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Two novel energetic compounds, 3-nitroxymethyl-5-(4-nitro-furazan-3-yl)-1,2,4-oxadiazole (4) and 3-nitroxymethyl-5-(4-azido-furazan-3-yl)-1,2,4-oxadiazole (5), were synthesized. Both of them were fully characterized, and the structure of 4 was further confirmed by X-ray single crystal diffraction. The thermal behaviors, detonation performances and the sensitivities of 4 and 5 were also investigated by differential scanning calorimetry (DSC), EXPLO5 program and BAM standard techniques. In addition, the electrostatic potential energy surface (ESP) was studied by Multiwfn program and density functional theory at B3LPY/6-31G (d, p). Both compounds have low melt-point, good energetic performance and mechanical sensitivity, which endow them with promising properties as plasticizing ingredients in propellant formulations.

As a promising cathode material, Na3V2(PO4)2F3 (NVPF) has attracted wide attention for sodium-ion batteries (SIBs) because of its high operating voltage and high structural stability. However, the low intrinsic electronic conductivity and insufficient Na ion mobility of NVPF limit its development. Herein, K-doping NVPF is prepared through a facile ball-milling combined calcination method. The effects of K-doping on the crystal structure, kinetic properties and electrochemical performance are investigated. The results demonstrate that the Na2.90K0.10V2(PO4)3F3 (K0.10-NVPF) exhibits a high capacity (120.8 mAh g−1 at 0.1 C), high rate capability (66 mAh g−1 at 30 C) and excellent cycling performance (a capacity retention of 97.5% at 1 C over 500 cycles). Also, the occupation site of K ions in the lattice, electronic band structure and Na-ion transport kinetic property in K-doped NVPF are investigated by density functional theory (DFT) calculations, which reveals that the K-doped NVPF exhibits improved electronic and ionic conductivities, and located K+ ions in the lattice to contribute to high reversible capacity, rate capability and cycling stability. Therefore, the K-doped NVPF serves as a promising cathode material for high-energy and high-power SIBs.

In this work, the impact of the doping process on the photoluminescence emission of CaWO4 as a function of the concentration of Eu3+ cation (0.01 mol%, 0.02 mol%, 0.04 mol%, 0.06 mol%, 0.08 mol%, and 0.10 mol%) is discussed in detail. Ca1−xWO4:xEu3+ samples were successfully synthesized by a simple co-precipitation method followed by microwave irradiation. The blue shift in the absorption edge confirmed the quantum confinement effect and the band gap energy cover the range from 3.91 to 4.18 eV, as the amount of Eu3+ cations increases. The experimental results are sustained by first-principles calculations, at the density functional theory level, to decipher the geometry and electronic properties, thereby enabling a more accurate and direct comparison between theory and experiment for the Ca1−xWO4:xEu3+ structure. Funding for open access charge: CRUE-Universitat Jaume I

Electrochemical CO2 reduction to higher-value hydrocarbons beyond C1 products has attracted much attention recently. Single-atom catalysts (SACs) are regarded as promising CO2 reduction electrocatalysts. However, most SACs only show activity to C1 products. In this work, we considered the activity and the synergetic effect of dual active sites for metal SACs supported on graphitic carbon nitride (g-C3N4) as CO2 reduction electrocatalysts. Density functional theory (DFT) calculations are employed. First, by using the adsorption energies of CO* on the metal site and that of H* on the nitrogen site as bi-descriptors, we predicted seven out of 14 metal centers have the propensity to generate beyond CO products. To further evaluate the catalyst activity on beyond CO product formation, we established reaction pathways towards ethylene through M/N or M/C. Ru has the best performance (the limiting potential is −0.90 V) by taking M/N as active sites. A dual volcano-shaped plot is built up based on the CO adsorption energies on metal sites, which can be used to indicate whether M/C or M/N shows better performance for a specific metal center. Our work shed light on developing criteria to guide the design of CO2 reduction electrocatalysts with dual active sites.

Although the direct synthesis of hydrogen peroxide (DSHP) is a potential alternative to the current anthraquinone auto-oxidation process, the low H2O2 selectivity of the former presents a major challenge. Previous studies have reported that the addition of halides improves the H2O2 selectivity of Pd-based catalysts. In this study, the H2O2 selectivity of Pd/SiO2 and PdBrx/SiO2 catalysts was observed to increase with the Br content. Furthermore, density functional theory (DFT) calculations on clean and Br-adsorbed Pd (1 1 1), (1 0 0), and (2 1 1) surfaces confirmed that the activation energies of the side reactions on the Pd (1 1 1) surface increased slightly after Br adsorption, whereas those of the main reactions were less affected. The repulsion between Br and O on the Pd (1 0 0) surface increased the O2 dissociation barrier by changing reaction configurations. Considering that the Pd (1 0 0) surface adsorbed O2 more strongly than did the Pd (1 1 1) surface, inhibiting O2 dissociation on the Pd (1 0 0) surface improved the H2O2 selectivity of PdBrx/SiO2 catalysts. On the Pd (2 1 1) surface, Br blocked an edge site and induced the reactions on the Pd (1 1 1) surface. In conclusion, DFT calculation confirmed that the repulsion and site blocking by adsorbed Br improved the H2O2 selectivity of PdBrx/SiO2 catalysts.

Electrochemical catalysts for the hydrogen evolution reaction (HER) have attracted increasing attentions. Noble metal-free cocatalysts play a vital role in HER applications. Herein, a novel strategy to prepare a Ni2P/MoS2 cocatalyst through a simple hydrothermal-phosphorization method was reported, and the prepared cocatalyst was then loaded on an N-doped carbon substrate with excellent conductive performance. The large surface area of the carbon substrate provided many active sites, and the interface between Ni2P and MoS2 improved the catalytic performance for the HER. Compared with pure Ni2P catalyst and MoS2 catalyst, the prepared Ni2P/MoS2 cocatalyst exhibited enhanced catalytic performance. In addition, the results indicate that the prepared cocatalyst has a wide pH range and low onset potential values of 280, 350 and 40 mV in acidic, phosphate-buffered saline and alkaline solutions, respectively, and the corresponding Tafel slopes are 75, 121 and 95 mV dec−1, respectively. Density functional theory (DFT) was adopted to calculate the hydrogen adsorption free energy (△GH∗). The results showed that the interface between Ni2P and MoS2 reduced △GH∗, which was beneficial to the adsorption of hydrogen. Present preparation of cocatalysts with unique interfaces provides a new strategy for improving the catalytic performance of HER.

Rely on the density functional theory (DFT) calculation, the catalytic performance of PdxCuy/GDY (x = 1, 2, 3, 4; x + y ≤ 4) for CO oxidative coupling reaction was obtained. The Pdx/GDY (x = 1, 2, 3, 4) are not ideal catalyst for dimethyl oxalate (DMO) formation because by-product dimethyl carbonate (DMC) is easily formed on Pd1/GDY and Pd2/GDY, and high activation energies are needed on Pd3/GDY and Pd4/GDY. Therefore the second metal Cu is doped to regulate the performance of Pdx/GDY (x = 1, 2, 3, 4). Doping Cu not only improve the activity of DMO formation, but more importantly, controlling the ratio of Cu:Pd can effectively regulate the selectivity of DMO. Thus taking into account the activity and selectivity of the reaction for the preparation of DMO by CO oxidative coupling, the Pd1Cu1/GDY and Pd1Cu2/GDY with the activation energies of 105.2 and 99.2 kJ/mol to generate DMO show excellent catalytic activity and high DMO selectivity, which are considered as good catalysts for CO oxidative coupling. The differential charge density analysis shows the decrease in the charge density of metal clusters is an important reason for improving the selectivity of the catalyst.

Tuning surface electron transfer process by sulfur (S)-vacancies engineering is an efficient strategy to develop high-efficient catalysts for electroreduction N2 reaction (NRR). Herein, the distinct Sb2S3 nanorods with S-vacancies (Sv-Sb2S3) have been synthesized by a simple two-step method including hydrothermal and hydrogenation in H2/Ar atmosphere, which shows improved performance for NRR with the NH3 yield rate of 10.85 μg h−1 mgcat−1 at −0.4 V vs. RHE, the faradaic efficiency (FE) of 3.75% at −0.3 V vs. RHE and excellent stability for 24 h, largely outperforming bulk Sb2S3. X-ray photoelectron spectroscopy (XPS) and density function theory (DFT) calculations demonstrate that the abundant S-vacancies can create an electron-deficient environment and modulate the electron delocalization in Sv-Sb2S3, which can not only facilitate the N2 molecule adsorption, but also activate the N[tbnd]N, resulting in the enhanced performance for NRR. © 2020 Institute of Process Engineering, Chinese Academy of Sciences

The goal of this study is to look at the development and use of green inhibitors in the electropolishing process (EP), as well as their potential as an anti-corrosive coating for C-steel in an acidic medium. We can replace environmentally dangerous substances with inexpensive, effective molecules that have little or no negative environmental impact like amino acids which are employed as safe inhibitors. The EP characteristics of C-steel were measured by galvanostatic techniques with different concentrations of amino acids over a wide range of (1-1000 × 10−6 mol/l) and temperatures (298–313 K). The findings indicate that the electropolishing behavior of C-steel is governed by mass transfer, with Fe2+ being proposed as the governing species for the salt film mechanism during anodic dissolution in the limiting current plateau. The experimental results indicate that increases in the amino acid concentrations inhibit the EP by 83.33% in the case of L-Methionine at 298 K. Density Functional Theory (DFT) was used to optimize geometry in the gas and liquid phases. The inhibition efficiency was associated with global reactivity descriptors, Fukui indices and dual local descriptors. The inhibitory performance is in good agreement with the estimated quantum chemical parameters, according to our findings.

Whereas the proper choice of reaction solvent constitutes the cornerstone of the green solvent concept, solvent effects on chemical reactions are not mechanistically well understood due to the lack of feasible molecular models. Herein, by taking the case study of nucleophilic addition reaction in aqueous solution, we extend the proposed multiscale reaction density functional theory (RxDFT) method to investigate the intrinsic free energy profile and total free energy profile, and study the solvent effect on the activation and reaction free energy for the nucleophilic addition reactions of hydroxide anion with methanal and carbon dioxide in aqueous solution. The predictions of the free energy profile in aqueous solution for these two nucleophilic addition reactions from RxDFT have a satisfactory agreement with the results from the RISM and MD-FEP simulation. Meanwhile, the solvent effect is successfully addressed by examining the difference of the free energy profile between the gas phase and aqueous phase. In addition, we investigate the solvent effect on the reactions occurred near solid–liquid interfaces. It is shown that the activation free energy is significantly depressed when reaction takes place in the region within 10 A distance to the substrate surface owing to the decrease of hydration free energy at the solid–liquid interface.

International audience; The mechanisms of H 2 dissociation on three stoichiometric anatase TiO 2 terminations, (001), (100) and (101), have been studied by means of density functional theory (PBE+U) calculations. A two-step process was considered: first, H 2 dissociation into H + and H − pair, and second the H − species migrates to a neighboring O site, transferring the electrons to the substrate. On (001), it shows the lowest activation barriers for hydrogen dissociation, 0.37 eV, whereas the highest value was found on (101), 0.98 eV. For hydrogen transfer from Ti to near O, the activation barriers are higher (from 1.10 to 2.37 eV), which indicates the dissociation step is kinetically more favorable than the H transfer process, although the latter is thermodynamically more favorable. Electronic structure, vibrational frequency analysis as well as temperature effects are studied to characterize the reactivity. The relationship between electronic structure, geometry and reactivity is analyzed by means of reactivity descriptors, and the results are compared with ceria and rutile TiO 2 facets.

Hemoglobins M (Hbs M) are human hemoglobin variants in which either the α or β subunit contains a ferric heme in the α

N-doped reduced graphene oxide quantum dots (N-rGQDs) have attracted more and more attention in efficient catalytic degradation of aqueous organic pollutants. However, the synthesis of N-rGQDs is generally a complex and high energy required process for the reduction and N-doping steps. In this study, a facile and green fabrication approach of N-rGQDs is established, based on a metal-free Fenton reaction without additional energy-input. The N structures of N-rGQDs play a significant role in the promotion of their catalytic performance. The N-rGQDs with relatively high percentage of aromatic nitrogen (NAr-rGQDs) perform excellent catalytic activities, with which the degradation efficiency of pollutant is enhanced by 25 times. Density functional theory (DFT) calculation also indicates aromatic nitrogen structures with electron-rich sites are prone to transfer electron, presenting a key role in the catalytic reaction. This metal-free Fenton process provides a green and cost-effective strategy for one-step fabrication of N-rGQDs with controllable features and potential environmental catalytic applications.

Two-dimensional (2D) materials have exhibited great potential for replacing costly Pt for oxygen reduction reaction (ORR) because of their distinctive structural features and high pre-site activity. However, their performance is generally hindered by the limited density of active sites (e.g., at the layer edges). Although they feature a high exposure of surface sites, these sites are typically inert for ORR. Herein, through density functional theory calculations, we propose a promising ORR catalyst candidate, a 2D TaTe2 nanosheet, which has an intrinsic high basal-plane activity. Both of the thermodynamic and kinetic processes are explored, which demonstrates that the basal-plane Te sites of the TaTe2 nanosheet have great potential for facilitating ORR. Specifically, we construct a microkinetic model of ORR proceeding on TaTe2, which unveils its dynamic intermediate coverage under different electrode potentials and identifies the dominating associative pathway. The theoretical half-wave potential of TaTe2 is predicted to be 0.87 V, which exceeds those of the well-established Pt (111) and Fe–N–C single-atom catalysts computed at the same level. This study not only presents the first 2D, non-Pt ORR catalyst candidate with an intrinsic basal-plane activity but also offers a rational methodology for unveiling the mechanism/activity of ORR and other electrochemical reactions.

Density functional theory (DFT) calculations have been performed to investigate the hydrogen dissociation and diffusion on Mg (0001) surface with Ni incorporating at various locations. The results show that Ni atom is preferentially located inside Mg matrix rather than in/over the topmost surface. Further calculations reveal that Ni atom locating in/over the topmost Mg (0001) surface exhibits excellent catalytic effect on hydrogen dissociation with an energy barrier of less than 0.05 eV. In these cases, the rate-limiting step has been converted from hydrogen dissociation to surface diffusion. In contrast, Ni doping inside Mg bulk not only does little help to hydrogen dissociation but also exhibits detrimental effect on hydrogen diffusion. Therefore, it is crucial to stabilize the Ni atom on the surface or in the topmost layer of Mg (0001) surface to maintain its catalytic effect. For all the case of Ni-incorporated Mg (0001) surfaces, the hydrogen atom prefers firstly immigrate along the surface and then penetrate into the bulk. It is expected that the theoretical findings in the present study could offer fundamental guidance to future designing on efficient Mg-based hydrogen storage materials.

Solid adsorbents that simultaneously have high selectivity and uptake capacity are highly promising as alternatives to conventional cryogenic distillation of propene/propane (C3H6/C3H8) separation. Coordinatively unsaturated metal sites (CUS) plays a vital role in selective adsorption of olefins over paraffins. Ultrathin poly (triazine imide) (PTI) nanosheets can reach rapid gas adsorption equilibrium, due to its large surface-to-volume ratio. In this work, combining the advantages of the CUS and the PTI nanosheets, Li CUSs were introduced into the PTI nanosheets for C3H6/C3H8 separation. Density functional theory (DFT) calculations demonstrated the thermodynamic feasibility of incorporating Li CUSs into the PTI nanosheets. These highly exposed Li CUSs were predicted to have a higher adsorption affinity toward C3H6 than C3H8. Using the DFT-derived force field parameters, we further performed grand canonical Monte Carlo (GCMC) simulations to investigate C3H6/C3H8 adsorption on the Li−PTI complexes slit pore model with different pore widths (H). We found that the Li−PTI complexes display considerable C3H6/C3H8 selectivity (4.2∼7.9) under relevant conditions. Moreover, the Li−PTI complexes slit pore have large C3H6 working capacities (1.5∼4.0 mmol g-1), superior to those calculated for the most of adsorbent materials that have been reported. The Li−PTI complexes with slit pore architecture show potential as C3H6/C3H8 separation materials.

International audience; The molecular-scale understanding of the genesis of the MoS2 phase from Mo-oxide precursors supported on alumina is highly challenging with a strong impact on the activation process of heterogeneous industrial catalysts. By means of density functional theory (DFT), we quantify the activation free energies of the elementary steps involved in the sulfo-reduction mechanisms of Mo-trioxide oligomers and the stability of the corresponding Mo-oxysulfide intermediates supported on the γ-alumina (1 0 0) surface. The Gibbs free energy profiles highlight the characteristic chemical reactivity of various oxygen sites involved in the O/S exchange mechanism and reveal that interfacial oxygen atoms (Mo-O-Al) are the most challenging sites to be exchanged with S. We quantitatively compare the two main paths proposed experimentally: the one involving Mo-oxysulfide and Mo-trisulfide intermediates and the second one involving only Mo-oxysulfide. While O/S exchange requires moderate activation energies, the rate-determining steps correspond to S- and O-removal on small MonO3n-xSx or MonS3n (n ≤ 3) oligomeric intermediates. To overcome these high energy steps, the small Mo-trisulfide (MonS3n) oligomers are proposed to be fast diffusing surface species and to promote the growth process towards the targeted MoS2 phase. A reconstruction from a chain to a triangular Mo3S9 conformer also facilitates this phase transformation.

The transformations of CO2 molecules into valuable products are of increasing interest due to the negative impact of anthropogenic CO2 emissions on global warming. The CO2-to-methanol hydrogenation is an economically profitable reaction of carbon fixation, but it still steps away from widespread industrialization because of the lack of efficient and selective catalysts. Recently, single-atom alloy (SAA) catalysts have been developed to work remarkably in CO2 hydrogenation reactions. Doping isolated single atoms into metallic catalyst can dramatically alter the catalytic performance of the host. We have performed a screening discovery on Ru and 6 RuX (X = Fe, Co, Ni, Cu, Ir and Pt) SAAs using density functional theory (DFT) computations. We considered 13 possible elementary reactions in 4 possible reaction pathways on Ru and all RuX surfaces. In the computed mechanisms, we found that the formation of *H2COOH and *HCOO intermediates plays a critical role in determining catalysts’ activities. Doping Co and Pt isolated single atoms into Ru surface can thermodynamically and kinetically facilitate these intermediates formation processes, eventually promoting the production of methanol. The combination of weak binding and enhanced charge redistribution on RuCo and RuPt surfaces give them improved catalytic activities over pure Ru. This work will ultimately facilitate the discovery and development of SAAs for CO2 to methanol, serving as guidance to experiments and theoreticians alike.

This study shows that the mechanical strength of the composite of Fe matrix and titanium carbide (TiC) ceramic particles is significantly enhanced with addition of molybdenum (Mo) atoms. TiC reinforced Fe (Fe-0.2C-7Mn) composites with and without Mo were fabricated by a liquid pressing infiltration (LPI) process and the effect of Mo on interfacial properties of TiC–Fe composite was investigated using atomic probe tomography (APT) analysis, molecular dynamics (MD) simulations, first-principle density functional theory (DFT), and thermodynamic calculations. First, DFT calculations showed that total energies of the Mo-doped TiC–Fe superlattices strongly depend on the position of Mo defects, and are minimized when the Mo atom is located at the TiC/Fe interface, supporting the probable formation of MoC-like interphase at the TiC/Fe interface region. Then, APT analysis confirmed the DFT predictions by finding that about 6.5 wt.% Mo is incorporated in the TiC–Fe(Mo) composite and that sub-micrometer thick (Ti,Mo)C interphase is indeed formed near the interface. The MD simulations show that Mo atoms migrate to the Mo-free TiC–Fe interface at elevated temperatures and the mechanical strength of the interface is considerably enhanced, which is in good agreement with experimental observations.

A dendritic PdCu/Ce0.3Zr0.7O2 (PdCu/CZ-3) catalyst with uniform spherical morphology was prepared for boosting the catalytic performance of CO2 hydrogenation to methanol (MeOH). The open dendritic pore channels and small particle sizes could reduce not only the diffuse resistance of reactants and products but also increase the accessibility between the active sites (PdCu and oxygen vacancy) and the reactants (H2 and CO2). More spillover hydrogen could be generated due to the highly dispersed PdCu active metals over the PdCu/CZ-3 catalyst. PdCu/CZ-3 can stimulate the generation of more Ce3+ cations, which is beneficial to produce more oxygen vacancies on the surface of the CZ-3 composite. Spillover hydrogen and oxygen vacancy could promote the formate and methoxy routes over PdCu/CZ-3, the primary intermediates producing MeOH. PdCu/CZ-3 displayed the highest CO2 conversions (25.5 %), highest MeOH yield (6.4 %), highest PdCu-TOFMeOH (7.7 h-1) and superior 100 h long-term stability than those of other PdCu/CexZr1-xO2 analogs and the reference PdCu/CeO2 and PdCu/ZrO2 catalysts. Density functional theory (DFT) calculations and in situ DRIFTS were performed to investigate the CO2−MeOH hydrogenation mechanism.

Single Atom Catalysts (SACs) have shown that the miniaturization of the active site implies new phenomena like dynamic charge transfer between isolated metal atoms and the oxide. To obtain direct proof of this character is challenging, as many experimental techniques provide averaged properties or have limitations with poorly conductive materials, leaving kinetic measurements from catalytic testing as the only reliable reference. Here we present an integrated Density Functional Theory-Microkinetic model including ground and metastable states to address the reactivity of Pt1/CeO2 for CO oxidation. Our results agree with experimentally available kinetic data in the literature and show that CO oxidation activity of Pt1/CeO2 is tunable via the electronic properties of the support. Particularly, samples with higher n-doping via oxygen depletion should be better in CO oxidation, as they help maintain the active state Pt0 of the catalyst. This provides an alternative strategy for tuning the performance of low-temperature oxidations in single-atom catalysts via charge transfer control. peerReviewed

A computational study for the competitive conversion of glycerol to 1,2-propanediol and 1,3-propanediol is presented, considering a two-step sequence of dehydration followed by hydrogenation. The elementary steps for dehydration, i.e., breaking of C–H followed by C–OH or vice versa, were studied computationally both on the Rh metal surface and the acid-modified ReOH–Rh surface in order to understand the role of the acid promoter. While the acid modifier can catalyze the C–OH cleavage, the activation energy for the C–H cleavage was found to be considerably smaller on both pure and acid-doped Rh(111) surfaces, and breaking the secondary C–H bond is kinetically favored over breaking the terminal C–H bond. This is in complete agreement with experimental protocols favoring the formation of 1,2-propanediol. Another potential feedstock, glycidol, was studied for the epoxide ring opening to yield 1,2-propanediol and 1,3-propanediol, and the reaction was found to be metal-catalyzed even in the presence of acid. peerReviewed

Hypothesis The interactions of organic molecules with mineral surfaces are influenced by several factors such as adsorbate speciation, surface atomic and electronic structure, and environmental conditions. When coupled with thermodynamic techniques, energetics from atomistic modeling can provide a molecular-level picture of which factors determine reactivity. This is paramount for evaluating the chemical processes which control the fate of these species in the environment. Experiments Inner-sphere adsorption of oxalate and pyrocatechol on (001), (110), and (012) α-Fe2O3 surfaces was modeled using Density Functional Theory (DFT). Unique bidentate binding modes were sampled along each facet to study how different adsorbate and surface factors govern site preference. Adsorption energetics were then calculated using a DFT + thermodynamics approach which combines DFT energies with tabulated data and Nernst-based corrective terms to incorporate different experimental parameters. Findings Instead of a universal trend, each facet displays a unique factor that dominates site preference based on either strain (001), functional groups (110), or topography (012). Adsorption energies predict favorable inner-sphere adsorption for both molecules but opposite energetic trends with varying pH. Additionally, vibrational analysis was conducted for each system and compared to experimental IR data. The work presented here provides an effective, computational methodology to study numerous adsorption processes occurring at the surface-aqueous interface.

The fault type of GIS during running is related to the decomposition of the insulating gas SF6. In this paper, the adsorption behavior of three representative gases (SO2, SOF2, and SO2F2) decomposed by SF6 under unfavorable conditions at high temperature on the surface of Sc-doped WSe2 monolayers was discussed based on density functional theory. Adsorption systems of three target gases on Sc-WSe2 were developed, and the structural parameters, density of states and frontier molecular orbitals were calculated. The results show that the adsorption performance of target gases on Sc-WSe2 is better than that on intrinsic WSe2, indicating that the effectiveness of utilizing Sc atoms for modification. The strong interaction between WSe2 monolayers embedded with Sc atoms and gases confirmed the stability of the system in complex environments. Our findings are of great significance in the construction of atomically modified WSe2 gas sensors for detecting SF6 decomposition gases.

The development of highly-efficient electrocatalysts with bifunctional catalytic activity for oxygen reduction reaction (ORR) and oxygen evolution reaction. (OER) still remains a great challenge for the large-scale application of renewable energy conversion and storage technologies. Herein, by means of comprehensive density functional theory (DFT) computations, we systematically explored the potential of pyrrolic-N doped graphene (pyrrolic-N4-G) supported various transition metal atoms (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Pd, W, Os, Ir, and Pt) as electrocatalysts for the ORR and OER. Our results revealed that these TM/pyrrolic-N4-G candidates exhibit high electrochemical stability due to their positive dissolution potentials. Especially, the Ir/pyrrolic-N4-G can perform as a promising bifunctional electrocatalyst for both ORR and OER with the low overpotentials (ηORR = 0.34 V and ηOER = 0.32 V). Interestingly, multiple-level descriptors, including energy descriptor (ΔGOH* - ΔGO*), (ΔGOH*), structure descriptor ( φ ), and d-band center (e) can well rationalize the origin of the high catalytic activity of Ir/pyrrolic-N4-G for the ORR/OER. Our findings not only further enrich the SACs, but also open a new avenue to develop novel 2D materials-based SACs for highly efficient oxygen electrocatalysts.

In order to study the effect of MgO on the microstructure and macroscopic thermos-physical properties of calcium silicate melt, quantitative analysis of the various silicon-oxygen Qi species in magnesium-calcium silicate glasses and melts at a constant alkalinity has been performed by in-situ high temperature Raman spectroscopy, 29Si MAS NMR and DFT (Density Functional Theory) calculation. Several cluster models, probably existed in magnesium-calcium silicate glasses and melts, modified by Ca2+ or Mg2+ have been designed, their Raman vibrational modes and scattering activities were thus simulated and calculated. A function correlating the wavenumbers of Si-Onb (non-bridge oxygen) of various SiOTs (silicon-oxygen tetrahedrons) with their RSCS (Raman scattering cross sections) was constructed and used to calibrate the experimental Raman spectra. The abundance of each primary Qi species of various magnesium-calcium silicate glasses can be composed by all the deconvoluted hyperfine peaks within the same Qi species. The quantitative description for glasses was proven to be consistent with the result from 29Si MAS NMR. Thus, Qi species distributions for melts were also quantitatively derived. It demonstrated that the abundances of Q1 and Q3 species increased while Q2 species decreased with the increasing replacing amount of MgO. The relationship between the viscosity and Qi species distributions as well as different cations has been investigated and correlated. Q3 species was predominantly responsible for the contribution of viscosity of melt.

All-inorganic perovskite quantum dots have been widely used in solar cells, LED, laser and scintillator in recent years. However, the essence of ion migration in perovskite lattice can cause the ion vacancies exist, which can directly affect the luminescence process. Herein, we focus on the effect of monovalent cation vacancies on the CsPbBr3 lattice, and realize the adjusting lattice structure of the CsPbBr3 QDs to change the luminescence lifetime by controlling the formation of monovalent cation vacancies. The results show that the existence of monovalent cation vacancies can be controlled by controlling dosages of Cs + precursor and can make the CsPbBr3 lattice produce local lattice micro distortion and reduce luminescence lifetime, which is beneficial to realize the rapid and efficient X-ray imaging of scintillating crystals. Experimental result is also verified by density functional theory (DFT).

In this study, non-noble metal Cd decorated cubic phase CdS (CdS/Cd) thin layer on a millimeter-scale chitosan-Mg(OH)2 xerogel beads (CMB) were elaborately designed and successfully synthesized via facile hydrated electrons (eaq•−) assistant strategy. The in-situ formation of metallic Cd was driven by eaq•− generated from UV/Na2SO3 process. Owing to metallic Cd, CMB@CdS/Cd exhibited better visible-light absorption ability and more efficient separation capability for photo-induced carriers, its hydrogen production efficiency was about threefold improved compared to CMB@CdS. Both characterization methods and density functional theory calculations determined a built-in electric field from metallic Cd to CdS and Ohmic-contact between Cd and CdS, which largely promoted the carriers transfer efficiency. Moreover, the introduction of metallic Cd on the CdS could reduce the ΔGH*, thus greatly boosting the photocatalytic hydrogen production efficiency. This work provides a simple and green approach to construct metallic Cd coupled semiconductor to achieve efficient photocatalytic applications.

Graphite carbon nitride (g-C3N4) is regarded as a potential candidate to settle environmental and energy issues, but its activity remains unsatisfactory due to the huge exciton effect and delayed charge transfer. Herein, the effects of phosphorus-doping and two-dimensional (2D) porous structures on the transition among singlet excitons, triplet excitons, and carriers and consequently the regulation mechanism of reactive oxygen species have been intensively studied. The calculations of the density functional theory and experimental results confirmed that P-doping could induce a dual built-in electric field to provide a driving force (up to 0.3 eV) for exciton dissociation. The light response capability, exciton dissociation, and carrier migration efficiency were significantly enhanced by the synergistic effect of the dual electric field and 2D porous structure. The optimal sample exhibited excellent H2 evolution rate and tetracycline degradation rate under visible-light irradiation which were approximately 25 and 7.1 times higher than those of bulk g-C3N4, respectively. The improved photocatalytic activity can also be demonstrated by a 2.9-fold and 3.2-fold increase in ·O2– and H2O2 production, respectively. This work provides a new perspective and approach to improve the performance of polymer photocatalysts and the targeted regulation of active species using exciton engineering.

Exploring novel structures consisting of multiple highly active components is a crucial challenge for supercapacitor applications. Using an in-situ self-templated method, we demonstrate the controlled fabrication of a fibrous hierarchical nanocomposite made of carbon microfibers covered with a layer of metal–organic framework (MOF) derived from nickel-cobalt layered double-hydroxide (NiCo-LDH) nanosheets decorated with (NiCo)Se2 nanoparticles. The (NiCo)Se2 nanoparticles attached tightly onto the surface of the two-dimensional NiCo-LDH, both of which were generated by the decomposition of the NiCo-based MOF, and exhibited multiple active sites that contributed to improved electrical conductivity, high capacity, and structural stability. Density functional theory calculations revealed that the density of states near the Fermi level was significantly enhanced, favoured OH– adsorption, and promoted the kinetics of the electrochemical reaction. Benefiting from the intrinsic synergetic contributions from the hierarchical nanoscale structure, the electrode made from the nanocomposite delivered an impressive capacity of 1394.2 F g−1 (702.7 C g−1) at 1 A g−1. Furthermore, a hybrid supercapacitor based on the developed nanocomposite demonstrated an energy density of 50.6 W h kg−1 and a power density of 800 W kg−1 with high cyclic stability. Our results suggest that the hierarchical nanocomposite can be a powerful electrode for advanced next-generation supercapacitors.

Single crystal (SC) MAPbBr3 perovskite is regarded as a promising material to fabricate high-performance photodetectors (PDs) due to its impressive optoelectronic properties and good chemical stability. Cs+ doping has been proved to be an effective method to significantly improve the optoelectronic properties of MAPbBr3 SC. However, the intrinsic effect of Cs+ on the crystal structure is still unclear. Herein, we grew a series CsxMA(1-x)PbBr3 SCs. X-ray rocking curves (XRC) of CsxMA(1-x)PbBr3 SCs prove that appropriate Cs-doping concentration could reduce defect density effectively. X-ray photoelectron spectroscopy (XPS) measurements indicate that Cs-doping enhances the atoms interaction in CsxMA(1-x)PbBr3 lattice due to isoelectronic impurity effect. Single-crystal PDs were fabricated to compare the optoelectronic properties of MAPbBr3 SCs with different Cs-doping concentration, and the 2% Cs-doped CsxMA(1-x)PbBr3 PD shows the optimum performance. Density functional theory (DFT) calculations demonstrate that Cs-doping leads to lattice relaxation effect which is benefit to reduce trap density of CsxMA(1-x)PbBr3 SCs. The Pb-6p level of CsxMA(1-x)PbBr3 slightly shifts to lower energy region compared with MAPbBr3, resulting in the decrease of band gap of CsxMA(1-x)PbBr3.

A new metal-oxo-clusters-based inorganic framework [NaCo2Mo2O7(OH)3]n (NaCoMo), named as 3D platelike ternary-oxo-cluster, has been hydrothermally synthesized and characterized by single-crystal X-ray diffraction structure analysis, FT-IR spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) analyses, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). Structure analysis reveals that there are no classical building units in NaCoMo, and the asymmetric units of NaCoMo are directly extended into a new platelike 3D structure. Density functional theory calculations (DFT) indicates that the crystal formation process is exothermic and the structure is extremely stable. In addition, the compound presents excellent catalytic activity in the condensation and cyclization reaction of sulfonyl hydrazides and 1,3-diketones to synthesize pyrazoles, and the yield of the desired product is up to 99%. The successful synthesis of NaCoMo represents the discovery of a new kind of non-classical polyoxometalates.

Multilayered structures with abundant interfaces are highly desired for reducing the thickness and improving electromagnetic (EM) attenuation ability. Herein, elaborately designed laminar Fe3O4/MXene nanosheets exhibit great potential as high-efficiency and lightweight absorbers due to heterogeneous structure coupled with intensive magnetic-dielectric synergistic effect. The MXene nanosheets with metallic conductivity not only serve as a supporter to carry the magnetic Fe3O4, but also provide massive interfaces to facilitate the transport of charge carriers. Hollow Fe3O4 microspheres were evenly dispersed without apparent agglomeration on the MXene surface, giving rise to largely enhanced consumption ability of –42.7 dB over a broad qualified bandwidth (5.7 GHz) at 2.5 mm. Besides, static density functional theory (DFT) method was introduced to shed light on the absorption mechanism by portraying the interaction between the Fe3O4 and MXene. This study provides a crucial strategy for designing magnetic-supported composites by means of a large family of MXenes as thin and lightweight EM absorbers.

The sorption-enhanced water-gas shift (SE-WGS) reaction promoted by Ni-doped CaO (Ni-CaO) was sufficiently investigated by experiments that only displayed macroscopic results instead of microscopic reaction mechanisms. In this work, density functional theory (DFT) was employed to clarify the mechanisms of SE-WGS reaction which was catalyzed by Ni in the presence of CaO. The SE-WGS reaction only promoted by CaO was used as a comparison to clarify the catalysis of Ni. The analysis of electron differential densities, the partial density of states, and formation energy indicate that Ni causes the higher stability and reactivity of the Ni-CaO model than the CaO model. The Ni promotes the release of H2* by rising the adsorption energy of H2* (-0.05 eV) and retains the efficient CO2 capture with the adsorption energy of -1.56 eV. The transient state calculations indicate the SE-WGS reaction prefers to proceed along with the redox mechanism compared with the carboxyl and formate mechanisms on the Ni-CaO surface. The energy barriers for the CO2* generation, H2* generation and desorption are respectively 0.74, 1.77 and 0.10 eV on the Ni-CaO surface, which are lower than those on the CaO surface. Therefore, Ni helps to improve CO conversion and H2 productivity which is consistent with the previous experimental results.

The lack of the green, economical and high-efficient catalysts restrict the development of electrochemical nitrogen reduction reaction (NRR). By means of density functional theory (DFT) calculations, we have systematically investigated the NRR catalytic performance of single atoms decorated v-Mo2CT2 (T = O, F, OH, Cl, and Li) MXene (TM@v-Mo2CT2). Our calculation results reveal the introduction of single atom can significantly improve the NRR activity and selectivity on v-Mo2CO2, and Ir@v-Mo2CO2 system possesses the lowest limiting potential of only −0.33 V among all studied systems. The termination effects of TM@v-Mo2CT2 are further discussed and a descriptor of the adsorption energy of *NNH species (ΔE(*NNH)) is proposed to establish the relationship with NRR limiting potential (UL(NRR)), in which a moderate (ΔE(*NNH)) is required for high NRR activity. Moreover, a good linear relationship between the ΔE(*NNH) and the excess electrons on Ir atom shows that different ΔE(*NNH) originates from the difference of valence state of Ir atom, which is due to the change of coordination environment. Importantly, the synergistic effects of Ir atom and the surface O-terminations during the first hydrogenation step lead to a promoted NRR performance. Our study might provide new possibilities for rational design of cost-effective MXene-based NRR electrocatalysts.

CuPbBi5S9 compounds have been investigated as gladite for years. However, there have been no significant studies on their physical and chemical properties. This work demonstrates that upon alloying with moderate Cu, Pb, Bi, and S using an appropriate preparation method, quaternary CuPbBi5S9 compounds can exhibit excellent figure of merit ZT within the temperature range 298–723 K. A low average velocity, low Young’s modulus and Debye temperature, and large Gruneisen parameter, determined experimentally, indicate strong lattice anharmonicity in CuPbBi5S9 crystals. Furthermore, density functional theory calculations (local vibration of low-frequency acoustic phonons) justify the low lattice thermal conductivity of CuPbBi5S9 compounds. Because of the low thermal conductivity (0.514 W m−1K−1) and a relatively high power factor (293 μW m−1K−2), a maximum ZT of 0.42 was achieved at 723 K for CuPbBi5S9 prepared by mechanical alloying combined with solid-state melting. Thus, CuPbBi5S9 materials are promising candidates for use as high-performance thermoelectric materials in the intermediate-temperature range.

In this article, the thermoelectric properties of five different polymorphs of gallium phosphide (GaP) such zinc-blende (zb-GaP), wurtzite (wz-GaP), sphalerite (sp-GaP), Beryllium oxide (β-BeO-GaP), and Silicon carbide (SiC-GaP) have been reported in detail. In this regard, the prerequisite electronic structure calculations have been performed in the framework of density functional theory (DFT), whereas the results for thermoelectric properties have been obtained via Boltzmann transport theory (BTT). We found that these GaP polymorphs exhibit relatively higher electrical conductivity corresponding to holes as a result larger power factors (PFs) have been realized for n-type doping than p-type. The highest values of PF corresponding to n-type doping have been recorded as 27.492 × 1010 W/mK2s, 27.999 × 1010 W/mK2s, 29.491 × 1010 W/mK2s, 15.706 × 1010 W/mK2s, and 26.557 × 1010 W/mK2s respectively, for zb-GaP, wz-GaP, sp-GaP, β-BeO- GaP, and SiC-GaP. Moreover, their PF has been further enhanced by the increase in temperature. In contrast, the Seebeck coefficients (thermopowers) have been found relatively larger for p-type doping than n-type. The relatively large thermopowers and lower thermal conductivity for p-type doping have resulted in the enhancement of Figure-of-merit (zT) by holes rather than electrons. The highest zT values have been recorded as 0.997, 1.004, 0.998, 1.001, and 1.010 in the case of zb-GaP, wz-GaP, sp-GaP, β-BeO-GaP, and SiC-GaP respectively. Our study indicates the adequate potential of these different polymorphs of GaP for thermoelectric applications.

To understand the microscopic mechanism of the CO oxidation reaction at PtCu nanoparticles, which have unique geometric and electronic structures compared to their component metals, we present here a theoretical study, based on density functional theory calculations, of the main reaction steps of this reaction. We examine the O2 dissociation, the CO adsorption and the CO + O2 reaction at an atomic level and use the computed geometries, Bader charges, and vibrational frequencies to rationalize the role of the intermetallic nanoparticles surface structure on the experimentally observed much higher activity of these nanoparticles as catalysts of the preferential oxidation of CO. By comparing with clean Pt (111) surface and with different Cu-doped models of this same surface, our results show that, at the surface, the presence of Cu induces the segregation of CO molecules at Pt sites and of O2 molecules at Cu sites. Contrarily to Pt surfaces, the unassisted O2 dissociation has a high barrier at the intermetallic nanoparticle surface and proceeds through a CO-assisted mechanism in which the new CO bond is formed while the O O bond is broken with a kinetic barrier much lower than on either Pt (111) or in Pt-doped surfaces. The particular structure of the intermetallic surface is shown to have a significant role in the low kinetic barrier for the reaction, allowing for an easy approach of the CO to the adsorbed O2 molecule that permits an early transition state with a low energetic barrier.

Summary Energetically driven reduction of porosity through entanglement is ubiquitous in nature and synthetic systems. This entanglement decreases valuable internal pore space useful for applications, such as catalysis, storage, and sensing. Here, we describe the discovery of spontaneous de-interpenetration in a 6-fold interpenetrated uranium-based metal-organic framework (MOF), NU-1303-6. De-interpenetration transforms NU-1303-6 (14.2 and 19.8 A pores) to its larger pore (40.7 A) non-interpenetrated counterpart, which possesses a record-high 96.6% void fraction and 9.2 cm3g−1 pore volume. Density functional theory calculations reveal that charged point-point repulsions between anionic, closely positioned uranium-based nodes drive this phenomenon. These repulsions compete with water molecules that hydrogen bond nearby networks together, favoring interpenetration. Controlling the interplay between these intermolecular forces enables the reversal of omnipresent energetic equilibria, leading to thermodynamically favored open pore structures. The discovery of charged point-point repulsion will likely lead to the re-evaluation of non-interpenetrated network design, synthesis, and wide-reaching applications.

Examination of thermal expansion of two-dimensional (2D) nanomaterials is a challenging theoretical task with either ab-initio or classical molecular dynamics simulations. In this regard, while ab-initio molecular dynamics (AIMD) simulations offer extremely accurate predictions, but they are excessively demanding from computational point of view. On the other side, classical molecular dynamics simulations can be conducted with affordable computational costs, but without predictive accuracy needed to study novel materials and compositions. Herein, we explore the thermal expansion of several carbon-based nanosheets on the basis of machine-learning interatomic potentials (MLIPs). We show that passively trained MLIPs over inexpensive AIMD trajectories enable the examination of thermal expansion of complex nanomembranes over wide range of temperatures. Passively fitted MLIPs could also with outstanding accuracy reproduce the phonon dispersion relations predicted by density functional theory calculations. Our results highlight that the devised methodology on the basis of passively trained MLIPs is computationally efficient and versatile to accurately examine the thermal expansion of complex and novel materials and compositions using the molecular dynamics simulations.

Interatomic potentials based on neural-network machine learning method have attracted considerable attention in recent years owing to their outstanding ability to balance the accuracy and efficiency in atomistic simulations. In this work, a neural-network potential (NNP) for carbon is generated to simulate the structural properties of various carbon structures. The potential is trained using a database consisting of crystalline and liquid structures obtained by the first-principles density functional theory (DFT) calculations. The developed potential accurately predicts the energies and forces in crystalline and liquid carbon structures, the energetic stability of defected graphene, and the structures of amorphous carbon as the function of density. The excellent accuracy and transferability of the NNP provide a promising tool for accurate atomistic simulations of various carbon materials with faster speed and much lower cost.

Despite the huge expansion of GO/rGO market, there is a clear lack of experimental studies on getting high quality, large scale GO and rGO nanosheets/thin films, which is a critical requirement for electronic applications. In this work, a detailed experimental study on the effect of lateral sheet size on properties of GO/rGO, supported by density functional theory (DFT) calculations, is presented for the first time, to help prepare pristine graphene-like rGO. Furthermore, we investigated the effect of thermal reduction at low temperature (200 °C), under ambient pressure, on the corresponding electronic properties of rGO. Current-voltage (I–V) analysis, optical and electron microscopy, atomic force microscopy, Raman, XPS, and quantitative 13C NMR spectroscopy were used to study and optimize rGO. The optimized rGO-field-effect transistor (rGO-FET) device exhibited the highest charge carrier mobilities, i.e. 2,962 (holes) and 2,183 (electrons) cm [2]/V.s. Furthermore, the transconductance characteristics curve of rGO-FET showed the ambipolar behavior of high-quality graphene, with Dirac point around zero. In addition, the optical band gap of rGO nanosheets (∼0.4 eV), prepared in this work, is among the smallest reported band gaps for rGO. These findings highlight the significance of our study for synthesizing large-scale graphene-like rGO thin film, for ultra-fast, low-power transistor applications.

The development of dual-function anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) is exceedingly essential. Herein, with rationally designed hierarchical metal-organic framework (MOF)@MXene as a precursor, a novel sandwich-like CoP-NC@Ti3C2Tx composite has been successfully fabricated by the following phosphorization reaction. As anode material for LIBs, the CoP-NC@Ti3C2Tx composite exhibits remarkable electrochemical performance with high-rate capability (147.8 mAh g−1 at 2000 mA g−1; 245.6 mAh g−1 at 100 mA g−1) and ultralong cycling life (2000 cycles with a capacity retention over 100%). For SIBs, it delivers a discharge capacity of 101.6 mAh g−1 at a current density of 500 mA g−1 after 500 cycles. The well-designed sandwich-like composite effectively supports the easy access to electrolyte, facilitate the Li/Na ion transportation, and protect the active material from pulverization upon long cycling. In addition, the electrochemical reaction kinetics and Li-migration kinetics of the CoP-NC@Ti3C2Tx composite have been pioneeringly illuminated by pseudocapacitive behavior calculation and density functional theory (DFT) computations, respectively. This work sheds light on the rational design and development of MOF/MXene-derived dual-function anode materials for Li/Na-storage.