Crystal Orbital Hamilton Population Research Articles

Computational insight into transition metal atoms anchored on B2C3P as single‐atom electrocatalysts for nitrogen reduction reaction

NH3 is not only an important chemical raw material, but also a high energy storage chemical with zero carbon. Electrocatalytic nitrogen reduction reaction (NRR), which can be driven by clean electric energy under ambient conditions, have become a promising technology for NH3 synthesis due to their environmentally friendly properties. Due to the limitations of low yield and high overpotential, efficient catalysts are urgently needed to solve this problem. In this study, based on density functional theory method and high throughput screening strategy, the NRR was investigated on transition metal single atom anchored to two‐dimensional B2C3P surface (TM@B2C3P) as single‐atom catalysts (SACs). The results showed that V@B2C3P and Ti@B2C3P have good catalytic properties, and the limiting potentials via the enzymatic pathway were −0.10 and −0.24 V, respectively. Furthermore, the charge density difference and crystal orbital Hamilton population calculations demonstrated that the high catalytic activity can be attributed to the obvious charge transfer between TM@B2C3P and the adsorption intermediates. It is hoped that this work can play a certain role in exploring the application of SACs in NRR.

Metal-enhanced carbon-nitrogen material for selective detection of hazardous gases: Insights from interface electronic states

In this study, utilizing density functional theory, the C3N1 monolayer modified by Ir, Pd, Pt, and Rh atoms (Ir/Pd/Pt/Rh-C2N1) was chosen for selective adsorption of C2H2 amidst multiple gases (H2O, C2H2, and C4H10O2). According to the results of cohesive energy and ab initio molecular dynamics simulations, it is indicated that precious metal atoms can be stably anchored on the monolayer while enhancing the conductivity of the material The analysis of the electrostatic potential and work function determined the highly active sites and electron release capacity. In addition, the adsorption energy and distance disclosed the gas-solid interface structure of multiple gases on the Ir/Pd/Pt/Rh-C2N1 monolayer. Importantly, C2H2 exhibits strong responses to p-type semiconductor Pt-C2N1 and n-type semiconductor Ir-C2N1, respectively. Crystal Orbital Hamilton Population reveals the difference in adsorption energy due to modifications involving four precious metals. Interestingly, for the first time, the density of states calculation reveals that under the coexistence of multiple gases, the Pt/Ir-C2N1 monolayer effectively eliminates the interference of other gases and has a unique response only to C2H2. In real situations, with the basis of Gibbs free energy and Einstein's law of diffusion, it was determined that Pt-C2N1 and Ir-C2N1 showed excellent hydrophobicity, a wider temperature range, and a low diffusion activation energy barrier. In summary, Pt-C2N1 and Ir-C2N1 detect C2H2 without interference, maintaining fundamental principles, responsiveness, stability, and versatility unaffected by external factors.

Electronic and adsorption properties of halogen molecule X2 (X=F, Cl) adsorbed arsenene: First-principles study

The geometry, electronic structure, and adsorption properties of halogen molecule X2(X = F, Cl) on arsenene were investigated using first-principles calculations. The adsorption of molecules was considered at various sites and in various orientations on the pristine arsenene (p-As) surface. Both molecules show chemisorption and the crystal orbital Hamiltonian population (COHP) analysis reveals the formation of strong X-As bonds. In particular, the adsorbed molecules spontaneously dissociate into atomic halogen atoms, with a diffusion barrier of 1.91 (1.72) eV for F2(Cl2). The adsorbed X2 molecules induced distortions in the local geometry due to strong interaction with arsenene. Importantly, the formation of X-As bonding remarkably changed the electronic properties, evidenced by the decrease of the actual band gap due to the emergence of defect states within the band gap. For instance, the F2 adsorbed arsenene system (F2-As) exhibited an average band gap of 1.17 eV, and Cl2 adsorbed arsenene (Cl2-As) showed an average band gap of 0.83 eV. In particular, indirect to direct band gap transition was observed for some adsorption configurations. The reduction in band gap resulted in the enhancement of electrical conductivity. These findings suggest that the electronic properties of arsenene can be tuned by halogen decoration.

Investigating the microscopic enhancement mechanisms of adsorption-based CO2 capture with Cu-loaded γ−Al2O3 using density functional theory

Transition-metal-loaded γ−alumina (Al2O3) is considered to be an effective adsorbent for CO2 capture, but its microscopic process and mechanisms of CO2 adsorption are not fully understood. To investigate the microscopic enhancement role of Cu atoms in CO2 adsorption, this work compares various adsorption configurations and parameters of CO2 on γ−Al2O3 (110) facets with or without Cu atoms and small Cu cluster loading (Cun (n=1,2,3)/γ−Al2O3) using the first-principles approach. According to the adsorption energy, charge transfer, difference charge density, and other parameters of different configurations, the γ−Al2O3 (110) slab loaded with the Cu atom is found to exhibit enhanced adsorption of CO2 molecules compared to that without Cu loading. Moreover, the surface stability increases with the number of loaded Cu atoms. However, the hydroxyl groups in the active sites partially undermine the adsorption effect during the CO2 adsorption process. The density of states indicates that the doping of Cu atoms in the system creates an orbital peak closer to the Fermi energy level. This facilitates the transfer of charge within the slab, making the activation of CO2 easier and promoting stable adsorption. Finally, the amount of crystal orbital overlap population and crystal orbital Hamilton population shows that the stability of adsorption is due to the formation of C-Cu and C-Al bonds. It is demonstrated that the Cun-loaded γ−Al2O3 (110) slab improves the adsorption performance and contributes to a better understanding of the effect of transition-state metal loaded γ−Al2O3 on CO2 adsorption.

Cation-induced interface electric field redistribution and molecular orbital coupling in Co-FeS/MoS2 for boosting electrocatalytic overall water splitting

A green hydrogen economy requires efficient bifunctional electrocatalysts for simultaneous hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this study, a mild sulfuration strategy was used to create a Co-FeS/MoS2 catalyst from metal-organic frameworks (MOFs) on foam nickel. This catalyst exhibits exceptional activity in 1 M KOH, only requiring ultralow overpotentials of 63 mV and 230 mV to achieve current densities of 10 mA cm−2 and 100 mA cm−2 for the HER and OER processes. Additionally, it achieves a low cell voltage of 1.45 V at 10 mA cm−2, surpassing reported catalysts. DFT calculations and XPS tests show that Co introduction induces high-valence Fe active sites and facilitates interface electric field redistribution. Crystal orbital Hamilton population (COHP) calculations reveal d-p orbital hybridization, enhancing conductivity and charge transfer kinetics. This research sheds light on the catalytic impacts of metal cations on transition metal sulfides to design high efficient electrocatalysts.

Large Number of Direct or Pseudo-Direct Band Gap Semiconductors among A3TrPn2 Compounds with A = Li, Na, K, Rb, Cs; Tr = Al, Ga, In; Pn = P, As.

Due to the high impact of semiconductors with respect to many applications for electronics and energy transformation, the search for new compounds and a deep understanding of the structure-property relationship in such materials has a high priority. Electron-precise Zintl compounds of the composition A3TrPn2 (A = Li - Cs, Tr = Al - In, Pn = P, As) have been reported for 22 possible element combinations and show a large variety of different crystal structures comprising zero-, one-, two- and three-dimensional polyanionic substructures. From Li to Cs, the compounds systematically lower the complexity of the anionic structure. For an insight into possible crystal-structure band-structure relations for all compounds (experimentally known or predicted), their band structures, density of states and crystal orbital Hamilton populations were calculated on a basis of DFT/PBE0 and SVP/TZVP basis sets. All but three (Na3AlP2, Na3GaP2 and Na3AlAs2) compounds show direct or pseudo-direct band gaps. Indirect band gaps seem to be linked to one specific structure type, but only for Al and Ga compounds. Arsenides show smaller band gaps than phosphides due to weaker Tr-As bonds. The bonding situation was confirmed by a Mullikan analysis, and most states close to the Fermi level were assigned to non-bonding orbitals.

Fe Crystalline Phases in Fe/C Composites Modulated the Selective Adsorption of Pb(II) from Industrial Wastewater with Cd(II): An Electronic-Scale Perspective.

Fe oxide or Fe0-based materials display weak removal capacity for Pb(II), especially in the presence of Cd(II), and the electronic-scale mechanisms are not reported. In this study, Fe3C(220) modified black carbon (BC) [Fe3C(220)@BC] with high adsorption and selectivity for Pb(II) from industrial wastewater with Cd(II) was developed. The quantitative experiment suggested that Fe species accounted for 80.5-100 and 18.4-33.8% of Pb(II) and Cd(II) removal, respectively. Based on X-ray absorption near-edge structure analysis, 57.3% of adsorbed Pb2+ was reduced to Pb0; however, 61.6% of Cd2+ existed on Fe3C@BC. Density functional theory simulation unraveled that Cd(II) adsorption was attributed to the cation-π interaction with BC, whereas that of Pb(II) was ascribed to the stronger interactions with different Fe phases following the order: Fe3C(220) > Fe0(110) > Fe3O4(311). Crystal orbital bond index and Hamilton population analyses were innovatively applied in the adsorption system and displayed a unique discovery: the stronger Pb(II) adsorption on Fe phases was mediated by a combination of covalent and ionic bonding, whereas ionic bonding was mainly accounted for Cd(II) adsorption. These findings open a new chapter in understanding the functions of different Fe phases in mediating the fate and transport of heavy metals in both natural and engineered systems.

Coordination Engineering of Fe-Centered Catalysts for Superior Li-S Battery Performance.

Iron-nitrogen functionalized graphene has emerged as a promising cathode host for rechargeable lithium-sulfur batteries (RLSBs) due to its affordability and enhanced battery performance. To optimize its catalytical efficiency, we propose a novel approach involving coordination engineering. Our investigation spans a plethora of catalysts with varied coordination environments, focusing on elements B, C, N and O. We revealed that Fe-C4 and Fe-B2C2-h are particularly effective for promoting Li2S oxidation, whereas Fe-N4 excels in catalyzing the sulfur reduction reaction (SRR). Importantly, our study identified specific descriptors - namely, the Integrated Crystal Orbital Hamilton Population (ICOHP) and the bond length between Fe and S in Li2S adsorbed state - as the most effective predictive descriptors for Li2S oxidation barriers. Meanwhile, Li2S adsorption energy emerges as a reliable descriptor for assessing the SRR barrier. These identified descriptors are expected to be instrumental in rapidly identifying promising cathode hosts across various metal-centered systems with diverse coordination environments. Our findings not only offer valuable insights into the role of coordination environment, but also present an effective path for rapidly identifying high performance catalysts for RLSBs, enabling the acceleration of advanced RLSBs development.

Manipulating the Spin State of Spinel Octahedral Sites via a π-π Type Orbital Coupling to Boost Water Oxidation.

Spin state is often regarded as the crucial valve to release the reactivity of energy-related catalysts, yet it is also challenging to precisely manipulate, especially for the active center ions occupied at the specific geometric sites. Herein, a π-π type orbital coupling of 3d (Co)-2p (O)-4f (Ce) was employed to regulate the spin state of octahedral cobalt sites (CoOh) in the composite of Co3O4/CeO2. More specifically, the equivalent high-spin ratio of CoOh can reach to 54.7 % via tuning the CeO2 content, thereby triggering the average eg filling (1.094) close to the theoretical optimum value. The corresponding catalyst exhibits a superior water oxidation performance with an overpotential of 251 mV at 10 mA cm-2, rivaling most cobalt-based oxides state-of-the-art. The π-π type coupling corroborated by the matched energy levels between Ce t1u/t2u-O and CoOh t2g-O π type bond in the calculated crystal orbital Hamilton population and partial density of states profiles, stimulates a π-donation between O 2p and π-symmetric Ce 4fyz 2 orbital, consequently facilitating the electrons hopping from t2g to eg orbital of CoOh. This work offers an in-depth insight into understanding the 4f and 3d orbital coupling for spin state optimization in composite oxides.

Manipulating the Spin State of Spinel Octahedral Sites via a π–π Type Orbital Coupling to Boost Water Oxidation

AbstractSpin state is often regarded as the crucial valve to release the reactivity of energy‐related catalysts, yet it is also challenging to precisely manipulate, especially for the active center ions occupied at the specific geometric sites. Herein, a π–π type orbital coupling of 3d (Co)‐2p (O)‐4f (Ce) was employed to regulate the spin state of octahedral cobalt sites (CoOh) in the composite of Co3O4/CeO2. More specifically, the equivalent high‐spin ratio of CoOh can reach to 54.7 % via tuning the CeO2 content, thereby triggering the average eg filling (1.094) close to the theoretical optimum value. The corresponding catalyst exhibits a superior water oxidation performance with an overpotential of 251 mV at 10 mA cm−2, rivaling most cobalt‐based oxides state‐of‐the‐art. The π–π type coupling corroborated by the matched energy levels between Ce t1u/t2u‐O and CoOh t2g‐O π type bond in the calculated crystal orbital Hamilton population and partial density of states profiles, stimulates a π‐donation between O 2p and π‐symmetric Ce 4fyz2 orbital, consequently facilitating the electrons hopping from t2g to eg orbital of CoOh. This work offers an in‐depth insight into understanding the 4f and 3d orbital coupling for spin state optimization in composite oxides.

Development of Activity-Stability Descriptors for Transition Metal Oxide Electrocatalysis

The discovery of high-performing catalysts for the oxygen reduction and oxygen evolution reactions (ORR/OER) and related oxidative reactions is critical for the development of energy-efficient hydrogen fuel cells and electrolyzers. To achieve this goal, affordable and abundant alternatives to precious metal catalysts with sufficient stability and catalytic activity must be discovered. Ab-initio catalytic simulations combined with machine learning (ML) methods can play an important role in screening a larger search space of potential electrocatalysts materials of higher structural and compositional complexity, such as class of transition metal oxides (TMOs).In this talk, we will show how electronic and structural descriptors derived from bulk DFT calculations can improve ML models for the OER and ORR on transition metal oxides. In our previous work [1] we demonstrated that the electronic structure of the bulk TMOs, obtained as the crystal orbital Hamiltonian populations (COHP) of the metal-oxygen bond, is an accurate descriptor for O and OH adsorption. Here, we will discuss our extended model for O* and OH* adsorption across crystal structures and oxidation states, utilizing a new dataset of adsorption on binary (AxOy) oxide surfaces spanning the entire transition metal series. Building on our recent work, we extend the COHP-based model to a ML-based prediction of adsorption across multiple oxidation states to obtain a MAE < 0.2 eV for the O-OH and OH adsorption energy descriptors. These results can enable a more efficient screening of catalysts on the bulk level of DFT computation to significantly reduce the computational cost [2]. Furthermore, we will discuss how the COHP analysis can be directly applied to oxide surfaces to understand the impact of metal valency, structural reorganization, and magnetization on adsorption energetics [3]. Our prediction models of stability of bulk phases from COHP and oxidation state beyond binary alloys will also be highlited [4]. Lastly, we will discuss recent progress on collecting and accessing computational and underlying experimental data on catalysis-hub.org.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] Comer, B. M., Li, J., Abild-Pedersen, F., Bajdich, M., Winther, K. T. (2022). Unraveling Electronic Trends in O∗ and OH∗ Surface Adsorption in the MO2Transition-Metal Oxide Series. , JPCC 2022 126 (18)(2022)[2] Comer, B. M., Bothra, .N, Lunger, J., Abild-Pedersen, F., Bajdich, M., Winther, K. T., Generalized Prediction of O and OH Adsorption on Transition Metal Oxide Surfaces from Bulk Descriptors (under review)[3] Bothra, .N, Comer, B. M., Winther, K. T., Bajdich, M., Understanding the Effects of Surface Bonding in Metal-Oxides Beyond the Limit of the Active Site (in preparation)[4] Craig, M. J., Kleuker, F., Bajdich, M., & Garcia-Melchor, M. (2023). FEFOS: A method to derive oxide formation energies from oxidation states. Catalysis Science & Technology.

Insights into the Activity and Stability of Dual-Site Single Atom Catalysts for Oxygen Reduction Reaction Using a 2D Phthalocyanine-MOF

Hydrogen fuel cells have been considered as an effective strategy to shift fossil-fuel based economy to hydrogen economy. The performance of the fuel cells is often limited by the slow kinetics of the cathodic oxygen reduction reaction (ORR). Metal-organic frameworks (MOFs) based on 2D Phthalocyanine offer dual-site single atom catalyst (SAC) where M1 site typically amine coordinated node and M2 site is the phthalocyanine center (M1/M2 = Co, Cu, Ni). Here we conduct both computational studies and experimental measurements to elucidate the site selectivity and activity of two- and four-electron ORR process for pure (contains same element on both sites) and mixed (different M1 and M2) MOF system, and their overall stability. Using density functional theory (DFT), we find that regardless of site, Cobalt (Co) element shows better four-electron ORR activity than other elements in the mixed MOF system. Our integrated crystal orbital Hamilton population (ICOHP) calculations indicate that for pure MOF system, M1(d)-4N(2p) bonds are stronger than M2(d)-4N(2p), which raises d-band center of M2 sites closer to Fermi level, hence improves its activity towards four-electron ORR process. For mixed systems, M2 sites activity largely depends on the geometrical effects caused by M1 site elements. Our activity calculations reveal that Co (as M2) in the Ni-Co mixed MOF systems predicts lowest overpotential for ORR among all studied MOF system. Our dissolution mechanism and stability calculations show that Cu (as M1) causes stress/strain within the mixed MOF system denoting least stable among all studied during ORR process. In experiment, we found Co-based MOF, particularly Ni-Co demonstrates the highest kinetic activity and Cu is the least stable element, showing excellent agreement with computational studies. We hope this study will help in understanding the insight into the rational design of highly active and stable MOF for electrochemical processes. 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.

Uncovering the Interfacial Strengthening Mechanisms of α-Mg/Mg2Sn/β-Li Interfaces Using First-Principle Calculations and HAADF-STEM.

Previously, we reported our new invention of an ultralight (ρ = 1.61 g/cm3) and super high modulus (E = 64.5 GPa) Mg-Li-Al-Zn-Mn-Gd-Y-Sn (LAZWMVT) alloy. Surprisingly, the minor additions of Sn contribute to significant strength and stiffness increases. In this study, we found that Mg2Sn was not only the simple precipitate but also acted as the glue to bind the α-Mg/β-Li interface in a rather complicated way. To explore its mechanism, we have performed first-principle calculations and HAADF-STEM experiments on the interfacial structures. It was found that the interfacial structural models of α-Mg/β-Li, α-Mg/Mg2Sn, and β-Li/Mg2Sn composite interfaces prefer to form α-Mg/Mg2Sn/β-Li ternary composite structures due to the stable formation enthalpy (ΔH: -1.95 eV/atom). Meanwhile, the interface cleavage energy and critical cleavage stress show that Mg2Sn contribute to the interfacial bond strength better than the β-Li/α-Mg phase bond strength (σb(β-Li/Mg2Sn): 0.82 GPa > σb(α-Mg/Mg2Sn): 0.78 GPa > σb(β-Li/α-Mg): 0.62 GPa). Based on the interfacial electronic structure analysis, α-Mg/Mg2Sn and β-Li/Mg2Sn were found to have a denser charge distribution and larger charge transfer at the interface, forming stronger chemical bonds. Additionally, according to the crystal orbital Hamiltonian population analysis, the bonding strength of the Mg-Sn atom pair was 2.61 eV, which was higher than the Mg-Li bond strength (0.39 eV). The effect of the Mg2Sn phase on the stability and interfacial bonding strength of the alloying system was dominated by the formation of stronger and more stable Mg-Sn metal covalent bonds, which mainly originated from the contribution of the Mg 3p-Sn 5p orbital bonding states.

Asymmetrical TiSSe Monolayers as Catalytic Materials for Lithium-Sulfur Batteries: A DFT Study

Asymmetrical Janus TiSSe monolayers as cathode materials for lithium-sulfur batteries were studied by first-principles calculations, encompassing adsorption, catalytic, and conductive properties. The polarization effect, arising from the asymmetric arrangement of constituent elements, results in variability in adsorption energy and bonding processes across S/Se surfaces. The moderate adsorption energy of Lithium Polysulfides (LiPSs) on the TiSSe monolayer effectively mitigates the shuttle effect. The bond formation process investigated by charge transfer, physical/chemical adsorption, and projected crystal orbital Hamiltonian population (pCOHP), revealed its emergence in the early lithiation stage. The Gibbs free energies for the reduction reaction of sulfur on the S/Se surface demonstrate a significant enhancement in the transformation kinetics. The low decomposition and diffusion energy barriers for lithium atoms on the S/Se surface of the TiSSe monolayer indicate its catalytic potential in facilitating sulfur redox transformation. The TiSSe monolayer exhibits metallic properties before and after polysulfide absorption, thereby enhancing electron transport capacity in Li-S batteries. Therefore, the Janus TiSSe monolayer presents a new perspective for the selection of battery adsorption materials in lithium-sulfur batteries.

Insights into enhanced thermoelectric performance of the n-type Mg3Sb2-based materials by amphoteric Al doping

Doping has the potential to alter the levels of anharmonicity in compounds by attenuating bonding strength. In this study, we explore the efficacy of amphoteric Al doping for stimulating anharmonicity in n-type Mg3.25AlxSb1.48Bi0.48Te0.04 to attain enhanced phonon scattering and thermoelectric performance. First-principles calculations and experimental data reveal the occupation of both Sb and Mg2 sites by amphoteric Al atoms in the anionic framework of Mg3.25AlxSb1.48Bi0.48Te0.04. A marginal variation in both carrier concentration and mobility sustains the high power factor without affecting the Seebeck coefficient, implying amphoteric doping induced charge compensation. While phonon velocity, Grüneisen parameter, and crystal orbital Hamilton population calculations results indicate that phonon softening and bond weakening are realized via Al doping, leading to an enhanced lattice anharmonicity and a reduced lattice thermal conductivity. A remarkable enhancement ∼16% in the peak figure of merit ZTpeak and the average ZTavg, was attained for the x = 0.015 sample, when compared with the un-doped sample. Hence, the amphoteric doping can serve as an effective means to optimize ZT values by decoupling the intertwined thermoelectric transport properties.

Judicious Fluorination of Perovskite Quantum Wells Enables Over 25% Efficiency in Inverted Solar Cells

AbstractThe photovoltaic performance of inverted perovskite solar cells (PSCs) is often hindered by trap‐induced non‐radiative recombination and photochemical degradation occurring at the upper interfaces and the grain boundaries of perovskite films. Herein, ortho‐, meta‐, and para‐isomers of fluorophenylethylammonium iodine (F‐PEAI) organic spacer molecules are evaluated for the construction of perovskite quantum wells (2D or quasi‐2D, PQWs) to encapsulate 3D perovskites. Among the three variants, p‐F‐PEAI leads to the most symmetric charge distribution and the weakest steric hindrance which resulting in reinforced interactions with PbI2 and perovskite, the enhanced out‐of‐plane orientation is confirmed by Grazing incidence wide‐angle X‐ray scattering (GIWAXS) results. Density functional theory and crystal orbital Hamilton population (COHP) calculations further confirm that p‐F‐PEAI engages most strongly with the perovskite structure. Moreover, transmission electron microscopy (TEM) characterization is used to illustrate that p‐F‐PEAI‐assisted 2D PQWs effectively passivate both the grain boundaries and surfaces of perovskites. This configuration facilitates effective surface passivation, improves charge carrier transport, and significantly suppresses non‐radiative recombination. The resultant inverted PSCs achieve an excellent power conversion efficiency (PCE) of 25.03% with a fill factor (FF) of 85.11%. The unencapsulated devices exhibit enhanced long‐term stability under ambient environments and continuous light illumination.

Activation of efficient hydrogen evolution on 1T-VS2 nanoribbons by low-cost transition metals: A first-principles study

Electrocatalytic water splitting is a very important energy conversion technology that utilizes renewable energy sources to produce hydrogen for sustainable energy development. In this work, the catalytic performance of 1T-VS2 (1T phase of vanadium disulfide) nanoribbons in the hydrogen evolution reaction (HER) was investigated based on first-principles calculations. It was found that 1T-VS2 nanoribbons have a Gibbs free energy (ΔGH*) of 0.05 eV, demonstrating its excellent HER performance. Moreover, some transition metal substitutions can further improve this performance (e.g. the ΔGH* of the Ti/Fe-1T-VS2 are as low as −0.02/0.04 eV). The mechanism of the performance enhancement is thoroughly investigated. The improved catalytic performance of HER is mainly promoted by hybridization between the V-d and TM-d-orbitals. The crystal orbital Hamiltonian population (COHP) and integral crystal orbital Hamiltonian habitation (ICOHP) calculations show that the HER properties are closely related to the filling of bonding and antibonding states. The differential charge density indicates that the adsorption of H results in an effective charge transfer at the interface and an increase in the conductivity, leading to an increase in the HER. The HER activity of the TM-1T-VS2 (TM stands for transition metal) nanoribbons is also related to the proximity of the adsorption site to the edge. Our work suggests that the TM-1T-VS2 nanoribbons are expected to be low cost and highly efficient catalysts.

Exploring the key role of electronic effects in Pd catalysts supported on Ni-modified N-doped porous carbon for direct synthesis of H2O2 under atmospheric pressure

Developing high-performance catalysts for direct synthesis of hydrogen peroxide (H2O2; DSHP) remains challenging. The paper proposes a strategy to optimize Pd catalysts by enriching Ni-modified N-doped porous carbon. The theoretical studies indicate that Ni modulates the electronic structure of Pd through charge transfer and strain effects, effectively reducing the adsorption energy of reaction intermediates. Furthermore, the Crystal Orbital Hamilton Population (COHP) analysis demonstrated that the energy-integrated COHP (ICOHP) of the OO bonds in O2* (* denotes the adsorbed state), OOH*, and HOOH* were positively correlated with dissociation activation energies and negatively correlated with hydrogenation activation energies. The modulation of the electronic structure of Pd by Ni reduces the hydrogenation activation energies of O2* and OOH* and increases the dissociation activation energies of O2*, OOH*, and HOOH*, thereby enhancing the selectivity and productivity of H2O2. The experimental results aligned with the theoretical predictions, showcasing that the optimized Pd-Ni7.5/NPCs catalyst exhibited remarkable H2O2 selectivity and productivity of 70.5 % and 230.31 mol kgcat-1·h-1, respectively, surpassing the performance of Pd/NPCs (47.1 % and 52.3 mol kgcat-1·h-1). This study offers profound insights into the crucial role of electron effects in DSHP using nickel-modified palladium catalysts, providing strong evidence into the design and optimization of Pd catalysts.

First-principles study of phase-dependent carrier transport mechanism for MASnI3 Sn-based halide perovskite

Organic-inorganic hybrid perovskites have attracted tremendous attentions owing to their excellent properties as next-generation photovoltaic devices. With soft covalent framework, organic-inorganic hybrid perovskites exhibit different phases at different temperatures. The band-edge features of perovskites are mainly contributed by inorganic framework, which means the structural differences between these phases would lead to complex carrier transport. We investigated the carrier transport of Sn-based organic-inorganic hybrid perovskite CH3NH3SnI3 (MASnI3), considering acoustic deformation potential scattering, ionized impurity scattering, and polar optical phonon scattering. It is found that the electron mobility of each phase of MASnI3 is strongly correlated with the Sn–I–Sn bond angle and there is in-plane/out-of-plane anisotropy. The projected crystal orbital Hamilton population analysis suggested that the tilt and rotation of the [SnI6]4− octahedron influence the Sn(p)–I(p) orbital electron coupling and the electron transport, leading to different band-edge features in multiple phases. The carrier mobility with respect to temperature was further calculated for each phase of MASnI3 in respective temperature intervals, showing lower carrier mobility in high temperature. Comparing the contribution of different scattering mechanisms, it was found that the dominant scattering mechanism is polar optical phonon scattering, while multiple scattering mechanisms compete in individual cases.

Effects of Mg and Al doping on the desorption energetics and electronic structure of a Ti-V-Zr-Nb alloy hydride

Refractory high-entropy alloys (HEAs) show promise for novel hydrogen storage technology, but addressing their limited gravimetric hydrogen storage capacity necessitates exploration of light alloying elements including Mg and Al. Here, we employ density-functional theory to investigate the hydrogen desorption energetics of Ti0.325V0.275Zr0.125Nb0.275 alloy and the impact of doping with Mg and Al. Our analysis reveals that Mg and Al addition thermodynamically destabilize the Ti0.325V0.275Zr0.125Nb0.275-hydride and lower its storage capacity. The observed destabilization is attributed to reduced chemical contributions to the desorption enthalpy in the Mg and Al-doped hydrides. Detailed examination of the electronic density of states, electron localization function, and crystal orbital Hamilton population analysis unveils fundamental features of chemical bonding in these hydrides. Notably, H-H antibonding states occur for hydrogen atoms located in the nearest-neighbor interstices of Mg and Al atoms. Charge transfer facilitates formation of these antibonding states. This comprehensive analysis enhances our understanding of the intricate interplay between electronic structure, hydrogen desorption energetics, and chemical bonding in HEA hydrides, offering valuable insights for the design and optimization of advanced hydrogen storage materials.