Construction of ultrathin solid electrolyte interface on Zn anode within 1 min for high current operating condition.

Organic acid treatment can facilitate the in-situ formation of a solid electrolyte interface (SEI) on Zn foil protecting the anode from corrosion. However, the generation of hydrogen (H2) during this process is inevitable, which is often considered detrimental to getting compact SEI. Herein, a H2 film-assisted method is proposed under concentrated Amino-Trimethylene-Phosphonic-Acid to construct ultrathin and dense SEI within 1 min. Specifically, the (002) crystal planes survive from the etching process of 1 min due to the adhered H2, inducing uniform deposition and enhanced corrosion-resistance. Moreover, the H2 can effectively regulate the reaction rate, leading to ultrathin SEI and initiating a morphology preservation behavior, which has been neglected by the previous reports. The quick-formed SEI has excellent compatibility, low resistance and effective isolation of electrolyte/anode, whose advantages work together with exposed (002) planes to get accustomed to high-current surge, leading to the ZAC1@Zn//ZAC1@Zn consistently cycling over 800 h at 15 mA cm-2 and 15 mAh cm-2, the ZAC1@Zn//Cu preserves high reversibility (CE 99.7 %), and the ZAC1@Zn//MVO exhibits notable capacity retention at 191.7 mAh/g after 1000 cycles.

Investigation of the sodium-ion transport mechanism and elastic properties of double anti-perovskite Na3S0.5O0.5I.

Sodium-rich anti-perovskites have unique advantages in terms of composition tuning and electrochemical stability when used as solid-state electrolytes in sodium-ion batteries. However, their Na+ transport mechanism is not clear and Na+ conductivity needs to be improved. In this paper, we investigate the stability, elastic properties and Na+ transport mechanisms of both the double anti-perovskite Na3S0.5O0.5I and anti-perovskite Na3OI. The results indicate that the NaI Schottky defect is the most favorable intrinsic defect for Na+ transport and due to the substitution of S2- for O2-, Na3S0.5O0.5I has stronger ductility and higher Na+ conductivity compared to Na3OI, despite the electrochemical window being slightly narrower. Divalent alkaline earth metal dopants can increase the Na+ vacancy concentration, while impeding Na+ migration. Among the dopants, Sr2+ and Ca2+ are the optimal dopants for Na3S0.5O0.5I and Na3OI, respectively. Notably, the Na+ conductivity of the non-stoichiometric Na3S0.5O0.5I at room temperature is 1.2 × 10-3 S cm-1, indicating its great potential as a solid-state electrolyte. Moreover, strain effect calculations show that biaxial tensile strain is beneficial for Na+ transport. Our work reveals the sodium-ion transport mechanism and elastic properties of double anti-perovskites, which is of great significance for the development of solid-state electrolytes.

A theoretical study of novel orthorhombic group-IVB nitride halide monolayers for photocatalytic overall water splitting.

Hydrogen energy is very important as a new clean energy source to combat the growing environmental problems. In this regard, novel photocatalyst materials for water splitting have a wide range of applications. Using first principles calculations, we theoretically studied three orthorhombic group-IVB nitride halide monolayers, Hf2N2Br2, Janus HfZrN2Br2 and Janus Hf2N2ClBr. The energy, dynamic and thermal stabilities are demonstrated for all three monolayers. Using the HSE hybrid functional, the calculations reveal that they are direct band gap semiconductors with suitable band edge positions, good optical absorptions, and anisotropic carrier mobilities, which makes them promising for water splitting applications. Importantly, the photogenerated carriers provide enough driving force to trigger the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) within wide pH ranges, and then overall water splitting can be achieved spontaneously. We conclude that orthorhombic group-IVB nitride halide monolayers have potential applications in photocatalytic nanodevices.

Insights on transport performance, thermodynamic properties, and mechanical properties of Ruddlesden-Popper antiperovskite LiBr(Li2OHBr)2 and LiBr(Li3OBr)2.

Due to high ion conductivity, low cost, and adjustable composition, antiperovskite has attracted much attention as a potentially useful material in solid-state batteries. Compared with simple antiperovskite, Ruddlesden-Popper (R-P) antiperovskite is an updated material, which is not only more stable but also reported to significantly enhance conductivity when added to simple antiperovskite. However, systematic theoretical research on R-P antiperovskite is scarce, hindering its further development. In this study, the recently reported easily synthesized R-P antiperovskite LiBr(Li2OHBr)2 is calculated for the first time. Comparative calculations were conducted on the transport performance, thermodynamic properties, and mechanical properties of H-rich LiBr(Li2OHBr)2 and H-free LiBr(Li3OBr)2. Our results indicate that due to the presence of protons, LiBr(Li2OHBr)2 is more prone to defects, and synthesizing more LiBr Schottky defects can improve its Li-ion conductivity. Young's modulus of the LiBr(Li2OHBr)2 is as low as 30.61 GPa, which is beneficial for its application as a sintering aid. However, the calculated Pugh's ratio (B/G) of 1.28 and 1.50, respectively, indicates that R-P antiperovskites LiBr(Li2OHBr)2 and LiBr(Li3OBr)2 exhibit mechanical brittleness, which is not conducive to its application as solid electrolytes. Through quasi-harmonic approximation, we found that the linear thermal expansion coefficient of LiBr(Li2OHBr)2 is 2.07 × 10-5 K-1, which is more advantageous in matching electrodes than LiBr(Li3OBr)2 and even simple antiperovskites. Overall, our research provides comprehensive insights into the practical application of R-P antiperovskite in solid-state batteries.

Mass-producible in-situ amorphous solid/electrolyte interface with high ionic conductivity for long-cycling aqueous Zn-ion batteries.

Although aqueous Zn-ion batteries (aZIBs) have garnered significant attention, they are yet to be commercialized due to severe corrosion and dendrite growth on Zn anodes. In this work, an artificial solid-electrolyte interface (SEI) with amorphous structure was created in-situ on the anode by immersing Zn foil in ethylene diamine tetra(methylene phosphonic acid) sodium (EDTMPNA5) liquid. This facile and effective method provides the possibility for Zn anode protection in large-scale applications. Experimental results, combined with theoretical calculations, indicate that the artificial SEI remains intact and adheres tightly to the Zn substrate. The negatively-charged phosphonic acid groups and disordered inner structure offer adequate sites for rapid Zn2+ transference and facilitate [Zn(H2O)6]2+ desolvation during charging/discharging. Due to the synergistic effect of the aforementioned advantages, the artificial SEI endows high Coulombic efficiency (CE, 99.75%) and smooth Zn deposition/stripping under the SEI. The symmetric cell exhibits a long cycling life of over 2400 h with low-voltage hysteresis. Additionally, full cells with MVO cathodes demonstrate the superiority of the modified anodes. This work provides insight into the design of in-situ artificial SEI on the Zn anode and self-discharge suppression to expedite the practical application of aZIBs.

Uncovering the Enhancement Mechanism of the Oxygen Reduction Reaction on Perovskite/Ruddlesden-Popper Oxide Heterostructures (Nd,Sr)CoO3/(Nd,Sr)2CoO4 and (Nd,Sr)CoO3/(Nd,Sr)3Co2O7.

Although the perovskite (Nd,Sr)CoO3 (NSC113)/Ruddlesden-Popper (R-P) oxide (Nd,Sr)2CoO4 (NSC214) heterostructure is reported to improve the oxygen reduction reaction (ORR) activity by 2-3 orders of magnitude, the enhancement mechanism remains unclear. For the first time, we conclude that there are two main factors that can enhance the ORR activity: (1) Oxygen adsorbed on such heterostructures would gain more electrons, promoting the oxygen adsorption. (2) The more distant rock-salt layers on the heterointerfaces can facilitate the insertion of interstitial oxygen and form a high-speed transport channel of interstitial oxygen. Moreover, the perovskite/double-layered R-P oxide heterostructure, which has not been reported yet, is predicted to have better ORR performance than the perovskite/single-layered R-P oxide heterostructure. Our work elucidates the ORR enhancement mechanism on perovskite/R-P oxide heterostructures from the atomic level, which is demonstrated by experiments and, thus, is very meaningful for the development of high-performance electrochemical devices.

Spin Hall effect from bipolaron dynamics in organics.

Using an extended Su-Schrieffer-Heeger model and a nonadiabatic dynamics method, we investigate the dynamics of bipolarons in coupled nondegenerate organic chains including the spin-orbit coupling and interchain coupling. By tracing the time-dependent evolution of the charges and spins in each chain, an obvious oscillating spin Hall effect (SHE) from the bipolaron transport is revealed. The results are compared with that from polaron-dominated transport. A reduction of amplitude and an increase of oscillating frequency are observed for the SHE from the bipolaron transport. The mechanism is attributed to the enhanced skew scattering off the larger transient deformations of the chains in the case of the bipolaron. Spectrum analysis by fast Fourier transform of the SHE signal demonstrates a distinct shift of two characteristic peaks to a higher onset frequency compared to the polaron transport. The charge-spin conversion efficiency is also compared, where a larger conversion efficiency is obtained from the bipolaron transport due to the lower saturated velocity. The effects of the strength of the electric field and the interactions are discussed. This work reveals the role of the bipolaron in organic SHE and provides a feasible way to achieve larger conversion efficiency by controlling the species of carriers with the concentration of the dopant.

Prediction ofπ-electrons mediated high-temperature superconductivity in monolayer LiC12.

Prediction and synthesis of two-dimensional high transition temperature (TC) superconductors is an area of extensive research. Based on calculations of the electronic structures and lattice dynamics, we predict that graphene-like layered monolayer LiC12is aπ-electrons mediated Bardeen-Cooper-Schrieffer-type superconductor. Monolayer LiC12is theoretically stable and expected to be synthesized experimentally. From the band structures and the phonon dispersion spectrum, it is found that the saddle point ofπ-bonding bands induces large density of states at the Fermi energy level. There is strongly coupled between the vibration mode in the in-plane direction of the lithium atoms and theπ-electrons of carbon atoms, which induces the high-TCsuperconductivity in LiC12. TheTCcan reach to 41 K under an applied 10% biaxial tensile strain based on the anisotropic Eliashberg equation. Our results show that monolayer LiC12is a good candidate asπ-electrons mediated electron-phonon coupling high-TCsuperconductor.

Studies on the photoelectronic properties of a manganese (Mn)-doped lead-free double perovskite.

Taking Cs2NaBiCl6, Cs2AgInCl6 and Cs2AgBiCl6 as examples of lead-free double perovskites (DPs), we study the photoluminescence (PL) properties of Mn-doped DPs. The electron localization function (ELF) reveals the more ionic nature of the Na-Cl bond in Cs2NaBiCl6 than that of the Ag-Cl bond in Cs2AgBiCl6. Bader charge calculations confirm the nominal +2 valence state of Mn ions in both DPs. Mn2+ ions introduce two defect levels in the band gap of the Cs2NaBiCl6 host, accounting for the d-d transition (4T1-6A1 transition) of Mn2+ and thus the subsequent orange PL. The changes of the crystal field and their influences on the emission energy of Mn2+ ions in different DPs are evaluated by calculating the Racah parameters (B and C) and the crystal field strength (Dq) obtained from energies of the terms of d5 in the Cs2NaBiCl6:Mn2+ and Cs2AgInCl6:Mn2+ systems. The results show that Dq in Cs2AgInCl6:Mn2+ is stronger than that in Cs2NaBiCl6:Mn2+. The analyses on bonding interactions of the Mn-Cl bond via ELF and the integrated projected pCOHP also confirm the stronger ionic bonding interactions and thus the boost of the crystal field strength in the Cs2AgInCl6:Mn2+ system, which results in the blue-shift of the Mn2+ introduced PL peak from Cs2AgInCl6 to Cs2NaBiCl6. Our results provide a new strategy to modulate the emission wavelengths, i.e., tuning the crystal field.

Intrinsic Valley-Polarized Quantum Anomalous Hall Effect and Controllable Topological Phase Transition in Janus Fe2SSe.

The valley-polarized quantum anomalous Hall effect (VP-QAHE) in topological materials, which usually is induced by applying external manipulations, has attracted intensive attention. Here, we predict the formation and regulation of the intrinsic VP-QAHE in ferromagnetic Janus monolayer Fe2SSe. Spontaneous valley polarization (VP) appears without external manipulations due to the Janus structure in monolayer Fe2SSe. The spontaneous VP in addition to the nonzero Chern number in Fe2SSe confirm the intrinsic VP-QAHE. Besides, the topologically protected chiral-spin-valley locking edge states can be regulated by reversing the magnetization. Topological phase transitions between metal, half-metal, topological insulator, and ferrovalley phases can be obtained by applying biaxial strains in Fe2SSe, and the nontrivial band gap reaches up to 441 meV. Also, the topological phase with the VP-QAHE is robust under certain conditions. Both the intrinsic VP-QAHE and controllable topological phase transitions can be achieved in Janus monolayer Fe2SSe, which provides an avenue for the applications of dissipationless valleytronic devices.

Intrinsic Valley Splitting and Direct-to-Indirect Band Gap Transition in Monolayer HfZrSiCO2.

Both a reasonably large valley splitting (VS) and a sufficiently long valley exciton lifetime are crucial in valleytronics device applications. Currently, no single system possesses both attributes simultaneously. Herein, we demonstrate that a Janus monolayer HfZrSiCO2 concurrently hosts a giant intrinsic VS and excitonic quasi-particles with long valley lifetime due to valley-sublayer coupling and built-in electric field. In addition, the band structure of the monolayer HfZrSiCO2 can be continuously manipulated by either an external electric field or a biaxial strain, giving rise to a tunable VS and driving a direct-to-indirect band gap transition. Moreover, the system exhibits valley-contrasting linear dichroism in exciton absorption. These results suggest that the Janus monolayer HfZrSiCO2 is a promising candidate for information applications.

Tunable ultrafast electron transfer in WSe2-graphene heterostructures enabled by atomic stacking order.

Efficient interfacial light-electric interconversion in van der Waals (vdW) heterostructures is crucial for their optoelectronic applications. However, an in-depth understanding of the necessary process for device operation, namely interfacial charge transfer (CT), has thus far remained elusive. In this study, by using photon energy-dependent transient THz spectroscopy, we complementarily investigate the interfacial CT process in heterostructures comprising monolayers of WSe2 and graphene with varying stacking orders on a sapphire substrate. We observe that the CT mechanism of the sub-A-exciton excitation is different from that of the above-A-exciton excitation. Notably, the CT process occurs via a photo-thermionic emission for sub-A-exciton excitations and a direct electron (or hole) transfer for above-A-exciton excitations. Furthermore, we demonstrate that the effective electric field induced by the sapphire substrate could adjust the Schottky barrier from a p-type contact (WSe2/Gr/sapphire) to an n-type contact (Gr/WSe2/sapphire). Consequently, it is more beneficial for the photo-thermionic electrons to transfer from graphene to WSe2 over the Schottky barrier in Gr/WSe2/sapphire. These results can provide new insights into the CT process in graphene-transition metal dichalcogenide (TMDC) vdW interfaces, which are critical to potential optoelectronic applications of graphene-TMDC heterostructures.

Self-powered topological insulator Bi2Te3/Ge heterojunction photodetector driven by long-lived excitons transfer.

Due to the wide spectral absorption and ultrafast electron dynamical response under optical excitation, topological insulator (TI) was proposed to have appealing application in next-generation photonic and optoelectronic devices. Whereas, the bandgap-free speciality of Dirac surface states usually leads to a quick relaxation of photoexcited carriers, making the transient excitons difficult to manipulate in isolated TIs. Growth of TI Bi2Te3/Ge heterostructures can promote the specific lifetime and quantity of long-lived excitons, offering the possibility of designing original near-infrared optoelectronic devices, however, the construction of TI Bi2Te3/Ge heterostructures has yet to be investigated. Herein, the high-quality Bi2Te3/Ge heterojunction with clear interface was prepared by physical vapor deposition strategy. A significant photoluminescence quenching behaviour was observed by experiments, which was attributed to the spontaneous excitation transfer of electrons at heterointerface via theoretical analysis. Then, a self-powered heterostructure photodetector was fabricated, which demonstrated a maximal detectivity of 1.3 × 1011Jones, an optical responsivity of 0.97 A W-1, and ultrafast photoresponse speed (12.1µs) under 1064 nm light illumination. This study offers a fundamental understanding of the spontaneous interfacial exciton transfer of TI-based heterostructures, and the as-fabricated photodetectors with excellent performance provided an important step to meet the increasing demand for novel optoelectronic applications in the future.

Manipulable Electronic and Optical Properties of Two-Dimensional MoSTe/MoGe2N4 van der Waals Heterostructures.

van der Waals heterostructures (vdWHs) can exhibit novel physical properties and a wide range of applications compared with monolayer two-dimensional (2D) materials. In this work, we investigate the electronic and optical properties of MoSTe/MoGe2N4 vdWH under two different configurations using the VASP software package based on density functional theory. The results show that Te4-MoSTe/MoGe2N4 vdWH is a semimetal, while S4-MoSTe/MoGe2N4 vdWH is a direct band gap semiconductor. Compared with the two monolayers, the absorption coefficient of MoSTe/MoGe2N4 vdWH increases significantly. In addition, the electronic structure and the absorption coefficient can be manipulated by applying biaxial strains and changing interlayer distances. These studies show that MoSTe/MoGe2N4 vdWH is an excellent candidate for high-performance optoelectronic devices.

Large valley polarization in a novel two-dimensional semiconductor H-ZrX2(X=Cl, Br, I).

Inspired by the new progress in the research field of two-dimensional valleytronics materials, we propose a new class of transition metal halides, i.e. H-ZrX2(X = Cl, Br, I), and investigated their valleytronics properties under the first-principles calculations. It harbors the spin-valley coupling at K and K' points in the top of valence band, in which the valley spin splitting of ZrI2can reach up to 115 meV. By carrying out the strain engineering, the valley spin splitting and Berry curvature can be effectively tuned. The long-sought valley polarization reaches up to 108 meV by doping Cr atom, which corresponds to the large Zeeman magnetic field of 778 T. Furthermore, the valley polarization in ZrX2can be lineally adjusted or flipped by manipulating the magnetization orientation of the doped magnetic atoms. All the results demonstrate the well-founded application prospects of single-layer ZrX2, which can be considered as great candidate for the development of valleytronics and spintronics.

Spin Polarization Properties of Two Dimensional GaP3 Induced by 3d Transition-Metal Doping.

The electronic structure and spin polarization properties of monolayer GaP3 induced by transition metal (TM) doping were investigated through a first-principles calculation based on density functional theory. The calculation results show that all the doped systems perform spin polarization properties, and the Fe-doped system shows the greatest spin polarization property with the biggest magnetic moment. Based on the analysis from the projected density of states, it was found that the new spin electronic states originated from the p-d orbital couplings between TM atoms and GaP3 lead to spin polarization. The spin polarization results were verified by calculating the spin density distributions and the charge transfer. It is effective to introduce the spin polarization in monolayer GaP3 by doping TM atoms, and our work provides theoretical calculation supports for the applications of triphosphide in spintronics.

Tuning Surface Energy of Zn Anodes via Sn Heteroatom Doping Enabled by a Codeposition for Ultralong Life Span Dendrite-Free Aqueous Zn-Ion Batteries.

Aqueous Zn-ion batteries (AZBs) have been considered as one of the most promising large-scale energy storage systems, owing to the advantages of raw material abundance, low cost, and eco-friendliness. However, the severe growth of Zn dendrites leads to poor stability and low Coulombic efficiency of AZBs. Herein, to effectively inhibit the growth of Zn dendrites, a new strategy has been proposed, i.e., tuning the surface energy of the Zn anode. This strategy can be achieved by in situ doping of Sn heteroatoms in the lattice of metallic Zn via codeposition of Sn and Zn with a small amount of the SnCl2 electrolyte additive. Density functional theory calculations have suggested that Sn heteroatom doping can sharply decrease the surface free energy of the Zn anode. As a consequence, driven by the locally strong electric field, metallic Sn tends to deposit at the tips of the Zn anode, thus decreases the surface energy and growth of Zn at the tips, resulting in a dendrite-free Zn anode. The positive effect of the SnCl2 additive has been demonstrated in both the Zn∥Zn symmetric battery and the Zn/LFP and Zn/HATN full cell. This novel strategy can light a new way to suppress Zn dendrites for long life span Zn-ion batteries.

[Au7(SR)7] Ring as a New Type of Protection Ligand in a New Atomic Structure of Au15(SR)13 Nanocluster.

We present a [Au7(SR)7] ring as a new type of protection ligand in a new atomic structure of Au15(SR)13 nanocluster for the first time based on the ring model developed to understand how interfacial interaction dictates the structures of protection motifs and gold cores in thiolate-protected gold nanoclusters. This new Au15(SR)13 model shows a tetrahedral Au4 core protected by one [Au7(SR)7] ring and two [Au2(SR)3] "staple" motifs. Density functional theory (DFT) calculations show that the newly predicted Au15(SR)13 (R = CH3/Ph) has a lower energy of 0.24/0.68 eV than previously proposed isomers. By comparing calculated optical absorption spectra (UV), circular dichroism (CD) spectra, and powder X-ray diffraction (XRD) patterns with related experimental spectra, the calculated CD spectra of the newly predicted Au15(SR)13 (R = CH3/Ph) cannot reproduce the experimental results, indicating that the newly predicted Au15(SR)13 is a new structure that needs to be confirmed by experiment. In addition, DFT calculations also show that the newly predicted Au15(SR)13 (R = CH3/Ph) exhibits a large HOMO-LUMO gap, suggesting its high chemical stability. The proposition of the [Au7(SR)7] ring as a protection ligand in the newly predicted Au15(SR)13 not only enriches the types of protection ligands in thiolate-protected gold nanoclusters but also further confirms the effectiveness and rationality of the ring model for understanding the interfacial interaction between the protection motifs and gold cores in thiolate-protected gold nanoclusters.

An optic-fiber graphene field effect transistor biosensor for the detection of single-stranded DNA.

Herein, a graphene field effect transistor (GFET) was constructed on an optic fiber end face to develop an integrated optical/electrical double read-out biosensor, which was used to detect target single-stranded DNA (tDNA). Two isolated Au electrodes were, respectively, prepared as the drain and source at the ends of an optic fiber and coated with a graphene film to construct a field effect transistor (FET). Probe aptamers modified with fluorophore 6'-carboxy-fluorescein (6'-FAM) were immobilized on the graphene for specific capture of tDNA. Graphene oxide (GO) was introduced to quench 6'-FAM and construct a fluorescence biosensor. Thus, a dual GFET and fluorescence biosensor was integrated on the end-face of an optic fiber. Following synchronous detection by fluorescence and FET methods, results showed satisfactory sensitivity for DNA detection. Compared with conventional biosensors using a single sensing technology, these dual sensing integrated biosensors significantly improved the reliability and accuracy of DNA detection. Furthermore, this proposed technique provides both a new biosensor for single-stranded DNA detection and a strategy for designing multi-sensing integrated biosensors.

Weak-field polaron dynamics in organic ferromagnets.

With a nonadiabatic dynamical method the polaron dynamics in organic ferromagnets with spin radicals is investigated under weak electric fields. The results reveal two novel phenomena different from those in normal polymers due to the existence of spin radicals. One is that the velocity of the polaron is asymmetric upon the reversal of the applied electric field, which is explained from the asymmetric polarity of the polaron charge density in different directions of the field, and hence its effect on the lattice distortion. The other is the 'intermittent rebound' of the polaron, where the polaron intermittently moves against the electric field force during a short interval behaving like a negative current. The details of lattice distortion and charge distribution of the polaron during the process have been revealed. We further found that there exist different critical fields for the above two phenomena. With an increase of the electric field, the 'intermittent rebound' of the polaron vanishes first and subsequently the asymmetric polaron velocity. This work demonstrates the unique properties of polaron transport in organic ferromagnets, and will be helpful in the future design of organic ferromagnetic devices.