Effect of External Electric Field on Nitrogen Activation on a Trimetal Cluster.

Efficient nitrogen (N2) fixation and activation under mild conditions are crucial for modern society. External electric fields (Felectric) can significantly affect N2 activation. In this work, the effect of Felectric on N2 activation by Nb3 clusters supported in a sumanene bowl was studied by density functional theory calculations. Four typical systems at different stages of N-N activation were studied, including two intermediates and two transition states. The impact of Felectric on various properties related to N2 activation was investigated, including the N-N bond length, overlap population density of states (OPDOS), total energy of the system, adsorption energy of N2, decomposition of energy changes, and electron transfer. The sumanene not only functions as a support and protective substrate, but also serves as a donor or acceptor under different Felectric conditions. Negative Felectric is beneficial to N-N bond activation because it promotes electron transfer to the N-N region and improves the d-π* orbital hybridization between metals and N2 in the activation process. Positive Felectric improves d-π* orbital hybridization only when the N-N is nearly dissociated. The microscopic mechanism of Felectric's effects provides insight into N2 activation and theoretical guidance for the design of catalytic reaction conditions for nitrogen reduction reactions (NRR).

Catalysts with Trimetallic Sites on Graphene-like C2N for Electrocatalytic Nitrogen Reduction Reaction: A Theoretical Investigation.

Electrocatalytic nitrogen reduction reaction (NRR) is a green and highly efficient way to replace the industrial Haber-Bosch process. Herein, clusters consisting of three transition metal atoms loaded on C2N as NRR electrocatalysts are investigated using density functional theory (DFT). Meanwhile, Ca was introduced as a promoter and the role of Ca in NRR was investigated. It was found that Ca anchored to the catalyst can act as an electron donor and effectively promote the activation of N2 on M3. In both M3@C2N and M3Ca@C2N (M=Fe, Co, Ni), the limiting potential (UL) is less negative than that of the Ru(0001) surface and has the ability to suppress the competitive hydrogen evolution reaction (HER). Among them, Fe3@C2N is suggested to be the most promising candidate for NRR with high thermal stability, strong N2 adsorption ability, low limiting potential, and good NRR selectivity. The concepts of trimetallic sites and alkaline earth metal promoters in this work provide theoretical guidance for the rational design of atomically active sites in electrocatalytic NRR.

Revisiting the thermal decomposition mechanism of MAPbI3.

The thermal stability of MAPbI3 poses a challenge for the industry. To overcome this limitation, a thorough investigation of MAPbI3 is necessary. In this work, thermal gravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy were conducted to identify the thermal decomposition products of MAPbI3, which were found to be CH3I, NH3, and PbI2. In situ X-ray diffraction (XRD) measurements were then performed in the temperature range from 300 to 700 K, which revealed the significant decomposition of the (110), (220), and (310) surfaces of MAPbI3 between 550 and 600 K. Density functional theory (DFT) calculations demonstrated that the (220) surface exhibited the highest stability. Additionally, the transition states of thermal decomposition showed that the energy barrier for the decomposition of the (110) surface was 2.07 eV. Our combined experimental and theoretical results provide a better understanding of the thermal decomposition mechanism of MAPbI3, providing valuable theoretical support for the design of long-term stable devices.

Exploring the stability and aromaticity of rare earth doped tin cluster MSn16- (M = Sc, Y, La).

Rare earth elements have high chemical reactivity, and doping them into semiconductor clusters can induce novel physicochemical properties. The study of the physicochemical mechanisms of interactions between rare earth and tin atoms will enhance our understanding of rare earth functional materials from a microscopic perspective. Hence, the structure, electronic characteristics, stability, and aromaticity of endohedral cages MSn16- (M = Sc, Y, La) have been investigated using a combination of the hybrid PBE0 functional, stochastic kicking, and artificial bee colony global search technology. By comparing the simulated results with experimental photoelectron spectra, it is determined that the most stable structure of these clusters is the Frank-Kasper polyhedron. The doping of atoms has a minimal influence on density of states of the pure tin system, except for causing a widening of the energy gap. Various methods such as ab initio molecular dynamics simulations, the spherical jellium model, adaptive natural density partitioning, localized orbital locator, and electron density difference are employed to analyze the stability of these clusters. The aromaticity of the clusters is examined using iso-chemical shielding surfaces and the gauge-including magnetically induced currents. This study demonstrates that the stability and aromaticity of a tin cage can be systematically adjusted through doping.

Heteronuclear Trimetallic MFe2 and M2 Fe (M=V, Nb, and Ta) Clusters for Dinitrogen Activation.

Catalysts with heteronuclear metal active sites may have high performance in the nitrogen reduction reaction (NRR), and the in-depth understanding of the reaction mechanisms is crucial for the design of related catalysts. In this work, the dissociative adsorption of N2 on heteronuclear trimetallic MFe2 and M2 Fe (M=V, Nb, and Ta) clusters was studied with density functional theory calculations. For each cluster, two reaction paths were studied with N2 initially on M and Fe atoms, respectively. Mayer bond order analysis provides more information on the activation of N-N bonds. M2 Fe is generally more reactive than MFe2 . The coordination mode of N2 on three metal atoms can be end-on: end-on: side-on (EES) for both MFe2 and M2 Fe. In addition, a unique end-on: side-on: side-on (ESS) coordination mode was found for M2 Fe, which leads to a higher degree of N-N bond activation. Nb2 Fe has the highest reactivity towards N2 when both the transfer of N2 and the dissociation of N-N bonds are taken into account, while Ta-containing clusters have a superior ability to activate the N-N bond. These results indicate that it is possible to improve the performance of iron-based catalysts by doping with vanadium group metals.

Comparison of Nitrogen Activation on Trinuclear Niobium and Tungsten Sulfide Clusters Nb3 Sn and W3 Sn (n=0-3): A DFT Study.

The reaction of N2 with trinuclear niobium and tungsten sulfide clusters Nb3 Sn and W3 Sn (n=0-3) was systematically studied by density functional theory calculations with TPSS functional and Def2-TZVP basis sets. Dissociations of N-N bonds on these clusters are all thermodynamically allowed but with different reactivity in kinetics. The reactivity of Nb3 Sn is generally higher than that of W3 Sn . In the favorite reaction pathways, the adsorbed N2 changes the adsorption sites from one metal atom to the bridge site of two metal atoms, then on the hollow site of three metal atoms, and at that place, the N-N bond dissociates. As the number of ligand S atoms increases, the reactivity of Nb3 Sn decreases because of the hindering effect of S atoms, while W3 S and W3 S2 have the highest reactivity among four W3 Sn clusters. The Mayer bond order, bond length, vibrational frequency, and electronic charges of the adsorbed N2 are analyzed along the reaction pathways to show the activation process of the N-N bond in reactions. The charge transfer from the clusters to the N2 antibonding orbitals plays an essential role in N-N bond activation, which is more significant in Nb3 Sn than in W3 Sn , leading to the higher reactivity of Nb3 Sn . The reaction mechanisms found in this work may provide important theoretical guidance for the further rational design of related catalytic systems for nitrogen reduction reactions (NRR).

Comparison of Nitrogen Activation on Trinuclear Niobium and Tungsten Sulfide Clusters Nb3 Sn and W3 Sn (n=0-3): A DFT Study.

The front cover artwork is provided by Prof. Xun-Lei Ding's group at North China Electric Power University (NCEPU). The image shows the cleavage of the triple bond of a dinitrogen molecule on trinuclear metal clusters with sulfide ligands, which is the critical step in nitrogen reduction reactions (NRR). Read the full text of the Research Article at 10.1002/cphc.202200124.

Exploring the Effects of Ionic Defects on the Stability of CsPbI3 with a Deep Learning Potential.

Inorganic metal halide perovskites, such as CsPbI3 , have recently drawn extensive attention due to their excellent optical properties and high photoelectric efficiencies. However, the structural instability originating from inherent ionic defects leads to a sharp drop in the photoelectric efficiency, which significantly limits their applications in solar cells. The instability induced by ionic defects remains unresolved due to its complicated reaction process. Herein, to explore the effects of ionic defects on stability, we develop a deep learning potential for a CsPbI3 ternary system based upon density functional theory (DFT) calculated data for large-scale molecular dynamics (MD) simulations. By exploring 2.4 million configurations, of which 7,730 structures are used for the training set, the deep learning potential shows an accuracy approaching DFT-level. Furthermore, MD simulations with a 5,000-atom system and a one nanosecond timeframe are performed to explore the effects of bulk and surface defects on the stability of CsPbI3 . This deep learning potential based MD simulation provides solid evidence together with the derived radial distribution functions, simulated diffraction of X-rays, instability temperature, molecular trajectory, and coordination number for revealing the instability mechanism of CsPbI3 . Among bulk defects, Cs defects have the most significant influence on the stability of CsPbI3 with a defect tolerance concentration of 0.32 %, followed by Pb and I defects. With regards to surface defects, Cs defects have the largest impact on the stability of CsPbI3 when the defect concentration is less than 15 %, whereas Pb defects act play a dominant role for defect concentrations exceeding 20 %. Most importantly, this machine-learning-based MD simulation strategy provides a new avenue to explore the ionic defect effects on the stability of perovskite-like materials, laying a theoretical foundation for the design of stable perovskite materials.

Facile N≡N Bond Cleavage by Anionic Trimetallic Clusters V3-x Tax C4- (x=0-3): A DFT Study.

Activation of N2 on anionic trimetallic V3-x Tax C4- (x=0-3) clusters was theoretically studied employing density functional theory. For all studied clusters, initial adsorption of N2 (end-on) on one of the metal atoms (denoted as Site 1) is transferred to an of end-on: side-on: side-on coordination on three metal atoms, prior to N2 dissociation. The whole reaction is exothermic and has no global energy barriers, indicating that the dissociation of N2 is facile under mild conditions. The reaction process can be divided into two processes: N2 transfer (TRF) and N-N dissociation (DIS). For V-series clusters, which has a V atom on Site 1, the rate-determining step is DIS, while for Ta-series clusters with a Ta on Site 1, TRF may be the rate-determining step or has energy barriers similar to those of DIS. The overall energy barriers for heteronuclear V2 TaC4- and VTa2 C4- clusters are lower than those for homonuclear V3 C4- and Ta3 C4- , showing that the doping effect is beneficial for the activation and dissociation of N2 . In particular, V-Ta2 C4- has low energy barriers in both TRF and DIS, and it has the highest N2 adsorption energy and a high reaction heat release. Therefore, a trimetallic heteronuclear V-series cluster, V-Ta2 C4- , is suggested to have high reactivity to N2 activation, and may serve as a prototype for designing related catalysts at a molecular level.

Trimetallic clusters in the sumanene bowl for dinitrogen activation.

It is of great importance to find catalysts for the nitrogen reduction reaction (NRR) with high stability and reactivity. A series of M3 clusters (M = Ti, Zr, V, and Nb) supported on sumanene (C21H12) were designed as potential catalysts for the NRR by taking advantage of the high reactivity of trimetallic clusters and the unique geometric and electronic properties of sumanene, a bowl-like organic molecule. Detailed mechanisms of NN bond cleavage on C21H12-M3 were investigated by DFT calculations and compared with those on bare M3 clusters. M3 in the sumanene bowl is very stable with large binding energies, which prohibits the cohesion of M3 into M6. In the bowl, M3 has a (quasi-) equilateral triangle structure with lengthened M-M bonds, which is particularly beneficial to the N2 transfer process on Ti3 and V3 clusters. The N-N bond can be dissociated by both M3 and C21H12-M3 clusters without the overall energy barriers. A blurring effect is found in which some geometric and electronic properties of different metal types become similar when M3 is supported on the substrate. Our work demonstrates that sumanene is a suitable substrate to support M3 in the activation of N2 with enhanced stability and maintained a high level of reactivity compared to bare M3.

Small practical cluster models for perovskites based on the similarity criterion of central location environment and their applications.

Developing universal theoretical models for perovskites (often denoted as ABX3) can contribute to the rational design of novel perovskite photovoltaic materials. However, few models can be successfully applied to study the intrinsic electronic structure due to the poor accuracy and unaffordable computational cost. Herein, we report the innovative construction of small practical cluster models through the similarity criterion of the central location environment, which retains only the central A-site as the original cation while the others are substituted by Cs to keep the clusters electrically neutral. The central cation has a chemical environment similar to that of the bulk perovskite. The binding energy between A and the BX framework, geometric structures (B-X distances and B-X-B angles), and the electronic structures (the gap and the spatial distribution of HOMO and LUMO, electron distribution) of these clusters have been investigated and compared with the corresponding properties of bulk materials. The results suggest that the cluster model with twelve B-atoms suitably describes these properties. The geometric structures and gaps are closer to the bulk situations than the quasi-one-dimensional and quasi-two-dimensional cluster models with all-primitive cations, respectively. Other organic cations, such as NH3(CH2)nCH3 (n = 1, 2, and 3 for EA, PA, and BA, respectively), and (NH2)2CH (FA) can, therefore, mimic perovskite materials. Clusters with different sizes of A indicate that PA and BA will distort the quasi-cubic structures, which is consistent with the judgment of the tolerance factor of bulk materials. The reliable cluster model provides the research foundation for some basic issues of perovskites, such as vibrational spectroscopy and hydrogen bonding strength, to gain detailed insight into the interactions between A and the BX framework.

High throughput screening of promising lead-free inorganic halide double perovskites via first-principles calculations.

Perovskite solar cells (PSCs) have been intensively investigated and made great progress due to their high photoelectric conversion efficiency and low production cost. However, poor stability and the toxicity of Pb limit their commercial applications. It is particularly important to search for new non-toxic, high-stability perovskite materials. In this study, 760 Cs2B2+B'2+X6 (X = F, Cl, Br, I) inorganic halide double perovskites are screened based on high-throughput first-principles calculations to obtain an ideal perovskite material. The band gaps of this type of double perovskite are mainly determined by the elements X and B2+, decreasing monotonously with the increase in the atomic number of X (from F to I). We obtain 14 optimal and unreported materials with suitable band gaps as potential alternative materials for Pb-based photovoltaic absorbers in PSCs. This theoretical investigation can provide theoretical guidance for developing novel lead-free PSC materials.

Non-Dissociative Activation of Chemisorbed Dinitrogen on One or Two Vanadium Atoms Supported by a Mo6 S8 Cluster.

Adsorption of N2 on Mo6 S8 q _Vx clusters (x=0, 1, 2; q=0, ±1) were systematically studied by density functional theory calculations with dispersion corrections. It was found that the N2 can be chemisorbed and undergo non-dissociative activation on single or double metal atoms. The adsorption and activation are influenced by metal types (V or Mo), N2 coordination modes and charge states of the clusters. Particularly, anionic Mo6 S8 - _V2 clusters have remarkable ability to fix and activate N2 . In Mo6 S8 - _V2 , two V atoms prefer to adsorb on two adjacent S-Mo-S hollow sites, leading to the formation of a supported V…V unit. The N2 is bridged side-on coordinated with these two V atoms with high adsorption energy and significant charge transfer. The bond order, bond length and vibration frequency of the adsorbed N2 are close to those of a N-N single bond.

Non-stoichiometric molybdenum sulfide clusters and their reactions with the hydrogen molecule.

Structures of non-stoichiometric MoxSy clusters (x = 2-4; y = 2-10) were studied by density functional calculations with global optimization. Besides 1T phase like structures, a novel regular grid structure in which Mo atoms are well separated by S atoms was found, which might be used as a building-block to construct a new type of two-dimensional molybdenum sulfide monolayer. The hydrogen molecule prefers to be adsorbed onto Mo atoms rather than S atoms, and Mo atoms with less S coordination have a higher ability to adsorb H2. In addition, the reaction pathways for H2 dissociation were studied on two clusters with the highest H2 adsorption energy (Mo2S4 and Mo3S3). The vacant bridge site of Mo-Mo in S-deficient clusters, which corresponds to the sulfur vacancy in the bulk phase MoS2, is favored by H atom adsorption and plays an important role in the H atom transfer on MoxSy clusters. Our results provide a new aspect to understand the reason why S defect in MoS2 and MoS2 with an Mo-edge could enhance the catalytic performance in the hydrogen evolution reaction.

A new perspective for evaluating the photoelectric performance of organic-inorganic hybrid perovskites based on the DFT calculations of excited states.

The high efficiency of organic-inorganic hybrid perovskites has attracted the attention of many scholars all over the world, the chemical formula of which is ABX3, where A is an organic cation, B is a metal cation, and X is a halogen ion. In addition, the micro-mechanism behind the efficient photoelectric conversion needs more in-depth exploration. Therefore, in this work, based on time-dependent density functional theory (TD-DFT), the electron transfer mechanism from the ground state to the first singlet excited state was systematically investigated by electron and hole analysis and an inter-fragment charge transfer amount method (IFCT). In this work, we optimized and analyzed 99 different perovskite cluster configurations, where A sites are CH3NH3+ (MA+), NH2CHNH2+ (FA+), CH3CH2NH3+ (EA+), NH2CHOH+ (JA+), NH3OH+ (BA+), N(CH3)4+ (DA+), CH3CH2CH2NH3+ (KB+), CH3CH2CH2CH2NH3+ (KC+), C3N2H5+ (RA+), CH(CH3)2+ (TA+), and CH3NH(CH3)2+ (UA+), B sites are Ge2+, Sn2+ and Pb2+, and X sites are Cl-, Br- and I-. According to the analysis of a series of perovskite clusters of the hole-electron distribution, the distribution is mainly concentrated on BX, and electrons and holes are respectively distributed on B and X sites. The exciton binding energy decreases when the metal element changes from Ge to Pb and the halogen element changes from Cl to I. A radar chart including the exciton binding energy, excited energy, amount of net charge transfer, electron and hole overlap index, distance between the centroid of holes and electrons, and the hole and electron separation index was proposed to intuitively describe the electron transmission characteristics of perovskites. Based on that, a comprehensive score index was innovatively proposed to evaluate the photoelectric property of perovskites, providing foundational guidance for the design of high-efficiency organic-inorganic hybrid perovskites.

Methane activation by heteronuclear diatomic AuRh+ cation: comparison with homonuclear Au2+ and Rh2.

The ability to activate methane differs appreciably for different transition metals, and it is attractive to find the most suitable metal for the direct conversion of methane to value-added chemicals. Herein, we performed a comparative study on the reactions of CH4 with Au2+, AuRh+ and Rh2+ cations by mass-spectrometry based experiments and DFT-based theoretical analysis. Different reactivity has been found for these cations: Au2+ has the lowest reactivity, and it can activate methane but only produce H-Au2-CH3+ without H2 release; Rh2+ has the highest reactivity, and it can produce both carbene-type Rh2-CH2+ and carbyne-type H-Rh2-CH+ with H2 release; AuRh+ also has high reactivity to produce only AuRh-CH2+ with H2, avoiding the excessive dehydrogenation of CH4. Our theoretical results demonstrate that Rh is responsible for the high reactivity, while Au leads to selectivity, which may be caused by the unique intrinsic bonding properties of the metals.

The effect of coordination environment on the kinetic and thermodynamic stability of single-atom iron catalysts.

The stability of a single-atom catalyst is directly related to its preparation and applications, especially for high-loading single-atom catalysts. Here, the effect of a coordination environment induced by nitrogen (N) atoms coordinated with iron on the kinetic and thermodynamic stabilities of single-atom iron catalysts supported with carbon-based substrates (FeSA/CS) was investigated by density functional theory (DFT) calculations. Five FeSA/CS with different numbers of N atoms were modelled. The kinetic stability was evaluated by analyzing the migration paths of iron atoms and energy barriers. The thermodynamic stability was studied by calculating the adsorption and formation energies. Our results indicated that the coordination environment induced by N can promote the kinetic and thermodynamic stability of FeSA/CS. N atoms on the substrate promote the kinetic stability by raising the energy barrier for iron migration and not only increase the thermodynamic stability, but also contribute to catalyst synthesis. Doping N on the substrate enhances charge transfer between the iron atoms and substrates simultaneously improving the kinetic and thermodynamic stabilities. This theoretical research provides guidance for synthesizing stable and high loading single-atom catalysts by tuning the coordination environment of single-atom elements.

Side-on-End-on Coordination of Dinitrogen on a Polynuclear Vanadium Nitride Cluster Anion [V5 N5 ].

The side-on-end-on coordination of N2 can be very important to activate and functionalize this very stable molecule. However, such coordination has rarely been reported. This study reports a gas-phase species (a polynuclear vanadium nitride cluster anion [V5 N5 ]- ) that can capture N2 efficiently (12 %), and the quantum chemistry modelling suggests an unusual side-on-end-on coordination. The cluster anions were generated by laser ablation and the reaction with N2 has been characterized by mass spectrometry, photoelectron imaging spectroscopy, and density functional theory calculations. The back-donation interactions between the localized d-d bonding orbitals on the low-coordinated dual metal (V) sites and the antibonding π* orbitals of N2 are the driving forces to adsorb N2 with a high binding energy (about 2.0 eV).

Activity of Atomically Precise Titania Nanoparticles in CO Oxidation.

Understanding the property evolution of atomically precise nanoparticles atom by atom along the size continuum is critical for selecting potential candidates to assemble nanomaterials with desired functionality, but it is very challenging experimentally especially for systems having mixtures of elements such as metal oxides. In this work, the capability to oxidize carbon monoxide has been measured experimentally for titania nanocluster anions of (TiO2 )n Om - (-3≤m≤3) across a broad size range in the gas phase. Stoichiometric (TiO2 )n O- exhibits superior oxidative activity over other clusters of (TiO2 )n Om - (m≠1) even when the cluster dimensions are scaled up to n=60, indicating that each atom still influences the chemical behavior of titania nanoparticles composed of ≈180 atoms. The fascinating result not only identifies a promising building block of Tin O2n+1 for devising new nanoscale titania materials with desirable oxidative activity, but also provides compelling molecular-level evidence for the Mars-van Krevelen mechanism of CO oxidation over titania supports.

Mechanistic Variants in Methane Activation Mediated by Gold(I) Supported on Silicon Oxide Clusters.

Cationic gold has been frequently identified as a suitable reactive species for activating methane in condensed-phase studies. However, it is far from clear how the coordination site manipulates the activity of such species. Herein, by anchoring AuI on silicon oxide cluster supports of variable sizes, the site-specific methane activation by AuI -Ox has been clarified by mass spectrometry in conjunction with quantum chemistry calculations. An unexpected mechanistic switch in C-H activation was identified for the cluster anions Au(SiO2 )n O- (n=1-3) that selectively activate one of the four C-H bonds of methane with different reaction efficiencies: a low efficiency was observed for the two-fold-coordinated gold ion (AuI, 2f ), which was anchored on an AuSiO3 - or AuSi2 O5 - cluster, through an oxidative addition mechanism (a homolytic process), and high efficiency was observed for the one-fold-coordinated gold ion (AuI, 1f ), which was supported on an AuSi3 O7 - cluster, through Lewis acid/base pairs mechanism (AuI, 1f ⋅⋅⋅O2- , a heterolytic process). Fine regulation of the 5d orbital level of the Au atom by the oxygen ligands accounted for the mechanistic difference between AuI, 2f and AuI, 1f species. The mechanistic understanding of the reactivity of AuI -Ox at a strictly molecular level can be used to clarify the dissimilar activity of gold anchored on different oxide supports.