Vacancy Formation Energy Research Articles

The intercalation cathode materials of heterostructure MnS/MnO with dual ions defect embedded in N-doped carbon fibers for aqueous zinc ion batteries

Manganese-based materials are often used as cathode materials for aqueous zinc ion batteries (AZIBs), which have the advantages of high theoretical capacity, low cost, low toxicity and various valence states. However, the inherent poor conductivity, sluggish zinc ion diffusion kinetics and terrible rate performance limit their practical application. Herein, MnS/MnO@NCF composite was synthesized by a simple electrospinning method. The N-doped carbon fibers (abbreviated as NCF) is produced during the carbonization process of PVP, which greatly improves the electronic conductivity of materials, and the formation of heterostructure MnS/MnO create abundant heterointerfaces with plentiful reaction active sites, which further improve the surface reaction kinetics. Meanwhile, an in-situ electrochemical approach inducing dual ions defect of Mn-defect and S-defect is used to unlock the electrochemical activity of MnS/MnO@NCF through the initial charge process for the first time, which can convert terrible electrochemical characteristic of MnS/MnO@NCF towards Zn2+ and H+ into high electrochemically active cathode for AZIBs. Finally, it exhibits a considerable capacity and superior cycleability with the specific discharge capacity of 151 mAh g−1 even after 400 cycles when used as the cathode material for AZIBs. Remarkably, it can even achieve a reversible capacity as high as 128.7 mAh g−1 at current density of 2 A g−1. Ex situ characterizations reveal the main co-insertion/extraction mechanism for H+ and Zn2+ without structural collapse, and the vacancy formation energies and the diffusion energy barrier of Zn2+calculated by density functional theory further explain the excellent rate performance and the energy storage mechanism of the MnS/MnO@NCF material.

The Orbital Nature of Electron Holes in BaFeO3 and Implications for Defect Chemistry

Understanding the nature of electron holes in mixed protonic–electronic conducting perovskites is key to the successful development of novel electrode materials for protonic ceramic fuel and electrolyzer cells (PCFCs). Here, we use density functional theory to investigate the orbital interactions and defect chemistry of BaFeO3−δ─a model material for more complex cation stoichiometries used in PCFCs. The calculations revealed BaFeO3−δ to be a negative charge-transfer material with a dominating d5L ( L = ligand hole) configuration. Chemical bonding analysis using the projected Crystal Orbital Hamilton Population (COHP) further showed that the ligand holes are partially delocalized in pdσ* bonds with an approximately 80% share at the oxygen ions. The defect chemistry of BaFeO3 was explored with respect to oxygen vacancies and protonic defects. The oxygen vacancy formation energy increases with decreasing ligand hole concentration due to a rising Fermi level at which electrons from the removed oxygen are accommodated. This effectively outweighs a concomitant decrease in the Fe–O bond strength evidenced by energy-integrated COHP analysis. The dissociative H2O absorption was studied, where OH– fills an oxygen vacancy and H+ is attached to a regular oxygen ion. The energy of this reaction becomes more negative with decreasing ligand hole concentration. This trend largely reflects a more favorable OH– affinity with decreasing ligand hole concentration.

Reshaping the Role of CO2 in Propane Dehydrogenation: From Waste Gas to Platform Chemical

The valorization of CO2 appeals to the chemical industry due to the reduction in greenhouse gas emissions and the ability to offer more renewable products. Propylene production is the second largest process in the chemical industry, and it strongly depends on fossil fuel feedstocks. Coupling CO2 reduction with propane dehydrogenation boosts conversion and produces CO, a valuable platform chemical currently synthesized by fossil-methane reforming. In this work, (i) we demonstrate the environmental benefits of coupling CO2 with a life-cycle assessment under industrial conditions, potentially reducing emissions by 3 tCO2-eq per ton of propylene produced. (ii) We screen supported catalytic materials─both known and novel─with a focus on propane and CO2 reaction mechanisms under industrial reaction conditions of 400–700 °C and pressures of 1–6 barg (redox: V, Galinstan, In, Mo, Mn, Bi, Sb, Ta; nonredox: Cr, Ga, co, Al, Zn, Au, Zr, Ag, W, La, Cu; and some alloy combinations). We evaluate each material under the kinetic regime, and we quantify reaction, side reaction, and deactivation kinetics (coking, cracking, and dry-reforming), as well as the regeneration ability. We then classify them based on their dominant mechanisms (direct CO2 assistance or indirect with H2 via reverse water gas shift) and identify each catalyst’s strengths and weaknesses. Finally, (iii) we correlate our database of experimental results of 22 active metals/metal oxides with the Tamman temperature and density functional theory (DFT)-based oxygen vacancy formation energies. We discovered that oxygen mobility plays a crucial role in the kinetics of reoxidation with CO2 and the overall balance of active sites related to dehydrogenation and reoxidation.

Avoiding oxygen induced Pb vacancies for high thermoelectric performance of n-type Bi-doped Pb1-xBixTe compounds

For n-type PbTe based compounds with relatively low optimal concentration (1019 cm−3), the accompanied structural defects play pivotal role on the charge transport upon doping with alien valent atoms. Herein, we report that Oxygen has huge influence on the defect evolution and thermoelectric properties in n-type PbTe for the first time. A boosted thermoelectric figure of merit ZT of ∼1.12 at 673 K and a ZTave of 0.84 in the range of 300–873 K are achieved for vacuum sintered Bi-doped PbTe with the powders ground under the protection of Ar. This is in sharp contrast with the same Bi-doped PbTe material sintered with the powders ground in the air, which reaches a ZTave of 0.52. This distinct thermoelectric properties in Bi-doped PbTe compounds are strongly correlated to Bi dopant, the vacancy defects (VPb″ and VTe⋅⋅) induced during the fracturing process, and oxygen in the air. The coexistence of Bi dopant and oxygen lowers the formation energy of Pb vacancies and induces large number of O–Bi related Pb vacancies in the structure, yielding an acceptor-like effect. Such negatively charged Pb vacancies in the structure exert a strong long-range coulombic repulsion force on the electrons, leading to a low doping efficiency, a low carrier mobility (200 cm2 V−1 s−1), and inferior electronic properties. Whereas, the protection provided by Ar effectively avoids the contamination by oxygen and prevents the formation of O–Bi related Pb vacancies, which appears remarkably effective in enhancing the electronic transport. A high carrier mobility of 1300 cm2 V−1 s−1 is attained in slightly doped Pb0·9995Bi0·0005Te sample and this contributes to an ultra-high power factor of 40 μW cm−1 K−2 for the Pb0·9995Bi0·0005Te sample at room temperature. The high PFave exceeds 25 μW cm−1 K−2 in the range of 300–723 K. The work provides a new insight into the formation mechanism of structural defects and a new avenue for suppressing the cation vacancies, resulting in higher performance of n-type PbTe-based compounds.

First-principles study of hydrogen-vacancy interactions in CoCrFeMnNi high-entropy alloy

Vacancies can easily capture H atoms in metals, forming hydrogen-vacancy complexes/clusters. In this work, the hydrogen-vacancy interactions in CoCrFeMnNi high-entropy alloy (HEA) were studied with first-principles calculations based on the density functional theory (DFT). The special quasi-random structure (SQS) method was used to construct a chemically disordered HEA, and the effects of solute H atoms on the formation energy of monovacancy, the formation energy and binding energy of multi-vacancy cluster were calculated. It is found that an H atom prefers to occupy an octahedral interstitial site neighboring a vacancy and attracts the charge from the surrounding first-nearest neighbor atoms (e.g. Co, Ni, Fe or Mn atom, excluding Cr atom), weakening the stability of the atoms around the vacancy and reducing the vacancy formation energy in CoCrFeMnNi HEA. After introducing H atoms, the formation energies of both vacancy and vacancy cluster decrease in CoCrFeMnNi HEA, but they are still higher than those in pure Fe and Ni. In addition, the reduction of the binding energy of vacancies in CoCrFeMnNi HEA is much lower than that in pure Fe and Ni, and the binding energy of vacancies even increases in some cases. The results of the first-principles calculations indicate that the solute hydrogen atoms, although promoting vacancies, unfavorably combining vacancies into clusters to form micro-voids. This provides a good explanation for the good resistance to hydrogen embrittlement of CoCrFeMnNi HEA observed in experiments.

Superior indicative and regulative function of Fe doping amount for MnO2 catalyst with an oxygen vacancy in NH3-SCR reaction: A DFT + U study

MnO2 was a promising catalyst in selective catalytic reduction (SCR) reaction at low temperature. In this research, density functional theory calculations were carried out to evaluate the NH3-SCR performance of MnO2 catalyst with an oxygen vacancy (MnO2-x). Results demonstrated that MnO2-x became the thermodynamically most preferred structure after Fe doping, and its structure was kept stable as the doping amount increased. The adsorption behaviors of gaseous molecules on the MnO2-x showed that NH3 and H2O preferred to be adsorbed on the Mn Lewis acid sites, while NO and SO2 preferred O sites. Good SO2-tolerance also exhibited in MnO2-x for its enhanced acidity after Fe doping. Moreover, outstanding linear relationships were emerged in doping ratio with oxygen vacancy formation energy and adsorption energy, suggesting its important role in the balance of redox and acidity properties. Thermodynamic calculation results confirmed the inhibitory effect of temperature on adsorption and found the implication of doping amount to H2O-tolerance. Overall, Fe2-MnO2-x catalyst performed best in our work. Strong indication of doping amount was found by further calculations of four physical quantities. In general, doping amount was an outstanding indicator to reflect the characteristics of catalysts, and can be employed in the future directional catalyst designs.

DFT insight into the adsorption behavior of H2PO2 on the reduced Ce0.899M0.111O1.785(111) (M = Ti, Zr) surface

To study the effect of Ti and Zr doping on the reducibility of CeO2(111) substrate and the adsorption of H2PO2 on KDP surface, the O vacancy formation energy of Ti/Zr-doped CeO2(111) surface was calculated using DFT+U method. The adsorption energy, bonding structure and local electronic structure of H2PO2 on Ti/Zr-doped CeO1.963(111) surface was analyzed. The results showed that the O vacancy formation energy of Ti/Zr-doped CeO2(111) surface was reduced and the surface magnetic moment was enhanced. P-O and O-O covalent bonds were formed at the adsorption interface between H2PO2 and the substrates. The adsorption energies of H2PO2 on the reduced substrates were Ce0.899Ti0.111O1.963(111) > CeO1.963(111) > Ce0.899Zr0.111O1.963(111). The adsorption energies of H2PO2 on the substrates containing subsurface O vacancy were greater than those on the substrates containing surface O vacancy. The most stable adsorption site of H2PO2 on the Ce0.899Ti0.111O1.963(111)-sub surface was Oh site, P was bonded with two surface O, and the adsorption energy (7.612 eV) was the maximum, therefore, the Ce0.899Ti0.111O1.963(111)-sub surface was the more suitable for polishing H2PO2 on KDP surface. These results may lead to a better understanding and improving for the Ti/Zr-doped CeO2 polishing powder.

Quantitative study on Ru local atomic structure in Ni-Al-Ru ternary alloys

The synchrotron radiation X-ray absorption fine structure (XAFS) technique is used to study the local structure of the key atom Ru in a series of Ni-Al-Ru ternary alloys with different Ru contents and heat treatments. All the investigated alloys consist of two phases, γ and γ', and especially Ru exists as an atom coordinated by 12 Ni atoms in the first shell without Ru clusters or intermetallic compounds. In γ phase Ru resides on the Ni lattice site introducing an outward relaxation of the neighboring atoms, while in the γ' phase Ru replaces the Al lattice site causing an inward relaxation. The interatomic distance of Ru–Ni bond and Debye-Waller factor are mainly affected by the composition and increase with the increasing Ru content. While the effect of heat treatment is obvious when the Ru content is higher than 6 at%. The variation of Ru local atomic structure can greatly influence the microstructural evaluation and deformation mechanism by changing the lattice misfit and the vacancy formation energy to control the creep properties of Ni-Ru-Al ternary alloys.

Deuterium retention and desorption behavior of W-Ta-Cr-V high entropy alloy

Deuterium retention and desorption behavior of W-Ta-Cr-V films under deuterium plasma irradiation were studied. The W-Ta-Cr-V films were prepared on the molybdenum (Mo) substrate by magnetron sputtering. Subsequently, all films annealed at 1000 °C were exposed to deuterium plasma at a flux of 8.13 × 1019 D/m2·s for 9 h to achieve an irradiation fluence of 2.63 ×1024 D/m2. Electron backscattered diffraction (EBSD) was used to characterize the texture and average grain size of films. Doppler broadening spectrometry of positron annihilation (DBS-PA) was carried out with an energy-variable slow positron beam to detect the concentration of vacancy-type defects in the films. The results suggest that there are fewer vacancy-type defects inside W-Ta-Cr-V grains. Deuterium retention and the desorption behavior of W-Ta-Cr-V were studied by compared to pure tungsten films. In the 300–800 K temperature range, the peaks of thermal desorption spectroscopy (TDS) of W-Ta-Cr-V films are substantially consistent with that of the W films. Notably, in the range of 800 K-1000 K, W-Ta-Cr-V film has no thermal desorption peak. We attribute this to the large lattice distortion and low vacancy formation energy, which inhibit the growth of voids inside the grains of W-Ta-Cr-V films. The total deuterium retention of W-Ta-Cr-V films is compared with that of W films. It is measured by TDS that the deuterium retention of W-Ta-Cr-V films is nearly 5 times that of W films. Based on the analysis of the TDS spectra, the higher deuterium retention in W-Ta-Cr-V films is due to the more grain boundary defects.

Active sites and deactivation of room temperature CO oxidation on Co3O4 catalysts: combined experimental and computational investigations

Co3O4 is a well-known low temperature CO oxidation catalyst, but it often suffers from deactivation. We have thus examined room temperature (RT) CO oxidation on Co3O4 catalysts by operando DSC, TGA and MS measurements, as well as by pulsed chemisorption to differentiate the contributions of CO adsorption and reaction to CO2. Catalysts pretreated in oxygen at 400 °C are most active, with the initial interaction of CO and Co3O4 being strongly exothermic and with maximum amounts of CO adsorption and reaction. The initially high RT activity then levels-off, suggesting that the oxidative pretreatment creates an oxygen-rich reactive Co3O4 surface that upon reaction onset loses its most active oxygen. This specific active oxygen is not reestablished by gas phase O2 during the RT reaction. When the reaction temperature is increased to 150 °C, full conversion can be maintained for 100 h, and even after cooling back to RT. Apparently, deactivating species are avoided this way, whereas exposing the active surface even briefly to pure CO leads to immediate deactivation. Computational modeling using DFT helped to identify the CO adsorption sites, determine oxygen vacancy formation energies and the origin of deactivation. A new species of CO bonded to oxygen vacancies at RT was identified, which may block a vacancy site from further reaction unless CO is removed at higher temperature. The interaction between oxygen vacancies was found to be small, so that in the active state several lattice oxygen species are available for reaction in parallel.

Modified extended Finnis Sinclair potential for cubic crystal metal

Unlike the modified embedded atom method (MEAM), which requires consideration of the bond angles, the embedded atom method (EAM) and Finnis Sinclair (FS) potential have achieved a wide range of applications in molecular dynamics simulations of amorphous alloys and disordered systems. In this paper, the potential functions of 10 cubic crystalline metals are reconstructed using the extended Finnis Sinclair (EFS) potential to improve the FS potential in terms of defects, surface energy and thermal properties. First of all, for the BCC crystal structure and FCC crystal structure, the fitted physical quantity expressions suitable for EAM potential and FS potential are deduced, including pressure, bulk modulus, shear elastic modulus elastic constant, vacancy formation energy and surface energy. Then, based on these physical quantities and the Rose equation of state, the least-squares method is used to fit the new potential parameters. Finally, using the current potential, the cohesive energy, elastic constants (C11, C12 and C44), vacancy formation energy, self-interstitial formation energy, surface energy, coefficient of thermal expansion, specific heat capacity and the melting point of 10 kinds of cubic crystals are calculated by molecular dynamics simulation. The reliability of the current potential is verified by comparing with other potential functions, experimental values and first-principles calculations. The results show that the current potential can well reproduce the characteristics of physical quantities such as lattice constant, cohesive energy and elastic constants (C11, C12 and C44). Compared with the previous EFS potential, the current potential is closer to the Rose equation of state. The calculated surface energy is more accurate, and the performance of defects and thermal properties shows the reliability of the current potential function, and these improvements are due to the improvement of the fitting method.

Tuning magnetic anisotropy and Dzyaloshinskii-Moriya interaction via interface engineering in nonisostructural SrCuO2/SrRuO3 heterostructures

We report a theoretical investigation on the effects of interface reconstruction on magnetic anisotropy (MA) and Dzyaloshinskii-Moriya interaction (DMI) for nonisostructural heterostructures formed by an infinite-layer oxide ${\mathrm{SrCuO}}_{2}$ and a perovskite oxide ${\mathrm{SrRuO}}_{3}$. Due to the atomic, charge, spin, and orbital reconstructions at interface, the SRO film thickness-dependent magnetic anisotropy oscillation behavior has been greatly tuned in two ${\mathrm{SrCuO}}_{2}/{\mathrm{SrRuO}}_{3}$ heterostructures. A strong DMI of 3.5 meV/Ru and a large DMI/exchange constant ratio $|D/J|$ of 0.63 are obtained at the ${\mathrm{CuO}}_{2}\text{\ensuremath{-}}\mathrm{Sr}\text{\ensuremath{-}}{\mathrm{RuO}}_{2}$ interface, which are beneficial to the creation and stability of skyrmions. Besides, the DMI is tunable, monotonically decreasing with the increase of the content of the apical oxygen ions in the interfacial layer, and takes the minimal value of 0.1 meV/Ru at the ${\mathrm{CuO}}_{2}\text{\ensuremath{-}}\mathrm{SrO}\text{\ensuremath{-}}{\mathrm{RuO}}_{2}$ interface. We evaluate the formation energy of oxygen vacancy in interface SRO layer, which turns out to be half as much as that in bulk SRO. This small value ensures the experimental feasibility towards two interfaces. Combining first-principles calculations with tight-binding model, we find that the effectively modulated MA and DMI at the ${\mathrm{CuO}}_{2}\text{\ensuremath{-}}\mathrm{Sr}\text{\ensuremath{-}}{\mathrm{RuO}}_{2}$ interface are mainly associated with the occupation of ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital, the enhanced interface symmetry breaking, and orbital hybridization. The present work demonstrates the distinct features of the interface formed between nonisostructural oxides and suggests a conceptually different strategy towards the modulation of MA and DMI.

Analyzing the TiO2 surface reactivity based on oxygen vacancies computed by DFT and DFTB methods

Titanium dioxide is a key material in many fields, including technological, industrial and biomedical applications. Many of these applications are related to the surface reactivity of TiO2 and involve its reducibility properties. Recently titania has been banned as a food additive due to its (nano)toxicity, and the release of reactive oxygen species plays a crucial role in many toxicological mechanisms. Determining chemical descriptors that account for the extension of reduction is necessary to understand such processes and necessary for predicting the reactivity of an unknown system. In the present work, we compute a set of chemical descriptors for selected surfaces of anatase and rutile TiO2. The aim is twofold: we want to provide chemically meaningful information on the surface reactivity, and benchmark the descriptors for two ab initio schemes. To do so, we compute the oxygen vacancy formation energy, and the corresponding electronic structure, in four slab models with two different computational schemes (DFT+U and DFTB). In this way, we characterize the robustness of the dataset, with the purpose of scaling up to more realistic model systems such as nanoparticles or explicit solvent, which are too computationally demanding for state-of-the-art density functional theory approaches.

Computational analysis of mechanical behavior and potential energy of thermoresponsive copper-tantalum nanoalloy.

Temperature, strain rate, and defects are important considerations in determining the mechanical properties of materials. The mechanical properties of nanocrystalline copper-tantalum (Cu-Ta) alloy are investigated using classical molecular dynamics simulation approach in which embedded atom method of potential with periodic boundary conditions in all directions has been adopted. Numerical simulation has been performed to predict the mechanical properties of nanocrystalline copper-tantalum alloy. The virtual tensile test has been conducted at a fixed strain rate and increasing temperature where the discreet change in temperature from 50 to 1600K has been used as a controlling parameter. The strain rate is fixed in the direction of the principal crystallographic planes and has not been affected by the change in temperature. The mechanical properties of the Cu-Ta nanocrystalline alloy such as yield strength, ultimate strength, and Young's modulus are observed. Further, simulations are carried out to analyze the vacancy formation energy with vacancy concentration and potential energy response at discrete temperatures. Nanocrystalline Cu-Ta alloy is observed to be more susceptible to failure at high temperatures. Particularly at 300K, the strength of nanocrystalline Cu-Ta is 6 GPa which decreases to 4 GPa at 1200K.

Influence of La doping concentration and A-site deficiency on electrical conductivity of La substituted SrTiO3 and its chemical compatibility with ScSZ

The influence of La doping concentration and A-site deficiency concentration on the electrical conductivity of La substituted SrTiO3 and its high-temperature chemical compatibility with ScSZ was investigated. It was found that the chemical compatibility between (LaxSr1-x)1-yTiO3-δ ((LxS1-x)1-yT) and 1CeO2-10Sc2O3–89ZrO2 (ScSZ) gradually deteriorates with the increase of La doping concentration from 10% to 40%. When the La doping concentration is 30–40%, chemical reaction will occur between LxS1-xT and ScSZ and La2Zr2O7 (LZO) will be generated, and the diffusion of Sc3+and Zr4+ in ScSZ to LxS1-xT is aggravated. A-site deficient (LxS1-x)1-yT can effectively inhibit the interfacial reaction and element interdiffusion between it and ScSZ. The first principle computation results indicate that the influence of La doping concentration and A-site deficiency on the vacancy formation energy (VFE) of Ti in (LxS1-x)1-yT determines its chemical compatibility with ScSZ. The results of electrical conductivity test and the first principle computation indicate that the La doping concentration and A-site deficiency will simultaneously influence the amount of Ti4+ to Ti3+ and the oxygen vacancy concentration in (LxS1-x)1-yT in reducing atmosphere, thus affecting its conductivity.

Molecular dynamics simulations of displacement cascade near precipitate in zirconium alloys

Precipitates play an important role in the evolution of irradiation-induced defects and mechanical property of irradiated metals. In this work, the effects of a Zr2Cu precipitate on the production and subsequent evolution of cascade-induced point defects (vacancies and interstitials) in ZrCu alloy were investigated by molecular dynamics simulations at room temperature. The simulation results show that the precipitate increases the number of residual point defects at the end of cascade. However, most of the residual defects reside in the precipitate and near precipitate boundary. In the matrix, more interstitials survive than vacancies. In addition, a defect-free region is seen in matrix and near precipitate boundary, indicating that the precipitate boundary traps vacancies/interstitials in matrix and retains them in the precipitate. To explain these observations, the formation energy and migration energy of point defects are calculated. The formation energies of both vacancy and interstitial decrease as they are moving to the precipitate boundary from matrix and precipitate, indicating that they can be absorbed by precipitate boundary and result in the defect-free region. However, the migration barrier of vacancy is lower than that of interstitial. Therefore, more vacancies in matrix are absorbed. The current work provides new insights into understanding the irradiation effects in zirconium alloys.

Investigation of the bulk and point defect properties in uranium–plutonium mixed oxides (U,Pu)O2 using DFT+U: Effect of a low americium content

We report an investigation of the effect of a low Am impurity content on bulk and point defect properties of mixed actinide oxide (U,Pu)O2. Using the generalized gradient approximation, (GGA + U) we study U0.75−zPu0.25AmzO2 with z = 3 and 6%. Several of its bulk properties have never been reported in the literature or are poorly known. The Hubbard term U is used to take into account the strong correlation effects related to the actinide 5f electrons. We find an electronic charge transfer between uranium and americium cations in the bulk crystal. Am(+IV) cations tend to easily reduce to Am(+III), and this reduction of Am(+IV) is compensated by the oxidation of U(+IV) to U(+V) in stoichiometric compounds. In turn, oxygen hypostoichiometry is accommodated by the reduction of U(+V) cations [which result from the presence of Am (+III) cations] before any reduction of the Pu cations. Furthermore, we show that Am induces a significant increase in the mixing enthalpy as well as a decrease in the lattice parameter of the (U,Pu)O2 solid solution, which is in agreement with early experimental studies. Finally, we show that americium facilitates the formation of oxygen vacancies in (U,Am)O2 compared to UO2, whereas it induces an increase in the formation energy of oxygen vacancies in (U,Pu,Am)O2 compared to (U,Pu)O2.

Mn-doped Ru/RuO2 nanoclusters@CNT with strong metal-support interaction for efficient water splitting in acidic media

Preparation of low-cost, highly activity and stable bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic media has great challenges. Here, a series of M-Ru/RuO2@CNT (M = Mn, Cd, Cu) bifunctional catalysts were synthesized by doping and strong metal-support interaction (SMSI) strategies to improve the activity and stability of the catalysts. The experiment results show that the optimized Mn–Ru/RuO2@CNT catalyst with ultra-small particle size (2.5 nm) has the best catalytic performance, and the OER and HER tests at 10 mA cm−2 in 0.5 M H2SO4 solution show excellent overpotentials of 177 mV and 30 mV respectively, which are better than most of the catalysts reported recently. In addition, current densities of 10 mA cm−2 and 100 mA cm−2 can be obtained at 1.43 V and 1.51 V when measuring water splitting and can last up to 100 h at a current density of 100 mA cm−2. And this is the first time to achieve the stability of acid water splitting of Ru-based catalyst under large current density. Density functional theory (DFT) calculations show that after manganese doping, the electronic structure is changed by charge redistribution between doped ions and ruthenium-based catalysts containing heterojunctions, and the binding energy of intermediates is optimized to improve the catalytic activity; the stability of the catalyst is improved by increasing the formation energy of ruthenium vacancy and preventing the formation of ruthenium vacancy.

Numerical study of defects in protactinium carbide

Actinide carbides, like ThC and UC, have been widely studied in recent years, on the contrary, protactinium carbide has merited less attention. One issue of PaC that has not been approached, neither experimentally nor theoretically is the formation of defects and the incorporation of impurities. Therefore, we will focus on these topics through a numerically study. To accomplish this, we calculate formation energies of vacancy, tetrahedral interstitial, Frenkel pair, Schottky and antisite defects. We find that C vacancies are the energetically preferred defect. We analyze density of states, charge densities and distortion of lattices with these kind of defects. We also study the effect of incorporation of oxygen and helium in vacancy and interstitial defects. In view of the lack of both theoretical and experimental results in PaC, we compared with UC and ThC. As a measure of the efficacy of the protactinium pseudopotential, which we generate, we calculate structural parameters and phonon spectrum.

Single vacancies at Σ5, Σ9 and Σ11 grain boundaries of copper and the geometrical factors that affect their site preference

The occurrence and distribution of vacancies has implications in many technologically relevant properties of materials. Despite their importance there is no detailed account of vacancy preference at atomic sites of frequently occurring grain boundaries (GBs) of fcc Cu. Here we present a computational investigation of single vacancy site preference at three high angle low index symmetric tilt GBs of fcc Cu: Σ5(310) [100], 36.9°; Σ9(2 2‾1‾) [110], 38.9°; and Σ11(1 1‾ 3) [110], 129.5°; performed with density functional theory (DFT). Using Voronoi tessellation data we developed a symmetry quantifying parameter (σ) based on the difference in surface area between the Voronoi polyhedron and the Wigner-Seitz sphere of the corresponding atomic site. We show that this parameter accurately quantifies changes in symmetry at each atomic site relative to the symmetry at the bulk fcc lattice. Subsequently, we performed a geometrical analysis that shows that the correlation between the values of σ with the coordination number (Cn) and with the volume expansion (Vx) are different for the three GBs, and that their dependencies on the distance from the GB planes are also different. We show that for most atomic sites, a reduction in symmetry is associated with changes in Vx and this is GB dependent. The GB that has the largest distortions relative to the bulk is the Σ5, closely followed by the Σ9, while the Σ11 has a decrease in symmetry which is only ¼ of the other two. At Σ5, changes in site Cn imply changes in the site symmetry to extents that do not occur for the other two GBs.For 100% of the sites at Σ5 and 50% of the sites at Σ9 and Σ11, the formation of vacancies is more favorable than in the bulk. However, the vacancy formation energies show that Σ11 has little ability to stabilize vacancies, which means that vacancies will occur at this GB with a similar frequency as in the bulk. These results show that the transferability of vacancy formation energies and vacancy distribution data between different GBs is nontrivial.