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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.

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.

Due to the water-insoluble nature of Hg0, its oxidization to Hg2+, which is water-soluble, is a viable approach for its effective removal at coal-fired plants using existing flue gas desulfurization (FGD) unit. In this study, the adsorption and oxidation of elemental mercury on an Mn-doped g-C3N4 material were investigated. The spin-polarized density functional theory method was adapted to optimize the geometry structures and then to determine the corresponding electronic structures, while the CI-NEB method was adopted to search for the stable intermediates during the reaction(s). The analysis of energy and project density of states shows that the Mn-g-C3N4 exhibits an excellent affinity to Hg atoms. It is found that it is feasible for Hg atoms to oxidize on the Mn-g-C3N4 surface via two possible E-R paths, but with relatively high energy barriers. This research provides insights into a viable way for mercury removal using O2 as the oxidizing agent.

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

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.

Calculations of AgSbTe2 thermoelectric material and 2d CdS/TiS2 and their heterostructures were carried out using Density Functional Theory in Cambridge Serial Total Energy Package code as implemented in Material Studio 2018 software. The work function, thermal transport, electronic and optical properties were calculated. The results revealed that the heterostructures are possible to be achieved with improved properties. The electronic and thermal transport properties were likened with the description of equations derived from Boltzmann transport theory and Mott expressed in the maximum achievable Figure merit. Orbital contributions from the electron movement show valence and conduction band atomic shells.

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.

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.

We present a study of the structure and differential capacitance of electric double layers of aqueous electrolytes. We consider electric double layer capacitors (EDLC) composed of spherical cations and anions in a dielectric continuum confined between a planar cathode and anode. The model system includes steric as well as Coulombic ion-ion and ion-electrode interactions. We compare results of computationally expensive, but “exact” , Brownian Dynamics (BD) simulations with approximate, but cheap, calculations based on classical Density Functional Theory (DFT). Excellent overall agreement is found for a large set of system parameters, including variations in concentration, ionic size- and valency-asymmetries, applied voltages and electrode separation, provided the differences between the canonical ensemble of the BD simulations and the grand-canonical ensemble of DFT are properly taken into account. In particular, a careful distinction is made between the differential capacitance $$C_N$$ C N at fixed number of ions and $$C_\mu $$ C μ at fixed ionic chemical potential. Furthermore, we derive and exploit their thermodynamic relations. In the future these relations will also be useful for comparing and contrasting experimental data with theories for supercapactitors and other systems. The quantitative agreement between simulation and theory indicates that the presented DFT is capable of accounting accurately for coupled Coulombic and packing effects. Hence it is a promising candidate to cheaply study room temperature ionic liquids at much lower dielectric constants than that of water.

Na0.5(Bi3/4RE1/4)0.5TiO3 (RENBT, RE = Nd, Gd, Dy, and Ho) compounds were investigated in the framework of first-principles calculations using the full potential linearized augmented plane wave (FP-LAPW) method based on the spin-polarized density functional theory implemented in the WIEN2k code. Combined charge density distribution and Ti K-edge X-ray absorption spectra revealed that the RENBT compositions with high polarization values were accompanied by a higher TiO6 distortion, DyNBT, and NdNBT compounds. The effect of the rare-earth elements on the polarization were confirmed experimentally with the collection of the hysteresis loops. The investigation of the electronic properties of the compounds highlighted the emergence of a magnetization owing to the 4f orbital effect of the rare-earth elements. Besides, the investigation of the chemical ordering showed a short-range chemical ordering for the pure composition and an increased A-site disorder for dysprosium doped NBT system. The increased disorder may speak for increased relaxor properties in the RE doped compositions.

Transition metal dichalcogenides (TMDCs) are promising materials for applications in nanoelectronics and correlated fields, where their metallic edge states play a fundamental role in the electronic transport. In this work, we investigate the transport properties of MoS$_2$ zigzag nanoribbons under a butadiene (C$_4$H$_6$) atmosphere, as this compound has been used to obtain MoS$_2$ flakes by exfoliation. We use density functional theory combined with non-equilibrium Green's function techniques, in a methodology contemplating disorder and different coverages. Our results indicate a strong modulation of the TMDC electronic transport properties driven by butadiene molecules anchored at their edges, producing the suppression of currents due to a backscattering process. Our results indicate a high sensitivity of the TMDC edge states. Thus, the mechanisms used to reduce the dimensionality of MoS$_2$ considerably modify its transport properties.

The Dzyaloshinskii-Moriya interaction (DMI) manifesting in asymmetric layered ferromagnetic films gives rise to non-colinear spin structures stabilizing magnetization configurations with nontrivial topology. In this work magnetization reversal, magnetic domain alignment, and strength of DMI are related to the crystalline structure of W/Co/Pt multilayers grown by molecular beam epitaxy. The applied growth method enables the fabrication of layered systems with higher crystalline quality than commonly applied sputtering techniques. A relatively high value of the D coefficient was determined from the aligned magnetic domain stripe structure, substantially exceeding 2 mJ m-2. The highest value of DMI strength Deff = 2.64 mJ m-2 and surface DMI parameter DS = 1.83 pJ m-1 have been observed for a repetition number equal to 10. The experimental results correlate exactly with those obtained from the micromagnetic modelling and density functional theory calculations performed for the well-defined layered stacks. This high value of DMI strength originates from the additive contributions of the interfacial atomic Co layers at the two types of interfaces.

Lead-based relaxor ferroelectrics are key functional materials indispensable for the production of multilayer ceramic capacitors and piezoelectric transducers. Currently there are strong efforts to develop novel environmentally benign lead-free relaxor materials. The structural origins of the relaxor state and the role of composition modifications in these lead-free materials are still not well understood. In the present contribution, the solid-solution (100-x)(Bi1/2Na1/2)TiO3-xBaTiO3 (BNT-xBT), a prototypic lead-free relaxor is studied by the combination of solid-state nuclear magnetic resonance (NMR) spectroscopy, dielectric measurements and ab-initio density functional theory (DFT). For the first time it is shown that the peculiar composition dependence of the EFG distribution width (ΔQISwidth) correlates strongly to the dispersion in dielectric permittivity, a fingerprint of the relaxor state. Significant disorder is found in the local structure of BNT-xBT, as indicated by the analysis of the electric field gradient (EFG) in 23Na 3QMAS NMR spectra. Aided by DFT calculations, this disorder is attributed to a continuous unimodal distribution of octahedral tilting. These results contrast strongly to the previously proposed coexistence of two octahedral tilt systems in BNT-xBT. Based on these results, we propose that considerable octahedral tilt disorder may be a general feature of these oxides and essential for their relaxor properties.

Stabilities, mechanical and thermodynamic properties of 87 intermetallics in Al–RE binary system were studied by first-principles based on density functional theory (DFT). The results show that the calculated stabilities at T = 0 K are in good agreement with experimental values. Al2RE intermetallics exhibit the best stability in Al–RE binary compounds; and the stabilities in descending order are Al2RE, Al3RE, AlRE, Al11RE3, AlRE2 and AlRE3. The calculated Al–RE intermetallics possess mechanical stabilities. The hardness and strength of the most Al–RE intermetallics are greater than pure aluminum except AlCe, AlPr, AlEu and AlYb. The hardness and strength in descending order are Al11RE3, Al3RE, Al2RE and AlRE. Part of AlRE intermetallics exhibit ductility; the others are brittle. The heat capacities of Al–RE intermetallics in ascending order are Al–Sc, Al–Y, Al–lanthanides. On the contrary, the coefficient of thermal expansion (CTE) in ascending order is Al–lanthanides, Al–Y and Al–Sc.

Amino acid family crystals play vital role in the field of nonlinear optics (NLO) due to needs of wide range of applications in the current era. In this report, NLO crystals (L-Isoleucine D-Norvaline (LIDNV) are grown by slow evaporation method at room temperature and various properties of the material are studied and reported. The functional groups present in the grown crystal were identified by the FT-IR spectral analysis. In this work, the hyperpolarizability is investigated using density functional theory. The thermal analysis studies indicate that the material possess optimum thermal stability. Kurtz Perry powder technique using pulsed Nd:YAG laser is employed to confirm the SHG potential of the grown crystal.

The structure of 3-Bromo Phenyl Acetic acid (3BPAA) is optimized and its special features are probed by the FTIR, FT-Raman, UV-Visible and NMR with density functional theory calculations by B3LYP level with 6-311++G(d,p) basis set. The electronic properties were discussed with help of UV-Vis spectrum, MEP (Molecular electrostatic potential) and HOMO-LUMO (Highest occupied molecular orbital and Lowest unoccupied molecular orbital) plots. The energy band gap is found as 4.4437eV. The chemical shift is determined from proton and carbon NMR (Nuclear magnetic resonance) plot by Gauge Independent Atomic Orbital (GIAO) method. The surface analysis such as ELF (Electron localization function), LOL (Localized orbital locator) and ESP (Electrostatic potential) maps are plotted by wave function analyzer. Thermodynamic functions are studied and correlated with the graph. FMO and Fukui functions were calculated and found that the title compound is a chemically soft material. The NLO behavior of the compound is also examined and reported to have higher hyperpolarizability value greater than urea, the reference material ensuring good non-linear optical (NLO) activity. The molecular docking is performed by AUTODOCK tool, its study reveals that the title compound binds well with the protein L- glucorante reductose inhibition. Thus the present work study reports the structural, chemical, electronic, thermodynamic and biological activities of 3BPAA.

Electronic structure calculation explores the molecular structure and geometric conformations of the molecules from only the knowledge of its constituent atoms. In the present work, quantum mechanical calculations of a 3-phenyl-1-(methyl-sulfonyl)-1H-pyrazolo[3,4-d]pyrimidine-4-amine molecule have been performed by Density Functional Theory using the standard 6-31G** basis set with the GAUSSIAN09. The electronic structure, dipole moment, frontier orbitals energy, thermal parameters (entropy, enthalpy, internal energy, and Gibb’s potential), Infrared (IR) spectral lines of the title molecule are elaborated. To study the chemical reactivity; molecular electrostatic potential (MEP) surface, HOMO-LUMO surface, and some other properties of the molecule were also investigated.

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.

Density functional theory (DFT) has become a powerful tool in the investigation of the molecular structure and vibrational spectrum of the compound. Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectra of the title compound were recorded experimental and theoretical study has been done by quantum computational calculations of DFT using Gaussian software package. The structural, vibrational and electronic properties of the title compound were presented using the B3LYP method with 6-311++G(d,p) basis set. The geometry of the title compound was optimized. The experimental vibrational spectra were compared with the calculated spectra and each wave number was assigned on the basis of potential energy distribution (PED). Molecular electrostatic potential for the title compound was calculated to predict the reactive sites for electrophilic and nucleophilic attack. Energy band gap of 3.62 eV was calculated from HOMO-LUMO energies and the charge transfer within the molecules was confirmed. The linear polarizability (α) and the first order hyperpolarizability (β) values of the investigated molecule have been calculated and the title compound exhibits NLO property. The biological activity has been confirmed theoretically for the treatment of lung cancer.

In this paper, the optimization of the structure of di(hydroxybenzyl) diselenide and its studies on HOMO and LUMO energy levels, hardness and Mulliken population using density functional theory (DFT)are reported. Molecular optimization is carried out at all the eight GGA functionals. The total minimum energy is calculated for the titled molecule at various functionals are in the order of BLYP > RPBE > BOP > PBE > PW91 > VWN-BP > BP > HCTH. Therefore, the results obtained at BLYP functional are considered for the remaining study of this work. From the contribution of the bands, the calculated HOMO-LUMO electronic transition is 2.101 eV. The study of HOMO and LUMO is extended to the calculation of the electron affinity, the ionization potential, and the chemical hardness. Chemical shifts for 1H and 13C NMR are also predicted. In 1H and 13C NMR, H25/ H32 and C5/C16 resonance signals are expected to be highly deshielded based on the Mulliken population analysis.

Semiorganic single crystals of L-Threonine Lithium Chloride were wealthy developed by slow evaporation method at ambient circumstances. The structure was illuminated by single crystal XRD technique and the structure be owned by orthorhombic system. Density functional theory computations using B3LYP/6-311++ G(d,p) base set gives optimized structural parameters of title compound. The Theoretically identified hyperconjugative molecular interactions are accountable for the stabilization of compound are obtain by NBO analysis. Besides, Mulliken atomic charges and molecular electrostatic potential were also executed.

Electrocatalytic oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in acidic media are vital for the applications of renewable energy electrolyzers. However, the low mass activity of noble Pt urgently needs to be improved due to the strong binding energetics of oxygen species (*O) with Pt sites. Here we report fine PtxSr alloy (~2 nm) supported on N-doped carbon (NC) pyrolyzing from ZIF-8 as bifunctional electrocatalysts toward ORR and HER in acidic media. The representative Pt2Sr/NC exhibits an onset potential of 0.94 V vs. RHE and half-wave potential of 0.84 V toward ORR, and a low overpotential of 27 mV (10 mA cm−2) toward HER, respectively. Significantly, the mass activities of Pt2Sr/NC are 6.2 and 2.6 times higher than that of Pt/C toward ORR (at 0.9 V) and HER (at −30 mV), respectively. Simultaneously, Pt2Sr/NC possesses a retention rate of 90.97% toward acidic ORR after 35000 s of continuous operation. Through density functional theory (DFT) calculations and X-ray photoelectron spectroscopy analysis, the incorporation of Sr into Pt forming Pt2Sr alloy redistributes the electronic structures of Pt–Pt bonds, changing the rate-determining step for the ORR on Pt sites from the formation of *OH from *O to the generation of *OOH along with decreasing the energy barrier, which is also confirmed by the downshift of d band center. Meanwhile, the downshift of d band center also leads to the optimization of the adsorption energy (H*) with Pt, significantly improving Pt2Sr/NC toward HER.

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.

Explore the photo-piezoelectric synergistic micro-mechanism by density functional theory (DFT) calculations at the electronic and atomic level is important. In this work, to understand the synergistic mechanism, atomic and electronic properties of typical piezoelectric and photocatalytic material BaTiO3 were initially investigated with different strains. Subsequently, the adsorption of volatile organic compounds (VOCs) on the BaTiO3 (001) surface was determined during the piezoelectric process. In addition, the relationship between deformation ratio, the electronic structure and adsorption energy was understood in the deformation ratio range of 7%-12% for the optimal catalytic effect. The results of charge density differences and Born effective charge reveal the synergistic mechanism of piezoelectric photocatalysis. The built-in electric field formed by polarization results in the enhanced separation of charges, which makes the surface charges aggregation, enhancing the adsorption of VOCs, and benefiting the subsequent photocatalytic degradation. This work can provide significant theoretical guidance for the piezoelectric photocatalytic degradation of pollutants with the optimal strain range.

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.

Theoretical and experimental investigations on the molecular structure of 2-amino-5-chloro-3-nitropyridine (2A5Cl3NP) are presented. The molecular equilibrium geometry of the title molecule is fully optimized. Quantum chemical calculations of the HOMO-LUMO energies, energy gap (ΔE), electron negativity (χ), and chemical potential (μ), global hardness (ƞ), and global softness (S) are calculated for the title molecule. The title compound has a low softness value (0.2770) and the calculated value of electrophilicity index (7.7250) describes the biological activity. The stability and charge delocalization of the title molecule are studied by Natural Bond Orbital Analysis (NBO), Non-Linear Optical (NLO) behaviour in terms of first order hyperpolarizability, dipole moment, anisotropy of polarizability are accounted. The computed values of dipole moment (μ) for 2A5Cl3NP molecule is 3.0173 Debye, polarizability (α) is 1.6017 × 10–23esu, hyperpolarizability (β) is 5.08173 × 10–30esu. The high β value and non-zero value of μ indicate that the title compound might be a good candidate for NLO material. The strength of the interaction between electron donors and electron acceptors is measured by the magnitude of energy of hyper conjugative interactions E (2). The second-order Fock matrix is calculated to study the donor–acceptor interactions in NBO analysis.

We report the synthesis of nitridation-induced NiFe-MOF through post-synthetic functionalization of terminal ligand in NiFe-MOF nanosheet. We directly identify the key factor of amino ligand in N-NiFe-MOF for boosting the OER performance through combining single X-ray crystallographic characterization and in-situ Raman tracking, as well as ex-situ spectroscopy analysis. Density functional theory (DFT) calculations and experimental results indicate irreversible phase reconstruction from amino ligand oxidation prior to OER could lead to the optimized ΔG*O, resulting in the remarkable OER performance with an overpotential of 258 mV to obtain the current density of 100 mA cm−2 in 1.0 M KOH solution. Our work will provide new strategy for rational designing advanced MOF-based OER electrocatalysts.

Single crystals of L-Argininium Hydrogen Squarate (LAHSQ) were obtained from slow evaporation solution growth method using deionised water (1:1) as a solvent. The molecular structure and vibrational spectrum of LAHSQ single crystal has been investigated by Density Functional Theory (DFT) method. Single crystal X-ray Diffraction (SXRD) analysis has been used to identify the structure, cell-parameters and space group of the LAHSQ grown singe crystal. It revealed that the present crystal structure is triclinic system with P1 space group. The molecular structure was analysed by identifying the functional groups from FT-IR spectra were calculated and the results are compared to the experimental data, exhibited a good overall agreement. HOMO-LUMO energy gap was found to be 3.1789 eV. The Kurtz-Perry powder technique has been used to found the Second Harmonic Generation (SHG) of LAHSQ crystal. Theory (DFT) calculations have been worked under solvation model to know the geometrical and electronic structural characters like frontier molecular orbital analysis (FMO), Mulliken population analysis, dipole moment, polarizability, and hyperpolarizability of the crystal. All these results agree that the LAHSQ crystal is appropriate for NLO applications.

This study describes structural, electronic and mechanical properties of SnTe and SnTe0.5Se0.5 compound by using the spin-polarized full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). The structural parameters, density of states and band structure have been analyzed using the generalized gradient approximation (GGA). The calculated density of states (DOS) of these compounds is discussed in terms of contribution from various s, p and d-states of the constituent atoms. The computed elastic constants indicate that SnTe and SnTe0.5Se0.5 are mechanically stable. Also, Bulk modulus, Shear modulus, Young’s modulus, Poison’s ratio and Hardness were investigated.

This paper describes the spectroscopic (FT-IR and UV–Visible), electronic, structural, vibrational properties of celecoxib compound using density functional theory. The optimized geometry structure of the titled molecule is explained by the method of B3LYP with 6–31 + G (d, p) basis set. We found that the simulated optimized geometry of the titled molecule is simulated to the experimental ones. The infrared spectrum of celecoxib compound is represented in the present work. The computational information about the organic molecule can be explained by the charge transfer properties, which is a computational tool for the precise quantum chemical calculations of space charge density distribution and HOMO-LUMO states. The transition states of celecoxib compound have explained by the time-dependent density functional theory (TD-DFT) which is observed by the UV–visible spectrum. Docking research [1] is a modeling method, with the help of docking method we can find out new drug and chemical behavior of the drug which is useful in the application purpose of the drug, the interaction between protein and legends provides the information of the binding energy and physical parameter like partition function, free energy, internal energy, entropy.

The compound of L-Glycinium 5-Nitrouracilate were grown by slow solvent evaporation technique at room temperature method. Structural investigation by single crystal XRD reveals that LGY5N crystallizes in monoclinic system with space group P21/c. Vibrational spectroscopic studies were performed by utilizing FT–IR spectral analysis along with DFT/B3LYP/6-311++G(d,p) method using GAUSSIAN 06 software. The molecular structure of LGY5N crystal has also been optimised by using Density Functional Theory (DFT) using method with B3LYP/6-311++G (d, p) basis methods in order to find the whole characteristics of the molecular complex. The HOMO and LUMO energy results show that good exchange of charge happened inside the molecule. The electronic absorption spectrum of organic molecules that shows alteration due to the solvation processes was evaluated by TD-DFT in the gas and solvent phase in addition to the recorded UV–visible spectrum. Second harmonic generation (SHG) efficiency measurement was done to examine the enhancement in the nonlinear optical characteristics of the grown crystal.

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.

(1S)-(+)-10-Camphorsulfonic Acid has a promising application in medical field as an anti-inflammatory drug. According to the present studies, the structural and spectral characteristics, and the reactivity of the title compound were carried out using Density Functional Theory (DFT), with B3LYP/6–311++G(d,p) as the basis set. Experimental techniques such as FT-IR, FT-Raman were in good agreement with the theoretical results. The intermolecular and intramolecular interactions of the title compound are interpreted from the NBO analysis. Molecular Electrostatic Potential (MEP), Frontier Molecular Orbitals (FMO), The intermolecular charge transfer within the molecule is confirmed from the charge transfer interactions, also among all the reagents Camphorsulfonic acid were found to be the best reagent. NLO and Thermodynamic Properties were also calculated. The molecular docking analysis were carried out to study the biological activity of the compound.

Organic nonlinear optical single crystal of L-Isoleucine D-Valine (LIDV) with dimensions 3 X 3 X 4 mm3 was successfully grown by the slow evaporation solution growth technique (SEST). The structural analysis of the grown crystals has been analyzed by Powder X-ray diffraction which revealed that grown (LIDV) crystal belongs to monoclinic crystal system with P21 space group. The structure of LIDV is optimized using Density Functional Theory (DFT) method. The vibrational band assignments were performed at B3LYP/6-31G + (d, p) theory level. The theoretical IR frequencies are found to be in good agreement with the experimental IR frequencies. Nonlinear optical (NLO) behavior of LIDV is examined by the theoretically predicted values of first hyper polarizability. The cut-off wavelength and the optical band gap value of the grown crystal is found using Optical studies. The SHG efficiency of the grown material is found to be 2.5 times the reference material.

Novel research avenues have been explored over the last decade on the use of transition metal carbides (TMCs) as catalytically active supports for metal nanoclusters, which display high catalytic activity despite the poor reactivity (or even inertness) of the bulk metal. It has been postulated that TMCs polarise the electron density of adsorbed metal particles in such a way that their catalytic activity ends up being superior to those dispersed on more traditional metal oxide supports. Herein, we investigate the structural and electronic properties of small clusters of precious metals (Rh, Pd, Pt and Au) and more affordable metals (Co, Ni and Cu) supported on TMCs with 1:1 stoichiometry (TiC, ZrC, HfC, VC, NbC, TaC, MoC and WC) by means of periodic Density Functional Theory calculations. Our high-throughput screening studies indicate that it is possible not only to have strongly bonded and stably dispersed metal nanoparticles on TMC surfaces, but also to manipulate their charge by carefully selecting elements with desired electronegativity for the host TMC and the metal cluster. By doing so, it is possible to tune the amount of charge density on the cluster hollow sites, which can facilitate the bonding of certain molecules. Moreover, we identify Pt, Pd and Rh clusters supported on hexagonal TMC (001) facets as the candidates with the highest potential catalytic activity -as estimated by the significant polarisation of the cluster electron density- and stability -as quantified by the strongly negative values of adsorption energy per atom and formation energy-.

The present work investigates on structural and chemical studies on 1-Phenyl Sulfonyl Pyrrole(1PSP) using quantum computational methods. The revamped geometric structure and its parameters were obtained through density functional theory (DFT). The electronic absorption transitions were discussed with different solvents were carried out by TD-DFT (Time Dependent Density Functional Theory) method. The IR intensities and Raman activites are tabulated for vibrational wavenunbers and its corresponding PED (Potential Energy Distribution) assignments in percentage were obtained from VEDA4 software. The inter and intra molecular interactions, electrophilic, nucleophilic and chemical reactivity sites are identified by Molecular electrostatic Potential (MEP), HOMO-LUMO (Highest Occupied Molecular Orbital and Lowest Unoccupied Molecular Orbital) and GCRD (Global chemical reactivity descriptors). Mulliken atomic charges were discussed with Natural Bond Orbital (NBO) analysis. Thermodynamic property and Non-linear optical deportment of the title compound is also talked about. Besides the electron localization function map, the density of states are also mapped with Multiwfn software, a wavefunction analyzer.

The synthesis, structure, and properties of pyrene-based conformationally adaptive macrocycles are described. This new type of conformationally adaptive macrocycle was constructed through Perkin reaction, followed by imidization. By changing the condensation partner as the linking unit, a family of conjugated macrocycles with different sizes of the cavity was synthesized, which provide a simple and modular synthetic strategy towards the conformationally adaptive macrocycles. Furthermore, the macrocycles provide two well-defined conformations through flipping pyrene subunit, which were unambiguously determined by single-crystal X-ray diffraction analysis. The conformational interconversion barrier was determined by density functional theory (DFT) calculations. This new macrocycle also demonstrated unique properties, such as vapochromic behavior and aggregation emission enhancement effect. Furthermore, we have also investigated the effect of the linker on the shape and photophysical properties of the resulting macrocyclic products.

The variation in geometrical and electronic properties of armchair graphene nanoribbon (AGNR) along with pristine and phosphorus (P-AGNR) doped configuration in the presence of ammonia gas (NH3) have been identified in this work. The density functional theory based calculations have been performed in order to detect and equate the sensitivity of modified armchair graphene nanoribbon towards NH3 sensing. Further, the variation in geometrical and electronic properties of AGNR and P-AGNR have been analyzed by considering the cohesive energy, band structure, density of states, and conductance. Hence, our findings shows that P doped AGNR can upsurge its sensitivity towards NH3 gas by the order of 106 times owing to the enhancement in the conductance. Overall, results shows the great potential in the area of designing the graphene nanoribbon based sensors.

The high degree of crystallinity of discharging intermediates of Li-S batteries (Li2S2/Li2S) causes a severe capacity attenuation at low temperatures. Herein, a sulfur-rich polymer is fabricated, which enables all the discharging intermediates to exist in an amorphous state without long-range order, promoting the substantial conversion of discharging intermediates and enhancing Li-S batteries' performance at low temperatures greatly. This cathode material exhibits excellent performance both at room and low temperatures. Even under an extremely low temperature (–40 ℃), the discharge capacity can remain 67% of that at room temperature. Besides, in-situ UV/Vis spectroscopy and density functional theory calculations reveal that this organosulfur cathode undergoes a new mechanism during discharge. Li2S6 and Li2S3 are the primary discharging intermediates that are quite different from conventional Li-S batteries. These results provide a new direction for a broader range of applications of Li-S batteries.

Density Function Theory is one of the most popular and recommended computational quantum Mechanical method used for the analysis of molecular structure and vibrational spectra. L-Isoleucine is one of the amino acid which is known to be a hydrophobic amino acid and it has zwitterion nature in solution. L-Maleic acids are also organic acid with large π-conjugation with which has attracted great deal of attention. A non-centrosymmetric Nonlinear Optical single crystal of L-Isoleucinium Hydrogen Maleate Hemihydrates (LIM) were grown from aqua solution by slow evaporation solution growth method. The Molecular structure of LIM single crystal were optimized using Density function theory (DFT) method B3LYP with 6-311++G(d,P) basis set. The molecular structure of LIM was then confirmed by SXRD and the crystal exhibited Monoclinic structure with the space group P21. FTIR, FT-RAMAN and Potential energy distribution of LIM molecules were calculated and compared with experimental values. Band gap energy of LIM crystal was calculated by HOMO-LUMO energies and it is found to be 5.621 eV which confirm the inter molecular charge transfer within the molecule. In the present work, Natural bond Orbital analysis (NBO), Fukui Functions calculations Molecular Electrostatic Potential (MEP), First Order Hyperpolarizability were discussed.

International audience; Halide perovskites doped with magnetic impurities (such as the transition metals Mn2+, Co2+, Ni2+) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable light-emitting diodes, single-photon emitters, and magneto-optical devices. However, despite several recent studies, there is no consensus on whether the doped magnetic ions will predominantly replace the octahedral B-site metal via substitution or reside at interstitial defect sites. Here, by performing correlated nanoscale X-ray microscopy, spatially and temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs2PbI2Cl2, we show that doping Mn2+ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn2+ does not replace the Pb2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn2+ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl– and two I– atoms, which results in a locally expanded structure. These measurements show the fate of the transition metal dopants, the local structure, and optical emission when they are doped at dilute concentrations into a wide band gap semiconductor.

Al-V-B master alloy is promising for refining Al-Si alloys, yet its optimal composition with superior efficacy remains to be explored. In this work, the evolution of refining phases in the Al-10Si/Al-V-B system with different V:B ratios was evaluated by thermodynamic calculations, based on which the Al-V-B refiners with V:B = 1:1 and 5:1 were designed. Refining trails demonstrated that they could significantly reduce the grain size of Al-10Si (wt.%) alloy from 1736 to 184–245 μm with industrial addition amount. Detailed examinations results clarify that when V:B ratio is 1:1 the nucleation particle is (V,Al)B2, which has a VB2-AlB2 core-shell structure and therefore presents the nucleation capability as AlB2 particle. When V:B ratio is as high as 5:1, the nucleation particle is pure VB2. Density functional theory (DFT) calculation indicates that (0 0 0 1) VB2/(1 1 1) α-Al interface has the lowest interfacial energy such that highest nucleation potency among other types of diboride/α-Al interfaces under consideration. The outcomes of this work provide fundamental guidance to develop superior V-B based refiners for Al-Si alloys.

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is one of the most widely used powerful explosives. The direct and selective detection of HMX, without the requirement of specialized equipment, remains a great challenge due to its extremely low volatility, unfavorable reduction potential and lack of aromatic rings. Here, we report the first chemical probe of direct identification of HMX at ppb sensitivity based on a designed metal-organic cage (MOC). The cage features two unsaturated dicopper units and four electron donating amino groups inside the cavity, providing multiple binding sites to selectively enhance host-guest events. It was found that compared to other explosive molecules the capture of HMX inside the cavity would strongly modulate the emissive behavior of the host cage, resulting in highly induced fluorescence “turn-on” (160 folds). Based on the density functional theory (DFT) simulation, the mutual fit of both size and binding sites between host and guest leads to the synergistic effects that perturb the ligand-to-metal charge-transfer (LMCT) process, which is probably the origin of such selective HMX-induced turn-on behavior.

Two–electron ( 2 e - ) oxygen reduction reaction (ORR) shows great promise for on–site electrochemical synthesis of hydrogen peroxide (H2O2). However, it is still a great challenge to design efficient electrocatalysts for H2O2 synthesis. To address this issue, the logical design of the active site by controlling the geometric and electronic structures is urgently desired. Therefore, using density functional theory (DFT) computations, two kinds of hybrid double–atom supported on C2N nanosheet (RuCu@C2N and PdCu@C2N) are screened out and their H2O2 performances are predicted. PdCu@C2N exhibits higher activity for H2O2 synthesis with a lower overpotential of 0.12 V than RuCu@C2N (0.59 V), Ru3Cu(110) facet (0.60 V), and PdCu(110) facet (0.54 V). In aqueous phase, the adsorbed O2 is further stabilized with bulk H2O and the thermodynamic rate–determining step of 2 e - ORR change. The activation barrier on PdCu@C2N is 0.43 eV lower than the one on RuCu@C2N with 0.68 eV. PdCu@C2N is near the top of 2 e - ORR volcano plot, and exhibits high selectivity of H2O2. This work provides guidelines for designing highly effective hybrid double–atom electrocatalysts (HDACs) for H2O2 synthesis.