Holey penta-hexagonal graphene: a promising anode material for Li-ion batteries.

Carbon allotropes are widely used as anode materials in Li batteries, with graphite being commercially successful. However, the limited capacity and cycling stability of graphite impede further advancement and hinder the development of electric vehicles. Herein, through density functional theory (DFT) computations and ab initio molecular dynamics (AIMD) simulations, we proposed holey penta-hexagonal graphene (HPhG) as a potential anode material, achieved through active site designing. Due to the internal electron accumulation from the π-bond, HPhG follows a single-layer adsorption mechanism on each side of the nanosheet, enabling a high theoretical capacity of 1094 mA h g-1 without the risk of vertical dendrite growth. HPhG also exhibits a low open circuit voltage of 0.29 V and a low ion migration barrier of 0.32 eV. Notably, during the charge/discharge process, the lattice only expands slightly by 1.1%, indicating excellent structural stability. This work provides valuable insights into anode material design and presents HPhG as a promising two-dimensional material for energy storage applications.

Suppressed Fermi Level Pinning and Wide-Range Tunable Schottky Barrier in CrX3 (X = I, Br)/2D Metal Contacts.

CrX3 (X = I, Br) monolayers exhibit outstanding performance in spintronic devices. However, the Schottky barrier at the CrX3/electrode interface severely impedes the charge injection efficiency. Herein, we propose two-dimensional (2D) metals as electrodes to form van der Waals (vdW) contact with CrX3 monolayers and systematically explore the contact properties of CrX3/metal by density functional theory (DFT) calculations. The results demonstrate that the strongly suppressed Fermi level pinning (FLP) effect and the wide-range tunable Schottky barrier can be achieved in CrX3/metal contacts. Specifically, the n-type and the p-type Schottky contacts can be realized in CrX3/metal contacts by choosing 2D metal electrodes with different work functions. Importantly, the pinning factors for CrX3/metal contacts are exceptionally larger than other commonly studied 2D semiconductors, indicating the strongly suppressed FLP in CrX3/metal contacts, which leads to the wide-range tunable Schottky barrier. Our findings provide guidance to the choice of electrodes and promote the development of CrX3-based spin devices.

A polymeric hydrogel electrocatalyst for direct water oxidation.

Metal-free electrocatalysts represent a main branch of active materials for oxygen evolution reaction (OER), but they excessively rely on functionalized conjugated carbon materials, which substantially restricts the screening of potential efficient carbonaceous electrocatalysts. Herein, we demonstrate that a mesostructured polyacrylate hydrogel can afford an unexpected and exceptional OER activity - on par with that of benchmark IrO2 catalyst in alkaline electrolyte, together with a high durability and good adaptability in various pH environments. Combined theoretical and electrokinetic studies reveal that the positively charged carbon atoms within the carboxylate units are intrinsically active toward OER, and spectroscopic operando characterizations also identify the fingerprint superoxide intermediate generated on the polymeric hydrogel backbone. This work expands the scope of metal-free materials for OER by providing a new class of polymeric hydrogel electrocatalysts with huge extension potentials.

Narrowing the band gap and suppressing electron-hole recombination in ß-Fe2O3 by chlorine doping.

The effects of halogen (F, Cl, Br, I, and At) doping in the direct-band-gap ß-Fe2O3 semiconductor on its band structures and electron-hole recombination have been investigated by density functional theory. Doping Br, I, and At in ß-Fe2O3 leads to transformation from a direct-band-gap semiconductor to an indirect-band-gap semiconductor because their atomic radii are too large; however, F- and Cl-doped ß-Fe2O3 remain as direct-band-gap semiconductors. Due to the deep impurity states of the F dopant, this study focuses on the effects of the Cl dopant on the band structures of ß-Fe2O3. Two impurity levels are introduced when Cl is doped into ß-Fe2O3, which narrows the band gap by approximately 0.3 eV. After doping Cl, the light-absorption edge of ß-Fe2O3 redshifts from 650 to 776 nm, indicating that its theoretical solar to hydrogen efficiency for solar water splitting increases from 20.6% to 31.4%. In addition, the effective mass of the holes in halogen-doped ß-Fe2O3 becomes significantly larger than that in undoped ß-Fe2O3, which may suppress electron-hole recombination.

A two-dimensional Be2Au monolayer with planar hexacoordinate s-block metal atoms: a superconducting global minimum Dirac material with two perfect Dirac node-loops.

Using a starlike Be6Au7 - cluster as a building block and following the bottom-up strategy, an intriguing two-dimensional (2D) binary s-block metal Be2Au monolayer with a P6/mmm space group was theoretically designed. Both the Be6Au7 - cluster and the 2D monolayer are global minima featuring rule-breaking planar hexacoordinate motifs (anti-van't Hoff/Le Bel arrangement), and their high stabilities are attributed to good electron delocalization and electronic-stabilization-induced steric force. Strikingly, the Be2Au monolayer is a rare Dirac material with two perfect Dirac node-loops in the band structure and is a phonon-mediated superconductor with a critical temperature of 4.0 K. The critical temperature can be enhanced up to 11.0 K by applying compressive strain at only 1.6%. This study not only identifies a new binary s-block metal 2D material, namely Be2Au, which features planar hexacoordination, and a candidate superconducting material for further explorations, but also provides a new strategy to construct 2D materials with novel chemical bonding.

He's Yangchao Recipe Ameliorates Ovarian Oxidative Stress of Aging Mice under Consecutive Superovulation Involving JNK- And P53-Related Mechanism.

Objective: To evaluate the effects of He's Yangchao Recipe (HSYC) on ameliorating ovarian oxidative stress of aging mice under consecutive superovulation. Methods: An 8-month-old C57BL/6 female mouse was chosen to establish an aging model under ovarian hyperstimulation. Mice were randomly separated into four groups: R1 as the control group, R4 as the model group, NR4 with N-acetyl-L-cysteine (NAC) administration, and TR4 with HSYC administration. Oocyte collection, in vitro fertilization, and embryo culture were performed. The serum hormone levels were measured by enzyme-linked immunosorbent assays (ELISA); the reactive oxygen species (ROS) level of oocytes, the number of growing follicles, corpus luteum, ovulated oocytes, and developing embryos at each stage, along with the proportions of fragmented oocytes and abnormal mitochondria in granulosa cells (GCs) and the apoptosis rate of GCs were calculated; the mRNA and protein levels of JNK, P53, BAX were detected by real-time PCR and the Simple Western System. Results: HSYC enhanced estradiol, progesterone, and inhibin-B levels and increased growing follicle and corpus luteum and ovulated egg counts compared to the R4 group (P < 0.05), whereas it decreased the proportions of fragmented oocytes (P < 0.01); Meanwhile, embryos from mice subjected to four superovulation cycles with HSYC treated had a higher hatching potential. The ROS level of oocytes is downregulated by HSYC (P < 0.01) and the percentage of abnormal mitochondrial in ovaries of the TR4 group was also significantly declined compared to the R4 group (P < 0.05); the most TUNEL-positive cells proportion was detected in the R4 group; nevertheless, HSYC effectively attenuated this detrimental effect (P < 0.05). The mRNA and protein expressions of JNK and P53 in ovary tissues were reduced in the TR4 group while these genes were upregulated by repeated superovulation (P < 0.05). Conclusions: HSYC exerted promising effects on promoting the diminished ovarian reserve and decreased oocyte quality induced by both aging and consecutive ovarian superovulation, potentially via the ROS/JNK/p53 pathway.

Particle Swarm Predictions of a SrB8 Monolayer with 12-Fold Metal Coordination.

Materials containing planar hypercoordinate motifs greatly enriched the fundamental understanding of chemical bonding. Herein, by means of first-principles calculations combined with global minimum search, we discovered the two-dimensional (2D) SrB8 monolayer, which has the highest planar coordination number (12) reported so far in extended periodic materials. In the SrB8 monolayer, bridged B8 units are forming the boron monolayer consisting of B12 rings, and the Sr atoms are embedded at the center of these B12 rings, leading to the Sr@B12 motifs. The SrB8 monolayer has good thermodynamic, kinetic, and thermal stabilities, which is attributed to the geometry fit between the size of the Sr atom and cavity of the B12 rings, as well as the electron transfer from Sr atoms to electron-deficient boron network. Placing the SrB8 monolayer on the Ag(001) surface shows good commensurability of the lattices and small vertical structure undulations, suggesting the feasibility of its experimental realization by epitaxial growth. Potential applications of the SrB8 monolayer on metal ions storage (for Li, Na, and K) are explored.

Understanding the CH4 Conversion over Metal Dimers from First Principles.

Inspired by the advantages of bi-atom catalysts and recent exciting progresses of nanozymes, by means of density functional theory (DFT) computations, we explored the potential of metal dimers embedded in phthalocyanine monolayers (M2-Pc), which mimics the binuclear centers of methane monooxygenase, as catalysts for methane conversion using H2O2 as an oxidant. In total, 26 transition metal (from group IB to VIIIB) and four main group metal (M = Al, Ga, Sn and Bi) dimers were considered, and two methane conversion routes, namely *O-assisted and *OH-assisted mechanisms were systematically studied. The results show that methane conversion proceeds via an *OH-assisted mechanism on the Ti2-Pc, Zr2-Pc and Ta2-Pc, a combination of *O- and *OH-assisted mechanism on the surface of Sc2-Pc, respectively. Our theoretical work may provide impetus to developing new catalysts for methane conversion and help stimulate further studies on metal dimer catalysts for other catalytic reactions.

Atomically Dispersed Uranium Enables an Unprecedentedly High NH3 Yield Rate.

The low NH3 yield rate is a grand challenge for electrocatalytic N2 reduction to NH3. Herein, we report the first uranium single-atom catalyst (SAC) capable of catalyzing the electrochemical N2 reduction reaction (NRR). The uranium SAC features a low limiting potential (<0.5 V) and near-zero free energy changes for N2 adsorption and NH3 desorption. The integration of these merits enables the uranium SAC to afford an unprecedentedly high NH3 yield rate, 3-4 orders of magnitude higher than that of the Ru(0001) surface, which is widely recognized as an excellent NRR electrocatalyst. Further theoretical analysis reveals that the N2 reduction catalyzed by the uranium SAC is synergistically regulated by the d and f electrons of atomic uranium. This work proposes a promising solution (that is, atomically dispersed uranium) to the daunting challenge associated with the low NH3 yield rate, thus enabling the scalable production of NH3 via electrochemical N2 reduction.

2D auxetic material with intrinsic ferromagnetism: a copper halide (CuCl2) monolayer.

The discovery of ferromagnetism in monolayer transition metal halides exemplified by CrI3 has opened a new avenue in the field of two-dimensional (2D) magnetic materials, and more such 2D materials are waiting to be explored. Herein, using an unbiased structure search combined with first-principles calculations, we have identified a novel CuCl2 monolayer, which exhibits not only intrinsic ferromagnetism but also auxetic mechanical properties originating from the interplay of lattice and Cu-Cl tetrahedron symmetries. The predicted Curie temperature of CuCl2 reaches ∼47 K, and its ferromagnetism is associated with the strong hybridization between the Cu 3d and Cl 3p states in the configuration. Moreover, upon biaxial tensile strain or carrier doping, the CuCl2 monolayer can be converted from ferromagnetic to non-magnetic and from half-metal to metal. These properties endow this CuCl2 monolayer with great potential for applications in auxetic/spintronic nanodevices.

Tunable electronic properties and enhanced ferromagnetism in Cr2Ge2Te6monolayer by strain engineering.

Recently, as a new representative of Heisenberg's two-dimensional (2D) ferromagnetic materials, 2D Cr2Ge2Te6(CGT), has attracted much attention due to its intrinsic ferromagnetism. Unfortunately, the Curie temperature (TC) of CGT monolayer is only 22 K, which greatly hampers the development of the applications based on the CGT materials. Herein, by means of density functional theory computations, we explored the electronic and magnetic properties of CGT monolayer under the applied strain. It is demonstrated that the band gap of CGT monolayer can be remarkably modulated by applying the tensile strain, which first increases and then decreases with the increase of tensile strain. In addition, the strain can increase the Curie temperature and magnetic moment, and thus largely enhance the ferromagnetism of CGT monolayer. Notably, the obvious enhancement ofTCby 191% can be achieved at 10% strain. These results demonstrate that strain engineering can not only tune the electronic properties, but also provide a promising avenue to improve the ferromagnetism of CGT monolayer. The remarkable electronic and magnetic response to biaxial strain can also facilitate the development of CGT-based spin devices.

Controllable CO2 electrocatalytic reduction via ferroelectric switching on single atom anchored In2Se3 monolayer.

Efficient and selective CO2 electroreduction into chemical fuels promises to alleviate environmental pollution and energy crisis, but it relies on catalysts with controllable product selectivity and reaction path. Here, by means of first-principles calculations, we identify six ferroelectric catalysts comprising transition-metal atoms anchored on In2Se3 monolayer, whose catalytic performance can be controlled by ferroelectric switching based on adjusted d-band center and occupation of supported metal atoms. The polarization dependent activation allows effective control of the limiting potential of CO2 reduction on TM@In2Se3 (TM = Ni, Pd, Rh, Nb, and Re) as well as the reaction paths and final products on Nb@In2Se3 and Re@In2Se3. Interestingly, the ferroelectric switching can even reactivate the stuck catalytic CO2 reduction on Zr@In2Se3. The fairly low limiting potential and the unique ferroelectric controllable CO2 catalytic performance on atomically dispersed transition-metals on In2Se3 clearly distinguish them from traditional single atom catalysts, and open an avenue toward improving catalytic activity and selectivity for efficient and controllable electrochemical CO2 reduction reaction.

C9N4 and C2N6S3 monolayers as promising anchoring materials for lithium-sulfur batteries: weakening the shuttle effect via optimizing lithium bonds.

The notorious polysulfide shuttle effect is a crucial factor responsible for the degradation of Li-S batteries. A good way to suppress the shuttle effect is to effectively anchor dissoluble lithium polysulfides (LPSs, Li2Sn) on appropriate substrates. Previous studies have revealed that Li of Li2Sn is prone to interact with the N of N-containing materials to form Li-N bonds. In this work, by means of density functional theory (DFT) computations, we explored the possibility to form Li bonds on ten different N-containing monolayers, including BN, C2N, C2N6S3, C9N4, a covalent triazine framework (CTF), g-C3N4, p-C3N4, C3N5, S-N2S, and T-N2S, by examining the adsorption behavior of Li2Sn (n = 1, 2, 3, 4, 6, 8) on these two-dimensional (2D) anchoring materials (AMs), and investigated the performance of the formed Li bonds (if any) in inhibiting the shuttle effect. By comparing and analyzing the nitrogen content, the N-containing pore size, charge transfer, and Li bonds, we found that the N content and N-containing pore size correlate with the number of Li bonds, and the formed Li-N bonds between LPSs and AMs correspond well with the adsorption energies of the LPSs. The C9N4 and C2N6S3 monolayers were identified as promising AMs in Li-S batteries. From the view of Li bonds, this work provides guidelines for designing 2D N-containing materials as anchoring materials to reduce the shuttle effect in Li-S batteries, and thus improving the performance of Li-S batteries.

Enhancing Ferromagnetism and Tuning Electronic Properties of CrI3 Monolayers by Adsorption of Transition-Metal Atoms.

Among first experimentally discovered two-dimensional (2D) ferromagnetic materials, chromium triiodide (CrI3) monolayers have attracted particular attention due to their potential applications in electronics and spintronics. However, the Curie temperature Tc of the CrI3 monolayer is below room temperature, which greatly limits practical development of the devices. Herein, using density functional theory calculation, we explore how the electronic and magnetic properties of CrI3 monolayers change upon adsorption of 3d transition-metal (TM) atoms (from Sc to Zn). Our results indicate that the electronic properties of the TM-CrI3 system can be tuned from semiconductor to metal/half-metal/spin gapless semiconductor depending on the choice of the adsorbed TM atoms. Moreover, the adsorption can improve the ferromagnetic stability of CrI3 monolayers by increasing both magnetic moments and Tc. Notably, Tc of CrI3 with Sc and V adatoms can be increased by nearly a factor of 3. We suggest postsynthesis doping of 2D CrI3 by deposition of TM atoms as a new route toward potential applications of TM-CrI3 systems in nanoelectronic and spintronic devices.

MX Anti-MXenes from Non-van der Waals Bulks for Electrochemical Applications: The Merit of Metallicity and Active Basal Plane.

Two-dimensional transition-metal compounds (2DTMCs) are promising materials for electrochemical applications, but 2DTMCs with metallicity and active basal planes are rare. In this work, we proposed a simple and effective strategy to extract 2DTMCs from non-van der Waals bulk materials and established a material library of 79 2DTMCs, which we named as anti-MXenes since they are composed of one M atomic layer sandwiched by two X atomic layers. By means of density functional theory computations, 24 anti-MXenes were confirmed to be thermodynamically, dynamically, mechanically, and thermally stable. The metallicity and active basal plane endow these anti-MXenes with potential as excellent electrode materials, for example, as electrocatalysts for hydrogen evolution reactions (HER). Among the noble-metal free anti-MXenes with favorable H-binding, CuS can boost HER at the whole range of H coverages, while CoSi, FeB, CoB, and CoP show promise for HER at some specific H coverages. The active sites are the tetra-coordinating nonmetal atoms at the basal planes, thus rendering a very high density of active sites for these materials. CoB is also a promising anode material for lithium-ion batteries, showing low Li diffusion energy barriers, a very high capacity, and a suitable open circuit voltage. This work promotes the "computational exfoliation" of 2D materials from non-van der Waals bulks and exemplifies the applications of anti-MXenes in various electrochemical processes.

Enhanced performance of Mo2P monolayer as lithium-ion battery anode materials by carbon and nitrogen doping: a first principles study.

By means of density functional theory (DFT) computations, we explored the potential of carbon- and nitrogen-doped Mo2P (CMP and NMP) layered materials as the representative of transition metal phosphides (TMPs) for the development of lithium-ion battery (LIB) anode materials, paying special attention to the synergistic effects of the dopants. Both CMP and NMP have exceptional stabilities and excellent electronic conductivity, and a high theoretical maximum storage capacity of ∼ 486 mA h g-1. Li-ion diffusion barriers on the two-dimensional (2D) CMP and NMP surfaces are extremely low (∼0.036 eV), and it is expected that on these 2D layers Li can diffuse 104 times faster than that on MoS2 and graphene at room temperature, and both monolayers have relatively low average open-circuit voltage (0.38 and 0.4 eV). All these exceptional properties make CMP and NMP monolayers as promising candidates for high-performance LIB anode materials, which also demonstrates that simple doping is an effective strategy to enhance the performance of anode materials in rechargeable batteries.

In Situ Observation of Non-Classical 2-Norbornyl Cation in Confined Zeolites at Ambient Temperature.

Carbonium ions are an important class of reaction intermediates, but their dynamic evolution is difficult to be monitored by in situ techniques under experimental conditions because of their extremely short lifetime. Probably the most famous case is 2-norbornyl cation (2NB+ ): its existing form (classical or non-classical) had been debated for decades, until the concrete proof of non-classical geometry was achieved by X-ray crystallographic characterization at ultra-low temperature (40 K) and super acidic environment. However, we lack the understanding about 2NB+ at ambient conditions. Herein, by taking advantage of the confinement effect and delocalized acidic environment of zeolites, we successfully stabilized 2NB+ and unequivocally confirmed its "non-classical" structure inside the ZSM-5 zeolite by ab initio molecular dynamics simulations and 13 C solid-state nuclear magnetic resonance experiments. It is the first time to in situ observe the non-classical 2NB+ without the super acidic environment at ambient temperature, which provides a new strategy to expand the carbocation chemistry.

Rational Prediction of Single Metal Atom Supported on Two-Dimensional Metal Diborides for Electrocatalytic N2 Reduction Reaction with Integrated Descriptor.

Nitrogen reduction reaction (NRR) plays an important role in chemical industry, so it is significant to develop low-cost and efficient electrocatalysts for nitrogen fixation instead of the traditional Haber-Bosch process. In this paper, the electrocatalytic performance of various single atoms doped on two-dimensional metal diborides with a B vacancy for N2 reduction to ammonia is calculated and predicted. By screening numerous catalysts, we find that Ti@VB2 is the most active catalyst for NRR, and the limiting potential of Ti@VB2 for NRR is -0.61 V. Through high-throughput search and LASSO regression, an integrated descriptor combining the intrinsic properties of the single transition metal atom (TM) and the substrate (MB2) is proposed, which can fit the relationship between intrinsic properties of catalysts and NRR activity well. Therefore, this study not only discovers a promising electrocatalyst for nitrogen fixation but also provides a strategy for predicting the activity of catalysts.

Enhanced Ferromagnetism and Tunable Magnetism in Fe3GeTe2 Monolayer by Strain Engineering.

Recent discovery of intrinsic ferromagnetism in Fe3GeTe2 (FGT) monolayer [Deng, Y.; Nature 2018, 563, 94-99; Fei, Z.; Nat. Mater. 2018, 17, 778-782] not only extended the family of two-dimensional (2D) magnetic materials but also stimulated further interest in the possibility to tune their magnetic properties without changing the chemical composition or introducing defects. By means of density functional theory computations, we explore strain effects on the magnetic properties of the FGT monolayer. We demonstrate that the ferromagnetism can be largely enhanced by the tensile strain in the FGT monolayer due to the competitive effects of direct exchange and superexchange interaction. The average magnetic moments of Fe atoms increase monotonically with an increase in biaxial strain from -5 to 5% in FGT monolayer. The intriguing variation of magnetic moments with strain in the FGT monolayer is related to the charge transfer induced by the changes in the bond lengths. Given the successful fabrication of the FGT monolayer, the strain-tunable ferromagnetism in the FGT monolayer can stimulate the experimental effort in this field. This work also suggests an effective route to control the magnetic properties of the FGT monolayer. The pronounced magnetic response toward the biaxial strain can be used to design the magnetomechanical coupling spintronics devices based on FGT.

Metallic FeSe monolayer as an anode material for Li and non-Li ion batteries: a DFT study.

By means of density functional theory computations, we explored the electrochemical performance of an FeSe monolayer as an anode material for lithium and non-lithium ion batteries (LIBs and NLIBs). The electronic structure, adsorption, diffusion, and storage behavior of different metal atoms (M) in FeSe were systematically investigated. Our computations revealed that M adsorbed FeSe (M = Li, Na and K) systems show metallic characteristics that give rise to good electrical conductivity and mobility with low activation energies for diffusion (0.16, 0.13 and 0.11 eV for Li, Na, and K, respectively) of electrons and metal atoms in the materials, indicative of a fast charge/discharge rate. In addition, the theoretical capacities of the FeSe monolayer for Li, Na and K can reach up to 658, 473, and 315 mA h g-1, respectively, higher than that of commercial graphite (372 mA h g-1 for Li, 284 mA h g-1 for Na, and 273 mA h g-1 for K), and the average open-circuit voltage is moderate (0.38-0.88 V for Li, Na and K). All these characteristics suggest that the FeSe monolayer is a potential anode material for alkali-metal rechargeable batteries.