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Li–O2 batteries are considered promising electrochemical energy storage devices due to their high specific capacity and low cost.

When benchmarked against the extended Pt(111), slightly weaker adsorption and stronger cohesion properties of surface Pt are required to improve activity and durability for the oxygen reduction reaction, respectively, making it challenging to meet both requirements on one surface. Here, using Pt(111) over-layers stressed and modified by Pt-TM (TM = Fe, Co, Ni, V, Cu, Ag, and Pd) intermetallics as examples, we theoretically identified ten promising catalysts by synergistically tailoring the skin thickness and substrate chemical ordering to simultaneously achieve weak adsorption and strong cohesion. More specifically, compared with Pt(111), all candidates exhibit 10-fold enhanced activity, half of which show improved durability, such as mono-layer skin on L1

In this work, based on first-principles calculations, we theoretically predict two kinds of two-dimensional tetragonal Si–Se compounds, Si2Se2 and SiSe2, as the anode materials for alkali metal-ion batteries.

In this work, the stacking fault energy (SFE), surface energy, and Rice ratio are systematically investigated to elucidate the effect of solute atoms (Cr, Ta, V, W, Y, and Zr) on the mechanical properties of TiC. As for the site preference of solute atoms, the calculation results show that all solutes prefer the Ti sites in the TiC. Considering the solute effect on the SFE, four slip systems, such as ( 001 ) 1 1 ‾ 0> , ( 110 ) 1 1 ‾ 0> , ( 111 ) 1 1 ‾ 0> , and ( 111 ) 11 2 ‾ > are systematically investigated. For the undoped structure, we found that the ( 110 ) 1 1 ‾ 0> slip system is most likely to occur in the TiC due to its lower SFE, which is consistent with the experimental results. Furthermore, it is found that solute atoms Cr, V, W will decrease the SFE and improve the ductility of TiC, while doping Ta and Zr will increase SFE and reduce its ductility. Besides, it is worth noting that doping Y atoms not only decrease the stacking fault energy but also reduces the ductility of the material. Furthermore, results also show that all doped solutes are beneficial to the formation of partial dislocation in the TiC.

Electrochemical cycling induces transition-metal (TM) ion migration and oxygen vacancy formation in layered transition-metal oxides, thus causing performance decay. Here, a combination of ab initio calculations and atomic level imaging is used to explore the TM migration mechanisms in LiNi1/3Mn1/3Co1/3O2 (NMC333). For the bulk model, TM/Li exchange is an favorable energy pathway for TM migration. For the surface region with the presence of oxygen vacancies, TM condensation via substitution of Li vacancies (TMsub) deciphers the frequently observed TM segregation phenomena in the surface region. Ni migrates much more easily in both the bulk and surface regions, highlighting the critical role of Ni in stabilizing layered cathodes. Moreover, once TM ions migrate to the Li layer, it is easier for TM ions to diffuse and form a TM-enriched surface layer. The present study provides vital insights into the potential paths to tailor layered cathodes with a high structural stability and superior performance.

The impact of interfacial electric fields on electrochemical reaction kinetics is assessed in the context of hydrogen electrocatalysis. Recent efforts have proposed that interfacial electric field strength, as described by the electrode’s potential of zero free charge (pzfc), contributes to the slow kinetics of the alkaline hydrogen evolution and oxidation reactions (HER/HOR) by hindering solvent reorganization. In this work, we examine through single-crystal voltammetry the importance of the interfacial electric field strength on hydrogen reaction kinetics using three complementary approaches: (1) correlating the pzfc with reaction kinetics using caffeinated Pt as a model surface; (2) varying the electrolyte ionic strength at constant pH; and (3) probing solvent dynamics via caffeinated kinetic isotope effects (KIEs). Our results show that pzfc seems to correlate with HER/HOR kinetics, but also suggest that the effect more likely originates from activation barriers to the reaction elementary steps than from electric field effects on solvent dynamics. Although the importance of interfacial phenomena such as the electrode’s pzfc and water reorganization energy are well established, the pzfc may not be a mechanistic descriptor of the alkaline hydrogen reaction kinetics. Surface additives such as caffeine may help elucidate the origin behind the slow alkaline HER/HOR kinetics and ways to manipulate it.

To understand the hydrogen (H) behavior in the carbide precipitates, the dissolution and diffusion properties of interstitial H in the transition metal carbide (TMC; TM = Hf, Nb, Ta, Ti, V, and Zr) were studied by first-principles calculations. In these carbides, it can be seen that H tends to occupy the trigonal site (tri2-site) surrounded by three transition metal atoms and one carbon atom rather than the face center (fc-site) and the body center (bc-site) which with the larger space. We found that the bonding interaction between H atom and the nearest-neighbor (1NN) carbon atom is the dominant influence on the stability of H dissolution. Besides, we obtained the temperature-dependent solubility and diffusion coefficients of H in TMC and pure vanadium through Sievert's law and transition state theory. Compared with pure vanadium, H shows the worse solubility in TMC, and it is more difficult for hydrogen to migrate in TMC, but segregate toward the interface. Furthermore, it is interesting to note that, the diffusion barrier and the H solution energy show a linear relationship for transition metal carbides in the same period. These results can help us deepen the understanding of H behavior in vanadium alloys strengthened by carbide precipitates, and furtherly providing the theoretical guidance for the design of alloys with excellent performance.

Ni-based layered transition-metal oxides are advanced cathode materials used in rechargeable Na-ion batteries due to their high specific capacity; however, their applications are blocked by irrever...

Selenium (Se) is a promising cathode material for next-generation alkali metal–ion batteries due to its high volumetric capacity and good conductivity. Using a first-principles approach, the presen...

High-entropy alloys (HEAs) have received much attention for the development of nuclear materials because of their excellent irradiation tolerance. In the present study, the generation and evolution of irradiation-induced defects in the NiCoCrFe HEA were investigated by molecular dynamics (MD) simulations to understand the mechanisms of its irradiation tolerance compared with bulk Ni. The displacement cascades were simulated for the energies of primary knock-on atoms (PKA) ranging from 10 to 50 keV to understand the irradiation resistance in HEAs. In general, there are more displaced atoms produced in the thermal spike phase, but fewer defects survived at the end of the cascades in the NiCoCrFe alloy than in Ni. Both interstitial and vacancy clusters increase in size or number with increasing PKA energy in both materials, but they do so more slowly in the NiCoCrFe HEA. The delayed damage accumulations in the NiCoCrFe HEA are attributed to the high defect recombination caused by the following two mechanisms. First, the enhanced thermal spike and the low thermal conductivity of HEAs for heat dissipation result in the higher efficiency of defect recombination. Furthermore, the substantially small binding energies of interstitial loops in the NiCoCrFe HEA, as compared with those in Ni, are responsible for the delayed interstitial clustering in the NiCoCrFe HEA.

The structure and properties of materials under neutron irradiation are an important basis in future fusion reactors. In the absence of fusion neutron sources for irradiation experiments, it is increasingly important and urgent to carry out neutron irradiation simulations on fusion reactor materials and then establish complete databases of defect properties and collisional cascades, where the first and foremost step is to select suitable interatomic potentials for atomistic-level simulations. In this work, six typic interatomic potentials for tungsten (W) are evaluated and reviewed systematically for radiation damage simulations. The relative lattice stability and elastic constants of bulk W are considered first with those potentials; then, the properties of point defects and defect clusters at interstitial sites and vacancies are obtained by molecular statics/dynamics simulations. The formation energies of interstitial/vacancy clusters, 1/2 〈111〉 and 〈100〉 dislocation loops in W and the threshold displacement energies along different directions are also determined. In addition, the extended defects are further investigated, such as free surfaces and the energy profiles of 1/2 〈111〉 {110} and 1/2 〈111〉 {112} stacking faults. The current results provide a reference for selecting W potentials to simulate the radiation damage.

The development of alkali metal-ion batteries requires anode materials with high capacity and fast kinetics. The present study theoretically investigates the double-layer honeycomb (DLHC) AlP as a ...

Towards practical lithium–sulfur batteries, the rational design of a sulfur host that enables highly efficient sulfur electrochemistry and high areal sulfur loading is essential but still a challenge. Here, a class of 3D nanocomposite architecture characterised by a necklace-like structure that contains intertwined carbon-nanotubes (CNTs) and defective Prussian blue (PB) nanocrystals is developed as the sulfur host. Benefiting from the fact that a 3D CNT conductive skeleton can provide efficient ion/electron channels and the abundant Lewis acidic sites in PB can effectively entrap lithium polysulfide (LiPS) species, the S@PB/CNT composite cathode exhibits high reversibility, stable cycling performance, and fast kinetics. More importantly, the LiPS adsorption capacity of PB materials and the kinetics of LiPS conversion on PB is highly dependent on the amount of [Fe(CN)6] vacancies based on both theoretical and experimental studies, which may further shed light on the interfacial phenomena between the PB sulfur host and soluble LiPS in the electrolyte.

Li2TiSiO5 (LTSO) has a theoretical specific capacity of up to 315 mA h g−1 with a suitable working potential (0.28 V vs. Li/Li+). However, the electronic structure of Li2TiSiO5 is firstly investigated by theoretical calculation based on the first-principles approach, and the results demonstrate that Li2TiSiO5 acts as the insulator for transferring electrons. Therefore, the framework with better conductivity is very essential for Li2TiSiO5 to enhance the charge transfer kinetics. Nitrogen-doped carbon encapsulated Li2TiSiO5 nanofibers (LTSO/NDC nanofibers) are obtained by using carbamide as a nitrogen source through an electrospinning technique. The nitrogen-doped carbon matrix with high electronic conductivity improves the electrochemical properties of LTSO significantly. The diffusion coefficient of lithium ions (DLi+) is greatly improved by manual calculation. The LTSO/NDC nanofiber electrode can deliver 371.7 mA h g−1 at 0.1 A g−1 and 361.1 mA h g−1 at 0.2 A g−1, and also shows a comparable cycle performance which could endure a long cycle over 800 cycles at 0.5 A g−1 almost without capacity decay. Hence, the LTSO/NDC nanofiber anode with a high rate and a long life provides a new direction for the realization of LTSO-based compounds in lithium ion batteries.

Ta-doped TiO2/C nanofibers are synthesized by an electrospinning method. First-principles calculations reveal that the Ta dopant can lower the Li/K diffusion barrier, which is beneficial for improving the rate capability. According to the electronic structure analysis, the dopant can obviously shift the conduction band of TiO2 downward, resulting in significantly improved electronic conductivity. Ta doping causes phase transformation from anatase to rutile, and increases the specific surface area. The well-designed rutile Ta-doped TiO2/C nanofibers show outstanding electrochemical properties in both Li-metal half cells and K-metal half cells, which are much better than those of pristine anatase TiO2/C nanofibers. At 2 A g−1, 5% rutile Ta-doped TiO2/C nanofibers could deliver high reversible specific capacities of 399 mA h g−1 in Li-ion batteries after 1000 cycles whereas deliver 148 mA h g−1 in K-ion batteries after 800 cycles. When assembled, the full cells with 5% rutile Ta-doped TiO2/C nanofibers as the anode and commercial LiFePO4/perylene-3,4,9,10-tetracarboxylic dianhydride as the cathode show excellent cycling performance and can light up more than 18 LEDs. These results demonstrate that Ta-doped TiO2/C nanofibers are a promising anode material for Li/K ion batteries.

Mechanical responses of tungsten (W) and its alloys are strongly controlled by the properties of 1/2 screw dislocations. Rhenium (Re), as a typical alloying and transmutation element in W, can substantially modify the properties of the dislocations, thus the plasticity of the materials. In this study, we investigate the interaction of Re and Re clusters with the screw dislocations in W by first-principles calculations in combination with theoretical models. Specifically, we propose two competing and Re-distribution dependent mechanisms, i.e. “ductilizing effect” and “hardening effect”; both are crucial to the mechanical properties of W. For the ductilizing effect, dispersed Re atoms weaken the surrounding interatomic interaction and reduce the shear resistance, thus facilitating the motion of the dislocation. In contrast, for the hardening effect, Re clusters formed by aggregated Re atoms due to irradiation can increase the Peierls stress and energy, thus hindering the motion of the dislocations. The proposed mechanisms shed light on the experimental observations that there is a Re-induced transition from ductilizing to hardening due to irradiation. The current work provides a theoretical guidance to the development of W-based future fusion materials in search of ductilizing alloying elements.

High-entropy alloys (HEAs) hold promise as candidate structural materials in future nuclear energy systems. Body-centred cubic V-Ti-Ta-Nb HEAs have received extensive attention due to their excellent mechanical properties. In this work, the Finnis-Sinclair interatomic potential for quaternary V-Ti-Ta-Nb HEAs has been fitted based on the defect properties obtained with the density functional theory (DFT) calculations. The new potential for Nb accurately reproduces the vacancy formation energy, vacancy migration energy and interstitial formation energy. The typical radiation defect properties predicted by the alloy potential were consistent with the DFT results, including the binding energies between substitutional solute atoms, the binding energy between substitutional atoms and vacancies, and the formation energy of interstitial solute atoms. In addition, the mixing enthalpies of the alloys were also consistent with the DFT results. The present potential can also describe reasonably the collision cascade process of quaternary V-Ti-Ta-Nb HEAs.

In this paper, we report a formation mechanism of $1/2\ensuremath{\langle}111\ensuremath{\rangle}$ interstitial dislocation loops via the collapse of C15 clusters in bulk tungsten. The interstitial atoms formed C15 clusters in only a few picoseconds within a displacement cascade, and the transformation from C15 clusters to $\ensuremath{\langle}111\ensuremath{\rangle}$ interstitial loops was observed in both classical molecular dynamics and accelerated molecular dynamics simulations. This transformation was further confirmed under compressive stress, and it was determined to be accelerated once the $\ensuremath{\langle}111\ensuremath{\rangle}$ loops reacted with the C15 clusters. Three possible transformation processes were proposed, namely the C15 cluster directly transforming to $\ensuremath{\langle}111\ensuremath{\rangle}$ loops/clusters, a partial transformation to a $\ensuremath{\langle}111\ensuremath{\rangle}$ cluster with high mobility, thus leaving a shrunken C15 cluster behind, and a partially transformed $\ensuremath{\langle}111\ensuremath{\rangle}$ cluster but pinned by the adjacent shrunken C15 cluster. The formation mechanism provides an essential reference for predicting the evolution of microstructures in tungsten-based materials under irradiation.

High-entropy alloys (HEAs) and medium-entropy alloys (MEAs) have attracted a great deal of attention for developing nuclear materials because of their excellent irradiation tolerance. Herein, formation and evolution of radiation-induced defects in NiCoFe MEA and pure Ni are investigated and compared using molecular dynamics simulation. It is observed that the defect recombination rate of ternary NiCoFe MEA is higher than that of pure Ni, which is mainly because, in the process of cascade collision, the energy dissipated through atom displacement decreases with increasing the chemical disorder. Consequently, the heat peak phase lasts longer, and the recombination time of the radiation defects (interstitial atoms and vacancies) is likewise longer, with fewer deleterious defects. Moreover, by studying the formation and evolution of dislocation loops in Ni–Co–Fe alloys and Ni, it is found that the stacking fault energy in Ni–Co–Fe decreases as the elemental composition increases, facilitating the formation of ideal stacking fault tetrahedron structures. Hence, these findings shed new light on studying the formation and evolution of radiation-induced defects in MEAs.

An effective and reliable Finnis–Sinclair (FS) type potential is developed for large-scale molecular dynamics (MD) simulations of plasticity and phase transition of magnesium (Mg) single crystals under high-pressure shock loading. The shock-wave profiles exhibit a split elastic–inelastic wave in the [0001]HCP shock orientation and a three-wave structure in the [10-10]HCP and [-12-10]HCP directions, namely, an elastic precursor, a followed plastic front, and a phase-transition front. The shock Hugoniot of the particle velocity (U p) vs the shock velocity (U s) of Mg single crystals in three shock directions under low shock strength reveals apparent anisotropy, which vanishes with increasing shock strength. For the [0001]HCP shock direction, the amorphization caused by strong atomic strain plays an important role in the phase transition and allows for the phase transition from an isotropic stressed state to the product phase. The reorientation in the shock directions [10-10]HCP and [-12-10]HCP, as the primary plasticity deformation, leads to the compressed hexagonal close-packed (HCP) phase and reduces the phase-transition threshold pressure. The phase-transition pathway in the shock direction [0001]HCP includes a preferential contraction strain along the [0001]HCP direction, a tension along [-12-10]HCP direction, an effective contraction and shear along the [10-10]HCP direction. For the [10-10]HCP and [-12-10]HCP shock directions, the phase-transition pathway consists of two steps: a reorientation and the subsequent transition from the reorientation hexagonal close-packed phase (RHCP) to the body-centered cubic (BCC). The orientation relationships between HCP and BCC are (0001)HCP ⟨-12-10⟩HCP // {110}BCC ⟨001⟩BCC. Due to different slipping directions during the phase transition, three variants of the product phase are observed in the shocked samples, accompanied by three kinds of typical coherent twin-grain boundaries between the variants. The results indicate that the highly concentrated shear stress leads to the crystal lattice instability in the elastic precursor, and the plasticity or the phase transition relaxed the shear stress.