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Heterostructures, such as van der Waals (vdW) heterostructures, provide a versatile platform for engineering the physical properties of two-dimensional (2D) layered materials, spanning electronics, mechanics, optics, as well as electron-phonon couplings. Furthermore, vdW heterostructures, which are composed of metal/semiconductor or semiconductor/semiconductor combinations, not only maintain the unique properties of their individual constituents but also exhibit tunable physical and chemical properties that can be externally adjusted through strain, heat, and electric fields. These externally tunable properties offer significant advances in the fields of solid-state devices and renewable energy applications. Additionally, 2D material-based heterostructures, such as those composed of 0D clusters or quantum dots, as well as 1D nanotubes/wires in combination with 2D materials, also show immense potential for advancing next-generation nanodevices. The vast design space of vdW heterostructures enables their versatile applications spanning numerous fields, such as light-emitting diodes, field-effect transistors, photocatalysis, solar cells, photodetectors, and so on.
In the Special Issue of Journal of Physics: Condensed Matter, entitled "Two-dimensional Materials-based Heterostructures for Next-generation Nanodevices", we have gathered a comprehensive collection of 14 articles, presenting the latest achievements in the fields of designing novel 2D materials and 2D heterostructures. Below, we have briefly condensed the essential research findings from these studies.&#xD., (NA.)

Understanding the origin of ultralow lattice thermal conductivity κ L of halide perovskites is of great significance in the energy conversion field. The soft phonon modes and the large anharmonicity corresponding to the dynamic rotation of halogen atoms play an important role in limiting the thermal transport of halide perovskites. The dynamic rotation has long been thought to originate from the electrostatic repulsion of lone pairs around halogen atoms. Here, by studying the layered perovskite Cs 3 Bi 2 I 6 Cl 3 , it is found that the interaction between the lone pairs contributed by the s bands of halogen atoms is short-range, and the dynamic rotation is really driven by the occupied p-band electrons. It dominates Cs 3 Bi 2 I 6 Cl 3 with ultralow κ L , < 0.2 W mK -1 at 300 K. Moreover, soft optical phonons are presented ≈1 and 2.2 THz that constitute relatively flat and dense bands due to the rattling Cs and Cl atoms, contributing a large glass-like component to the κ L . The results have important implications for understanding the origin of the ultralow κ L in halide perovskites and for designing novel perovskites to serve the energy conversion field., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Uncontrollable growth of Zn dendrites, irreversible dissolution of cathode material and solidification of aqueous electrolyte at low temperatures severely restrict the development of aqueous Zn-ion batteries. In this work, 2,2,2-trifluoroethanol (TFEA) with a volume fraction of 50% as a highly compatible polar-solvent is introduced to 1.3 M Zn(CF 3 SO 3 ) 2 aqueous electrolyte, achieving stable high-performance Zn-ion batteries. Massive theoretical calculations and characterization analysis demonstrate that TFEA weakens the tip effect of Zn anode and restrains the growth of Zn dendrites due to electrostatic adsorption and coordinate with H 2 O to disrupt the hydrogen bonding network in water. Furthermore, TFEA increases the wettability of the cathode and alleviates the dissolution of V 2 O 5 , thus improving the capacity of the full battery. Based on those positive effects of TFEA on Zn anode, V 2 O 5 cathode, and aqueous electrolyte, the Zn//Zn symmetric cell delivers a long cycle-life of 782 h at 5 mA cm -2 and 2 mA h cm -2 . The full battery still declares an initial capacity of 116.78 mA h g -1 , and persists 87.73% capacity in 2000 cycles at -25 °C. This work presents an effective strategy for fully compatible co-solvent to promote the stability of Zn anode, V 2 O 5 cathode and aqueous electrolyte for high-performance Zn-ion batteries., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

The continuous pursuit of novel two-dimensional (2D) materials with intriguing properties has been a driving force in advancing various scientific and technological frontiers. Here, based on a wide range of first-principles calculations, we predicted the existence of a novel family of 2D transition-metal oxides, the Ti 3 O M O enes (MXene-like 2D transition oxides), and determined its distinctive electronic and topological properties. A pair of 2D antiferromagnetic (AFM) Dirac points precisely located at the Fermi level in the absence of spin-orbit coupling (SOC) is observed in the 1T-Ti 3 O monolayer. Moreover, upon halogenation on a bare monolayer, 1T-Ti 3 OCl 3 and 1T-Ti 3 OBr 3 monolayers display the quantum spin Hall (QSH) effect with nontrivial helical edge states within the gapless bulk states. Specifically, single layer 1T-Ti 3 OF 3 behaves as an indirect semiconductor with a gap of 0.81 eV, exhibiting a strong light-harvesting capability. The indirect-gap feature can be switched to a direct one by only exerting a small tensile strain of 1.5%. These findings broaden emerging phenomena in a rich family of M O enes, suggesting a novel platform for the development of next-generation nanodevices.

NiFe-based nanomaterials are extensively studied as one of the promising candidates for the oxygen evolution reaction (OER). However, their practical application is still largely impeded by the unsatisfied activity and poor durability caused by the severe leaching of active species. Herein, a rapid and facile combustion method is developed to synthesize the vertical graphene (VG) supported N-doped carbon modified (Ni x Fe 1-x )Se composites (NC@(Ni x Fe 1-x )Se/VG). The interconnected heterostructure of obtained materials plays a vital role in boosting the catalytic performance, offering rich active sites and convenient pathways for rapid electron and ion transport. The incorporation of Se into NiFe facilitates the formation of active species via in situ surface reconstruction. According to density functional theory (DFT) calculations, the in situ formation of a Ni 0.75 Fe 0.25 Se/Ni 0.75 Fe 0.25 OOH layer significantly enhances the catalytic activity of NC@(Ni x Fe 1-x )Se/VG. Furthermore, the surface-adsorbed selenoxide species contribute to the stabilization of the catalytic active phase and increase the overall stability. The obtained NC@(Ni x Fe 1-x )Se/VG exhibits a low overpotential of 220 mV at 20 mA cm -2 and long-term stability over 300 h. This work offers a novel perspective on the design and fabrication of OER electrocatalysts with high activity and stability., (© 2024 Wiley‐VCH GmbH.)

Dynamic crystals with directional deformations in response to external stimuli through molecular reconfiguration, are observed predominantly in certain organic crystals and metal complexes. Low-dimensional hybrid halides, resemble these materials due to the presence of strong hydrogen bonds between bulky organic moieties and inorganic units, whereas their dynamic behavior remains largely unexplored. Here we show that a one-dimensional hybrid halide (MV)BiBr 5 (MV = methylviologen) undergoes an isosymmetric phase transition at hydrostatic pressure of 0.20 GPa, accompanied by a remarkable length expansion of 20-30% and red to dark yellow color change. Unexpectedly, the backward transition can be fully reversed by mechanical stimulation rather than decompression. In the high-pressure phase, the coexistence of strong Bi 3+ lone pair stereochemical activity and large reorientations of the planar MV 2+ cations, together with the newly formed CH···Br hydrogen interactions, are the structural features that facilitate microscopic changes and stabilize the metastable high-pressure phase at ambient conditions., (© 2024. The Author(s).)

Semiconductors with long-range interactions (LRI) due to resonant bonding exhibit delocalized electronic states and low lattice thermal conductivity, contributing to the efficiency of heat-to-electricity conversion. Here, we build a descriptor for high-throughput screening of LRI materials from the second-order interaction force constants. We identify 75 semiconducting candidates from the binary compounds in the MatHub-3d database that contain LRI. By analyzing the bonding properties of LRI atoms, we classify LRI in materials into two categories: type I and type II. In the structural unit of type I LRI, the atoms have strong bond connections, while a weak bond exists between the two groups in the structural unit of type II LRI. We have identified atypical type I LRI formed by Sb-Sb and Mg-Mg pairs in the emerging thermoelectric material Mg 3 Sb 2 , resulting in the softening of TA 1 phonons and large anharmonicity. For type II LRI, the LRI of Ge-Ge and Se-Se pairs in R 3 m -GeSe can cross different layers. Moreover, we observe a combination of type II LRI and rattling effect in BaSe 2 to restrict thermal transport. This work is of great significance for understanding the relationship between LRI and thermal transport properties, and for designing new LRI-induced low lattice thermal conductivity materials.

We investigate the electronic structure and linear and nonlinear [second-harmonic generation (SHG)] spectra of the NbOCl 2 monolayer, bilayer, and bulk by using a real-time first-principles approach based on many-body theory. First, the interlayer couplings between NbOCl 2 layers are very weak, due to the relatively large interlayer distance, saturation of the p orbital of Cl atoms, and high degree of localization of charge density around the Nb atom for both the lowest conduction band and the highest valence band. Second, the quasiparticle gaps and exciton binding energy for the three systems show layer-dependent features and decrease with an increase in layer thickness. Most importantly, the linear and SHG spectra of the NbOCl 2 monolayer, bilayer, and bulk are dominated by strong excitonic resonances and exhibit layer-independent features due to the weak interlayer couplings. Our findings demonstrate that excitonic effects should be included in studying the optical properties of not only two-dimensional materials but also layered bulk materials with weak interlayer couplings.

Intentional distortions of [BX 6 ] octahedra within perovskite structures have been recognized as a potent strategy for precise band gap adjustments and optimization of their photovoltaic properties, yet information regarding charge carrier dynamics linked to octahedral distortion under ambient conditions for chalcogenide perovskites remains limited. In this study, we utilize ab initio nonadiabatic molecular dynamics to explore the dynamics of photogenerated carriers in a representative two-dimensional Ba 3 Zr 2 S 7 material in the Ruddlesden-Popper phase. The theoretical results highlight the influence of octahedral rotation on the materials' stability and carrier recombination lifetime of the system. Specifically, the octahedrally rotating P 4 2 / mnm phase exhibits a prolonged nonradiative carrier recombination lifetime attributed to the stabilized electron-phonon coupling. These findings offer valuable insights into the fundamental physical characteristics of imposed octahedral distortion and its potential for optimizing the optoelectronic performance of 2D Ruddlesden-Popper Ba-Zr-S chalcogenide materials.

Hydrogen generation by photocatalytic water-splitting holds great promise for addressing the serious global energy and environmental crises, and has recently received significant attention from researchers. In this work, a method of assembling GeC/MXY (M = Zr, Hf; X, Y = S, Se) heterojunctions (HJs) by combining GeC and MXY monolayers (MLs) to construct direct Z-scheme photocatalytic systems is proposed. Based on first-principles calculations, we found that all the GeC/MXY HJs are stable van der Waals (vdW) HJs with indirect bandgaps. These HJs possess small bandgaps and exhibit strong light-absorption ability across a wide range. Furthermore, the built-in electric field (BIEF) around the heterointerface can accelerate photoinduced carrier separation. More interestingly, the suitable band edges of GeC/MXY HJs ensure sufficient kinetic potential to spontaneously accomplish water redox reactions under light irradiation. Overall, the strong light-harvesting ability, wide light-absorption range, small bandgaps, large heterointerfacial BIEFs, suitable band alignments, and carrier migration paths render GeC/MXY HJs highly efficient photocatalysts for overall water decomposition.

Intrinsic half-metallic nanomaterials with 100% spin polarization are highly demanded for next-generation spintronic devices. Here, by using first-principles calculations, we have designed a class of new two-dimensional (2D) p-type half-metals, MSi 2 N 4 (M = Al, Ga, In and Tl), which show high mechanical, thermal and dynamic stabilities. MSi 2 N 4 not only have ultrawide electronic bandgaps for spin-up channels in the range of 4.05 to 6.82 eV but also have large half-metallic gaps in the range of 0.75 to 1.47 eV, which are large enough to prevent the spin-flip transition. The calculated magnetic moment is 1 μ B per cell, resulting from polarized N1-p x /p y orbitals. Moreover, MSi 2 N 4 possess robust long-range ferromagnetic orderings with Curie temperatures in the range of 35-140 K, originating from the interplay of N1-M-N1 superexchange interactions. Furthermore, spin dependent electronic transport calculations reveal 100% spin polarization. Our results highlight new promising 2D ferromagnetic half-metals toward future spintronic applications.

Nonlinear optical (NLO) crystals based on oxides typically have wide bandgaps and large laser damage thresholds (LDTs), which are important for generating high-power and continuous terahertz radiation. Recently, a new family of NLO materials α-A 2 BB'O 6 including Li 2 TiTeO 6 (LTTO) with a strong second harmonic generation (SHG) efficiency of 26 × KH 2 PO 4 (KDP) and a large LDT of 550 MW cm -2 were reported. Herein, we systematically study the electronic structures and NLO properties of α-A 2 BB'O 6 (A = Li, Na, K; B = Ti, Zr, Hf; B' = Se, Te) to explore the relationship between the structure and SHG coefficient. First, 15 members of the A 2 BB'O 6 family are demonstrated to be highly stable and NLO materials, excluding K 2 TiTeO 6 , K 2 TiSeO 6 and K 2 ZrSeO 6 . Then, the electronic band structure, dipole moment and distortion of BO 6 /B'O 6 octahedrons, SHG coefficient and terahertz absorption spectrum are calculated comprehensively with the element variation of A-site, B-site and B'-site. Finally, the magnitude of the SHG coefficient is found to be directly proportional to the value of total dipole moment and distortion, and inversely proportional to the bandgap value. Most importantly, among the A 2 BB'O 6 materials, K 2 HfSeO 6 shows the smallest direct bandgap of 2.99 eV, the largest SHG coefficient d 33 of about 5 × LTTO and low terahertz absorbance from 0.1 to 9 THz. Our results provide new NLO crystals that may have potential application in terahertz radiation sources and other nonlinear electronics.

Chalcogenide perovskites provide a promising avenue for nontoxic, stable thermoelectric materials. Here, the thermal transport and thermoelectric properties of BaZrS 3 as a typical orthorhombic perovskite are investigated. An extremely low lattice thermal conductivity κ L of 1.84 W/mK at 300 K is revealed for BaZrS 3 , due to the softening effect of Ba atoms on the lattice and the strong anharmonicity caused by the twisted structure. We demonstrate that coherence contributions to κ L , arising from wave-like phonon tunneling, lead to an 18% thermal transport contribution at 300 K. The increasing temperature softens the phonons, thus reducing the group velocity of materials and increasing the scattering phase space. However, it simultaneously reduces the anharmonicity, which is dominant in BaZrS 3 and ultimately improves the particle-like thermal transport. In addition, via replacement of the S atom with Se- and Ti-alloying strategy, the ZT value of BaZrS 3 is significantly increased from 0.58 to 0.91 at 500 K, making it an important candidate for thermoelectric applications.

Lithium (Li)-rich ternary alloy, comprising a multi-alloy phase as the built-in three-dimensional (3D) framework and a Li metal phase as a reversible Li reservoir, is a promising high-energy-density anode for rechargeable Li metal batteries. The introduction of metal/metalloid components to the alloy can effectively regulate Li deposition and maintain the dimensional integrity of the Li anode. Herein, the lithium-copper-zinc (Li-Cu-Zn) ternary alloy, as a new type of alloy anode, is synthesized via a facile thermal melting method. The fully delithiated 3D scaffold comprised two Cu-Zn alloy phases named CuZn and CuZn 5 . These alloy phases exhibit higher lithiophilicity and structural stability than Li-Zn and Li-Cu alloys. Moreover, the CuZn phase is electrochemically inert, ensuring the geometric stability of the anode, while the CuZn 5 phase can readily undergo alloying reaction with Li to form the LiZn phase, thereby facilitating uniform Li nucleation and deposition. The hybridized multiphase alloy structure and specific energy storage mechanism of the Cu-Zn based alloy scaffold in the ternary alloy anode facilitate dendrite-free Li deposition and prolonged cycle lifetime. The Li metal full battery based on lithium iron phosphate (LiFePO 4 ) cathode exhibits high cycling stability with high-capacity retention of 95.4% after 1000 cycles at 1C., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Although the efficient separation of electron-hole (e-h) pairs is one of the most sought-after electronic characteristics of materials, due to thermally induced atomic motion and other factors, they do not remain separated during the carrier transport process, potentially leading to rapid carrier recombination. Here, we utilized real-time time-dependent density functional theory in combination with nonadiabatic molecular dynamics (NAMD) to explore the separated dynamic transport path within Ruddlesden-Popper oxysulfide perovskite Y 2 Ti 2 O 5 S 2 caused by the dielectric layer and phonon frequency difference. The underlying origin of the efficient overall water splitting in Y 2 Ti 2 O 5 S 2 is systematically explored. We report the existence of the bi-directional e-h separate-path transport, in which, the electrons transport in the Ti 2 O 5 layer and the holes diffuse in the rock-salt layer. This is in contrast to the conventional e-h separated distribution with a crowded transport channel, as observed in SrTiO 3 and hybrid perovskites. Such a unique feature finally results in a long carrier lifetime of 321 ns, larger than that in the SrTiO 3 perovskite (160 ns) with only one carrier transport channel. This work provides insights into the carrier transport in lead-free perovskites and yields a novel design strategy for next-generation functionalized optoelectronic devices.

The search for lead-free perovskite materials has triggered intensive interest. Here, we study the electronic structures and optical properties of cation-deficient Ruddlesden-Popper oxysulfide perovskites Ln 2 Ti 2 O 5 S 2 (Ln = Sc, Y, or La), with a tunable band gap of 1.45-2.1 eV and a small exciton binding energy of ∼0.1 eV, among which Y 2 Ti 2 O 5 S 2 has been synthesized experimentally. Sc 2 Ti 2 O 5 S 2 possesses the largest light absorbance in the visible region. We further rationalize the light absorption via the transition dipole moment and suggest potential applications of Sc 2 Ti 2 O 5 S 2 in solar cells and Y 2 Ti 2 O 5 S 2 and La 2 Ti 2 O 5 S 2 in water splitting. In addition, this family exhibits small effective masses within the x - y plane and large ones along the z direction. Most importantly, electron gas-like carrier behaviors are observed within the Ti-O bond region, offering a diffusion channel for electron transport. These findings greatly advance our understanding of lead-free perovskites and offer a novel material platform for future optoelectronic devices.

Electrochemical chlorine evolution reaction is of central importance in the chlor-alkali industry, but the chlorine evolution anode is largely limited by water oxidation side reaction and corrosion-induced performance decay in strong acids. Here we present an amorphous CoO x Cl y catalyst that has been deposited in situ in an acidic saline electrolyte containing Co 2+ and Cl - ions to adapt to the given electrochemical condition and exhibits ~100% chlorine evolution selectivity with an overpotential of ~0.1 V at 10 mA cm -2 and high stability over 500 h. In situ spectroscopic studies and theoretical calculations reveal that the electrochemical introduction of Cl - prevents the Co sites from charging to a higher oxidation state thus suppressing the O-O bond formation for oxygen evolution. Consequently, the chlorine evolution selectivity has been enhanced on the Cl-constrained Co-O * sites via the Volmer-Heyrovsky pathway. This study provides fundamental insights into how the reactant Cl - itself can work as a promoter toward enhancing chlorine evolution in acidic brine., (© 2023. Springer Nature Limited.)

Na 3 PS 4 crystals with high ionic conductivity are promising solid-state electrolytes. Here, a novel phase of Na 3 PS 4 ( β '-NPS) crystallizing in a cubic lattice with a space group of P 4̄3 m was systematically investigated using first-principles calculations. First of all, β '-NPS is determined to be thermodynamically, dynamically and mechanically stable. The phase transition from tetragonal Na 3 PS 4 (α -NPS) to a cubic β '-NPS system occurs at approximately 480 K, suggesting high feasibility of experimental access. Moreover, the β '-NPS is an insulator with a large band gap of 4.05 eV and a low migration energy barrier of 0.10 eV for an interstitial Na ion. Significantly, a novel Na ion diffusion mechanism, that is, interstitial diffusion, is proposed, in contrast to traditional vacancy diffusion or kick-off diffusion as observed in most solid electrolytes. This work proposes β '-NPS as a promising superionic conductor for sodium ion batteries and provides theoretical guidance towards designing future ideal solid-state electrolytes.

The thermal transport properties of buckled phosphorene (β-P) and antimonene (β-Sb) are investigated using first-principles methods. The large acoustic-optical phonon gaps of 3.8 THz and 2.2 THz enable the four-phonon interaction to play an important role in phonon scattering for both β-P and β-Sb. Considering the electron-phonon coupling, the lattice thermal conductivity can further undergo 84% decrease to 4.9 W mK -1 for p-type β-P at n = 5 × 10 13 cm -2 . By quantitatively describing the scattering probability of electrons in different paths combined with electron-phonon coupling matrix element analysis, it is found that multi-valley features of electronic band structure and strong electron-phonon coupling strength make electrons have strong intervalley scattering behavior in β-P. The former plays an important role in the energy conservation condition of the scattering process, and the latter determines the selection rule. Our work elucidates the contribution of higher-order phonon interactions as well as electron-phonon coupling effects to lattice thermal conductivity, and provides a new idea for finding materials with low lattice thermal conductivity induced by intervalley scattering.

Constructing two-dimensional (2D) van der Waals (vdW) heterostructures is an effective strategy for tuning and improving the characters of 2D-material-based devices. Four trilayer vdW heterostructures, BP/BP/MoS 2 , BlueP/BlueP/MoS 2 , BP/graphene/MoS 2 and BlueP/graphene/MoS 2 , were designed and simulated using the first-principles calculation. Structural stabilities were confirmed for all these heterostructures, indicating their feasibility in fabrication. BP/BP/MoS 2 and BlueP/BlueP/MoS 2 lowered the bandgaps further, making them suitable for a greater range of applications, with respect to the bilayers BP/MoS 2 and BlueP/MoS 2 , respectively. Their absorption coefficients were remarkably improved in a wide spectrum, suggesting the better performance of photodetectors working in a wide spectrum from mid-wave (short-wave) infrared to violet. In contrast, the bandgaps in BP/graphene/MoS 2 and BlueP/graphene/MoS 2 were mostly enlarged, with a specific opening of the graphene bandgap in BP/graphene/MoS 2 , 0.051 eV, which is much larger than usual and beneficial for optoelectronic applications. Accompanying these bandgap increases, BP/graphene/MoS 2 and BlueP/graphene/MoS 2 exhibit absorption enhancement in the whole infrared, visible to deep ultraviolet or solar blind ultraviolet ranges, implying that these asymmetrically graphene-sandwiched heterostructures are more suitable as graphene-based 2D optoelectronic devices. The proposed 2D trilayer vdW heterostructures are prospective new optoelectronic devices, possessing higher performance than currently available devices.

The lack of efficient catalysts and research on the mechanism for the methanol oxidation reaction (MOR) impedes the development of direct methanol fuel cells. In this work, based on density functional theory calculations, we systematically investigated the activity trends of electrochemical MOR on a single transition-metal atom embedded in N-coordinated graphene (M@N 4 C). By calculating the free energy diagrams of MOR on M@N 4 C, Co@N 4 C was screened out to be the most effective MOR catalyst with a low limiting potential of 0.41 V due to the unique charge transfers and electronic structures. Importantly, one- and two-dimensional volcano relationships in MOR on M@N 4 C catalysts are established based on the d-band center and the Gibbs free energy of Δ G *C H 3 O H and Δ G *CO , respectively. In one word, this work provides theoretical guides toward the improved activity of MOR on M@N 4 C and hints for the design of active and efficient MOR electrocatalysts.

Low-dimension perovskite materials have attracted wide attention due to their excellent optical properties and stability. Herein, Sb 3+ -doped Cs 2 ZrCl 6 crystals are synthesized by a coprecipitation method in which Sb 3+ ions partially replace Zr 4+ ions. The Cs 2 ZrCl 6 : x Sb 3+ powder shows blue and orange-red emissions under a 254 and 365 nm light, respectively, due to the [ZrCl 6 ] 2- octahedron and [SbCl 6 ] 3- octahedron. The photoluminescence quantum yield (PLQY) of Cs 2 ZrCl 6 : x Sb 3+ ( x = 0.1) crystals is up to 52.5%. According to experimental and computational results, the emission mechanism of the Cs 2 ZrCl 6 : x Sb 3+ crystals is proposed. On the one hand, a wide blue emission with a large Stokes shift is caused by the self-trapping excitons of [ZrCl 6 ] 2- octahedra under a 260 nm excitation. On the other hand, the luminescence mechanism of [SbCl 6 ] 3- octahedron is divided into two parts: 1 P 1 → 1 S 0 (490 nm) and 3 P 1 → 1 S 0 (625 nm). The broad-band emission, high PLQY, and excellent stability endow the Cs 2 ZrCl 6 : x Sb 3+ powders with the potential for the fabrication of white light-emitting diodes (WLEDs). A WLED device is fabricated using a commercial 310 nm NUV chip, which shows a high color rendering index of 89.7 and a correlated color temperature of 5333 K. In addition, the synthesized Cs 2 ZrCl 6 : x Sb 3+ crystals can be also successfully used for information encryption. Our work will provide a deep understanding of the photophysical properties of Sb 3+ -doped perovskites and facilitate the development of Cs 2 ZrCl 6 : x Sb 3+ crystals in encrypting multilevel optical codes and WLEDs.

Using a density functional theory-based thermal transport model, which includes the effects of temperature (T)-dependent potential energy surface, lattice thermal expansion, force constant renormalization, and higher-order quartic phonon scattering processes, it is found that the recently synthesized nitride perovskite LaWN 3 displays strong anharmonic lattice dynamics manifested into a low lattice thermal conductivity (κ L ) and a non-standard κ L ∝T -0.491 dependence. At high T, the departure from the standard κ L ∝T -1 law originates in the dual particle-wave behavior of the heat carrying phonons, which includes vibrations tied to the N atoms. While the room temperature κ L =2.98 W mK -1 arises mainly from the conventional particle-like propagation of phonons, there is also a significant atypical wave-like phonon tunneling effect, leading to a 20% glass-like heat transport contribution. The phonon broadening effect lowers the particle-like contribution but increases the glass-like one. Upon T increase, the glass-like contribution increases and dominates above T = 850 K. Overall, the low κ L with a weak T-dependence points to a new utility for LaWN 3 in energy technology applications, and motivates synthesis and exploration of nitride perovskites., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Bulk III-nitride materials MN (M = Al, Ga and In) and their alloys have been widely used in high-power electronic and optoelectronic devices, but stable two-dimensional (2D) III-nitride materials, except h-BN, have not been realized yet. A new kind of 2D III-nitride material M2Si2N4 (M = Al, Ga and In) is predicted by choosing Si as the appropriate passivation element. The stability, electronic and optical properties of 2D M2Si2N4 materials are studied systematically based on first-principles calculations. The results show that Al2Si2N4 and Ga2Si2N4 are found to be indirect bandgap semiconductors, while In2Si2N4 is a direct bandgap semiconductor. Moreover, Al2Si2N4 and In2Si2N4 have good absorption ability in the visible light region, while Ga2Si2N4 is an ultraviolet-light-absorbing material. Furthermore, the carrier lifetimes of Ga2Si2N4 and In2Si2N4 are as large as 157.89 and 103.99 ns, respectively. All these desirable properties of M2Si2N4 materials make them attractive for applications in electronics and photoelectronics.

Regulating redox kinetics is able to spur the great-leap-forward development of room-temperature sodium-sulfur (RT Na-S) batteries, especially on propelling their Na-ion storage capability. Here, an innovative metal oxide kinetics accelerator, orthorhombic Nb 2 O 5 Na-ion conductor, is proposed to functionalize porous carbon nanoreactors (CNR) for S cathodes. The Nb 2 O 5 is shown to chemically immobilize sodium polysulfides via strong affinity. Theoretical and experimental evidence reveals that the Nb 2 O 5 can bidirectionally regulate redox behaviors of S cathodes, which accelerates reduction conversions from polysulfides to sulfides as well as promotes oxidation reactions from sulfides to S. In situ and ex situ characterization techniques further verify its electrochemical lasting endurance in catalyzing S conversions. The well-designed S cathode demonstrates a high specific capacity of 1377 mA h g -1 at 0.1 A g -1 , outstanding rate capability of 405 mA h g -1 at 2 A g -1 , and stable cyclability with a capacity retention of 617 mA h g -1 over 600 cycles at 0.5 A g -1 . An ultralow capacity decay rate of 0.0193% per cycle is successfully realized, superior to those of current state-of-the-art RT Na-S batteries. This design also suits emerging Na-Se batteries, which contribute to outstanding electrochemical performance as well., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Renewable electricity-powered CO evolution from CO 2 emissions is a promising first step in the sustainable production of commodity chemicals, but performing electrochemical CO 2 reduction economically at scale is challenging since only noble metals, for example, gold and silver, have shown high performance for CO 2 -to-CO. Cu is a potential catalyst to achieve CO 2 reduction to CO at the industrial scale, but the C-C coupling process on Cu significantly depletes CO* intermediates, thus limiting the CO evolution rate and producing many hydrocarbon and oxygenate mixtures. Herein, we tune the CO selectivity of Cu by alloying a second metal Sb into Cu, and report an antimony-copper single-atom alloy catalyst (Sb 1 Cu) of isolated Sb-Cu interfaces that catalyzes the efficient conversion of CO 2 -to-CO with a Faradaic efficiency over 95%. The partial current density reaches 452 mA cm -2 with approximately 91% CO Faradaic efficiency, and negligible C 2+ products are observed. In situ spectroscopic measurements and theoretical simulations reason that the atomic Sb-Cu interface in Cu promotes CO 2 adsorption/activation and weakens the binding strength of CO*, which ends up with enhanced CO selectivity and production rates., (© 2023. The Author(s).)

The trade-off between light absorption and carrier transport in semiconductor thin film photoelectrodes is a major limiting factor of their solar-to-hydrogen efficiency for photoelectrochemical water splitting. Herein, we develop a heterogeneous doping strategy that combines surface doping with bulk gradient doping to decouple light absorption and carrier transport in a thin film photoelectrode. Taking La and Mg doped Ta 3 N 5 thin film photoanode as an example, enhanced light absorption is achieved by surface La doping through alleviating anisotropic optical absorption, while efficient carrier transport in the bulk is maintained by the gradient band structure induced by gradient Mg doping. Moreover, the homojunction formed between the La-doped layer and the gradient Mg-doped layer further promotes charge separation. As a result, the heterogeneously doped photoanode yields a half-cell solar-to-hydrogen conversion efficiency of 4.07%, which establishes Ta 3 N 5 as a leading performer among visible-light-responsive photoanodes. The heterogeneous doping strategy could be extended to other semiconductor thin film light absorbers to break performance trade-offs by decoupling light absorption and carrier transport., (© 2022. The Author(s).)

The surface and interface chemistry are of significance on controlling the properties of two-dimensional transition metal carbides and nitrides (MXenes). Numerous efforts have been devoted to the regulation of Ti 3 C 2 T x MXene, however, tuning interlayer spacing and surface halogen termination of other MXenes (besides Ti 3 C 2 T x ) is rarely reported while demanded. Here we propose a Lewis-basic halides treatment, which is capable of simultaneously engineering the interlayer spacing and surface termination of various MXenes. Benefited from the abundant desolvated halogen anions and cations in molten state Lewis-basic halides, the -F termination was substituted by nucleophilic reaction and the interlayer spacing was enlarged. Ti 3 C 2 T x MXene treated by this method showed a high specific capacity of 229 mAh g -1 for Li + storage, which is almost 2 times higher than pristine one. Considering the universality, our method provides an approach to regulating the properties of MXenes, which may expand their potential applications in energy storage, optoelectronics and beyond., (© 2022. The Author(s).)

The electromagnetic spectrum between microwave and infrared light is termed the "terahertz (THz) gap," of which there is an urgent lack of feasible and efficient room-temperature (RT) THz detectors. Type-II Weyl semimetals (WSMs) have been predicted to host significant RT topological photoresponses in low-frequency regions, especially in the THz gap, well addressing the shortcomings of THz detectors. However, such devices have not been experimentally realized yet. Herein, a type-II WSM (NbIrTe 4 ) is selected to fabricate THz detector, which exhibits a photoresponsivity of 5.7 × 10 4  V W -1 and a one-year air stability at RT. Such excellent THz-detection performance can be attributed to the topological effect of type-II WSM in which the effective mass of photogenerated electrons can be reduced by the large tilting angle of Weyl nodes to further improve mobility and photoresponsivity. Impressively, this device shows a giant intrinsic anisotropic conductance (σ max /σ min  = 339) and THz response (I ph-max /I ph-min  = 40.9), both of which are record values known. The findings open a new avenue for the realization of uncooled and highly sensitive THz detectors by exploring type-II WSM-based devices., (© 2022 Wiley-VCH GmbH.)

Although Ti 3 C 2 T x MXene is a promising material for many applications such as catalysis, energy storage, electromagnetic interference shielding due to its metallic conductivity and high processability, it's poor resistance to oxidation at high temperatures makes its application under harsh environments challenging. Here, we report an air-stable Ti 3 C 2 T x based composite with extracted bentonite (EB) nanosheets. In this case, oxygen molecules are shown to be preferentially adsorbed on EB. The saturated adsorption of oxygen on EB further inhibits more oxygen molecules to be adsorbed on the surface of Ti 3 C 2 T x due to the weakened p-d orbital hybridization between adsorbed O 2 and Ti 3 C 2 T x , which is induced by the Ti 3 C 2 T x /EB interface coupling. As a result, the composite is capable of tolerating high annealing temperatures (above 400 °C for several hours) both in air or humid environment, indicating highly improved antioxidation properties in harsh condition. The above finding is shown to be independent on the termination ratio of Ti 3 C 2 T x obtained through different synthesis routes. Utilized as terahertz shielding materials, the composite retains its shielding ability after high-temperature treatment even up to 600 °C, while pristine Ti 3 C 2 T x is completely oxidized with no terahertz shielding ability. Joule heating and thermal cycling performance are also demonstrated., (© 2022. The Author(s).)

The number of semiconducting MXenes with direct band gaps is extremely low; thus, it is highly desirable to broaden the MXene family beyond carbides and nitrides to expand the palette of desired chemical and physical properties. Here, we theoretically report the existence of the single-layer (SL) dititanium oxide 2H-Ti 2 O MOene (MXene-like 2D transition oxides), showing an Ising superconducting feature. Moreover, SL halogenated 2H- and 1T-Ti 2 O monolayers display tunable semiconducting features and strong light-harvesting ability. In addition, the external strains can induce Weyl fermions via quantum phase transition in 2H-Ti 2 OF 2 and Ti 2 OCl 2 monolayers. Specifically, 2H- and 1T-Ti 2 OF 2 are direct semiconductors with band gaps of 0.82 and 1.18 eV, respectively. Furthermore, the carrier lifetimes of SL 2H- and 1T-Ti 2 OF 2 are evaluated to be 0.39 and 2.8 ns, respectively. This study extends emerging phenomena in a rich family of 2D MXene-like MOene materials, which provides a novel platform for next-generation optoelectronic and photovoltaic fields.

Nowadays, trace CH 4 emitted from vehicle exhausts severely threaten the balance of the ecology system of our earth. Thereby, the development of active and stable catalysts capable of methane conversion under mild conditions is critical. Here, we present a convenient method to redisperse catalytically inert PdO nanoparticles (NPs) (>10 nm) into reactive PdO x nanoclusters (∼2 nm) anchored on a Ce-doped LaFeO 3 parent. Isothermally activated in an N 2 flow, the redispersed catalyst achieved a CH 4 conversion of 90% at 400 °C, which is significantly higher than the fresh and H 2 - and O 2 -treated counterparts (625, 616, and 641 °C, respectively), indicating the importance of the gas atmosphere in the redispersion of PdO NPs. In addition, the comprehensive catalyst characterizations demonstrated that the isolated Ce ions in the perovskite lattice play an irreplaceable role in the redispersion of reactive sites and the reduction of the energy barrier for C-H scission. More importantly, the Ce additive helps to stabilize the PdO x species by reducing overoxidation, resulting in significant lifetime extension. Through a thorough understanding of structural manipulation, this study sheds light on the design of highly performing supported catalysts for methane oxidation.

Manipulating spin in antiferromagnetic (AFM) materials has great potential in AFM opto-spintronics. Laser pulses can induce a transient ferromagnetic (FM) state in AFM metallic systems but have never been proven in two-dimensional (2D) AFM semiconductors and related van der Waals (vdW) heterostructures. Herein, using 2D vdW heterostructures of FM MnS 2 and AFM MXenes as prototypes, we investigated optically induced interlayer spin transfer dynamics based on real-time time-dependent density functional theory. We observed that laser pulses induce significant spin injection and interfacial atom-mediated spin transfer from MnS 2 to Cr 2 CCl 2 . In particular, we first demonstrated the transient FM state in semiconducting AFM-FM heterostructures during photoexcited processes. The proximity magnetism breaks the magnetic symmetry of Cr 2 CCl 2 in heterostructures. Our results provide a microscopic understanding of optically controlled interlayer spin dynamics in 2D magnetic heterostructures and open a new way to manipulate magnetic order in 2D materials for ultrafast opto-spintronics.

Transition-metal perovskite chalcogenides (TMPCs) have emerged as lead-free alternatives to lead-halide perovskites and have been currently of increasing interest for optoelectronic applications because of their suitable band gaps, high carrier mobility, strong light absorption, and high stability. Here, we systematically report a study on the effects of Ti- and Se-alloying strategies on polaron behavior and carrier lifetimes in nonradiative recombination. Although such alloying can effectively tune the band gap of BaZrS 3 , we observe localized small polaron formation upon Ti alloying and large polarons generating in Se alloying. Ti-alloying strengthens the electron-phonon coupling, leading to a reduced carrier lifetime. Remarkably, Se-alloying weakens the electron-phonon coupling and prolongs the nonradiative electron-hole recombination lifetime by up to 60% compared to that in pristine BaZrS 3 material. The simulations rationalize the difference in carrier lifetimes in TMPC alloys and provide guidelines for further improvements in TMPC-based photoelectronic devices.

Beryllium polynitride (BeN 4 ) has been recently synthesized under high-pressure conditions [Bykov et al . Phys. Rev. Lett. 2021, 126, 175501]. Its anisotropic lattice structure dependent on the applied pressure motivates exploration of its thermal transport properties with a theoretical framework that combines the Boltzmann transport equation with ab initio calculations. The bonding anisotropy (impacting the phonon and electron group velocities) and bonding anharmonicity (captured through three- and four-phonon scatterings) are reflected in the strong anisotropy of both phononic and electronic components of the thermal conductivity. Moreover, the pressure-driven evolution of the interlayer Be-N bonding, from partially covalent (under high-pressure synthesis conditions) to van der Waals (under ambient pressure), drives a largely interlayer thermal conductivity. These findings highlight an alternative strategy for achieving directional control of the thermal transport in synthetic materials.

Fluorescence intensity ratio (FIR) thermometry, a new contactless temperature measurement, can achieve accurate measurements in a harsh environment. In this work, all-inorganic lead-free Cs 2 AgInCl 6 : Er-Yb and Cs 2 AgBiCl 6 : Er-Yb microcrystals emit bright green up-conversion emission, which are synthesized by precipitation at a low temperature (80 °C). In up-conversion emission, FIR of the 2 H 11/2 → 4 I 15/2 band to the 4 S 3/2 → 4 I 15/2 band exhibits temperature dependence, which can be used as the temperature measurement parameter, so-called FIR thermometry. Moreover, the theoretically accurate measurement range is from 100 to 600 K, achieving maximum absolute sensitivities from 0.0130 to 0.0113 K -1 , respectively. The principle of up-conversion and high sensitivity is well explained by calculating the partial density of states. Compared to the reported thermometry materials based on the FIR method, the prepared all-inorganic lead-free Cs 2 AgInCl 6 : Er-Yb and Cs 2 AgBiCl 6 : Er-Yb microcrystals show outstanding temperature measurement width and sensitivity, becoming a potential candidate for high-sensitivity optical temperature sensors.

Ultrafast optical control of magnetism had great potential to revolutionize magnetic storage technology and spintronics, but for now, its potential remains mostly untapped in two-dimensional (2D) magnets. Here, using the state-of-the-art real-time time-dependent density functional theory (rt-TDDFT), we demonstrate that an ultrafast laser pulse can induce a ferromagnetic state in nonmagnetic MoSe 2 monolayers interfaced with van der Waals (vdW) ferromagnetic MnSe 2 . Our results show that the transient ferromagnetism in MoSe 2 derives from photoinduced direct ultrafast interlayer spin transfer from Mn to Mo via a vdW-coupled interface, albeit with a delay of approximately a few femtoseconds. This delay was strongly dependent on laser duration and interlayer coupling, which could be used to tune the amplitude and rate spin transfer. Furthermore, we have also shown that ferromagnetic states can be photoinduced in other transition metal dichalcogenides (TMDs), such as PtS 2 and TaSe 2 monolayers. Overall, our findings provide crucial physical insights for exploring light-induced interlayer spin and charge dynamics in 2D magnetic systems.

The extensive emission of CO 2 results in critical environmental issues, such as global warming. Photocatalytic CO 2 conversion is a meaningful route to convert CO 2 into useful chemicals. However, the highly selective reduction of CO 2 with the avoidance of hydrogen evolution is still challenging. Herein, the photocatalytic reduction CO 2 to synthesis gas (syngas) was achieved on a metal Ag socketed perovskite LaFeO 3 (LFO) catalytic interface prepared by an in-situ exsolution method. The conduction band of Ag-exsolved LFO is more negative than LFO, benefiting efficient CO 2 reduction. By tuning the dopant Ag cation in the lattice to nanoparticles pinned on the surface, the CO formation rate was improved around five-fold from 0.51 to 2.41 μmol g -1  h -1 . Meanwhile, the H 2 /CO molar ratio also showed strong dependence on the modality of Ag at the metal-perovskite interface. The design offers a promising pathway for transforming CO 2 to valuable chemicals based on efficient photocatalysts design., (© 2022 Wiley-VCH GmbH.)

Recently, two-dimensional (2D) Janus semiconductors have attracted great attention in photocatalytic applications owing to their extraordinary properties, especially the intrinsic polarization-induced spontaneous carrier separation, strong optical absorption, and ultrahigh solar-to-hydrogen (STH) efficiency. However, experimental achievable candidates for 2D intrinsic Janus semiconductors are rarely reported. Herein, based on density functional theory (DFT) calculations, we uncovered two new 2D photocatalysts, namely, Janus Nb 3 SBr 7 and Ta 3 SBr 7 bilayers. We revealed that both structures are highly feasible to be obtained from their bulk counterparts. Excitingly, intrinsic charge separations emerge in both structures, which are beneficial to the repression of recombinations of their photoexcited carriers. Optical absorptions of both structures can be activated in the visible and even infrared regions. Most interestingly, Nb 3 SBr 7 and Ta 3 SBr 7 bilayers can exhibit ultrahigh STH efficiencies of 35% and 31%, respectively, which are larger than those of most 2D Janus structures. In addition, we further found that these distinguished photocatalytic properties are rather robust and are independent of their stacking modes. Experimental feasibilities and robust coexistences of intrinsic charge separations, ultrahigh STH efficiencies, and strong absorptions endow Nb 3 SBr 7 and Ta 3 SBr 7 bilayers as hopeful photocatalysts for water splitting.

Borophenes and related two-dimensional materials have exhibited many exotic properties, especially for superconductivity, although the superconductivity of single-layer borophene is suppressed by the strains or doping from its substrates. Intriguingly, bilayer (BL) borophenes can be stabilized by appropriate pillar density and hexagonal holes density, rather than being supported by Ag(111) or Cu(111) substrates. Thus, we studied the two most stable structures, namely BL-B8 and BL-B30, stabilized by the above-mentioned two methods. Within density functional theory and Bardeen-Cooper-Schrieffer theory framework, their stability, electron structures, and phonon properties, as well as possible superconductivity are systematically scrutinized. The metallic BL-B8 and BL-B30 exhibit intrinsic superconducting features with superconductivity transition temperatures ( T c ) of 11.9 and 4.9 K, respectively. The low frequency (below 400 cm -1 ) consisting of out-of-plane vibrations of boron atoms plays crucial rule in their superconductivity. In particular, a Kohn anomaly appears at the Γ point in BL-B8, leading to substantial electron-phonon coupling. Here, our findings will provide instructive clues for experimentally determining the superconductivity of borophene and will broaden the two-dimensional superconductor family., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Polynary transition-metal atom catalysts are promising to supersede platinum (Pt)-based catalysts for oxygen reduction reaction (ORR). Regulating the local configuration of atomic catalysts is the key to catalyst performance enhancement. Different from the previously reported single-atom or dual-atom configurations, a new type of ternary-atom catalyst, which consists of atomically dispersed, nitrogen-coordinated Co-Co dimers, and Fe single sites (i.e., Co 2 -N 6 and Fe-N 4 structures) that are coanchored on highly graphitized carbon supports is developed. This unique atomic ORR catalyst outperforms the catalysts with only Co 2 -N 6 or Fe-N 4 sites in both alkaline and acid conditions. Density functional theory calculations clearly unravels the synergistic effect of the Co 2 -N 6 and Fe-N 4 sites, which can induce higher filling degree of Fe-d orbitals and favors the binding capability to *OH intermediates (the rate determining step). This ternary-atom catalyst may be a promising alternative to Pt to drive the cathodic ORR in zinc-air batteries., (© 2021 Wiley-VCH GmbH.)

Two-dimensional (2D) transition metal di-nitrides (TMN 2 ) have been arousing great interest for their unique mechanic, electronic, optoelectronic, and magnetic properties. The recent successful growth of monolayer MSi 2 N 4 (M = Mo and W) further motivates us to explore new physics and unusual properties behind this family. By using first-principles calculations and Bardeen-Cooper-Schrieffer theory, we predicted the existence of the superconductivity in single-layer (SL) 1T- and 1H-TaN 2 with superconducting transition temperatures ( T c ) of ∼0.86 and 1.3 K. Specifically, the T c could be greatly enhanced to ∼24.6 K by passivating the TaN 2 monolayer with Si-N bilayers. Furthermore, the superconductivity could be increased to ∼30.4 K via substituting lighter Nb for Ta. This enhancement of superconductivity mainly stems from the softer vibration modes consisting of in-plane Ta/Nb vibrations mixed with Si- xy vibrations. The superconductivity can be further tuned by applying external strains and carrier doping. This enhancement strategy of surface passivation and light atom substitution would suggest a new platform for 2D superconductors and provide an instructive pathway for next-generation nanoelectronics.

Due to their low-symmetry lattice characteristics and intrinsic in-plane anisotropy, 2D pentagonal materials, a new class of 2D materials composed entirely of pentagonal atomic rings, are attracting increasing research attention. However, the existence of these 2D materials has not been proven experimentally until the recent discovery of PdSe 2 . Herein, penta-PdPSe, a new 2D pentagonal material with a novel low-symmetry puckered pentagonal structure, is introduced to the 2D family. Interestingly, a peculiar polyanion of [SePPSe] 4- is discovered in this material, which is the biggest polyanion in 2D materials yet discovered. Strong intrinsic in-plane anisotropic behavior endows penta-PdPSe with highly anisotropic optical, electronic, and optoelectronic properties. Impressively, few-layer penta-PdPSe-based phototransistor not only achieves excellent electronic performances, a moderate electron mobility of 21.37 cm 2 V -1 s -1 and a high on/off ratio of up to 10 8 , but it also has a high photoresponsivity of ≈5.07 × 10 3 A W -1 at 635 nm, which is ascribed to the photogating effect. More importantly, penta-PdPSe also exhibits a large anisotropic conductance (σ max /σ max  = 3.85) and responsivity (R max /R min  = 6.17 at 808 nm), superior to most 2D anisotropic materials. These findings make penta-PdPSe an ideal material for the design of next-generation anisotropic devices., (© 2021 Wiley-VCH GmbH.)

Recently, two-dimensional (2D) metal halides have brought out an intensive interest for their unique mechanical, electronic, magnetic, and topological properties. Here, we theoretically report the existence of the single-layer (SL) zirconium dihalide materials ZrX 2 (X = Cl, Br, and I) using first-principles calculations. SL ZrX 2 , which can be obtained from its bulk phase through simple mechanical exfoliation, shows the dynamic, thermodynamic, and mechanical stability. Halogen atoms can effectively tune the electronic structure, dipole moment transition, band alignment, and light absorption. Specifically, ZrX 2 monolayers intrinsically exhibit a ferroelasticity with an abnormal 120° orientation rotation, possessing a moderate switching barrier of 24-39 meV/atom. Importantly, we observe superior anisotropic light absorption responses on SL ZrX 2 in the visible region. Besides, a series of ZrX 2 -based excitonic solar cells have been proposed, which hold a large power conversion efficiency limit of 12.4-18.7%.

Photocathodes emit electrons when illuminated, a process utilized across many technologies. Cutting-edge applications require a set of operating conditions that are not met with current photocathode materials. Meanwhile, halide perovskites have been studied extensively and have shown a lot of promise for a wide variety of optoelectronic applications. Well-documented halide perovskite properties such as inexpensive growth techniques, improved carrier mobility, low trap density, and tunable direct band gaps make them promising candidates for next-generation photocathode materials. Here, we use density functional theory to explore the possible application of pure inorganic perovskites (CsPbBr 3 and CsPbI 3 ) as photocathodes. It is determined that the addition of a Cs coating improved the performance by lowering the work function anywhere between 1.5 and 3 eV depending on the material, crystal surface, and surface coverage. A phenomenological model, modified from that developed by Gyftopoulos and Levine, is used to predict the reduction in work function with Cs coverage. The results of this work aim to guide the further experimental development of Cs-coated halide perovskites for photocathode materials.

The rational design and construction of inexpensive and highly active electrocatalysts for hydrogen evolution reaction (HER) is of great importance for water splitting. Herein, we develop a facile approach for preparation of porous carbon-confined Ru-doped Cu nanoparticles (denoted as Ru-Cu@C) by direct pyrolysis of the Ru-exchanged Cu-BTC metal-organic framework. When served as the electrocatalyst for HER, strikingly, the obtained Ru-Cu@C catalyst exhibits an ultralow overpotential (only 20 mV at 10 mA cm -2 ) with a small Tafel slope of 37 mV dec -1 in alkaline electrolyte. The excellent performance is comparable or even superior to that of commercial Pt/C catalyst. Density functional theory (DFT) calculations confirm that introducing Ru atoms into Cu nanocrystals can significantly alter the desorption of H 2 to achieve a close-to-zero hydrogen adsorption energy and thereby boost the HER process. This strategy gives a fresh impetus to explore low-cost and high-performance catalysts for HER in alkaline media., Competing Interests: Conflict of interest The authors declare that they have no conflict of interest., (Copyright © 2020 Science China Press. Published by Elsevier B.V. All rights reserved.)

Using the first-principles calculations, we report the existence of the single-layer (SL) dititanium oxide Ti 2 O (labeled as MOene) that constructs a novel family of MXene based on transition-metal oxides. This MOene material strongly contrasts the conventional ones consisting of transition-metal carbides and/or nitrides. SL Ti 2 O has high thermal and dynamical stabilities because of the strong Ti-O ionic bonding interactions. Moreover, this material is an intrinsic electride and exhibits extremely low diffusion barriers of ∼12.0 and 6.3 meV for Li and Na diffusion, respectively. When applied as anode materials in lithium-ion batteries and sodium-ion batteries, it possesses a high energy storage capacity (960.23 mAhg -1 ), surpassing the traditional MXenes-based anodes. The superb electrochemical performance stems from the existing anionic electron on Ti 2 O surface. Astonishingly, SL Ti 2 O is also determined to be a superconductor with a superconducting transition temperature ( T c ) of ∼9.8 K, which originates from the soft-mode of the first acoustic phonon branch and enhanced electron-phonon coupling in the low-frequency region. Furthermore, this soft-mode behaves much softer upon applying a compressive strain of 2%, leading to a higher T c of 11.9 K. Our finding broadens the family of MXenes and could facilitate more experimental efforts toward future nanodevices.

Recently, two-dimensional (2D) metal halides have triggered an enormous interest for their tunable mechanical, electronic, magnetic, and topological properties, greatly enriching the family of 2D materials. Here, based on first-principles calculations, we report a systematic study of group 11 transition-metal halide MX (M = Cu, Ag, Au; X = Cl, Br, I) monolayers. Among them, CuBr, CuI, AgBr, and AgI monolayers exhibit high thermodynamic, dynamic, and mechanic stability. The four stable monolayers have a direct band gap of ∼3.12-3.36 eV and possess high carrier mobility (∼10 3 cm 2 V -1 s -1 ), suggestive of future photocatalysts for water splitting applications. What is more, the simulations of optical properties confirm that the stable MX monolayers hold the potential for further applications in ultraviolet optical devices and quantum cutting solar materials.

2D noble-transition-metal chalcogenides (NTMCs) are emerging as a promising class of optoelectronic materials due to ultrahigh air stability, large bandgap tunability, and high photoresponse. Here, a new set of 2D NTMC: Ta 2 PdS 6 atomic layers is developed, displaying the excellent comprehensive optoelectronic performance with an ultrahigh photoresponsivity of 1.42 × 10 6 A W -1 , detectivity of 7.1 × 10 10 Jones and a high photoconductive gain of 2.7 × 10 6 under laser illumination at a wavelength of 633 nm with a power of 0.025 W m -2 , which is ascribed to a photogating effect via study of the device band profiles. Especially, few-layer Ta 2 PdS 6 exhibits a good broadband photoresponse, ranging from 450 nm in the ultraviolet region to 1450 nm in the shortwave infrared (SIR) region. Moreover, this material also delivers an impressive electronic performance with electron mobility of ≈25 cm 2 V -1 s -1 , I on /I off ratio of 10 6 , and a one-year air stability, which is better than those of most reported 2D materials. Our studies underscore Ta 2 PdS 6 as a promising 2D material for nano-electronic and nano-optoelectronic applications., (© 2020 Wiley-VCH GmbH.)

Two-dimensional (2D) Janus structures, which are totally different from prevailing 2D structures, are more interesting for photocatalytic water splitting. Here we proposed some inartificial 2D Ge 4 Se 9 Janus structures. Excellent photocatalytic properties are revealed: (a) Ge 4 Se 9 structures exhibit layer-independent direct gap character with appropriate band gaps of 2.53, 2.22, 2.11, and 2.03 eV for monolayered, bilayered, triple-layered, and four-layered structures, respectively. (b) Band edge positions of these 2D structures are suitable for the driving of the evolution reaction of water splitting. (c) More importantly, owning to intrinsic electric polarization, the charge densities of the valence band maximum (VBM) and the conduction band minimum (CBM) of triple-layered and four-layered Ge 4 Se 9 structures can be notably separated. (d) In addition, we also observed that these 2D structures can possess rather pronounced optical absorption in the visible light region. This work discloses some inartificial 2D Janus structures whose fascinating properties render them as promising photocatalysts for water splitting.