Crystal Orbital Hamilton Population Research Articles

Rational design single-atom modified Zr2CO2 MXene as a promising catalyst for nitrogen reduction reaction

Renewable production of ammonia via the electrocatalytic nitrogen reduction reaction (NRR) is highly desirable. However, rational design of electrocatalysts with high promising activity under ambient conditions is a challenging subject. In this work, the stability, NRR activity and selectivity of single transition metal (TM, TM = Ti, V, Fe, Ni, Nb, Mo, Ru, and W), nonmetal B and N, and TM and N3 co-modification Zr2CO2 (named TM/Zr2CO2, B(N)/Zr2CO2, and TMN3/Zr2CO2, respectively) are investigated by density functional theory (DFT) calculations. The results revealed that single atom (both transition metal and nonmetal atoms) modification can greatly enhance the NRR catalytic activity and selectivity of original Zr2CO2, and different nonmetal doping concentration can deliver different NRR activity by adjust the interaction strength between doping atom and Zr atom. Among the studied materials, W/Zr2CO2 possesses the highest NRR performance via the distal pathway with the NRR overpotential (ηNRR) of 0.14 V, B/Zr2CO2 possesses the highest NRR performance (ηNRR = 0.26 V) and selectivity via the enzymatic pathway, and for the co-doped systems, RuN3/Zr2CO2 delivers the highest NRR activity with the corresponding ηNRR of 0.54 V. The crystal orbital Hamilton population (COHP), density of states, charge transfers, and work function (Φ) results indicated that the TM and nonmetal atoms can adjust the electronic properties of the Zr2CO2 surface to break the inertness of N2 and form the key intermediate *NNH or *N-*NH, and therefore enhance their NRR activity. The ab initio molecular dynamics (AIMD) simulation results suggested that the structures of the modified Zr2CO2 are dynamically stable at reaction temperature. These results indicated that the proposed surface modifications by W and nonmetal B are the effective approaches for achieving promising NRR electrocatalysts for N2 fixation.

Unveil the potential in hydrogen activation and spillover towards NiMoS by Ni3S2 - A theoretical study

Using density functional theory calculation (DFT) as well as ab initio molecular dynamics (AIMD) simulation, the capabilities of hydrogen dissociation and hydrogen spillover over Ni3S2 (111) surface are examined. The steady state, energy change, transition state of hydrogen dissociation and the spillover pathway, stability of S-H bond during hydrogen spillover are all calculated. The results show that several S-top site and S-Ni-bridge site are available for dissociation, among them, “S1-top”, “S3-top” and “S1-Ni1” sites could be recognized as distinct sites, and one hydrogen molecule could be efficiently dissociated by one S3-top site and the adjacent S1-Ni1 site. The crystal orbital Hamilton population analysis and AIMD simulation for S-H bonds both confirm the tendency towards breaking, then the spillover coordinate calculation gives a self-consistent pathway among three district sites. In short, the Ni3S2 surface shows excellent performance in the aspect of hydrogen dissociation and hydrogen spillover, which displays tremendous potential for hydrogen spillover in NiMoS catalytic system. We hope these findings could shed light on the theory of “remote control” model.

Facile dehydrogenation of MgH2 enabled by γ-graphyne based single-atom catalyst

Solid-state hydrogen storage is a promising roadmap for the safe and efficient utilization of hydrogen energy due to its moderate operating environment and high hydrogen storage density. However, as a representative solid-state hydrogen storage material, magnesium hydride (MgH2) is significantly limited in the commercial application due to its sluggish kinetics in the dehydrogenation process. Single-atom catalysts are a promising solution to this dilemma. However, the promising graphene-based single-atom catalysts are not yet sufficient to meet the dehydrogenation needs in engineering. To further address this dilemma, we designed a novel γ-graphyne based single-atom catalysts including eight 3d transition metals for promoting the dehydrogenation process of MgH2. Through using spin-polarized density functional theory calculations, we found that the energy barrier for MgH2 dehydrogenation has been significantly reduced even to 0.70 eV, which is far lower than the current graphene-based single-atom catalyst. In detail, the migration trajectory of hydrogen atom in the dehydrogenation process has been observed and confirmed using the ab initio molecular dynamics simulations. To investigate the intrinsic origin for its high catalytic activity of single-atom catalyst, we analyze the HMg bond activation mechanism through the electron localization function, charge density difference and crystal orbital Hamiltonian population. Finally, we found the relationship between energy barrier with electronic structure of single-atom catalyst, such as electrostatic potential and system electronegativity. This work can not only provide new ideas for the optimize of dehydrogenation catalyst, but also lay a theoretical foundation for the design of novel energy storage material.

Multi-doped borophene catalysts with engineered defects for CO2 reduction: A DFT study

Carbon dioxide reduction reaction (CO2RR) to convert carbon dioxide (CO2) into value-added products via the electrochemical method is a conducive way to tackle the hazard of high CO2 emissions. The present DFT study reports a novel dual chromium-anchored tri-vacancy borophene (Cr2/TV-β12) electrocatalyst, which showed high selectivity and stability for CO2RR. A tri-vacancy defect was introduced in β12 borophene to create an 11-membered ring borophene sheet (TV-β12), and 28 different electrocatalysts were explored via doping various transition metals (Co, Cr, Cu, Fe, Mn, Ni, Zn). Density functional theory simulation results revealed that the Cr2/TV-β12 electrocatalyst adsorbs and activates CO2 efficiently, which was validated by the partial density of states, charge density difference, Bader charge, and crystal orbital Hamilton population analyses. The limiting potential for CO2RR was evaluated to be −0.45 V, against hydrogen evolution reaction (HER) (0.57 V), with the main product being formaldehyde. The catalyst showed selectivity towards CO2 reduction and suppressed HER. The usual problem of carbon monoxide poisoning encountered in CO2 reduction was also assessed and a high resistance against the same was established. At the outset, the research revealed that dual atom-doped tri-vacancy β12 borophene has tremendous potential to be utilized as an efficient catalyst for CO2RR.

Noble Metal Single-Atom Coordinated to Nitrogen, Oxygen, and Carbon as Electrocatalysts for Oxygen Evolution

Tuning the coordination environment centering metal atoms has been regarded as a promising strategy to promote the activities of noble metal single-atom catalysts (SACs). In the present work, first-principle calculations are employed to explore the oxygen evolution reaction (OER) performance of Ir and Ru SACs with chemical coordination being nitrogen (M-N4-C), oxygen (M-O4-C), and carbon (M-C4-C) in graphene, respectively. A “three-step” strategy was implemented by progressively investigating these metrics (stability, catalytic activity, structure–activity relationship). A volcano plot of reactivity is established by using the adsorption-free energy of O* (∆GO*) as a theoretical descriptor. The intrinsic OER activity is IrN4-C > IrO4-C > RuO4-C > RuN4-C > IrC4-C > RuC4-C. The in-depth tuning mechanism of ∆GO* can be indicated and interpreted by the d-band centers of the active sites and the crystal orbital Hamilton population analysis of metal-oxygen bonds, respectively.

Heterogeneous C[sbnd]C bonding induced anomalous phonon transport in superhard BC[formula omitted]N polymorphs

In this work, the effect of chemical bonding on thermal transport in superhard BC2N polymorphs has been comparatively evaluated by the first-principles calculations. Compared with the high-symmetry phase, a cliff-like drop of lattice thermal conductivity occurs in the C121 phase with the monoclinic lattice. The findings can be attributed to the heterogeneous CC bonding induced suppression of thermal transport via the transverse phonon modes. The crystal orbital Hamilton population analysis shows that there exists an extremely weak CC bond in the C121 phase of BC2N. Despite the presence of stronger BN and CN bonds in the C121 phase, the weak CC bond predominantly results in softened acoustic phonon branches, strong lattice anharmonicity, and low elastic moduli. These factors enhance the phonon–phonon scattering and are thereby responsible for the suppression of phonon thermal conductivity. This study gives fundamental insights into structure and chemical bonding effects on phonon transport and provides guidance toward designing superhard materials with tunable thermal conductivity under extreme conditions.

Exploring the ultra-low lattice thermal conductivity of a two-dimensional compound Tl2Se3

Two-dimensional (2D) materials have attracted extensive attention in the field of thermoelectric (TE) materials, where heat transport properties play an important role in determining the performance of TE devices. In this paper, we investigate the thermal transport properties of novel 2D Tl2Se3 by means of first-principles approach combined with the Boltzmann transport equation (BTE). The small phonon sound group speed and strong anharmonicity are responsible for an ultra-low kl of 0.28 W/mK of 2D Tl2Se3 at room temperature. Meanwhile, the lattice thermal conductivity gradually decreases with the increase of temperature, indicating its potential value at high-temperature. The anti-bonding orbital filling between the Se-4p and Tl-6p states leads to the weak chemical bonds using the crystal orbital Hamiltonian population (COHP) analysis, which results in low phonon group velocities. Also, due to the strong acoustic-optical coupling in 2D Tl2Se3, the scattering processes of different acoustic modes is further studied to analyze how kl is suppressed. These findings demonstrate that 2D Tl2Se3 has potential applications in TE devices, which will motivate Tl2Se3 based experimental investigations.

Role of –O functional groups at the Ti3C2O2(MXene)/Al interface in enhancing the mechanical properties of aluminum matrix composites: A first-principles study

MXenes gradually become an ideal reinforcement for aluminum matrix composites (AlMCs) due to their excellent mechanical properties and the characteristics of surface groups. In this work, the structural, adhesive, mechanical and electronic properties of Ti3C2(O2)/Al composites are systematically investigated by first-principles calculations based on density functional theory (DFT), revealing the role of –O functional groups at the interface. The first-principles tensile simulation showed that the tensile strength of the composites increased from 6.93 GPa (Ti3C2/Al) to 8.49 GPa (Ti3C2O2/Al), indicating that the –O functional group was beneficial to enhance the tensile properties of the composites. The results of plane-averaged charge density difference and Bader charge quantitatively suggest that the Ti3C2O2/Al(111) system has greater charge transfer than Ti3C2/Al(111) system. In particular, the Ti3C2O2/Al interface has atomic orbital hybridization, forming highly localized Al–O and O–Ti bonds, which constitute an “Al–O–Ti” interlocking structure at the interface. Crystal orbital Hamilton population (COHP) indicate that the bonding strength at the Ti3C2O2/Al interface is higher than that at the Ti3C2/Al interface. Therefore, the “Al–O–Ti” interlocking structure enhances the load transfer capability of AlMCs and thus improves their mechanical properties. This work provides theoretical support for further understanding the strengthening mechanism of Mxene/Al composites.

S-Block Potassium Single-atom Electrocatalyst with K-N4 Configuration Derived from K+ /Polydopamine for Efficient Oxygen Reduction.

Currently, single-atom catalysts (SACs) research mainly focuses on transition metal atoms as active centers. Due to their delocalized s/p-bands, the s-block main group metal elements are typically regarded as catalytically inert. Herein, an s-block potassium SAC (K-N-C) with K-N4 configuration is reported for the first time, which exhibits excellent oxygen reduction reaction (ORR) activity and stability under alkaline conditions. Specifically, the half-wave potential (E1/2 ) is up to 0.908 V, and negligible changes in E1/2 are observed after 10,000 cycles. In addition, the K-N-C offers an exceptional power density of 158.1 mW cm-2 and remarkable durability up to 420 h in a Zn-air battery. Density functional theory (DFT) simulations show that K-N-C has bifunctional active K and C sites, can optimize the free energy of ORR reaction intermediates, and adjust the rate-determining steps. The crystal orbital Hamilton population (COHP) results showed that the s orbitals of K played a major role in the adsorption of intermediates, which was different from the d orbitals in transition metals. This work significantly guides the rational design and catalytic mechanism research of s-block SACs with high ORR activity.

S‐Block Potassium Single‐atom Electrocatalyst with K−N4 Configuration Derived from K+/Polydopamine for Efficient Oxygen Reduction

AbstractCurrently, single‐atom catalysts (SACs) research mainly focuses on transition metal atoms as active centers. Due to their delocalized s/p‐bands, the s‐block main group metal elements are typically regarded as catalytically inert. Herein, an s‐block potassium SAC (K−N−C) with K‐N4 configuration is reported for the first time, which exhibits excellent oxygen reduction reaction (ORR) activity and stability under alkaline conditions. Specifically, the half‐wave potential (E1/2) is up to 0.908 V, and negligible changes in E1/2 are observed after 10,000 cycles. In addition, the K−N−C offers an exceptional power density of 158.1 mW cm−2 and remarkable durability up to 420 h in a Zn‐air battery. Density functional theory (DFT) simulations show that K−N−C has bifunctional active K and C sites, can optimize the free energy of ORR reaction intermediates, and adjust the rate‐determining steps. The crystal orbital Hamilton population (COHP) results showed that the s orbitals of K played a major role in the adsorption of intermediates, which was different from the d orbitals in transition metals. This work significantly guides the rational design and catalytic mechanism research of s‐block SACs with high ORR activity.

Superelastic-like nonlinear deformation hidden in ferroelectric ceramics

The mechanical response of ferroelectric (piezoelectric) ceramics under high stress conditions has a crucial role from the perspective of engineering applications such as advanced actuator systems. In this study, we perform first-principles calculations to clarify the deformation behavior and (ideal) tensile strength for typical ferroelectric ceramics of PbTiO3 (PTO) under high mechanical loading. We find the superelastic-like nonlinear deformation behavior in ferroelectric PTO. In addition, it has several inflection points and shows a large critical strain compared to the paraelectric phase. We conclude that the unique nonlinear deformation in PTO originates from attributable to the displacement of oxygen atoms due to the ferroelectric phase transition based on analyzing the interatomic distances of each atom and an integrated crystal orbital Hamiltonian population with respect to strain. Furthermore, we also calculate the piezoelectric coefficient for PTO and reveal that it shows the singular peak at inflection points of the stress–strain curve. Unveiling and engineering the hidden superelastic-like deformation in the ferroelectric phase may open promising paradigms for functional piezoelectric devices.

The search for optimum host-guest interactions: Atomic hydrogen storage properties of the novel ternary ordered intermetallic compound Cu3ZnSb: A DFT study

Ternary Cu3ZnSb adopts the tetrahedral space group P4/nmm (129), with 10 atoms in the unit cell, distributed over four crystallographic positions in a perfectly ordered manner. It possesses two perfect tetrahedral interstitial positions, namely Cu3Sb and Cu2Zn2. The possible hydrogen storage properties in these two possible sites are explored by the aid of first-principles density functional theory calculations. The Cu-richer Cu3Sb site is energetically more favourable position for hydrogen atom, over the other one. The maximum possible H-uptake capacity would be within the range of ∼4 H per formula unit. The electronic structure modification, host-guest interactions, and electronic redistribution after hydrogen incorporation are explored from fundamental perspectives analyzing the density of states, crystal orbital Hamilton population, crystal orbital bond index, and Mulliken population calculations.

Toggling Stereochemical Activity through Interstitial Positioning of Cations between 2D V2O5 Double Layers.

The 5/6s2 lone-pair electrons of p-block cations in their lower oxidation states are a versatile electronic and geometric structure motif that can underpin lattice anharmonicity and often engender electronic and structural instabilities that underpin the function of active elements in nonlinear optics, thermochromics, thermoelectrics, neuromorphic computing, and photocatalysis. In contrast to periodic solids where lone-pair-bearing cations are part of the structural framework, installing lone-pair-bearing cations in the interstitial sites of intercalation hosts provides a means of a systematically modulating electronic structure through the choice of the group and the period of the inserted cation while preserving the overall framework connectivity. The extent of stereochemical activity and the energy positioning of lone-pair-derived mid-gap states depend on the cation identity, stoichiometry, and strength of anion hybridization. V2O5 polymorphs are versatile insertion hosts that can accommodate a broad range of s-, p-, and d-block cations. However, the insertion of lone-pair-bearing cations remains largely underexplored. In this article, we examine the implications of varying the 6s2 cations situated in interlayer sites between condensed [V4O10]n double layers. Systematic modulations of lattice distortions, electronic structure, and magnetic ordering are observed with increasing strength of stereochemical activity from group 12 to group 14 cations. We compare and contrast p-block-layered MxV2O5 (M = Hg, Tl, and Pb) compounds and map the significance of local off-centering arising from the stereochemical activity of lone-pair cations to the emergence of filled antibonding lone-pair 6s2-O 2p-hybridized mid-gap states mediated by second-order Jahn-Teller distortions. Crystallographic studies of cation coordination environments and the resulting modulation of V-V interactions have been used in conjunction with variable-energy hard X-ray photoelectron spectroscopy measurements, first-principles electronic structure calculations, and crystal orbital Hamilton population analyses to decipher the origins of stereochemical activity. Magnetic susceptibility measurements reveal antiferromagnetic signatures for all the three compounds. However, the differences in V-V interactions significantly affect the energy balance of the superexchange interactions, resulting in an ordering temperature of 160 and 260 K for Hg0.5V2O5 and δ-Tl0.5V2O5, respectively, as compared to 7 K for δ-Pb0.5V2O5. In δ-Pb0.5V2O5, the strong stereochemical activity of electron lone pairs and the resulting electrostatic repulsions enforce superlattice ordering, which strongly modifies the electronic localization patterns along the [V4O10] slabs, resulting in disrupted magnetic ordering and an anomalously low ordering temperature. The results demonstrate a versatile strategy for toggling the stereochemical activity of electron lone pairs to modify the electronic structure near the Fermi level and to mediate superexchange interactions.

High-pressure structure prediction and physical properties of MnN2: First-principles calculations

Manganese nitrides have attracted considerable research interest since their rich physical properties and important application prospects. By employing an evolutionary algorithm approach and first-principles calculations, the stable crystal structures of MnN2 in the pressure range of 0–200 GPa are systematically explored. Two novel high-pressure MnN2 phases, Pm and Cmc21, are predicted. The Pm phase is the most stable structure within the pressure range of 153.5–155.9 GPa, and it transforms into Cmc21 configuration at 155.9 GPa. By calculating the phonon spectra and molecular dynamics simulations, the dynamical stability and thermodynamic stability are examined. To uncover the potential applications of them, we investigate their mechanical properties and magnetism. Pm-MnN2, as a metal system, exhibits outstanding bulk modulus (296.1 GPa) and impressively high Vickers hardness (up to 30.5 GPa). Furthermore, the electronic mechanism underlying the excellent hardness of Pm-MnN2 is discussed by analyzing the crystal orbital Hamilton populations. Besides, Cmc21-MnN2 exhibits ferromagnetic configurations.

Computational Search for a Descriptor of Electrocatalysis in Transition Metal-Oxides

Currently, the most effective electrocatalysts for oxygen reduction (ORR) and oxygen evolution reactions (OER) are comprised of noble metal oxides, which bring issues of high cost and scarcity. Discovering earth-abundant alternatives is challenging due to the costly and time-consuming experiments. High-throughput atomistic simulation of catalysts can be an efficient route for enabling the better design and discovery of new electrocatalysts. The efficient use of this approach relies on an activity descriptor that can capture the qualitative and quantitative catalytic trends. In the past, multiple descriptors based on electronic properties have been proposed either reaction-specific or system specific. Therefore, we need a descriptor, which can capture the bonding strength accurately for any sort of reaction or system.In this work, we study the trends of O*/OH* adsorption energies for a wide range of pure metal oxide polymorphs[1] namely rocksalt (MO), corundum (M2O3), rutile (MO2), pentoxide (M2O5) and MO3 in all conceivable oxidation states i.e., +2, +3, +4, +5 and +6 respectively. The main drivers of the adsorption energy are the extent of filling of the bonding and anti-bonding orbitals, along with the spin-dependent coupling strength between the metal-d and oxygen-2p atomic orbitals. This property can be easily captured with the help of crystal orbital Hamiltonian population (COHP). We have observed a strong correlation between the integrated COHP I(COHP) of the bulk system and the adsorption energy, which indicates expensive surface-level electronic calculations can be replaced by bulk-level computations. However, this correlation does not hold on two classes of systems: (i) d0 systems and (ii) systems with significant surface distortion during the reaction. We have considered a different approach to address these systems, where instead of a single bond ICOHP, we account for the summation of the ICOHP around the active site.In search of promising catalysts, we also report tetrahedral systems for 3d, 4d and 5d transition metal oxides, i.e., zinc blende, wurtzite and square planar systems. This will broaden the horizon of possible catalysts along the octahedral systems. We correlate the bulk ICOHP with the surface reactivity of these systems, which highlights the applicability of ICOHP as a universal descriptor across a series of metal oxide systems and guide the design of novel catalysts.This research was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Catalysis Science Program to the SUNCAT Center for Interface Science and Catalysis.[1] "Unravelling Electronic Trends in O* and OH* Surface Adsorption in the MO2 Transition-Meta Oxide Series"; Benjamin M. Comer, Jiang Li, Frank Abild-Pedersen, Michal Bajdich, Kirsten Winther, 2022, (ACS J. Phys. Chem C.,)[2] “Predicting O* and OH* Surface Adsorption on Transition Metal Oxides from Bulk Structure”; Benjamin M. Comer, Neha Bothra, Jaclyn Lunger, Frank Abild-Pedersen, Michal Bajdich, Kirsten Winther, Manuscript under preparation.

Enhancement of electrocatalytic performance of Janus In2SSe monolayer for oxygen evolution reaction by the introduction of N

Non-metallic atom doping as efficient oxygen evolution reaction (OER) electrocatalysts has attracted much interest. In this work, the feasibility of N doped Janus In2SSe monolayers as an OER electrocatalyst is systematically investigated using first-principles calculations. The results suggest that the N substitution with high spin states for the S/Se atom in the Janus In2SSe monolayer can effectively enhance the electrocatalytic reactivity of adsorbed intermediates. The NS-In2SSe monolayer exhibit outstanding OER catalytic performance with small overpotential of 0.687 V. Moreover, the strong atomic interactions between the N dopant and intermediates can be contributed to the hybridization between the O- and N-p orbitals. Through the analysis of crystal orbital Hamilton population (COHP), the adsorption strength of OH species on the NS-In2SSe monolayer is stronger than that on the NSe-InSe monolayer, leading that the NS-In2SSe monolayer possesses a higher OER electrocatalytic activity. The fourth electron reaction step becomes exothermic when the real solution environment is considered, meaning that the desorption of O2 becomes easier under aqueous solution conditions. This work demonstrates the possibility of N doped Janus In2SSe monolayer as electrocatalyst and also offers new insights into designing SACs constructed by non-metal atoms.

Interaction of Si Atom with the (001) Surface of TiN, AlN and TaN Compounds

Nowadays, the application of multicomponent coatings with multiphase nanocrystalline structure is the most promising direction in the search for wear-resistant protective coatings with a full set of necessary operational properties. Nanocrystalline multicomponent coatings based on the Ti-Al-Ta-Si-N system have a high hardness combined with thermal stability and oxidation resistance. Silicon atoms are weakly soluble in the TiN, Ti1−xAlxN, and TaN crystalline phases of the Ti-Al-Ta-Si-N system and interact preferentially with N atoms, forming the amorphous Si3N4 phase. In this context, it is important to first study the peculiarities of the interaction of Si atoms with the simplest structural units of the Ti-Al-Ta-Si-N system, such as TiN, AlN, and TaN compounds with the NaCl structure. This work is devoted to the study of the interaction of a Si atom with the (001) surface of AlN, TiN, and TaN compounds with the NaCl structure using ab initio calculations. This provides information for a deep understanding of the initial stages of the formation of different crystallites of the considered composite. It was established that the adsorption of silicon on the (001) surface of AlN, TiN, and TaN significantly increases the relaxation of the surface layers and leads to an increase in the corrugation observed on the clean surfaces. The largest corrugation is observed on the surface of the TaN compound. The most energetically favorable adsorption positions of Si atoms were found to be the position of Si above the N atom on the TiN and TaN surfaces and the quadruple coordinated position on the AlN surface. The valence electron density distribution and the crystal orbital Hamiltonian population were studied to identify the type of Si atom bonding with the (001) surface of AlN, TiN, and TaN compounds. It was found that silicon forms predominantly covalent bonds with the nearest metal and nitrogen atoms, except for the quadruple coordinated position on the surface of TiN and TaN, where there is a high degree of ionic bonding of silicon with surface atoms.

Transition metal embedded in two‐dimensional bi‐BN as high activity single atom electrocatalyst for oxygen reduction reactions

AbstractSearching for stable, highly effective and cost‐efficient catalysts for the oxygen reduction reaction (ORR) is important to addressing the energy crisis and environmental issues. A single atom embedded in two‐dimensional boron nitride materials is a viable candidate for the ORR to replace Pt‐based catalysts. Herein, by making use of density functional theory (DFT) simulations, we systematically study a novel two‐dimensional boron nitride materials (bi‐BN) embedded by 23 kinds of transition metal (TM) atoms ranging from Ti to Au as high activity single atom electrocatalyst for the ORR. According to the initial screening criteria (−4.92 eV < ΔGO* < 0 eV), 13 kinds of TM‐bi‐BN (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Ru, Rh, Pd, Ag, Pt, Au) meet the criteria and are selected to study their ORR performance in this work. Our calculations indicate that Au‐bi‐BN has the most superior ORR performance with the lowest overpotential (0.43 V), which was lower than that of Pt (0.45 V) as ORR catalyst. The origin of the catalytic activity of the ORR is studied by the linear correlation between these oxygen‐containing intermediates, the volcanic curve, the d‐band center and the crystal orbital Hamilton populations. Ab Initio Molecular Dynamics simulation suggests that Au‐bi‐BN is thermodynamically stable at 300 K. Our results not only offer valuable insights into the utility of boron‐nitride materials as catalysts for ORR, but also facilitate the development of novel catalysts for ORR through improved comprehension of the material properties.

Revisiting the frontier of the Zintl–Klemm approach for the examples of three Mo2FeB2‐type intermetallics by means of quantumchemical techniques

AbstractThe Zintl–Klemm idea is a remarkable formalism that can guide us through the crystal structure–electronic structure relationships of solids showing a particular correlation between charge transfers, (8–N) rule and the corresponding structural fragments. Accordingly, this approach has been applied to interpret the relationships between the crystal and electronic structures for numerous intermetallics; yet, are all of these applications of the Zintl–Klemm idea indeed helpful? To answer this question, quantumchemical means were used to explore the electronic structures of three prototypical intermetallics, i.e. LiY2Si2, Sc2Si2Al, and Y2Pd2In. These compounds crystallize with the Mo2FeB2 type of structure whose structure model may be derived from that of the widely encountered U3Si2‐type. The explorations of the electronic structures included examinations of the Mulliken charges, the projected crystal orbital Hamilton populations (pCOHP), the recently introduced crystal orbital bond indices (COBI) and the respective integrated pCOHP as well as COBI values (IpCOHP and ICOBI). The outcome of these investigations indicates that widely diverse types of bonding are evident for the inspected intermetallics so that the predictive power of the Zintl–Klemm idea is limited.

Enhancing the hydrogen evolution reaction by group IIIA-VIA elements doping in SnS2 basal plane

Tin disulfide (SnS2) − a post-transition metal dichalcogenide − is a promising non-precious metal catalyst for the hydrogen evolution reaction (HER). However, the practical application of SnS2 for electrocatalytic HER is hampered by its poor electrical conductivity and catalytic performance at the basal plane. Herein, by doping 14 main-group elements on the S-defective SnS2 monolayer, the most promising SnS2-based catalysts for the HER are screened through density functional theory (DFT) calculations. Interestingly, the Sb/Ga atoms anchored on the S-defective SnS2 basal plane are judged to possess excellent HER performance, yielding almost nearly zero Δ GH (Δ GH = −0.07 and −0.178 eV, respectively), which is even better than that of platinum (Pt) catalysts. Based on the density of states (DOS), the improved catalytic performance is attributed to the introduction of Sb/Ga atoms, which enhance the conductivity of the pristine SnS2 surface and provide unoccupied states near the Fermi energy level, effectively reducing the energy barrier for charge transfer between the H radical and the M@ SnS2 surface. It has also been confirmed by an investigation of the electronic properties resulting in the HER activity improvement, including the crystal orbital Hamiltonian population (COHP), the Bader charge, and the charge difference density (CDD). This work reveals a promising strategy to activate the SnS2 basal plane for HER.