Density Functional Theory Predictions Research Articles

Electronic Configurations and the Effect of Peripheral Substituents of (Nitrosyl)iron Corroles.

There have been debates on the electronic configurations of (nitrosyl)iron corroles for decades. In this work, pentacoordinate [Fe(TPC)(NO)], [Fe(TTC)(NO)], and [Fe(TpFC)(NO)] with different para-substituted phenyl groups (TPC, TTC, and TpFC = tris(phenyl, 4-tolyl, or 4-fluorophenyl)corrole, respectively) have been isolated and investigated by various techniques including single-crystal X-ray diffraction, UV-vis spectroscopy, cyclic voltammetry, Fourier transform infrared, NMR, and absorption fine structure spectroscopy. Multitemperature and high-magnetic-field (3, 6, and 9 T) Mössbauer spectroscopy was also applied on all three complexes, which determined the S = 0 diamagnetic states, consistent with the magnetic susceptibility and electron paramagnetic resonance measurements. Density functional theory predictions by different functionals were compared, and the new calculation strategy, which gave remarkable agreement of the experimental Mössbauer parameters (ΔEQ and δ), allowed further assignment on the electronic configuration of {FeNO}6-(corrole3-) with antiferromagnetically coupled (S = 1/2, FeIII) and (S = 1/2, NO). Correlated sequences between the electronic donating/withdrawing capability of para substituents and the reduction/oxidation potentials, metal out-of-plane displacements (Δ4 and Δ23), and Mössbauer parameters (Vzz and ΔEQ) were also established, which suggests the strong effects of peripheral substituents.

Promoting electrocatalytic hydrogenation of 5-hydroxymethylfurfural using buffer electrolytes as proton-donating motifs: Theoretical predictions and experimental validations

Electrocatalytic hydrogenation (ECH) represents a promising alternative to conventional hydrogenation techniques with high-pressure H2 as a reductant. The proton-donating motif is an important factor governing the reaction efficiency but is usually overlooked in the ECH process. Herein, on the basis of density functional theory (DFT) predictions and experimental validations, we demonstrate that proton-buffer salts such as phosphate, carbonate and borate can greatly promote ECH efficiency. The DFT results predict that the buffer species can outperform water in donating protons for *CO hydrogenation into *C-OH via the Langmuir-Hinshelwood or proton-coupled electron transfer (PCET) mechanism, thus promoting the hydrogenation of carbonyl compounds. The experimental results demonstrate that with the buffer-promoting effects, 5-hydroxymethylfurfural (HMF) can be effectively converted at an efficiency of 96 % into the value-added 2,5-dihydroxymethylfuran (DHMF) with a yield of 80 % over cobalt oxide (Co3O4) nanoarray catalysts under near-neutral buffer electrolyte. In situ Raman analysis and kinetic isotope experimental results reveal that the real mechanism is a combined Langmuir-Hinshelwood and PCET process. Such a buffer-promoting strategy also exhibits wide applicability in ECH of various other carbonyl compounds with different electrode catalysts. This work may provide a deep understanding of the ECH process and open up new opportunities to design effective systems for the conversion of HMF into value-added products.

Adsorption energies on transition metal surfaces: towards an accurate and balanced description

Density functional theory predictions of binding energies and reaction barriers provide invaluable data for analyzing chemical transformations in heterogeneous catalysis. For high accuracy, effects of band structure and coverage, as well as the local bond strength in both covalent and non-covalent interactions, must be reliably described and much focus has been put on improving functionals to this end. Here, we show that a correction from higher-level calculations on small metal clusters can be applied to improve periodic band structure adsorption energies and barriers. We benchmark against 38 reliable experimental covalent and non-covalent adsorption energies and five activation barriers with mean absolute errors of 2.2 kcal mol−1, 2.7 kcal mol−1, and 1.1 kcal mol−1, respectively, which are lower than for functionals widely used and tested for surface science evaluations, such as BEEF-vdW and RPBE.

Erythrosin B as a New Photoswitchable Spin Label for Light-Induced Pulsed EPR Dipolar Spectroscopy.

We present a new photoswitchable spin label for light-induced pulsed electron paramagnetic resonance dipolar spectroscopy (LiPDS), the photoexcited triplet state of erythrosin B (EB), which is ideal for biological applications. With this label, we perform an in-depth study of the orientational effects in dipolar traces acquired using the refocused laser-induced magnetic dipole technique to obtain information on the distance and relative orientation between the EB and nitroxide labels in a rigid model peptide, in good agreement with density functional theory predictions. Additionally, we show that these orientational effects can be averaged to enable an orientation-independent analysis to determine the distance distribution. Furthermore, we demonstrate the feasibility of these experiments above liquid nitrogen temperatures, removing the need for expensive liquid helium or cryogen-free cryostats. The variety of choices in photoswitchable spin labels and the affordability of the experiments are critical for LiPDS to become a widespread methodology in structural biology.

Approach to High-Nitrogen Materials with Dual-Use Properties via Tetraaza-Nazarov Cyclization.

In this report, we describe the application of an electrocyclization toward the synthesis of a high-nitrogen heterocycle. It entails the synthesis of a novel, high-nitrogen, 2-3-disubstituted tetrazolium salt via the tetraaza-Nazarov cyclization (4π electrocyclization) of 3-bromo-1,5-bis(3-nitro-1,2,4-triazole-1H-5-yl)-formazan (BDNF). The cyclization takes place under mild conditions using the oxidant phenyliodine(III) diacetate (PIDA). The proposed electrocyclic mechanism is supported by density functional theory (DFT) calculations and data from previous studies of formazan cyclizations. This is noteworthy because while 4π electrocyclizations with one or two nitrogen atoms have been documented previously, this case represents the first example of generation and cyclization of a conjugated intermediate with four nitrogen atoms. The experimental behavior of electrocyclization is consistent with the predictions of DFT.

Effectiveness and degradation pathways of bisphenol A (BPA) initiated by hydroxyl radicals and sulfate radicals in water: Initial reaction sites based on DFT prediction

Bisphenol A (BPA), one of the widely known endocrine-disrupting chemicals, can be effectively degraded by advanced oxidation processes in water because of the powerful reactive oxygen species. In this study, Fenton, UV/Fenton, and metal ion/peroxymonosulfate (PMS) processes were compared to investigate BPA degradation efficiency and pathways initiated by hydroxyl radicals and sulfate radicals. In contrast to the Fenton system, which only degraded 60% of BPA within 15 min, the UV/Fenton system could degrade greater than 80% of BPA, because more hydroxyl radicals (•OH) were generated under the reduction of Fe3+ to Fe2+. The optimized parameters of the UV/Fenton system were as follows: 8 μmol/L of Fe2+, 80 μmol/L of H2O2, and a pH value of 3.0. As for the metal ion/PMS system, the BPA degradation efficiency was closely associated with the applied metal ions, and the order was as follows: Co2+/PMS (∼100%) > Fe2+/PMS (∼80%) > Cu2+/PMS (∼79%). The degradation pathways of BPA were theoretically interpreted through density functional theory prediction and degradation products during various processes. Two major initial reaction sites (4C and 6C) for •OH initiated using the UV/Fenton system and one initial reaction site (4C) for sulfate radicals (SO4•−) using the metal ion/PMS system were recognized for BPA degradation processes. The degradation products by •OH showed a larger average molecular weight than those by SO4•−. These studies are instructive for the application of different advanced oxidation systems in the treatment process of BPA in wastewater.

Hydrogen spillover effect enhanced by carbon quantum dots activated MoS2

The weak hydrogen adsorption and slow catalytic kinetics are unfavorable for MoS2 as a catalyst for hydrogen evolution reaction (HER) in alkaline solution. Herein, carbon quantum dots (CQDs) with high proton adsorption energy were expected to enhance the proton adsorption of MoS2 during the HER process. The CQDs activated MoS2 can establish a suitable hydrogen adsorption gradient due to the surface charge redistribution to promote the hydrogen spillover pathway. After the CQDs were loaded on MoS2, the charge distribution would gradually transfer from the C sites of CQDs to the S sites on MoS2 surface, showing a charge gradient distribution calculated by density functional theory predictions. The adsorbed hydrogen can spill over from hydrogen-enriched CQDs to hydrogen-deficient MoS2 in HER. The process could be monitored by the quasi in-situ electrochemical impedance spectroscopy. The enhanced hydrogen spillover effect by CQDs activated MoS2 can pave the way for the design and preparation of efficient and low-cost catalysts.

Synthesis and characterization of Co-Ti-Sn alloys: Co1.5TiSn as half-metal based on the Fe1.5TiSb layered Heusler prototype

The Co-Ti-Sn family of alloys from their half- to full-Heusler compositions are synthesized. Co1.5TiSn, a compound predicted by our theoretical calculations, is successfully synthesized in the L21 structure with cobalt vacancies in the tetrahedral sites. The saturated magnetic moment at 5 K is measured to be ~ 0.6 μB∕formula unit, consistent with density functional theory (DFT) predictions of half-metallicity in the compound. A cluster expansion-based analysis of the alloy system indicates the Co1.5TiSn compound to be nearly on the convex hull, within DFT accuracy. Our experimental realization of the Co1.5TiSn compound suggests that it is either kinetically or entropically stabilized.

Spectroscopic investigation and density functional theory prediction of first and second order hyperpolarizabilities of 1-(4-bromophenyl)-3-(2,4-dichlorophenyl)‑prop-2-en-1-one

This work presents the spectroscopic analysis and nonlinear optical (NLO) behaviour of 1-(4-Bromophenyl)-3-(2,4-dichlorophenyl)‑prop-2-en-1-one (DCBC). The motivation behind choosing chalcone derivative DCBC for NLO studies is its crystallization in non-centrosymmetric structure, excellent second harmonic generation efficiency (SHG) and flexibility in structure of chalcones due to donor-acceptor groups. The compound was characterized by FT-IR, FT-Raman, UV–vis and NMR techniques. The structural and spectroscopic features of the molecule were calculated using density functional theory (DFT) employing B3LYP/6–311++G(d,p) basis set and compared with the experimental values. The complete vibrational assignments were made on the basis of potential energy distribution (PED). The Natural Bond Orbital (NBO) analysis of DCBC has been done in order to provide the detailed insight into the nature of electronic conjugation between the bonds in this molecule. The second-order perturbation theory analysis of Fock matrix in the NBO basis of the molecule shows the strong intramolecular hyperconjugative interactions between σ (Cl3-C28) to σ*(C26-C28), n(1)(Cl3) to σ*(C26-C28) and π(C6-C8) to π*(C5-C13) resulting in large stabilization energies leading to large delocalization. A time-dependant variant of DFT (TD-DFT) is applied to calculate the electronic properties such as oscillator strengths, absorption maxima and HOMO and LUMO energies. The HOMO-LUMO energy gap is found to be 3.882 eV and is used to calculate global reactivity parameters. Isotropic chemical shifts were calculated using gauge invariant atomic orbital (GIAO) method and these matched well with the experimental results, indicating the accuracy of calculation method. Molecular Electrostatic Potential (MEP) surface has been depicted to know the chemically active regions of the molecule. The nonlinear optical properties of title molecule were addressed theoretically by the determination of two contributions, vibrational and electronic, to polarizability (α) and the first and the second order hyperpolarizabilities (β and γ). The electronic first and second order hyperpolarizabilities of DCBC determined by Finite Field approach method are found to be 17.805 × 10−30 and 6.0 × 10−41 e.s.u. respectively. These values are comparable to other chalcones and organic NLO materials which indicate that the studied molecule is responsive to nonlinear optical (NLO) effect and has enhanced applicability in the development of nonlinear optical devices.

Influence of ion irradiation-induced defects on phase formation and thermal stability of Ti0.27Al0.21N0.52 coatings

The influence of changes induced by ion irradiation on structure and thermal stability of metastable cubic (Ti,Al)N coatings deposited by cathodic arc evaporation is systematically investigated by correlating experiments and theory. Decreasing the nitrogen deposition pressure from 5.0 to 0.5 Pa results in an ion flux-enhancement by a factor of three and an increase of the average ion energy from 15 to 30 eV, causing the stress-free lattice parameter to expand from 4.170 to 4.206 Å, while the chemical composition of Ti0.27Al0.21N0.52 remains unchanged. The 0.9% lattice parameter increase is a consequence of formation of Frenkel pairs induced by ion bombardment, as revealed by density functional theory (DFT) simulations. The influence of the presence of Frenkel pairs on the thermal stability of metastable Ti0.27Al0.21N0.52 is investigated by scanning transmission electron microscopy, differential scanning calorimetry, atom probe tomography and in-situ synchrotron X-ray powder diffraction. It is demonstrated that the ion flux and ion energy induced formation of Frenkel pairs increases the thermal stability as the Al diffusion enabled crystallization of the wurtzite solid solution is retarded. This can be rationalized by DFT predictions since the presence of Frenkel pairs increases the activation energy for Al diffusion by up to 142%. Hence, the thermal stability enhancement is caused by a hitherto unreported mechanism - the Frenkel pair impeded Al mobility and thereby retarded formation of wurtzite solid solution.

Assessing the accuracy of compound formation energies with quantum Monte Carlo

Accurately predicting the formation energy of a compound, which describes its thermodynamic stability, is a key challenge in materials physics. Here, we employ many-body quantum Monte Carlo (QMC) with single-reference trial functions to compute the formation energy of two electronically disparate compounds, the intermetallic VPt$_2$ and the semiconductor CuI, for which standard density functional theory (DFT) predictions using both the Perdew-Burke Ernzerhof (PBE) and the strongly constrained and appropriately normed (SCAN) density functional approximations deviate markedly from available experimental values. For VPt$_2$, we find an agreement between QMC, SCAN, and PBE0 estimates, which therefore remain in disagreement with the much less exothermic experimental value. For CuI, the QMC result agrees with neither SCAN nor PBE pointing towards DFT exchange-correlation biases, likely related to the localized Cu $3d$ electrons. Compared to the behavior of some density functional approximations within DFT, spin-averaged QMC exhibits a smaller but still appreciable deviation when compared to experiment. The QMC result is slightly improved by incorporating spin-orbit corrections for CuI and solid I$_2$, so that experiment and theory are brought into imperfect but reasonable agreement within about 120~meV/atom.

Elucidation of Metal Local Environments in Single-Atom Catalysts Based on Carbon Nitrides.

The ability to tailor the properties of metal centers in single-atom heterogeneous catalysts depends on the availability of advanced approaches for characterization of their structure. Except for specific host materials with well-defined metal adsorption sites, determining the local atomic environment remains a crucial challenge, often relying heavily on simulations. This article reports an advanced analysis of platinum atoms stabilized on poly(triazine imide), a nanocrystalline form of carbon nitride. The approach discriminates the distribution of surface coordination sites in the host, the evolution of metal coordination at different stages during the synthesis of the material, and the potential locations of metal atoms within the lattice. Consistent with density functional theory predictions, simultaneous high-resolution imaging in high-angle annular dark field and bright field modes experimentally confirms the preferred localization of platinum in-plane in the corners of the triangular cavities. X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and dynamic nuclear polarization enhanced 15 N nuclear magnetic resonance (DNP-NMR) spectroscopies coupled with density functional theory (DFT) simulations reveal that the predominant metal species comprise Pt(II) bound to three nitrogen atoms and one chlorine atom inside the coordination sites. The findings, which narrow the gap between experimental and theoretical elucidation, contribute to the improved structural understanding and provide a benchmark for exploring the speciation of single-atom catalysts based on carbon nitrides.

Nuclear Mass Predictions of the Relativistic Density Functional Theory with the Kernel Ridge Regression and the Application to r-Process Simulations

The kernel ridge regression (KRR) and its updated version taking into account the odd-even effects (KRRoe) are employed to improve the mass predictions of the relativistic density functional theory. Both the KRR and KRRoe approaches can improve the mass predictions to a large extent. In particular, the KRRoe approach can significantly improve the predictions of the one-nucleon separation energies. The extrapolation performances of the KRR and KRRoe approaches to neutron-rich nuclei are examined, and the impacts of the KRRoe mass corrections on the r-process simulations are studied. It is found that the KRRoe mass corrections for the nuclei in the r-process path are remarkable in the light mass region, e.g., A<150, and this could influence the corresponding r-process abundances.

Reaction processes at step edges on S-decorated Cu(111) and Ag(111) surfaces: MD analysis utilizing machine learning derived potentials.

A variety of complexation, reconstruction, and sulfide formation processes can occur at step edges on the {111} surfaces of coinage metals (M) in the presence of adsorbed S under ultra-high vacuum conditions. Given the cooperative many-atom nature of these reaction processes, Molecular Dynamics (MD) simulation of the associated dynamics is instructive. However, only quite restricted Density Functional Theory (DFT)-level ab initio MD is viable. Thus, for M = Ag and Cu, we instead utilize the DeePMD framework to develop machine-learning derived potentials, retaining near-DFT accuracy for the M-S systems, which should have broad applicability. These potentials are validated by comparison with DFT predictions for various key quantities related to the energetics of S on M(111) surfaces. The potentials are then utilized to perform extensive MD simulations elucidating the above diverse restructuring and reaction processes at step edges. Key observations from MD simulations include the formation of small metal-sulfur complexes, especially MS2; development of a local reconstruction at A-steps featuring an S-decorated {100} motif; and 3D sulfide formation. Additional analysis yields further information on the kinetics for metal-sulfur complex formation, where these complexes can strongly enhance surface mass transport, and on the propensity for sulfide formation.

Synergistic interaction between in situ exsolved and phosphorized nanoparticles and perovskite oxides for enhanced electrochemical water splitting

Highly active and stable catalysts towards electrochemical water-splitting are critical for the sustainable energy conversion and storage. Perovskite oxides with in situ exsolved metal nanoparticles have emerged as promising candidates, while their activities are still unsatisfying and mechanisms unclear. Here we develop a novel hybrid catalyst with the in situ exsolved and phosphorized Co nanoparticles on Sr2FeMoO6 perovskite oxide surface based on density functional theory predictions, and use it as a model system to investigate the particle-substrate interactions with combined experimental studies and theoretical calculations. The as-prepared electrocatalyst exhibits boosted activity and stability for oxygen evolution reaction, hydrogen evolution reaction and overall water-splitting in alkaline solution, comparable to these of precious-metal catalysts. Further studies reveal the phase transformation during catalysis and the strong interactions between the phosphorized Co nanoparticles and perovskite oxide substrate. The modulated band structure, redistributed charge density and spillover effect lead to the enhanced charge transfer, increased O covalency, optimized intermediate adsorption and reduced energy barrier, enhancing the overall activity synergistically.

Structural evolution, electronic properties and spectra of titanium clusters

The ground-state structures, electronic properties and spectra of Ti n c ( n = 3–16 and c = 0, ±1) clusters have been investigated based on density functional theory (DFT) and CALYPSO structure prediction. Geometry optimizations show that the neutral, cationic and anionic titanium clusters have the same growth pattern. The pentagonal bipyramid plays an important role in the growth process. Analysis of electronic properties shows that the thermal stability of cationic and anionic clusters is greater than that of neutral cluster. The pentagonal bipyramid and icosahedron clusters have relatively high stability. Chemical activity of titanium clusters decreases with the cluster size. The preferred dissociation pathway of Ti n + clusters is the loss of a single Ti atom to form Ti n − 1 + . Optical absorption of Ti n clusters and infrared and Raman spectra of Ti n + clusters have been simulated and can be used for their structural identification. The ground states of Ti n − clusters have been determined by comparing experimental and theoretical photoelectron spectra. • The pentagonal bipyramid plays an important role in the growth process of titanium clusters • The titanium cluster with pentagonal bipyramid or icosahedron geometry is more table than other clusters. • The preferred dissociation pathway of Ti n + clusters is the loss of a single Ti atom to form Ti n − 1 + . • The ground state of anionic Ti n − clusters are identified by photoelectron spectra.s

Meta-Hybrid Density Functional Theory Prediction of the Reactivity, Stability, and IGM of Azepane, Oxepane, Thiepane, and Halogenated Cycloheptane.

The application of plain cycloalkanes and heterocyclic derivatives in the synthesis of valuable natural products and pharmacologically active intermediates has increased tremendously in recent times with much attention being paid to the lower cycloalkane members. The structural and molecular properties of higher seven-membered and nonaromatic heterocyclic derivatives are less known despite their stable nature and vast application; thus, an insight into their structural and electronic properties is still needed. Appropriate quantum chemical calculations utilizing the ab initio (MP2) method, meta-hybrid (M06-2X) functional, and long-range-separated functionals (ωB97XD) have been utilized in this work to investigate the structural reactivity, stability, and behavior of substituents on cycloheptane (CHP) and its derivatives: azepane, oxepane, thiepane, fluorocycloheptane (FCHP), bromocycloheptane (BrCHP), and chlorocycloheptane (ClCHP). Molecular global reactivity descriptors such as Fukui function, frontier molecular orbitals (FMOs), and molecular electrostatic potential were computed and compared with lower members. The results of two population methods CHELPG and Atomic Dipole Corrected Hirshfeld Charges (ADCH) were equally compared to scrutinize the charge distribution in the molecules. The susceptibility of intramolecular interactions between the substituents and cycloalkane ring is revealed by natural bond orbital analysis and intramolecular weak interactions by the independent gradient model (IGM). Other properties such as atomic density of states, intrinsic bond strength index (IBSI), and dipole moments are considered. It is acclaimed that the strain effect is a major determinant effect in the energy balance of cyclic molecules; thus, the ring strain energies and validation of spectroscopic specificities with reference to the X-ray crystallographic data are also considered.

Effect of molybdenum on interfacial properties of titanium carbide reinforced Fe composite

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.

Interface charge density modulation of a lamellar-like spatially separated Ni9S8 nanosheet/Nb2O5 nanobelt heterostructure catalyst coupled with nitrogen and metal (M = Co, Fe, or Cu) atoms to accelerate acidic and alkaline hydrogen evolution reactions

A first report of the rational design of novel heterostructure of M−N−Ni 9 S 8 /Nb 2 O 5 catalysts ( M = Co, Fe, or Cu) via facile two-step hydrothermal approach. The synergy of spatially separated nanosheets of Ni 9 S 8 /Nb 2 O 5 nanobelts with N and M (Co, Fe, or Cu) atoms were examined in depth. This work highlights a rational heterostructure design strategy and demonstrates the importance of optimizing the HER kinetics. • Novel M−N−Ni 9 S 8 /Nb 2 O 5 ( M = Co, Fe, or Cu) heterostructure was made by a facile method. • Synergy of spatially separated nanosheet of Ni 9 S 8 /Nb 2 O 5 nanobelt with N and metal atoms was examined in depth. • Interface engineering of M−N−Ni 9 S 8 /Nb 2 O 5 ( M = Co, Fe, or Cu) heterostructures facilitates the acidic/alkaline HER activity. • Enhancement in HER kinetics of heterostructures was examined in detail by DFT predictions. The creation of heterostructures based on non-precious metals with platinum-like hydrogen evolution reaction (HER) performance remains a challenge for hydrogen fuel technologies. Motivated by the fascinating properties of heterostructures, we establish here an effective approach to fabricate the heterostructured M−N−Ni 9 S 8 /Nb 2 O 5 ( M = Co, Fe, or Cu) catalysts using spatially separated Ni 9 S 8 nanosheet/Nb 2 O 5 nanobelts that are coupled with nitrogen (N) and metal atoms. Due to its improved intrinsic activity, interface-rich structure, abundant active sites, and large surface area the Co−N−Ni 9 S 8 /Nb 2 O 5 heterostructure achieved a low acidic HER overpotential of −171 mV at −10 mA cm −2 , thereby performing better than existing heterostructures. Moreover, for the alkaline HER, the Cu−N−Ni 9 S 8 /Nb 2 O 5 heterostructure required a low overpotential of −109 mV at −10 mA cm −2 , which is close to the performance of Pt/C catalyst. Density functional theory (DFT) predictions indicate that the local charge distribution and electronic properties at the heterointerface of Ni 9 S 8 /Nb 2 O 5 can be significantly modulated by co-doping of metals with N atoms, resulting in optimal adsorption energy and reduced water dissociation barrier; thereby accelerating the acidic and alkaline HER activity. This work, therefore, provides a new design principle to create advanced heterostructured catalysts.

Monolayer MoSi2N4- as promising electrocatalyst for hydrogen evolution reaction: A DFT prediction

l Defective MoSi 2 N 4 with surface nitrogen vacancy (NV) is predicted to be a promising HER electrocatalyst by DFT calculations. l Surface NV can be introduced in monolayer MoSi 2 N 4 under the N-poor condition. l The HER activity of defective MoSi 2 N 4 is surface NV concentration dependent. l The relationship between HER activity and the center of Si-3p band is revealed. The density functional theory (DFT) calculations have been performed to investigate the catalytic properties of monolayer MoSi 2 N 4 for hydrogen evolution reaction (HER). The DFT results show that similar to the majority of other two-dimensional (2D) materials, the pristine MoSi 2 N 4 is inert for HER due to its weak affinity toward hydrogen, while monolayer MoSi 2 N 4- x ( x = 0‒0.25) exhibits the highly desirable HER catalytic activities by introducing surface nitrogen vacancy (NV). The predicted HER overpotential (0‒60 mV) of monolayer MoSi 2 N 4- x is lower than that (90 mV) of noble metal Pt, when the concentration of surface NV is lower than 5.6%. Electronic structure calculations show that the spin-polarized states appear around the Fermi level after introducing surface NV, thus making the surface NV on 2D MoSi 2 N 4 a quite suitable site for HER. Moreover, the HER activity of MoSi 2 N 4- x is highly dependent on the surface NV concentration, which can be further related to the center of Si-3p band. Our results demonstrate that the newly discovered 2D MoSi 2 N 4 can be served as a promising electrocatalyst for HER via appropriate defect engineering.