Spectroscopic evidence of spin-state excitation in d-electron correlated semiconductor FeSb2.

Iron antimonide (FeSb2) has been investigated for decades due to its puzzling electronic properties. It undergoes the temperature-controlled transition from an insulator to an ill-defined metal, with a cross-over from diamagnetism to paramagnetism. Extensive efforts have been made to uncover the underlying mechanism, but a consensus has yet to be reached. While macroscopic transport and magnetic measurements can be explained by different theoretical proposals, the essential spectroscopic evidence required to distinguish the physical origin is missing. In this paper, through the use of X-ray absorption spectroscopy and atomic multiplet simulations, we have observed the mixed spin states of 3d 6 configuration in FeSb2. Furthermore, we reveal that the enhancement of the conductivity, whether induced by temperature or doping, is characterized by populating the high-spin state from the low-spin state. Our work constitutes vital spectroscopic evidence that the electrical/magnetical transition in FeSb2 is directly associated with the spin-state excitation.

Realizing Room-Temperature Ferromagnetism in Molecular-Intercalated Antiferromagnet VOCl.

Two-dimensional (2D) van der Waals (vdW) magnets are gaining attention in fundamental physics and advanced spintronics, due to their unique dimension-dependent magnetism and potential for ultra-compact integration. However, achieving intrinsic ferromagnetism with high Curie temperature (TC) remains a technical challenge, including preparation and stability issues. Herein, we develop an applicable electrochemical intercalation strategy to decouple interlayer interaction and guide charge doping in antiferromagnet VOCl, thereby inducing robust room-temperature ferromagnetism. The expanded vdW gap isolates the neighboring layers and shrinks the distance between the V-V bond, favoring the generation of ferromagnetic (FM) coupling with perpendicular magnetic anisotropy (PMA). Element-specific X-ray magnetic circular dichroism (XMCD) directly proves the source of the ferromagnetism. Detailed experimental results and density functional theory (DFT) calculations indicate that the charge doping enhances the FM interaction by promoting the orbital hybridization between t2 g and eg. Our work sheds new light on a promising way to achieve room-temperature ferromagnetism in antiferromagnets, thus addressing the critical materials demand for designing spintronic devices. This article is protected by copyright. All rights reserved.

Defective Tungsten Oxides with Stacking Faults for Proton Exchange Membrane Green-Hydrogen Generation.

Defects can introduce atomic structural modulation and tailor performance of materials. Herein, it demonstrates that semiconductor WO3 with inert electrocatalytic behavior can be activated through defect-induced tensile strains. Structural characterizations reveal that when simply treated in Ar/H2 atmosphere, oxygen vacancies will generate in WO3 and cause defective structures. Stacking faults are found in defects, thus modulating electronic structure and transforming electrocatalytic-inert WO3 into highly active electrocatalysts. Density functional theory (DFT) calculations are performed to calculate *H adsorption energies on various WOx surfaces, revealing the oxygen vacancy composition and strain predicted to optimize the catalytic activity of hydrogen evolution reaction (HER). Such defective tungsten oxides can be integrated into commercial proton exchange membrane (PEM) electrolyser with comparable performance toward Pt-based PEM. This work demonstrates defective metal oxides as promising non-noble metal catalysts for commercial PEM green-hydrogen generation.

Tunable Magnetism in Atomically Thin Itinerant Antiferromagnet with Room-Temperature Ferromagnetic Order.

Addressing the need for modulated spin configurations is crucial, as they serve as the foundational building blocks for next-generation spintronics, particularly in atomically thin structures and at room temperature. In this work, we realize intrinsic ferromagnetism in monolayer flakes and tunable ferro-/antiferromagnetism in (Fe0.56Co0.44)5GeTe2 antiferromagnets. Remarkably, the ferromagnetic ordering (≥1 L) and antiferromagnetic ordering (≥4 L) remain discernible up to room temperature. The TC (∼310 K) of the monolayer flakes sets a record high for known exfoliated monolayer van der Waals magnets. Within the framework of A-type antiferromagnetism, a notable odd-even layer-number effect at elevated temperatures (T = 150 K) is observed. Of particular interest is the strong ferromagnetic order in even-layer flakes at low temperatures. The intricate interplay among magnetic field strength, layer number, and temperature gives rise to a diverse array of phenomena, holding promise not only for new physics but also for practical applications.

Lattice Strain and Mott-Schottky Effect of the Charge-Asymmetry Pd1Fe Single-Atom Alloy Catalyst for Semi-Hydrogenation of Alkynes with High Efficiency.

The ideal interface design between the metal and substrate is crucial in determining the overall performance of the alkyne semihydrogenation reaction. Single-atom alloys (SAAs) with isolated dispersed active centers are ideal media for the study of reaction effects. Herein, a charge-asymmetry "armor" SAA (named Pd1Fe SAA@PC), which consists of a Pd1Fe alloy core and a semiconducting P-doped C (PC) shell, is rationally designed as an ideal catalyst for the selective hydrogenation of alkynes with high efficiency. Multiple spectroscopic analyses and density functional theory calculations have demonstrated that Pd1Fe SAA@PC is dual-regulated by lattice tensile and Schottky effects, which govern the selectivity and activity of hydrogenation, respectively. (1) The PC shell layer applied an external traction force causing a 1.2% tensile strain inside the Pd1Fe alloy to increase the reaction selectivity. (2) P doping into the C-shell layer realized a transition from a p-type semiconductor to an n-type semiconductor, thereby forming a unique Schottky junction for advancing alkyne semihydrogenation activity. The dual regulation of lattice strain and the Schottky effect ensures the excellent performance of Pd1Fe SAA@PC in the semihydrogenation reaction of phenylethylene, achieving a conversion rate of 99.9% and a selectivity of 98.9% at 4 min. These well-defined interface modulation strategies offer a practical approach for the rational design and performance optimization of semihydrogenation catalysts.

Oxygen Coordination Promotes Single-Atom Cu(II)-Catalyzed Azide-Alkyne Click Chemistry without Reducing Agents.

Unique active sites make single-atom (SA) catalysts promising to overcome obstacles in homogeneous catalysis but challenging due to their fixed coordination environment. Click chemistry is restricted by the low activity of more available Cu(II) catalysts without reducing agents. Herein, we develop efficient, O-coordinated SA Cu(II) directly catalyzed click chemistry. As revealed by theoretical calculations of the superior coordination structure to promote the click reaction, an organic molecule-assisted strategy is applied to prepare the corresponding SA Cu catalysts with respective O and N coordination. Although they both belong to Cu(II) centers, the O-coordinated one exhibits a 5-fold higher activity than the other and even much better activity than traditional homogeneous and heterogeneous Cu(II) catalysts. Control experiments further proved that the O-coordinated SA Cu(II) catalyst tends to be reduced by alkyne into Cu acetylide rather than the N-coordinated catalyst and thus facilitates click chemistry.

Nitrogen Doping-Roused Synergistic Active Sites in Perovskite Enabling Highly Selective CO2 Photoreduction into CH4.

The intricate protonation process in carbon dioxide reduction usually makes the product unpredictable. Thus, it is significant to control the reactive intermediates to manipulate the reaction steps. Here, we propose that the synergistic La-Ti active sites in the N-La2Ti2O7 nanosheets enable the highly selective carbon dioxide photoreduction into methane. In the photoreduction of CO2 over N-La2Ti2O7 nanosheets, in situ Fourier transform infrared spectra are utilized to monitor the *CH3O intermediate, pivotal for methane production, whereas such monitoring is not conducted for La2Ti2O7 nanosheets. Also, theoretical calculations testify to the increased charge densities on the Ti and La atoms and the regulated formation energy barrier of *CO and *CH3O intermediates by the constructed synergistic active sites. Accordingly, the methane formation rate of 7.97 µL h-1 exhibited by the N-La2Ti2O7 nanosheets, along with an electron selectivity of 96.6%, exceeds that of most previously reported catalysts under similar conditions.

Breaking the Scaling Relationship in C-N Coupling via the Doping Effects for Efficient Urea Electrosynthesis.

Electrochemical C-N coupling reaction based on carbon dioxide and nitrate have been emerged as a new "green synthetic strategy" for the synthesis of urea, but the catalytic efficiency is seriously restricted by the inherent scaling relations of adsorption energies of the active sites, the improvement of catalytic activity is frequently accompanied by the decrease in selectivity. Herein, a doping engineering strategy was proposed to break the scaling relationship of intermediate binding and minimize the kinetic barrier of C-N coupling. A thus designed SrCo0.39Ru0.61O3-δ catalyst achieves a urea yield rate of 1522 µg h-1 mgcat. -1 and faradic efficiency of 34.1 % at -0.7 V versus reversible hydrogen electrode. A series of characterizations revealed that Co doping not only induces lattice distortion but also creates rich oxygen vacancies (OV) in the SrRuO3. The oxygen vacancies weaken the adsorption of *CO and *NH2 intermediates on the Co and Ru sites respectively, and the strain effects over the Co-Ru dual sites promoting the occurrence of C-N coupling of the two monomers instead of selective hydrogenating to form by-products. This work presents an insight into molecular coupling reactions towards urea synthesis via the doping engineering on SrRuO3.

Solvent-free selective hydrogenation of nitroaromatics to azoxy compounds over Co single atoms decorated on Nb2O5 nanomeshes.

The solvent-free selective hydrogenation of nitroaromatics to azoxy compounds is highly important, yet challenging. Herein, we report an efficient strategy to construct individually dispersed Co atoms decorated on niobium pentaoxide nanomeshes with unique geometric and electronic properties. The use of this supported Co single atom catalysts in the selective hydrogenation of nitrobenzene to azoxybenzene results in high catalytic activity and selectivity, with 99% selectivity and 99% conversion within 0.5 h. Remarkably, it delivers an exceptionally high turnover frequency of 40377 h-1, which is amongst similar state-of-the-art catalysts. In addition, it demonstrates remarkable recyclability, reaction scalability, and wide substrate scope. Density functional theory calculations reveal that the catalytic activity and selectivity are significantly promoted by the unique electronic properties and strong electronic metal-support interaction in Co1/Nb2O5. The absence of precious metals, toxic solvents, and reagents makes this catalyst more appealing for synthesizing azoxy compounds from nitroaromatics. Our findings suggest the great potential of this strategy to access single atom catalysts with boosted activity and selectivity, thus offering blueprints for the design of nanomaterials for organocatalysis.

Light-Driven C-C Coupling for Targeted Synthesis of CH3 COOH with Nearly 100 % Selectivity from CO2.

Targeted synthesis of acetic acid (CH3 COOH) from CO2 photoreduction under mild conditions mainly limits by the kinetic challenge of the C-C coupling. Herein, we utilized doping engineering to build charge-asymmetrical metal pair sites for boosted C-C coupling, enhancing the activity and selectivity of CO2 photoreduction towards CH3 COOH. As a prototype, the Pd doped Co3 O4 atomic layers are synthesized, where the established charge-asymmetrical cobalt pair sites are verified by X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy spectra. Theoretical calculations not only reveal the charge-asymmetrical cobalt pair sites caused by Pd atom doping, but also manifest the promoted C-C coupling of double *COOH intermediates through shortening of the coupled C-C bond distance from 1.54 to 1.52 Å and lowering their formation energy barrier from 0.77 to 0.33 eV. Importantly, the decreased reaction energy barrier from the protonation of two*COOH into *CO intermediates for the Pd-Co3 O4 atomic layer slab is 0.49 eV, higher than that of the Co3 O4 atomic layer slab (0.41 eV). Therefore, the Pd-Co3 O4 atomic layers exhibit the CH3 COOH evolution rate of ca. 13.8 µmol g-1 h-1 with near 100% selectivity, both of which outperform all previously reported single photocatalysts for CO2 photoreduction towards CH3 COOH under similar conditions.

Selective Photoreduction of CO2 to CH4 Triggered by Metal-Vacancy Pair Sites.

Selectively achieving the photoreduction of carbon dioxide (CO2) to methane (CH4) remains a significant challenge, which primarily arises from the complexity of the protonation process. In this work, we designed metal-vacancy pair sites in defective metal oxide semiconductors, which anchor the reactive intermediates with a bridged linkage for the selective protonation to produce CH4. As an example, oxygen-deficient Nb2O5 nanosheets are synthesized, in which the niobium-oxygen vacancy pair sites are demonstrated by X-ray photoelectron spectroscopy and electron paramagnetic resonance spectra. In situ Fourier transform infrared spectroscopy monitors the *CH3O intermediate, a key intermediate for CH4 production, during the CO2 photoreduction in oxygen-deficient Nb2O5 nanosheets. Importantly, the built metal-vacancy pair sites regulate the *CH3O formation step as a spontaneous process, making the reduction of CO2 to CH4 the preferred method. Therefore, the oxygen-deficient Nb2O5 nanosheets exhibit a CH4 formation rate of 19.14 µmol g-1 h-1, with an electron selectivity of ∼94.1%.

Selective CO2 Photoreduction Enabled by Water-stable Cu-based Metal-organic Framework Nanoribbons.

The goal of photocatalytic CO2 reduction system is to achieve near 100 % selectivity for the desirable product with reasonably high yield and stability. Here, two-dimensional metal-organic frameworks are constructed with abundant and uniform monometallic active sites, aiming to be an emerged platform for efficient and selective CO2 reduction. As an example, water-stable Cu-based metal-organic framework nanoribbons with coordinatively unsaturated single CuII sites are first fabricated, evidenced by X-ray diffraction patterns and X-ray absorption spectroscopy. In situ Fourier-transform infrared spectra and Gibbs free energy calculations unravel the formation of the key intermediate COOH* and CO* is an exothermic and spontaneous process, whereas the competitive hydrogen evolution reaction is endothermic and non-spontaneous, which accounts for the selective CO2 reduction. As a result, in an aqueous solution containing 1 mol L-1 KHCO3 and without any sacrifice reagent, the water-stable Cu-based metal-organic framework nanoribbons exhibited an average CO yield of 82 µmol g-1 h-1 with the selectivity up to 97 % during 72 h cycling test, which is comparable to other reported photocatalysts under similar conditions.

Modulation of Buried Interface by 1-(3-aminopropyl)-Imidazole for Efficient Inverted Formamidinium-Cesium Perovskite Solar Cells.

Considering the direct influence of substrate surface nature on perovskite (PVK) film growth, buried interfacial engineering is crucial to obtain ideal perovskite solar cells (PSCs). Herein, 1-(3-aminopropyl)-imidazole (API) is introduced at polytriarylamine (PTAA)/PVK interface to modulate the bottom property of PVK. First, the introduction of API improves the growth of PVK grains and reduces the Pb2+ defects and residual PbI2 present at the bottom of the film, contributing to the acquisition of high-quality PVK film. Besides, the presence of API can optimize the energy structure between PVK and PTAA, which facilitates the interfacial charge transfer. Density functional theory (DFT) reveals that the electron donor unit (R-C ═ N) of the API prefers to bind with Pb2+ traps at the PVK interface, while the formation of hydrogen bonds between the R-NH2 of API and I- strengthens the above binding ability. Consequently, the optimum API-treated inverted formamidinium-cesium (FA/Cs) PSCs yields a champion power conversion efficiency (PCE) of 22.02% and exhibited favorable stability.

Two-Step Catalytic Against Polysulfide Shuttling to Enhance Redox Conversion for Advanced Lithium-Sulfur Batteries.

The development of lithium-sulfur batteries is seriously hindered by the shuttle effect of lithium polysulfides (LiPSs) and the low electrical conductivity of sulfur. To solve these problems, efficient catalysts can be used to improve the conversion rate of LiPSs and the conductivity of sulfur cathode. Herein, annealed melamine foam supported MoSe2 (NCF@MoSe2) is used as interlayer and the MoSe2/MoP heterojunction obtained by phosphating MoSe2 is further used as the catalyst material for metal fusion with a sulfur element. The interlayer can not only improve the electrical conductivity and effectively adsorb and catalyze LiPSs, but more importantly, the MoSe2/MoP heterojunction can also effectively adsorb and catalyze LiPSs, so that the batteries have a dual inhibition shuttling effect strategy. Furthermore, the rapid anchor-diffusion transition of LiPSs, and the suppression of shuttling effects by catalyst materials are elucidated using theoretical calculations and in situ Raman spectroscopy. The two-step catalytic strategy exhibits a high reversibility of 983 mAh g-1 after 200 cycles at 0.5 C and a high-rate capacity of 889 mAh g-1 at 5 C. This work provides a feasible solution for the rational design of interlayer and heterojunction materials and is also conducive to the development of more advanced Li-S batteries.

Multifunctional Imidazolidinyl Urea Additive Initiated Complex with PbI2 Toward Efficient and Stable Perovskite Solar Cells.

High-quality perovskite absorption layer is the fundamental basis for efficient and stable perovskite solar cells (PSCs). Due to the ionic nature of perovskite components, plentiful charged defects and suspension bonds remain on the surface of perovskite grains after continuous high-temperature annealing. Here, the complex initiated by the introduction of a multifunctional imidazolidinyl urea (IU) additive into the PbI2 precursor solution could serve as nucleation sites and crystallization templates for perovskite crystals to optimize the growth of high-quality perovskite films. By anchoring at the grain boundaries of perovskite films, IU molecules could passivate various types of defects, improve the hydrophobic properties, and inhibit lead leakage. Attributed to reduced defect density, improved charge transport, and inhibited α-FAPbI3 transition, the PSCs prepared based on IU additives achieved a champion power conversion efficiency of 23.18% (21.51% for the control PSCs) with negligible hysteresis and satisfactory stability.

Interface Engineering a High Content of Co3+ Sites on Co3O4 Nanoparticles to Boost Acidic Oxygen Evolution.

Non-noble metal oxides have emerged as potential candidate electrocatalysts for acidic oxygen evolution reactions (OERs) due to their earth abundance; however, improving their catalytic activity and stability simultaneously in strong acidic electrolytes is still a major challenge. In this work, we report Co3O4@carbon core-shell nanoparticles on 2D graphite sheets (Co3O4@C-GS) as mixed-dimensional hybrid electrocatalysts for acidic OER. The obtained Co3O4@C-GS catalyst exhibits a low overpotential of 350 mV and maintains stability for 20 h at a current density of 10 mA cm-2 in H2SO4 (pH = 1) electrolyte. X-ray photoelectron and X-ray absorption spectroscopies illustrate that the higher content of Co3+ sites boosts acidic OER. Operando Raman spectroscopy reveals that the catalytic stability of Co3O4@C nanoparticles during the acidic OER is enhanced by the introduction of graphite sheets. This interface engineering of non-noble metal sites with high valence states provides an efficient approach to boost the catalytic activity and enhance the stability of noble-metal-free electrocatalysts for acidic OER.

Symmetry-Breaking p-Block Antimony Single Atoms Trigger N-Bridged Titanium Sites for Electrocatalytic Nitrogen Reduction with High Efficiency.

The electrochemical nitrogen reduction reaction (eNRR) under mild conditions emerges as a promising approach to produce ammonia (NH3) compared to the typical Haber-Bosch process. Herein, we design an asymmetrically coordinated p-block antimony single-atom catalyst immobilized on nitrogen-doped Ti3C2Tx (Sb SA/N-Ti3C2Tx) for eNRR, which exhibits ultrahigh NH3 yield (108.3 µg h-1 mgcat-1) and excellent Faradaic efficiency (41.2%) at -0.3 V vs RHE. Complementary in situ spectroscopies with theoretical calculations reveal that the nitrogen-bridged two titanium atoms triggered by an adjacent asymmetrical Sb-N1C2 moiety act as the active sites for facilitating the protonation of the rate-determining step from *N2 to *N2H and the kinetic conversion of key intermediates during eNRR. Moreover, the introduction of Sb-N1C2 promotes the formation of oxygen vacancies to expose more titanium sites. This work presents a strategy for single-atom-decorated ultrathin two-dimensional materials with the aim of simultaneously enhancing NH3 yield and Faradaic efficiency for electrocatalytic nitrogen reduction.

Intrinsic room-temperature ferromagnetism in a two-dimensional semiconducting metal-organic framework.

The development of two-dimensional (2D) magnetic semiconductors with room-temperature ferromagnetism is a significant challenge in materials science and is important for the development of next-generation spintronic devices. Herein, we demonstrate that a 2D semiconducting antiferromagnetic Cu-MOF can be endowed with intrinsic room-temperature ferromagnetic coupling using a ligand cleavage strategy to regulate the inner magnetic interaction within the Cu dimers. Using the element-selective X-ray magnetic circular dichroism (XMCD) technique, we provide unambiguous evidence for intrinsic ferromagnetism. Exhaustive structural characterizations confirm that the change of magnetic coupling is caused by the increased distance between Cu atoms within a Cu dimer. Theoretical calculations reveal that the ferromagnetic coupling is enhanced with the increased Cu-Cu distance, which depresses the hybridization between 3d orbitals of nearest Cu atoms. Our work provides an effective avenue to design and fabricate MOF-based semiconducting room-temperature ferromagnetic materials and promotes their practical applications in next-generation spintronic devices.

Controlled synthesis of van der Waals CoS2for improved p-type transistor contact.

Two-dimensional (2D) van der Waals (vdW) p-type semiconductors have shown attractive application prospects as atomically thin channels in electronic devices. However, the high Schottky hole barrier of p-type semiconductor-metal contacts induced by Fermi-level pinning is hardly removed. Herein, we prepare a vdW 1T-CoS2nanosheet as the contact electrode of a WSe2field-effect transistor (FET), which shows a considerably high on/off ratio > 107and a hole mobility of ∼114.5 cm2V-1s-1. The CoS2nanosheets exhibit metallic conductivity with thickness dependence, which surpasses most 2D transition metal dichalcogenide metals or semimetals. The excellent FET performance of the CoS2-contacted WSe2FET device can be attributed to the high work function of CoS2, which lowers the Schottky hole barrier. Our work provides an effective method for growing vdW CoS2and opens up more possibilities for the application of 2D p-type semiconductors in electronic devices.

Effects of Alkaline Hydrogen Peroxide and Cellulase Modifications on the Physicochemical and Functional Properties of Forsythia suspensa Dietary Fiber.

Besides active substances, Forsythia suspensa is rich in dietary fiber (DF), but it is often wasted or discarded and not put to good use. In order to improve the function of Forsythia DF, it was modified using alkaline hydrogen peroxide (AHP) and cellulase (EM). Compared to the control DF (ODF), the DF modified using AHP (AHDF) and EM (EMDF) had a looser microstructure, lower crystallinity, and higher oil holding capacity (OHC) and cation exchange capacity (CEC). The AHP treatment significantly increased the water holding capacity (WHC) and water swelling ability (WSA) of the DF, while the EM treatment achieved just the opposite. Moreover, the functional properties of AHDF and EMDF, including their cholesterol adsorption capacity (CAC), nitrite ion adsorption capacity (NAC), glucose adsorption capacity (GAC), glucose dialysis retardation index (GDRI), α-amylase inhibitory activity, and DPPH radical scavenging activity, were far better than those of ODF. Together, the results revealed that AHP and EM modifications could effectively improve or enhance the physicochemical and functional properties of Forsythia suspensa DF.