@CNFs) as electrocatalysts to convert nitrate to ammonia. In phosphate buffer saline containing 0.1 mol L−1 NaNO3, such catalyst achieves a large NH3 yield of 25.64 mg h−1 mg−1cat. and a high faradaic efficiency of 90.08% at −1.1 V vs the reversible hydrogen electrode, which also shows excellent electrochemical durability and structural stability. Theoretical calculations reveal the adsorption energy for nitrate at Cr3C2 surfaces reaches −1.92 eV and the potential determining step (*NO→*N) for Cr3C2 hits a low energy increase of 0.38 eV.

Interfacial Engineering of Polycrystalline Pt5 P2 Nanocrystals and Amorphous Nickel Phosphate Nanorods for Electrocatalytic Alkaline Hydrogen Evolution.

Electrocatalytic hydrogen evolution reaction (HER) in alkaline media is important for hydrogen economy but suffers from sluggish reaction kinetics due to a large water dissociation energy barrier. Herein, Pt5 P2 nanocrystals anchoring on amorphous nickel phosphate nanorods as a high-performance interfacial electrocatalyst system (Pt5 P2 NCs/a-NiPi) for the alkaline HER are demonstrated. At the unique polycrystalline/amorphous interface with abundant defects, strong electronic interaction, and optimized intermediate adsorption strength, water dissociation is accelerated over abundant oxophilic Ni sites of amorphous NiPi, while hydride coupling is promoted on the adjacent electron-rich Pt sites of Pt5 P2 . Meanwhile, the ultra-small-sized Pt5 P2 nanocrystals and amorphous NiPi nanorods maximize the density of interfacial active sites for the Volmer-Tafel reaction. Pt5 P2 NCs/a-NiPi exhibits small overpotentials of merely 9 and 41mV at -10 and -100mA cm-2 in 1M KOH, respectively. Notably, Pt5 P2 NCs/a-NiPi exhibits an unprecedentedly high mass activity (MA) of 14.9mA µgPt -1 at an overpotential of 70mV, which is 80 times higher than that of Pt/C and represents the highest MA of reported Pt-based electrocatalysts for the alkaline HER. This work demonstrates a phosphorization and interfacing strategy for promoting Pt utilization and in-depth mechanistic insights for the alkaline HER.

Preparation of degradable bio-based silicone/epoxy hybrid resins towards low dielectric composites

Epoxy resins are well-known adhesive materials, however, the high dielectric constant (Dk) limited their application in microelectronic devices. Additionally, non-degradability is a bottleneck for all thermosetting resins, and the discarded resins posed the great threat to environment. Herein, a bio-based eugenol epoxy was grafted onto the polymethylhydrosiloxane (PMHS-x) main chain via a hydrosilylation reaction to simultaneously lower the Dk and enable degradability. The curing kinetics of bio-based silicone/epoxy hybrid resins with methyl hexahydrophthalic anhydride (MHHPA) or 4,4′-diaminodiphenylmethane (DDM) were studied. The cured resins exhibited low Dk and hydrophobicity by taking advantage of the low polarity, large molecular volume and high dissociation energy of the siloxane segments. The polysiloxane degradation process took place under alkaline conditions, allowing the retrieval of reinforced fibers from the composites. To better illustrate the superiority of the bio-based silicone/epoxy hybrid resins, quartz fiber reinforced composites were prepared. Compared to the commercial epoxy based composite, the impact strength of the PMHS-x with a silicon hydrogen content of 0.8 × 10-2 mol·g−1 was increased by 26.5 %, meanwhile, the Dk was decreased by 16.7 %. The bio-based silicone/epoxy hybrid resins not only alleviated the environmental pollution but also provided a reliable approach for fiber recycling from epoxy composites. The low polarity and degradability were integrated into bio-based silicone/epoxy hybrid resins, which provided a novel way to prepare environment-friendly materials suitable for microelectronic devices.

Advances and Challenges of Photocatalytic Methane C—C Coupling

Comprehensive SummaryMethane, the main component of natural gas and shale gas, can be converted to upgraded fuels, syngas and value‐added chemicals. Due to the nonpolar character of methane and large bond dissociation energy of sp3 C—H bond, methane conversion requires strong oxidants or acids/bases for its activation. Photocatalysis capable of inducing highly oxidative surrogates enables methane C—H bond scission at room temperature, thereby avoiding side reactions and coke formation caused by high reaction temperature. The scission of methane C—H bond generates •CH3 that may undergo C—C bond coupling with carbon radicals, which is a versatile way to obtain C2+ chemicals. Apart from the kinetically slow activation of methane C—H bond, photocatalysis also suffers from complex product distributions owing to the presence of varieties of radicals during photocatalytic methane conversion, and a low selectivity of desired C2+ products was achieved. In this review, we summarize the recent advances of photocatalytic methane conversion with emphasis on methane C—C bond coupling. Methods of methane C—H bond activation and radical manipulation for selective C—C bond coupling were discussed in detail. We hope this review may be a valuable guide of future work in photocatalytic methane C—C coupling.

Metastable Brominated Nanodiamond Surface Enables Room Temperature and Catalysis-Free Amine Chemistry.

Bromination of high-pressure, high-temperature (HPHT) nanodiamond (ND) surfaces has not been explored and can open new avenues for increased chemical reactivity and diamond lattice covalent bond formation. The large bond dissociation energy of the diamond lattice-oxygen bond is a challenge that prevents new bonds from forming, and most researchers simply use oxygen-terminated NDs (alcohols and acids) as reactive species. In this work, we transformed a tertiary-alcohol-rich ND surface to an amine surface with ∼50% surface coverage and was limited by the initial rate of bromination. We observed that alkyl bromide moieties are highly labile on HPHT NDs and are metastable as previously found using density functional theory. The strong leaving group properties of the alkyl bromide intermediate were found to form diamond-nitrogen bonds at room temperature and without catalysts. This robust pathway to activate a chemically inert ND surface broadens the modalities for surface termination, and the unique surface properties of brominated and aminated NDs are impactful to researchers for chemically tuning diamond for quantum sensing or biolabeling applications.

Nitrogen fixation and transformation with main group elements.

Nitrogen fixation is essential for the maintenance of life and development of society, however, the large bond dissociation energy and nonpolarity of the triple bond constitute a considerable challenge. The transition metals, by virtue of their combination of empty and occupied d orbitals, are prevalent in the nitrogen fixation studies and are continuing to receive a significant focus. The main group metals have always been considered incapable in dinitrogen activation owing to the absence of energetically and symmetrically accessible orbitals. The past decades have witnessed significant breakthroughs in the dinitrogen activation with the main group elements and compounds via either matrix isolation, theoretical calculations or synthetic chemistry. The successful reactions of the low-valent species of the main group elements with inert dinitrogen have been reported via the π back-donation from either the d orbitals (Ca, Sr, Ba) or p orbitals (Be, B, C…). Herein, the significant achievements have been briefly summarized, along with predicting the future developments.

High-entropy R2O3-Y2O3-TiO2-ZrO2-Al2O3 glasses with ultrahigh hardness, Young's modulus, and indentation fracture toughness

SummaryGlasses with high hardness, high Young's modulus, and high fracture toughness become crucial materials which are urgently needed in the protective covers for various electronic displays. Here, a paradigm is presented that the conceptual design of high-entropy materials is adaptable to high performance oxide glasses. We designed the multi-component glass compositions of 18.77R2O3-4.83Y2O3-28.22TiO2-8.75ZrO2-39.43Al2O3 (R = La, Sm, Gd) and elaborated successfully the glassy samples through a containerless solidification process. The as-prepared samples demonstrated the outstanding mechanical and optical properties. The measured hardness, Young's modulus, and indentation fracture toughness of the high-entropy (R = Gd) glass are 12.58 GPa, 177.9 GPa, and 1.52 MPa·m0.5, respectively, in which the hardness and Young's modulus exhibit the highest value among the reported oxide glasses. Structural analysis revealed that the excellent mechanical properties are attributed to the large dissociation energies and the high field strength of Al2O3, TiO2, and ZrO2 and the complex interaction between atoms caused by high entropy.

Revisiting the Bonding Scenario of Two Donor Ligand Stabilized C2 Species.

Quantum chemical calculations using density functional methods were performed for complexes of type L2C2 with L = NHCMe (1), SNHCMe (2) (S = saturated), cAACMe (3), and diamidocarbene (DACMe) (4). The equilibrium structures of 1-4 possess almost linear C4 cores. A high thermochemical stability of the complexes with respect to dissociation, L2C2 → C2 + 2L, is indicated by the large bond dissociation energy following the order 3 > 4 > 2 > 1. The results show that the use of SNHCMe and DACMe as ligands is preferable over NHCMe. The bonding analysis using charge and energy decomposition methods reveals that (cAACMe)2C2 and (DACMe)2C2 possess genuine cumulene C4 moieties, which results from the electron-sharing bonding between quintet L2 and quintet C2 fragments. In contrast, the bonding in (NHCMe)2C2 and (SNHCMe)2C2 comes from a combination of dative and electron-sharing interactions between doublet L2+ and doublet C2- fragments.

The Importance of Strain (Preorganization) in Beryllium Bonds.

In order to explore the angular strain role on the ability of Be to form strong beryllium bonds, a theoretical study of the complexes of four beryllium derivatives of ortho closo-carboranes with eight molecules (CO, N2, NCH, CNH, OH2, SH2, NH3, and PH3) acting as Lewis bases has been carried out at the G4 computational level. The results for these complexes, which contain besides Be other electron-deficient elements, such as B, have been compared with the analogous ones formed by three beryllium salts (BeCl2, CO3Be and SO4Be) with the same set of Lewis bases. The results show the presence of large and positive values of the electrostatic potential associated to the beryllium atoms in the isolated four beryllium derivatives of ortho-carboranes, evidencing an intrinsically strong acidic nature. In addition, the LUMO orbital in these systems is also associated to the beryllium atom. These features led to short intermolecular distances and large dissociation energies in the complexes of the beryllium derivatives of ortho-carboranes with the Lewis bases. Notably, as a consequence of the special framework provided by the ortho-carboranes, some of these dissociation energies are larger than the corresponding beryllium bonds in the already strongly bound SO4Be complexes, in particular for N2 and CO bases. The localized molecular orbital energy decomposition analysis (LMOEDA) shows that among the attractive terms associated with the dissociation energy, the electrostatic term is the most important one, except for the complexes with the two previously mentioned weakest bases (N2 and CO), where the polarization term dominates. Hence, these results contribute to further confirm the importance of bending on the beryllium environment leading to strong interactions through the formation of beryllium bonds.

New Y-shaped structures of tetra-gold cation clusters stabilised by absorption of oxygen molecules

Theoretically calculated research studies of oxygen absorption on gold cluster surface were used to simulate chemical reactions on the surfaces of gold nanoparticles. Low-energy conformational structures of tetra-nuclear gold cluster complexes with multiple oxygen molecule ligands, Au4(O2) n + (n = 1∼4), were theoretically investigated by the DFT calculations with long-range-corrected hybridisation functional CAM-B3LYP. In addition to known low-energy structures with tetragonal four-gold core, new low-energy isomers with Y-shaped four-gold core were revealed to be stable. The rationality of new structures was confirmed by the agreement of calculated infrared vibrational spectra with experimental results. The findings of new structures successfully interpreted the features of the vibrational spectra of this series of clusters. Highlights: New low-energy complex structures, containing a Y-shaped four-gold core, are stabilised by absorption of oxygen molecules and possess large first dissociation energy of oxygen molecule. The O–O stretching fundamental frequency of the Au–O–O–Au tetragon in the complexes with the Y-shaped four-gold core is found to be the origin of experimental vibrational absorption at about 1250 cm−1. Sum frequency of the stretching vibrations of the Au–O bond and the O–O bond is responsible for absorption observed at 1470 cm−1. A new activation mode of oxygen molecule is found in the Au–O–O–Au tetragon of new Y-core complexes, where the O-O bond length is ca. 1.30 angstrom (normally, ca. 1.20 angstrom).

Impact of low-cost methods in the description of excimer and exciplex formation: pyrene–pyrene and pyrene–naphthalene case studies

The formation of excimers and exciplexes is relevant to a number of photochemical and photophysical processes such as fluorescence quenching and exciton trapping. Theoretical evaluation of the properties and dynamics of such systems often relies on approximate methods to reduce computational time. In this work, we present an assessment of calculations of the excited states of pyrene–pyrene and pyrene–naphthalene pairs with RI-SOS-ADC(2) and the TD-DFT functionals CAM-B3LYP-D3 and ωB97-XD. We find that ADC(2) yields dissociation energies with relatively small errors for the pyrene–pyrene excimer in S1 and a consistent picture of the splitting of monomer La and Lb states into the L− , L+ , L− , and L+ states as the rings approach. TD-DFT, on the other hand, predicts too large dissociation energies for the excimer and is unfit for the description of the pyrene–pyrene dimer. The pyrene–naphthalene exciplex is predicted by RI-SOS-ADC(2) to have a very small dissociation energy, comparable to that of the benzene–benzene excimer.

Indium Silicon Oxide TFT Fully Photolithographically Processed for Circuit Integration

A new class of amorphous oxide semiconductors based on InOx doped with Ti, W or Si seems to show great promise for large area, flexible, electronics. Of particular interest is the In2O3:SiO2 system as it has a relatively large bond dissociation energy, hence highly suited for long-term environmental stability. In this paper, we present a sub-200°C fully photolithographically-processed indium oxide thin film transistor that is fully compatible to circuit integration on plastic substrates. The TFTs typically showed a mobility of 5 cm2/Vs, a threshold voltage of −0.16 V and a subthreshold swing of 312 mV/dec. We report on its stability behavior when subject to electrical bias stress and negative bias illumination stress, along with a pulse-based compensation solution for persistent photoconductivity arising from the latter. Following static characterization and subsequent parameter extraction of the indium silicon oxide TFT, design considerations are presented along with measurement results of a fully integrated TFT voltage amplifier with high impedance subthreshold loading.

Phosphorene: A promising candidate for H2 storage at room temperature

Owing to the existence of periodic channels in phosphorene, this 2D material can be a good candidate for room temperature reversible hydrogen storage. The density functional theory calculations (DFT), including van der Waals interactions (vdW-DF2) coupled with the cooper exchange functional (C09), has been applied to study the potential of phosphorene as a new 2D material for hydrogen storage. Our results show that the adsorption energy (−292 to −277 meV) of H2 on phosphorene is appropriate for storage. The analysis of diffusion pathways between different physisorbed states on phosphorene shows that a single hydrogen molecule diffuses very easily along the open channel (less than 1 meV along the zigzag direction), as compared to 14 meV for diffusion across the channels (along the armchair direction). The potential energy surfaces for the dissociative chemisorption of H2 was computed on highly symmetric sites of phosphorene and the highest activation barrier was found to be 2.77 eV. The very large dissociation energy coupled with a strong physisorption of H2 on phosphorene and facile diffusion, makes this 2D material a promising candidate for H2 storage at room temperature.

Functionalized Silica Particle Based Single Ion Conducting Hybrid Electrolyte for Li-Ion Battery

For advanced energy storage (batteries and supercapacitors), energy conversion (fuel cells and solar cells), and electromechanical transduction devices (electroactive ionic actuators and sensors), it is vital to utilize single-ion polymer conductors (ionomers) that have been designed by covalently attaching anions (or cations) to the polymer chains. This allows the high lithium transference number in lithium polymer batteries as well as the fast response time under low voltage operating conditions in ionic polymer actuators. However, current single-ion conductors exhibit relatively low conductivities, precluding use of these materials in potential applications. This is predominantly due to relatively slow polymer segmental motion, resulting in decreased ion mobility, and large ion dissociation energy, lowering the number of simultaneous charge carries. In order to overcome the issues, we have synthesized porous silica-based lithium single-ion conducting nanoparticles containing anions with lithium counter ions. These nanoparticles are then introduced into poly(ethylene oxide) matrix, allowing us to prepare nanocomposite polymer electrolytes. Anion functionalized mesoporous silica (FMS-TFSISPE) nanoparticles were prepared by the two-step selective functionalization method. Poly(ethylene glycol) group was attached using sol-gel method on mesoporous silica particles. Trifluoromethanesulfonimide group functionalized to silica particles for binding lithium cation. The particles are uniformly distributed with an average size of 50 nm. HRTEM measurement further suggests that the clear mesoporous structure is observed. In order to extensively investigate the structural information on FMS-TFSISPE, the N2 adsorption/desorption isotherm is obtained as shown, where FMS-TFSISPE shows type IV isotherms of typical mesoporous materials, and the BET surface area is 995 m2 g- 1. The average pore size of the FMS-TFSISPE nanoparticles is about 3 nm which is close to that observed by the HRTEM measurement. The small angle XRD analysis shows three resolved peaks from which the pore structure corresponds to a 2D hexagonal (P6mm) structure. From the structure analysis, we successfully synthesized the FMS-TFSISPE nanoparticles with well-ordered hexagonal arrays of mesopore channels and exceptionally high surface area and pore volume. It is apparent that FMS-TFSISPE nanoparticles have a considerable effect on the enhancement of the ionic conductivity of these electrolytes, and their conductivities increase monotonically with increasing FMS-TFSISPE content. The maximum enhancement in conductivity is found for the nanohybrid electrolyte containing 30 wt % FMS-TFSISPE and order of sDC ~ 10- 3 S/cm at 25 oC, 10 times higher than the minimum practical requirement for single-ion conductors. We develop a novel nanohybrid single-ion conductor based porous silica structure. These systems display exceptional ionic conductivity and lithium transference number. It is shown that such nanohybrid electrolytes significantly immobilize the anion movement and pave the way for fast lithium ion-only conducting pathway. Provided that the optimization of the nanohybrid electrolytes with high-energy and -power electrodes is realized, the use of our highly conducting single-ion conductor in practical polymer electrolyte batteries will be envisaged.

Quantitative and Mechanistic Mechanochemistry in Ferrocene Dissociation.

Ferrocene is classically regarded as being highly inert owing to the large dissociation energy of metal-cyclopentadienyl (Cp) bonds. We show that the Fe-Cp bond in ferrocene is the preferential site of mechanochemical scission in the pulsed ultrasonication of main-chain ferrocene-containing polybutadiene-derived polymers. Quantitative studies reveal that the Fe-Cp bond is similar in strength to the carbon-nitrogen bond of an azobisdialkylnitrile (bond dissociation energy < -0 kcal/mol), despite the significantly higher Fe-Cp bond dissociation energy (approximately 90 kcal/mol). Mechanistic studies are consistent with a predominately heterolytic mechanism of chain scission. DFT calculations provide insights into the origins of ferrocene's mechanical lability.