Integrating Sulfur Doping with a Multi-Heterointerface Fe7S8/NiS@C Composite for Wideband Microwave Absorption

Heterointerface engineering is presently considered a valuable strategy for enhancing the microwave absorption (MA) properties of materials via compositional modification and structural design. In this study, a sulfur-doped multi-interfacial composite (Fe7S8/NiS@C) coated with NiFe-layered double hydroxides (LDHs) is successfully prepared using a hydrothermal method and post-high-temperature vulcanization. When assembled into twisted surfaces, the NiFe-LDH nanosheets exhibit porous morphologies, improving impedance matching, and microwave scattering. Sulfur doping in composites generates heterointerfaces, numerous sulfur vacancies, and lattice defects, which facilitate the polarization process to enhance MA. Owing to the controllable heterointerface design, the unique porous structure induced multiple heterointerfaces, numerous vacancies, and defects, endowing the Fe7S8/NiS@C composite with an enhanced MA capability. In particular, the minimum reflection loss (RLmin) value reached -58.1 dB at 15.8 GHz at a thickness of 2.1 mm, and a broad effective absorption bandwidth (EAB) value of 7.3 GHz is achieved at 2.5 mm. Therefore, the Fe7S8/NiS@C composite exhibits remarkable potential as a high-efficiency MA material owing to the synergistic effects of the polarization processes, multiple scatterings, porous structures, and impedance matching.

Constructing Heterointerfaces in Dual-Phase High-Entropy Oxides to Boost O2 Activation and SO2 Resistance for Mercury Removal in Flue Gas

The low O2 activation ability at low temperatures and SO2 poisoning are challenges for metal oxide catalysts in the application of Hg0 removal in flue gas. A novel high-entropy fluorite oxide (MgAlMnCo)CeO2 (Co-HEO) with the second phase of spinel is synthesized by the microwave hydrothermal method for the first time. A high efficiency of Hg0 removal (close to 100%) is achieved by Co-HEO catalytic oxidation at temperatures as low as 100 °C and in the atmosphere of 145 μg m-3 Hg0 at a high GHSV (gas hourly space velocity) of 95,000 h-1. According to O2-TPD and in situ FT-IR, this extremely superior catalytic oxidation performance at low temperatures originates from the activation ability of Co-HEO to transform O2 into superoxide and peroxide, which is promoted by point defects induced from the spinel/fluorite heterointerfaces. Meanwhile, SO2 resistance of Co-HEO for Hg0 removal is also improved up to 2000 ppm due to the high-entropy-stabilized structure, construction of heterointerfaces, and synergistic effect of the multicomponents for inhibiting the oxidation of SO2 to surface sulfate. The design strategy of the dual-phase high-entropy material launches a new route for metal oxides in the application of catalytic oxidation and SO2 resistance.

Phase-Transition of Mo2 C Induced by Tungsten Doping as Heterointerface-Rich Electrocatalyst for Optimizing Hydrogen Evolution Activity

Electrochemical hydrogen evolution reaction (HER) from water splitting driven by renewable energy is considered a promising method for large-scale hydrogen production, and as an alternative to noble-metal electrocatalysts, molybdenum carbide (Mo2 C) has exhibited effective HER performance. However, the strong bonding strength of intermediate adsorbed H (Hads ) with Mo active site slows down the HER kinetics of Mo2 C. Herein, using phase-transition strategy, hexagonal β-Mo2 C could be easily transferred to cubic δ-Mo2 C through electron injection triggered by tungsten (W) doping, and heterointerface-rich Mo2 C-based composites, including β-Mo2 C, δ-Mo2 C, and MoO2 , are presented. Experimental results and density functional theory calculations reveal that W doping mainly contributes to the phase-transition process, and the generated heterointerfaces are the dominant factor in inducing remarkable electron accumulation around Mo active sites, thus weakening the Mo─H coupling. Wherein, the β-Mo2 C/MoO2 interface plays an important role in optimizing the electronic structure of Mo 3d orbital and hydrogen adsorption Gibbs free energy (ΔGH* ), enabling these Mo2 C-based composites to have excellent intrinsic catalytic activity like low overpotential (η10 = 99.8 mV), small Tafel slope (60.16 dec-1 ), and good stability in 1 m KOH. This work sheds light on phase-transition engineering and offers a convenient route to construct heterointerfaces for large-scale HER production.

Oxygen-Vacancy-Reinforced Vanadium Oxide/Graphene Heterojunction for Accelerated Zinc Storage with Long Life Span

Vanadium trioxide (V6 O13 ) cathode has recently aroused intensive interest for aqueous zinc-ion batteries (AZIBs) due to their structural and electrochemical diversities. However, it undergoes sluggish reaction kinetics and significant capacity decay during prolonged cycling. Herein, an oxygen-vacancy-reinforced heterojunction in V6 O13- x /reduced graphene oxide (rGO) cathode is designed through electrostatic assembly and annealing strategy. The abundant oxygen vacancies existing in V6 O13- x weaken the electrostatic attraction with the inserted Zn2+ ; the external electric field constructed by the heterointerfaces between V6 O13- x and rGO provides additional built-in driving force for Zn2+ migration; the oxygen-vacancy-enriched V6 O13- x highly dispersed on rGO fabricates the interconnected conductive network, which achieves rapid Zn2+ migration from heterointerfaces to lattice. Consequently, the obtained 2D heterostructure exhibits a remarkable capacity of 424.5 mAh g-1 at 0.1 A g-1 , and a stable capacity retention (96% after 5800 cycles) at the fast discharge rate of 10 A g-1 . Besides, a flexible pouch-type AZIB with real-life practicability is fabricated, which can successfully power commercial products, and maintain stable zinc-ion storage performances even under bending, heavy strikes, and pressure condition. A series of quantitative investigation of pouch batteries demonstrates the possibility of pushing pouch-type AZIBs to realistic energy storage market.

Plasma-Induced 2D Electron Transport at Hetero-Phase Titanium Oxide Interface

Interfaces of metal oxide heterojunctions display a variety of intriguing physical properties that enable novel applications in spintronics, quantum information, neuromorphic computing, and high-temperature superconductivity. One such LaAlO3 /SrTiO3 (LAO/STO) heterojunction hosts a 2D electron liquid (2DEL) presenting remarkable 2D superconductivity and magnetism. However, these remarkable properties emerge only at very low temperatures, while the heterostructure fabrication is challenging even at the laboratory scale, thus impeding practical applications. Here, a novel plasma-enabled fabrication concept is presented to develop the TiO2 /Ti3 O4 hetero-phase bilayer with a 2DEL that exhibits features of a weakly localized Fermi liquid even at room temperature. The hetero-phase bilayer is fabricated by applying a rapid plasma-induced phase transition that transforms a specific portion of anatase TiO2 thin film into vacancy-prone Ti3 O4 in seconds. The underlying mechanism relies on the screening effect of the achieved high-density electron liquid that suppresses the electron-phonon interactions. The achieved "adiabatic" electron transport in the hetero-phase bilayer offers strong potential for low-loss electric or plasmonic circuits and hot electron harvesting and utilization. These findings open new horizons for fabricating diverse multifunctional metal oxide heterostructures as an innovative platform for emerging clean energy, integrated photonics, spintronics, and quantum information technologies.

Constructing Symmetry-Mismatched RuxFe3-xO4 Heterointerface-Supported Ru Clusters for Efficient Hydrogen Evolution and Oxidation Reactions

Ru-related catalysts have shown excellent performance for the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR); however, a deep understanding of Ru-active sites on a nanoscale heterogeneous support for hydrogen catalysis is still lacking. Herein, a click chemistry strategy is proposed to design Ru cluster-decorated nanometer RuxFe3-xO4 heterointerfaces (Ru/RuxFe3-xO4) as highly effective bifunctional hydrogen catalysts. It is found that introducing Ru into nanometric Fe3O4 species breaks the symmetry configuration and optimizes the active site in Ru/RuxFe3-xO4 for HER and HOR. As expected, the catalyst displays prominent alkaline HER and HOR performance with mass activity much higher than that of commercial Pt/C as well as robust stability during catalysis because of the strong interaction between the Ru cluster and the RuxFe3-xO4 support, and the optimized adsorption intermediate (Had and OHad). This work sheds light on a promsing approach to improving the electrocatalysis performance of catalysts by the breaking of atomic dimension symmetry.

Engineering Phase to Reinforce Dielectric Polarization in Nickel Sulfide Heterostructure for Electromagnetic Wave Absorption

Engineering phase transition in micro-nanomaterials to optimize the dielectric properties and further enhance the electromagnetic microwave absorption (EMA) performance is highly desirable. However, the severe synthesis conditions restrict the design of EMA materials featuring controllable phases, which hinders the tunability of effective absorption bandwidth (EAB) and leads to an unclear loss mechanism. Herein, a seed phase decomposition-controlled strategy is proposed to induct nickel sulfide (NiSx ) absorbers with controllable phases and hollow sphere nature. Transmission electron microscopy holography and theoretical calculations evidence that the reconstruction of atoms in phase transition induces numerous heterogeneous interfaces and lattice defects/sulfur vacancies to cause varied work functions and local electronic redistribution, which contributes to reinforced dielectric polarization. As a result, the optimized NiS2 /NiS heterostructure enables enhanced EM attenuation capability with a wide EAB of 5.04 GHz at only 1.6 mm, compared to that of NiS2 and NiS. Moreover, the correlation between EAB and NiS phase content is demonstrated as the "volcano" feature. This study on the concept of phase transition of micro-nanomaterials can offer a novel approach to constructing highly efficient absorbers for EMA and other functionalities.

Metal-Organic Framework-Manipulated Dielectric Genes Inside Silicon Carbonitride toward Tunable Electromagnetic Wave Absorption

Heterointerface engineering for different identifiable length scales has emerged as a key research area for obtaining materials capable of high-performance electromagnetic wave absorption; however, achieving controllable architectural and compositional complexity in nanomaterials with environmental and thermal stabilities remains challenging. Herein, metal-containing silicon carbonitride (SiCN/M) nanocomposite ceramics with multiphase heterointerfaces were in situ synthesized via coordination crosslinking, catalytic graphitization, and phase separation processes using trace amounts of metal-organic frameworks (MOFs). The results reveal that the regulation of dielectric genes by MOFs can yield considerable lattice strain and abundant lattice defects, contributing to strong interfacial and dipole polarizations. The as-prepared SiCN/M ceramics demonstrate excellent microwave absorption performance: the minimum reflection loss (RLmin ) is -72.6 dB at a thickness of only 1.5 mm and -54.1 dB at an ultralow frequency of 3.56 GHz for the SiCN/Fe ceramics and the RLmin is -55.1 dB with a broad bandwidth of 3.4 GHz at an ultralow thickness of 1.2 mm for the SiCN/CoFe ceramic. The results are expected to provide guidance for the design of future dielectric microwave absorption materials based on heterointerface engineering while offering a paradigm for developing MOF-modified SiCN nanocomposite ceramics with desirable properties.

From Forces to Assemblies: van der Waals Forces-Driven Assemblies in Anisotropic Quasi-2D Graphene and Quasi-1D Nanocellulose Heterointerfaces towards Quasi-3D Nanoarchitecture

In the pursuit of advanced functional materials, the role of low-dimensional van der Waals (vdW) heterointerfaces has recently ignited noteworthy scientific interest, particularly in assemblies that incorporate quasi-2D graphene and quasi-1D nanocellulose derivatives. The growing interest predominantly stems from the potential to fabricate distinct genres of quasi-2D/1D nanoarchitecture governed by vdW forces. Despite the possibilities, the inherent properties of these nanoscale entities are limited by in-plane covalent bonding and the existence of dangling π-bonds, constraints that inhibit emergent behavior at heterointerfaces. An innovative response to these limitations proposes a mechanism that binds multilayered quasi-2D nanosheets with quasi-1D nanochains, capitalizing on out-of-plane non-covalent interactions. The approach facilitates the generation of dangling bond-free iso-surfaces and promotes the functionalization of multilayered materials with exceptional properties. However, a gap still persists in understanding transition and alignment mechanisms in disordered multilayered structures, despite the extensive exploration of monolayer and asymmetric bilayer arrangements. In this perspective, we comprehensively review the sophisticated aspects of multidimensional vdW heterointerfaces composed of quasi-2D/1D graphene and nanocellulose derivatives. Further, we discuss the profound impacts of anisotropy nature and geometric configurations, including in-plane and out-of-plane dynamics on multiscale vdW heterointerfaces. Ultimately, we shed light on the emerging prospects and challenges linked to constructing advanced functional materials in the burgeoning domain of quasi-3D nanoarchitecture.

Interfacial Engineering of Copper-Nickel Selenide Nanodendrites for Enhanced Overall Water Splitting in Alkali Condition

Fabricating heterogeneous interfaces is an effective approach to improve the intrinsic activity of noble-metal-free catalysts for water splitting. Herein, 3D copper-nickel selenide (CuNi@NiSe) nanodendrites with abundant heterointerfaces are constructed by a precise multi-step wet chemistry method. Notably, CuNi@NiSe only needs 293 and 41 mV at 10 mA cm-2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Moreover, the assembled CuNi@NiSe system just requires 2.2 V at 1000 mA cm-2 in anion exchange membrane (AEM) electrolyzer, which is 2.0 times better than Pt/C//IrO2 . Mechanism studies reveal Cu defects on the Cu2-x Se surface boost the electron transfer between Cu atoms and Se atoms of Ni3 Se4 via Cu2-x Se/Ni3 Se4 interface, largely lowering the reaction barrier of rate-determining step for HER. Besides, the intrinsic activity of Ni atoms for in situ generated NiOOH is largely enhanced during OER because of the electron-modulating effect of Se atoms at Ni3 Se4 /NiOOH interface. The unique 3D structure also promotes the mass transfer during catalysis process. This work emphasizes the essential role of interfacial engineering for practical water splitting.

Advanced In Situ Electrochemical Induced Dual-Mechanism Heterointerface toward High-Energy Aqueous Zinc-Ion Batteries

In situ electrochemical activation brings unexpected electrochemical performance improvements to electrode materials, while the mechanism behind is still needed to study deeply. Herein, an in situ electrochemically approach is developed for the activation of heterointerface MnOx /Co3 O4 by inducing Mn-defect, wherein the Mn defects are formed through a charge process that converts the MnOx with poor electrochemical activities toward Zn2+ into high electrochemically active cathode for aqueous zinc-ion batteries (ZIBs). Guided by the coupling engineering strategy, the heterointerface cathode exhibits an intercalation/conversion dual-mechanism without structural collapse during storage/release of Zn2+ . The heterointerfaces between different phases can generate built-in electric fields, reducing the energy barrier for ion migration and facilitating electron/ion diffusion. As a consequence, the dual-mechanism MnOx /Co3 O4 shows an outstanding fast charging performance and maintains a capacity of 401.03 mAh g-1 at 0.1 A g-1 . More importantly, a ZIB based on MnOx /Co3 O4 delivered an energy density of 166.09 Wh kg-1 at an ultrahigh power density of 694.64 W kg-1 , which outperforms those of fast charging supercapacitors. This work provides insights for using defect chemistry to introduce novel properties in active materials for highly for high-performance aqueous ZIBs.

Superlattice Nanofilm on a Touchscreen for Photoexcited Bacteria and Virus Killing by Tuning Electronic Defects in the Heterointerface

Currently, the global COVID-19 pandemic has significantly increased the public attention toward the spread of pathogenic viruses and bacteria on various high-frequency touch surfaces. Developing a self-disinfecting coating on a touchscreen is an urgent and meaningful task. Superlattice materials are among the most promising photocatalysts owing to their efficient charge transfer in abundant heterointerfaces. However, excess electronic defects at the heterointerfaces result in the loss of substantial amounts of photogenerated charge carrier. In this study, a ZnOFe₂ O₃ superlattice nanofilm is designed via atomic layer deposition for photocatalytic bactericidal and virucidal touchscreen. Additionally, electronic defects in the superlattice heterointerface are engineered. Photogenerated electrons and holes will be rapidly separated and transferred into ZnO and Fe₂ O₃ across the heterointerfaces owing to the formation of ZnO, FeO, and ZnFe covalent bonds at the heterointerfaces, where ZnO and Fe₂ O₃ function as electronic donors and receptors, respectively. The high generation capacity of reactive oxygen species results in a high antibacterial and antiviral efficacy (>90%) even against drug-resistant bacteria and H1N1 viruses under simulated solar or low-power LED light irradiation. Meanwhile, this superlattice nanofilm on a touchscreen shows excellent light transmission (>90%), abrasion resistance (10⁶ times the round-trip friction), and biocompatibility.

Graphite-Based Composite Anodes with C-O-Nb Heterointerfaces Enable Fast Lithium Storage

To better satisfy the increasing demands for electric vehicles, it is crucial to develop fast-charging lithium-ion batteries (LIBs). However, the fast-charging capability of commercial graphite anodes is limited by the sluggish Li⁺ insertion kinetics. Herein, we report a synergistic engineering of uniform nano-sized T-Nb₂ O₅ particles on graphite (Gr@Nb₂ O₅ ) with C-O-Nb heterointerfaces, which prevents the growth and aggregation of T-Nb₂ O₅ nanoparticles. Through detailed theoretical calculations and pair distribution function analysis, the stable existence of the heterointerfaces is proved, which can accelerate the electron/ion transport. These heterointerfaces endow Gr@Nb₂ O₅ anodes with high ionic conductivity and excellent structural stability. Consequently, Gr@10-Nb₂ O₅ anode, where the mass ratio of T-Nb₂ O₅ /graphite=10/100, exhibits excellent cyclic stability and incredible rate capabilities, with 100.5 mAh g^-1 after 10000 stable cycles at an ultrahigh rate of 20 C. In addition, the synergistic Li⁺ storage mechanism is revealed by systematic electrochemical characterizations and in situ X-ray diffraction. This work offers new insights to the reasonable design of fast-charging graphite-based anodes for the next generation of LIBs.

Improving the intrinsic activity of ultrathin 2D-2D heterostructures by bridge-bonded Ni-O-Ti ligands for efficient oxygen evolution

The integration of ultrathin two-dimensional (2D) semiconductors with other conductive 2D materials to form hybrid electrocatalysts with abundant heterointerfaces can enhance the electrocatalytic activity by facilitating interfacial charge transfer. However, the hybrid electrocatalysts with weak interfacial bonding have limited effect on the electrocatalytic performance because the intrinsic activity of interfacial sites cannot be altered by weak interfacial interactions. As a proof-of-concept, we design ultrathin 2D-2D heterostructures with bridge-bonded Ni-O-Ti ligands based on single-layered Ti₃C₂T_xMXene and metal hydroxides, and further reveal the structure-activity correlation between interfacial bonding and electrocatalytic oxygen evolution reaction by combining theoretical and experimental studies. Density functional theory calculations reveal the modulation of the electronic structure of interfacial metal sites after the formation of bridged interfacial Ni-O-Ti bonding. Compared with the hydrogen-bond-linked heterostructure, the ultrathin 2D-2D heterostructure with bridge-bonded Ni-O-Ti ligands shows enhanced intrinsic activity and stability towards electrocatalytic oxygen evolution with a very low overpotential of 205 mV at 10 mA cm^-2and the long-term durability. This work provides a new understanding and approach for the design and development of 2D hybrid catalysts with highly efficient electrocatalytic activity.

Research Advances in Amorphous-Crystalline Heterostructures Toward Efficient Electrochemical Applications

Interface engineering of heterostructures has proven a promising strategy to effectively modulate their physicochemical properties and further improve the electrochemical performance for various applications. In this context related research of the newly proposed amorphous-crystalline heterostructures have lately surged since they combine the superior advantages of amorphous- and crystalline-phase structures, showing unusual atomic arrangements in heterointerfaces. Nonetheless, there has been much less efforts in systematic analysis and summary of the amorphous-crystalline heterostructures to examine their complicated interfacial interactions and elusory active sites. The critical structure-activity correlation and electrocatalytic mechanism remain rather elusive. In this review, the recent advances of amorphous-crystalline heterostructures in electrochemical energy conversion and storage fields are amply discussed and presented, along with remarks on the challenges and perspectives. Initially, the fundamental characteristics of amorphous-crystalline heterostructures are introduced to provide scientific viewpoints for structural understanding. Subsequently, the superiorities and current achievements of amorphous-crystalline heterostructures as highly efficient electrocatalysts/electrodes for hydrogen evolution reaction, oxygen evolution reaction, supercapacitor, lithium-ion battery, and lithium-sulfur battery applications are elaborated. At the end of this review, future outlooks and opportunities on amorphous-crystalline heterostructures are also put forward to promote their further development and application in the field of clean energy.

Heterointerface and Tensile Strain Effects Synergistically Enhances Overall Water-Splitting in Ru/RuO2 Aerogels

Designing robust electrocatalysts for water-splitting is essential for sustainable hydrogen generation, yet difficult to accomplish. In this study, a fast and facile two-step technique to synthesize Ru/RuO₂ aerogels for catalyzing overall water-splitting under alkaline conditions is reported. Benefiting from the synergistic combination of high porosity, heterointerface, and tensile strain effects, the Ru/RuO₂ aerogel exhibits low overpotential for oxygen evolution reaction (189 mV) and hydrogen evolution reaction (34 mV) at 10 mA cm^-2 , surpassing RuO₂ (338 mV) and Pt/C (53 mV), respectively. Notably, when the Ru/RuO₂ aerogels are applied at the anode and cathode, the resultant water-splitting cell reflected a low potential of 1.47 V at 10 mA cm^-2 , exceeding the commercial Pt/C||RuO₂ standard (1.63 V). X-ray adsorption spectroscopy and theoretical studies demonstrate that the heterointerface of Ru/RuO₂ optimizes charge redistribution, which reduces the energy barriers for hydrogen and oxygen intermediates, thereby enhancing oxygen and hydrogen evolution reaction kinetics.

Modulating Hydrogen Adsorption via Charge Transfer at the Semiconductor-Metal Heterointerface for Highly Efficient Hydrogen Evolution Catalysis

Designing and synthesizing highly efficient and stable electrocatalysts for hydrogen evolution reaction (HER) is important for realizing the hydrogen economy. Tuning the electronic structure of the electrocatalysts is essential to achieve optimal HER activity, and interfacial engineering is an effective strategy to induce electron transfer in a heterostructure interface to optimize HER kinetics. In this study, ultrafine RhP₂ /Rh nanoparticles are synthesized with a well-defined semiconductor-metal heterointerface embedded in N,P co-doped graphene (RhP₂ /Rh@NPG) via a one-step pyrolysis. RhP₂ /Rh@NPG exhibits outstanding HER performances under all pH conditions. Electrochemical characterization and first principles density functional theory calculations reveal that the RhP₂ /Rh heterointerface induces electron transfer from metallic Rh to semiconductive RhP₂ , which increases the electron density on the Rh atoms in RhP₂ and weakens the hydrogen adsorption on RhP₂ , thereby accelerating the HER kinetics. Moreover, the interfacial electron transfer activates the dual-site synergistic effect of Rh and P of RhP₂ in neutral and alkaline environments, thereby promoting reorganization of interfacial water molecules for faster HER kinetics.

Hybrid MOF Template-Directed Construction of Hollow-Structured In2 O3 @ZrO2 Heterostructure for Enhancing Hydrogenation of CO2 to Methanol

Direct hydrogenation of CO₂  to methanol using green hydrogen has emerged as a promising method for carbon neutrality, but qualifying catalysts represent a grand challenge. In₂ O₃ /ZrO₂  catalyst has been extensively applied in methanol synthesis due to its superior activity; however, the electronic effect by strong oxides-support interactions between In₂ O₃  and ZrO₂  at the In₂ O₃ /ZrO₂  interface is poorly understood. In this work, abundant In₂ O₃ /ZrO₂  heterointerfaces are engineered in a hollow-structured In₂ O₃ @ZrO₂  heterostructure through a facile pyrolysis of a hybrid metal-organic framework precursor MIL-68@UiO-66. Owing to well-defined In₂ O₃ /ZrO₂  heterointerfaces, the resultant In₂ O₃ @ZrO₂  exhibits superior activity and stability toward CO₂  hydrogenation to methanol, which can afford a high methanol selectivity of 84.6% at a conversion of 10.4% at 290 °C, and 3.0 MPa with a methanol space-time yield of up to 0.29 g_MeOH  g_cat ^-1  h^-1 . Extensive characterization demonstrates that there is a strong correlation between the strong electronic In₂ O₃ -ZrO₂  interaction and catalytic selectivity. At In₂ O₃ /ZrO₂  heterointerfaces, the electron tends to transfer from ZrO₂  to In₂ O₃  surface, which facilitates H₂  dissociation and the hydrogenation of formate (HCOO*) and methoxy (CH₃ O*) species to methanol. This study provides an insight into the In₂ O₃ -based catalysts and offers appealing opportunities for developing heterostructured CO₂  hydrogenation catalysts with excellent activity.

Facile Electron Transfer in Atomically Coupled Heterointerface for Accelerated Oxygen Evolution

An efficient and cost-effective approach for the development of advanced catalysts has been regarded as a sustainable way for green energy utilization. The general guideline to design active and efficient catalysts for oxygen evolution reaction (OER) is to achieve high intrinsic activity and the exposure of more density of the interfacial active sites. The heterointerface is one of the most attractive ways that plays a key role in electrochemical water oxidation. Herein, atomically cluster-based heterointerface catalysts with strong metal support interaction (SMSI) between WMn₂ O₄ and TiO₂ are designed. In this case, the WMn₂ O₄ nanoflakes are uniformly decorated by TiO₂ particles to create electronic effect on WMn₂ O₄ nanoflakes as confirmed by X-ray absorption near edge fine structure. As a result, the engineered heterointerface requires an OER onset overpotential as low as 200 mV versus reversible hydrogen electrode, which is stable for up to 30 h of test. The outstanding performance and long-term durability are due to SMSI, the exposure of interfacial active sites, and accelerated reaction kinetics. To confirm the synergistic interaction between WMn₂ O₄ and TiO₂ , and the modification of the electronic structure, high-resolution transmission electron microscopy (HR-TEM), X-ray photoemission spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) are used.

Elucidating the Synergic Effect in Nanoscale MoS2 /TiO2 Heterointerface for Na-Ion Storage

Interface engineering in electrode materials is an attractive strategy for enhancing charge storage, enabling fast kinetics, and improving cycling stability for energy storage systems. Nevertheless, the performance improvement is usually ambiguously ascribed to the "synergetic effect", the fundamental understanding toward the effect of the interface at molecular level in composite materials remains elusive. In this work, a well-defined nanoscale MoS₂ /TiO₂ interface is rationally designed by immobilizing TiO₂ nanocrystals on MoS₂ nanosheets. The role of heterostructure interface between TiO₂ and MoS₂ by operando synchrotron X-ray diffraction (sXRD), solid-state nuclear magnetic resonance, and density functional theory calculations is investigated. It is found that the existence of a hetero-interfacial electric field can promote charge transfer kinetics. Based on operando sXRD, it is revealed that the heterostructure follows a solid-solution reaction mechanism with small volume changes during cycling. As such, the electrode demonstrates ultrafast Na⁺ ions storage of 300 mAh g^-1 at 10 A g^-1 and excellent reversible capacity of 540 mAh g^-1 at 0.2 A g^-1 . This work provides significant insights into understanding of heterostructure interface at molecular level, which suggests new strategies for creating unconventional nanocomposite electrode materials for energy storage systems.

Oxygen Spillover Effect at Cu/Fe2O3 Heterointerfaces to Enhance Oxygen Electrocatalytic Reactions for Rechargeable Zn-Air Batteries

Rational design and synthesis of high-performance electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are critical for practical application of Zn-air batteries (ZABs). In this work, the bifunctional composite Cu-Fe₂O₃/PNC was prepared by a simple and effective wet-hydrothermal coupled dry-annealing synthesis strategy. The Cu-Fe₂O₃/PNC displayed excellent catalytic activity in ORR and OER with a potential difference of 0.63 V. More importantly, the ZAB assembled with Cu-Fe₂O₃/PNC exhibited a high-power density of 138.00 mW cm^-2 and an excellent long-term cyclability. X-ray photoelectron spectroscopy (XPS) demonstrated that the excellent performance is due to the strong electronic interaction between Cu and Fe₂O₃ that arises as a result of the fast electron transfer through the Cu-O-Fe bond and the higher concentration of surface oxygen vacancies. Meanwhile, the spillover factor Bsp/2zF of Cu/PNC and Cu-Fe₂O₃/PNC obtained by the rotating disk experiment was 1.00 × 10^-7 and 1.10 × 10^-7 cm²·s^-1, respectively, indicating that the oxygen spillover effect between Cu and Fe₂O₃ lowers the energy barrier, increases the number of active sites, and alters the rate-determining reaction step. This work demonstrated the significant potential of Cu-Fe₂O₃/PNC in energy conversion and storage applications, providing a new perspective for the rational design of bifunctional electrocatalysts.

Ionic-Liquid-Assisted Synthesis of FeSe-MnSe Heterointerfaces with Abundant Se Vacancies Embedded in N,B Co-Doped Hollow Carbon Microspheres for Accelerating the Sulfur Reduction Reaction

Currently, extensive research efforts are being devoted to suppressing the shuttle effect of polysulfides. The uncontrollable deposition of insulating Li₂ S onto the surface of sulfur host materials dramatically inhibits the continuous reduction of polysulfides in lithium-sulfur (Li-S) batteries. Herein, N,B co-doped hollow carbon microspheres embedded with dense FeSe-MnSe heterostructures and abundant Se vacancies (FeSe-MnSe/NBC) are rationally designed and synthesized via a facile hydrothermal reaction using ionic liquids as dopants. The introduction of abundant heterostructures subtly guides Li₂ S nucleation and deposition in 3D frameworks, thus avoiding the formation of the Li₂ S passivation layer and allowing for continuous Li⁺ diffusion and subsequent nucleation of Li₂ S. Owing to these beneficial features, Li-S batteries comprising an FeSe-MnSe/NBC electrode exhibit significantly improved performance, including a high initial capacity of 1334 mAh g^-1 at 0.2 C and ultralong cycle stability with a low capacity fading rate of 0.029% cycle^-1 over 1000 cycles at 1.0 C. Remarkably, the FeSe-MnSe/NBC pouch cell delivers a considerable areal capacity of 3.6 mAh cm^-2 at 0.1 C. This study provides valuable insight into heterostructures and Se vacancies for developing practical Li-S batteries.

Heterostructured V-Doped Ni2 P/Ni12 P5 Electrocatalysts for Hydrogen Evolution in Anion Exchange Membrane Water Electrolyzers

Regulating the electronic structure and intrinsic activity of catalysts' active sites with optimal hydrogen intermediates adsorption is crucial to enhancing the hydrogen evolution reaction (HER) in alkaline media. Herein, a heterostructured V-doped Ni₂ P/Ni₁₂ P₅ (V-Ni₂ P/Ni₁₂ P₅ ) electrocatalyst is  fabricated through a hydrothermal treatment and controllable phosphidation process. In comparison with pure-phase V-Ni₂ P, in/ex situ characterizations and theoretical calculations reveal a redistribution of electrons and active sites in V-Ni₂ P/Ni₁₂ P₅ due to the V doping and heterointerfaces effect. The strong coupling between Ni₂ P and Ni₁₂ P₅ at the interface leads to an increased electron density at interfacial Ni sites while depleting at P sites, with V-doping further promoting the electron accumulation at Ni sites. This is accompanied by the change of active sites from the anionic P sites to the interfacial Ni-V bridge sites in V-Ni₂ P/Ni₁₂ P₅ . Benefiting from the interface electronic structure, increased number of active sites, and optimized H-adsorption energy, the V-Ni₂ P/Ni₁₂ P₅ exhibits an overpotential of 62 mV to deliver 10 mA cm^-2 and excellent long-term stability for HER. The V-Ni₂ P/Ni₁₂ P₅ catalyst is applied for anion exchange membrane water electrolysis to deliver superior performance with a current density of 500 mA cm^-2 at a cell voltage of 1.79 V and excellent durability.

1D CNT-Expanded 3D Carbon Foam/Si3N4 Sandwich Heterostructure: Utilizing the Polarization Compensation Effect for Keeping Stable Electromagnetic Absorption Performance at Elevated Temperature

Modern electromagnetic (EM) absorbing materials (EAMs) are experiencing a revolution triggered by advanced information technology. Simultaneously, the diverse harsh EM application scenarios entail a more stringent appeal of practicability to EAMs, especially under high-temperature conditions. Therefore, exploring EAMs with both excellent absorbing performance and practicability at elevated temperatures is necessary. Herein, a novel 3D porous carbon foam/carbon nanotubes@Si₃N₄ (CF/CNTs@Si₃N₄) heterostructure was constructed by the chemical vapor infiltration process. The optimally grown 1D CNTs embedded in 3D CF/Si₃N₄ are utilized to provide abundant nanointerface coupling effects to compensate for the excessive increase in the conductive loss during rising temperature to realize a self-adjustment in response to high temperature. A high-efficiency EM absorption over a wide temperature range from 25 to 480 °C was achieved (with a ≥90% absorbing ratio covering the whole X-band). In addition, the Si₃N₄ coating can improve the thermal stability of the carbon matrix and maintain the tailored inner structure. Multiple investigations into other environmental adaptabilities also exhibited the application perspective of such a heterostructure. This work points out a new strategy for preparing designable, efficient, and high-temperature applicable EAMs, promoting the diverse development of electronic devices.

Customizing Heterointerfaces in Multilevel Hollow Architecture Constructed by Magnetic Spindle Arrays Using the Polymerizing-Etching Strategy for Boosting Microwave Absorption

Heterointerface engineering is evolving as an effective approach to tune electromagnetic functional materials, but the mechanisms of heterointerfaces on microwave absorption (MA) remain unclear. In this work, abundant electromagnetic heterointerfaces are customized in multilevel hollow architecture via a one-step synergistic polymerizing-etching strategy. Fe/Fe₃ O₄ @C spindle-on-tube structures are transformed from FeOOH@polydopamine precursors by a controllable reduction process. The impressive electromagnetic heterostructures are realized on the Fe/Fe₃ O₄ @C hollow spindle arrays and induce strong interfacial polarization. The highly dispersive Fe/Fe₃ O₄ nanoparticles within spindles build multi-dimension magnetic networks, which enhance the interaction with incident microwaves and reinforce magnetic loss capacity. Moreover, the hierarchically hollow structure and electromagnetic synergistic components are conducive to the impedance matching between absorbing materials and air medium. Furthermore, the mechanisms of electromagnetic heterointerfaces on the MA are systematically investigated. Accordingly, the as-prepared hierarchical Fe/Fe₃ O₄ @C microtubes exhibit remarkable MA performance with a maximum refection loss of -55.4 dB and an absorption bandwidth of 4.2 GHz. Therefore, in this study, the authors not only demonstrate a synergistic strategy to design multilevel hollow architecture, but also provide a fundamental guide in heterointerface engineering of highly efficient electromagnetic functional materials.

Iron Catalyzed Cascade Construction of Molybdenum Carbide Heterointerfaces for Understanding Hydrogen Evolution

The intercrystalline interfaces have been proven vital in heterostructure catalysts. However, it is still challenging to generate specified heterointerfaces and to make clear the mechanism of a reaction on the interface. Herein, this work proposes a strategy of Fe-catalyzed cascade formation of heterointerfaces for comprehending the hydrogen evolution reaction (HER). In the pure solid-phase reaction system, Fe catalyzes the in situ conversion of MoO₂ to MoC and then Mo₂ C, and the consecutive formation leaves lavish intercrystalline interfaces of MoO₂ -MoC (in Fe-MoO₂ /MoC@NC) or MoC-Mo₂ C (in Fe-MoC/β-Mo₂ C@NC), which contribute to HER activity. The improved HER activity on the interface leads to further checking of the mechanism with density functional theory calculation. The computation results reveal that the electroreduction (Volmer step) produced H* prefers to be adsorbed on Mo₂ C; then two pathways are proposed for the HER on the interface of MoC-Mo₂ C, including the single-molecular adsorption pathway (Rideal mechanism) and the bimolecular adsorption pathway (Langmuir-Hinshelwood mechanism). The calculation results further show that the former is favorable, and the reaction on the MoC-Mo₂ C heterointerface significantly lowers the energy barriers of the rate-determining steps.

Synergetic Anion Vacancies and Dense Heterointerfaces into Bimetal Chalcogenide Nanosheet Arrays for Boosting Electrocatalysis Sulfur Conversion

Vacancy and interface engineering are regarded as effective strategies to modulate the electronic structure and enhance the activity of metal chalcogenides. However, the practical application of metal chalcogenides in lithium-sulfur (Li-S) batteries is limited by their low conductivity, rapid decline in catalytic activity, and large volume variation during the discharging/charging process. Herein, bimetal sulfide (CoZn-S) nanosheet arrays with sulfur vacancies and dense heterointerfaces are proposed to accelerate sulfur conversion and improve the performance of Li-S batteries. Systematic investigations reveal that sulfur-vacancy and build-in interfacial field in CoZn-S facilitate the electron transfer and regulate the electronic structure. The well-designed 3D nanosheet array structures shorten the ion-transport pathway and inhibit the volume fluctuation of CoZn-S during the electrocatalysis process. Density functional theory studies confirm that the built-in interfacial field and sulfur vacancy can promote the thermodynamic formation and decomposition of Li₂ S, thus improving their intrinsic activity.

CoFe2O4nanoparticles dispersed on carbon rods derived from cotton for high-efficiency microwave absorption

Biomass-derived carbon materials have received a surge of scientific attention to develop lightweight and broadband microwave absorbers. Herein, rodlike porous carbon materials derived from cotton have been fabricated with uniformly dispersed CoFe₂O₄nanoparticles via facile and scalable process. The combination of magnetic particles and carbonaceous material is advantageous to realize the magnetic-dielectric synergistic effect which could effectively promote the dissipation of incident waves, giving rise to an optimal reflection loss value of -48.2 dB over a qualified bandwidth (4.8 GHz) at 2.5 mm. The cotton-derived carbon rods with conductive network not only act as a supporter to carry the CoFe₂O₄nanoparticles, but also provide massive heterointerfaces to facilitate the interfacial polarization. In consideration of the renewable and abundant resource of cotton, the as-prepared CoFe₂O₄/C composites would meet the increasing demand of lightweight and highly efficient microwave absorbers.

Comparative Study of Thermoelectric Properties of Sb2Si2Te6 and Bi2Si2Te6

Charge carrier transport and corresponding thermoelectric properties are often affected by several parameters, necessitating a thorough comparative study for a profound understanding of the detailed conduction mechanism. Here, as a model system, we compare the electronic transport properties of two layered semiconductors, Sb₂Si₂Te₆ and Bi₂Si₂Te₆. Both materials have similar grain sizes and morphologies, yet their conduction characteristics are significantly different. We found that phase boundary scattering can be one of the main factors for Bi₂Si₂Te₆ to experience significant charge carrier scattering, whereas Sb₂Si₂Te₆ is relatively unaffected by the phenomenon. Furthermore, extensive point defect scattering in Sb₂Si₂Te₆ significantly reduces its lattice thermal conductivity and results in high zT values across a broad temperature range. These findings provide novel insights into electron transport within these materials and should lead to strategies for further improving their thermoelectric performance.

Self-Optimizing Effect in Lithium Storage of GeO2 Induced by Heterointerface Regulation

Herein, a heterostructural hexagonal@tetragonal GeO₂ (HT-GeO₂ ) composite has been designed based on density functional theory (DFT) calculations and synthesized via an acidic-heating route dealt with rapid cooling, where the inner hexagonal GeO₂ (H-GeO₂ ) phase is covered by a porous layer of tetragonal GeO₂ (T-GeO₂ ) owing to HF etching. Interestingly, the HT-GeO₂ electrode has a self-optimizing effect in lithium storage induced by heterointerface regulation, where the porous T-GeO₂ layer on the surface of HT-GeO₂ can act as not only a Li⁺ /electron conducting layer, but also a buffer layer, while the inner H-GeO₂ phase can react preferentially with Li ions owing to lower intercalation energy, which is confirmed by operando XRD measurement contributing to thorough lithiation for HT-GeO₂ . Moreover, the heterointerface can enhance the pseudocapacitance effect, which can boost the Li storage and accelerate the discharge-charge process. As a result, a large capacity of 984 mAh g^-1 after 500 cycles at 2 A g^-1 and a capacity of 430 mAh g^-1 at a high current density of 20 A g^-1 are delivered. This work provides an easy and efficient way to improve the cycling stability of the GeO₂ anode, and the T-GeO₂ phase would be a novel anode material in energy storage devices.

Realize High Thermoelectric Properties in n-Type Bi2Te2.7Se0.3/Y2O3 Nanocomposites by Constructing Heterointerfaces

Due to the excellent thermoelectric performance, bismuth telluride (Bi₂Te₃) compounds are highly promising for the thermoelectric conversion in the room temperature range. However, the inferior thermoelectric performance of the n-type leg severely restricts the applications of Bi₂Te₃-based thermoelectric couples. Herein, n-type Bi₂Te_2.7Se_0.3 (BTS)-based thermoelectric materials incorporated with nanosized Y₂O₃ (0.5-3 wt %) are prepared and their thermoelectric properties are systematically studied. The dramatically improved thermoelectric performance is ascribed to the realization of a multiscale feature of Y₂O₃ nanoparticle (NP)-induced interfacial decorations distributed along grain boundaries, which creates massive BTS/Y₂O₃ interfaces for the manipulation of carrier and phonon transport properties. The geometric phase analysis is employed to further confirm the condition of local strain in the BTS composite incorporated with Y₂O₃ NPs. Due to the presence of heterointerfaces and high density of dislocations in BTS matrices, the minimum lattice thermal conductivity (κ_l) of the nanocomposites (NCs) is dramatically suppressed from 0.76 to 0.37 W m^-1 K^-1. With the incorporation of 3 wt % Y₂O₃ NPs, the Vickers hardness of the BTS/Y₂O₃ NC is increased by about 32%. Overall, the BTS + 1.5 wt % Y₂O₃ NC maintains excellent thermoelectric properties (ZT_ave = 1.1) in the whole operative temperature range (300-500 K). The present strategy of implementing high-density heterogeneous interfaces by Y₂O₃ NP addition offers an applicable pathway for fabricating high-performance thermoelectric materials with both optimized thermoelectric properties and mechanical properties.

Emerging of Heterostructure Materials in Energy Storage: A Review

With the ever-increasing adaption of large-scale energy storage systems and electric devices, the energy storage capability of batteries and supercapacitors has faced increased demand and challenges. The electrodes of these devices have experienced radical change with the introduction of nano-scale materials. As new generation materials, heterostructure materials have attracted increasing attention due to their unique interfaces, robust architectures, and synergistic effects, and thus, the ability to enhance the energy/power outputs as well as the lifespan of batteries. In this review, the recent progress in heterostructure from energy storage fields is summarized. Specifically, the fundamental natures of heterostructures, including charge redistribution, built-in electric field, and associated energy storage mechanisms, are summarized and discussed in detail. Furthermore, various synthesis routes for heterostructures in energy storage fields are roundly reviewed, and their advantages and drawbacks are analyzed. The superiorities and current achievements of heterostructure materials in lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), lithium-sulfur batteries (Li-S batteries), supercapacitors, and other energy storage devices are discussed. Finally, the authors conclude with the current challenges and perspectives of the heterostructure materials for the fields of energy storage.

Artificial Heterointerfaces Achieve Delicate Reaction Kinetics towards Hydrogen Evolution and Hydrazine Oxidation Catalysis

Electrochemical water splitting for H₂ production is limited by the sluggish anode oxygen evolution reaction (OER), thus using hydrazine oxidation reaction (HzOR) to replace OER has received great attention. Here we report the hierarchical porous nanosheet arrays with abundant Ni₃ N-Co₃ N heterointerfaces on Ni foam with superior hydrogen evolution reaction (HER) and HzOR activity, realizing working potentials of -43 and -88 mV for 10 mA cm^-2 , respectively, and achieving an industry-level 1000 mA cm^-2 at 200 mV for HzOR. The two-electrode overall hydrazine splitting (OHzS) electrolyzer requires the cell voltages of 0.071 and 0.76 V for 10 and 400 mA cm^-2 , respectively. The H₂ production powered by a direct hydrazine fuel cell (DHzFC) and a commercial solar cell are investigated to inspire future practical applications. DFT calculations decipher that heterointerfaces simultaneously optimize the hydrogen adsorption free energy (ΔG_H* ) and promote the hydrazine dehydrogenation kinetics. This work provides a rationale for advanced bifunctional electrocatalysts, and propels the practical energy-saving H₂ generation techniques.

Sequential Electrodeposition of Bifunctional Catalytically Active Structures in MoO3 /Ni-NiO Composite Electrocatalysts for Selective Hydrogen and Oxygen Evolution

Exploring earth-abundant and highly efficient electrocatalysts is critical for further development of water electrolyzer systems. Integrating bifunctional catalytically active sites into one multi-component might greatly improve the overall water-splitting performance. In this work, amorphous NiO nanosheets coupled with ultrafine Ni and MoO₃ nanoparticles (MoO₃ /Ni-NiO), which contains two heterostructures (i.e., Ni-NiO and MoO₃ -NiO), is fabricated via a novel sequential electrodeposition strategy. The as-synthesized MoO₃ /Ni-NiO composite exhibits superior electrocatalytic properties, affording low overpotentials of 62 mV at 10 mA cm^-2 and 347 mV at 100 mA cm^-2 for catalyzing the hydrogen and the oxygen evolution reaction (HER/OER), respectively. Moreover, the MoO₃ /Ni-NiO hybrid enables the overall alkaline water-splitting at a low cell voltage of 1.55 V to achieve 10 mA cm^-2 with outstanding catalytic durability, significantly outperforming the noble-metal catalysts and many materials previously reported. Experimental and theoretical investigations collectively demonstrate the generated Ni-NiO and MoO₃ -NiO heterostructures significantly reduce the energetic barrier and act as catalytically active centers for selective HER and OER, synergistically accelerating the overall water-splitting process. This work helps to fundamentally understand the heterostructure-dependent mechanism, providing guidance for the rational design and oriented construction of hybrid nanomaterials for diverse catalytic processes.

CoP/RGO-Pd Hybrids with Heterointerfaces as Highly Active Catalysts for Ethanol Electrooxidation

The ethanol oxidation reaction is of critical importance to the commercial viability of direct ethanol fuel cell technology. However, owing to the poor C-C bond cleavage capability, almost all ethanol oxidation is incomplete and suffers from low selectivity toward the C1 pathway. Herein, under the support of theoretical calculations that the heterointerfaces between CoP and Pd can reduce the energy barrier of C-C bond cleavage, rich heterointerfaces in CoP/RGO-Pd hybrids were designed to improve ethanol electrooxidation performance through enhancing the selectivity toward the C1 pathway. The experimental results show that the faradaic efficiency of the C1 pathway of CoP/RGO-Pd hybrids is as high as 27.6%, surpassing most reported catalysts in the literature. As a result of this enhancement, CoP/RGO-Pd10 exhibits mass activity as high as 4597 mA·mg_Pd^-1 and specific activity as high as 10 mA·cm^-2, which are much higher than those of other Pd-based electrocatalysts.

Understanding the Role of Nanoscale Heterointerfaces in Core/Shell Structures for Water Splitting: Covalent Bonding Interaction Boosts the Activity of Binary Transition-Metal Sulfides

The appropriate catalyst model with a precisely designed interface is highly desirable for revealing the real active site at the atomic level. Herein, we report a proof-of-concept strategy for creating an exposed and embedding interface model by constructing a unique Co₉S₈ core with a full WS₂ shell (Co₉S₈/FWS₂) and a half WS₂ shell (Co₉S₈/HWS₂) to uncover the synergistic effect of heterointerfaces on the catalytic performances. Tailoring the heteroepitaxial growth of WS₂ shell, Co₉S₈/HWS₂ with exposed Co-S-W interfaces leads to the exceptional electron density changes on edged-S atoms with large amounts of lone-pair electrons. Meanwhile, the unique Co₉S₈/HWS₂ could accelerate the kinetic adsorption of hydrogen- and oxygen-containing intermediates. Such Co₉S₈/HWS₂ electrocatalysts show extremely low overpotentials of 78 and 290 mV at a current density of 10 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction, respectively. Using Co₉S₈/HWS₂ as both the cathode and anode, an alkali electrolyzer delivers a current density of 10 mA cm^-2 at a quite low cell voltage of 1.60 V. The results of both operando Raman spectroscopy and electron spin resonance indicate the presence of S-S terminal and S-S bridging with unsaturated S atoms during the HER process. The present work reveals the synergistic effects of nanoscale interfaces on overall electrocatalytic water splitting.

Defect-Rich Heterogeneous MoS2/NiS2 Nanosheets Electrocatalysts for Efficient Overall Water Splitting

Designing and constructing bifunctional electrocatalysts is vital for water splitting. Particularly, the rational interface engineering can effectively modify the active sites and promote the electronic transfer, leading to the improved splitting efficiency. Herein, free-standing and defect-rich heterogeneous MoS2/NiS2 nanosheets for overall water splitting are designed. The abundant heterogeneous interfaces in MoS2/NiS2 can not only provide rich electroactive sites but also facilitate the electron transfer, which further cooperate synergistically toward electrocatalytic reactions. Consequently, the optimal MoS2/NiS2 nanosheets show the enhanced electrocatalytic performances as bifunctional electrocatalysts for overall water splitting. This study may open up a new route for rationally constructing heterogeneous interfaces to maximize their electrochemical performances, which may help to accelerate the development of nonprecious electrocatalysts for overall water splitting.

Heterointerface-Driven Band Alignment Engineering and its Impact on Macro-Performance in Semiconductor Multilayer Nanostructures

Interfaces in semiconductor heterostructures is of continuously greater significance in the trend of scaling materials down to the atomic limit. Since atoms tend to behave more irregularly around interfaces than in internal materials, accurate energy band alignment becomes a major challenge, which determines the ultimate performance of devices. Therefore, a comprehensive understanding of the interplay between heterointerface, energy band, and macro-performance is desiderated. Here, such interplay is explored by investigating asymmetric heterointerfaces with identical fabrication parameters in multiple-quantum-well lasers. The unexpected asymmetry derives from the atomic discrepancy around heterointerfaces, which ultimately improves the optical property through altered valence band offsets. Strain and charge distribution around heterointerfaces are characterized via geometric phase analysis and in situ bias electron holography, respectively. Combining experiments with theories, arsenic-enrichment at one of the interfaces is considered the origin of asymmetry. To reveal actual band alignment, valence band model is modified focusing on the transition around heterojunctions. The enhanced photoluminescence intensity reflects the alleviation of hole confinement insufficiency and the enlargement of valence band offset. The results help to advance the understanding of the general problem of interface in nanostructures and provide guidance applicable to various scenarios for micro-macro correlation.

Excitons: Modulation of New Excitons in Transition Metal Dichalcogenide‐Perovskite Oxide System (Adv. Sci. 12/2019)

In article number 1900446, Shi Jie Wang, Wenjing Zhang, Andrivo Rusydi, Andrew T. S. Wee, and co‐workers observe high‐energy excitons that are generated by a new mechanism in monolayer‐MoS₂ on SrTiO₃, which are attributed to the change in many‐body interactions that couples with interfacial orbital‐hybridization. The interfacial interactions lead to a fermi‐surface feature at the interface. The results provide an understanding of 2D‐transition metal dichalcogenides heterointerfaces and show the crucial role that many‐body interactions play at the atomic level.

Modulation of New Excitons in Transition Metal Dichalcogenide-Perovskite Oxide System

The exciton, a quasi-particle that creates a bound state of an electron and a hole, is typically found in semiconductors. It has attracted major attention in the context of both fundamental science and practical applications. Transition metal dichalcogenides (TMDs) are a new class of 2D materials that include direct band-gap semiconductors with strong spin-orbit coupling and many-body interactions. Manipulating new excitons in semiconducting TMDs could generate a novel means of application in nanodevices. Here, the observation of high-energy excitonic peaks in the monolayer-MoS2 on a SrTiO3 heterointerface generated by a new complex mechanism is reported, based on a comprehensive study that comprises temperature-dependent optical spectroscopies and first-principles calculations. The appearance of these excitons is attributed to the change in many-body interactions that occurs alongside the interfacial orbital hybridization and spin-orbit coupling brought about by the excitonic effect propagated from the substrate. This has further led to the formation of a Fermi-surface feature at the interface. The results provide an atomic-scale understanding of the heterointerface between monolayer-TMDs and perovskite oxide and highlight the importance of spin-orbit-charge-lattice coupling on the intrinsic properties of atomic-layer heterostructures, which open up a way to manipulate the excitonic effects in monolayer TMDs via an interfacial system.

Tunable Magnetic Phases at Fe3O4/SrTiO3 Oxide Interfaces

We demonstrate the emergence and control of magnetic phases between magnetite (Fe₃O₄), a ferrimagnetic halfmetal, and SrTiO₃, a transparent nonmagnetic insulator considered the bedrock of oxide-based electronics. The Verwey transition ( T_V) was detected to persist from bulk-like down to ultrathin Fe₃O₄ films, decreasing from 117 ± 4 K (38 nm) to 25 ± 4 K (2 nm), respectively. Element-selective electronic and magnetic properties of the ultrathin films and buried interfaces are studied by angle-dependent hard X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism techniques. We observe a reduction of Fe²⁺ ions with decreasing film thickness, accompanied by an increase of Fe³⁺ ions in both tetrahedral and octahedral sites and conclude on the formation of a magnetically active ferrimagnetic 2 u.c. γ-Fe₂O₃ intralayer. To manipulate the interfacial magnetic phase, a postannealing process causes the controlled reduction of the γ-Fe₂O₃ that finally leads to stoichiometric and ferrimagnetic Fe₃O₄/SrTiO₃(001) heterointerfaces.

Heterostructures Composed of N-Doped Carbon Nanotubes Encapsulating Cobalt and β-Mo2 C Nanoparticles as Bifunctional Electrodes for Water Splitting

Herein, we demonstrate the use of heterostructures comprised of Co/β-Mo₂ C@N-CNT hybrids for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline electrolyte. The Co can not only create a well-defined heterointerface with β-Mo₂ C but also overcomes the poor OER activity of β-Mo₂ C, thus leading to enhanced electrocatalytic activity for HER and OER. DFT calculations further proved that cooperation between the N-CNTs, Co, and β-Mo₂ C results in lower energy barriers of intermediates and thus greatly enhances the HER and OER performance. This study not only provides a simple strategy for the construction of heterostructures with nonprecious metals, but also provides in-depth insight into the HER and OER mechanism in alkaline solution.

Corrugated Heterojunction Metal-Oxide Thin-Film Transistors with High Electron Mobility via Vertical Interface Manipulation

A new strategy is reported to achieve high-mobility, low-off-current, and operationally stable solution-processable metal-oxide thin-film transistors (TFTs) using a corrugated heterojunction channel structure. The corrugated heterojunction channel, having alternating thin-indium-tin-zinc-oxide (ITZO)/indium-gallium-zinc-oxide (IGZO) and thick-ITZO/IGZO film regions, enables the accumulated electron concentration to be tuned in the TFT off- and on-states via charge modulation at the vertical regions of the heterojunction. The ITZO/IGZO TFTs with optimized corrugated structure exhibit a maximum field-effect mobility >50 cm2 V-1 s-1 with an on/off current ratio of >108 and good operational stability (threshold voltage shift <1 V for a positive-gate-bias stress of 10 ks, without passivation). To exploit the underlying conduction mechanism of the corrugated heterojunction TFTs, a physical model is implemented by using a variety of chemical, structural, and electrical characterization tools and Technology Computer-Aided Design simulations. The physical model reveals that efficient charge manipulation is possible via the corrugated structure, by inducing an extremely high carrier concentration at the nanoscale vertical channel regions, enabling low off-currents and high on-currents depending on the applied gate bias.

Nanocomposites Based on CoSe2-Decorated FeSe2 Nanoparticles Supported on Reduced Graphene Oxide as High-Performance Electrocatalysts toward Oxygen Evolution Reaction

FeCo-based materials are promising candidates as efficient, affordable, and sustainable electrocatalysts for oxygen evolution reaction (OER). Herein, a composite based on FeSe₂@CoSe₂ particles supported on reduced graphene oxide (rGO) was successfully prepared as an OER catalyst. In the catalyst, the CoSe₂ phase was located on the FeSe₂ surface, forming a large number of exposed heterointerfaces with acidic iron sites because of strong charge interaction between CoSe₂ and FeSe₂. It is believed that the exposed heterointerfaces act as catalytic active sites for OER via a two-site mechanism, manifesting an overpotential as low as 260 mV to reach the current density of 10 mA cm^-2 in 1 M KOH and excellent stability for at least 6 h, which is superior to those of CoSe₂/rGO, FeSe₂/rGO, as well as most of the FeNi- and FeCo-based electrocatalysts reported in recent literatures. It was demonstrated that the most optimal composite electrocatalysts release more Fe species into the electrolyte during the OER process, whereas the releasing of Co species is negligible. When the FeSe₂@CoSe₂/rGO catalysts were loaded on a α-Fe₂O₃ photoanode, the photocurrent density was increased by three times. These results may open up a promising avenue into the design and engineering of highly active and durable catalysts for water oxidation.

Designing Two-Dimensional Dirac Heterointerfaces of Few-Layer Graphene and Tetradymite-Type Sb2Te3 for Thermoelectric Applications

Despite the ubiquitous nature of the Peltier effect in low-dimensional thermoelectric devices, the influence of finite temperature on the electronic structure and transport in the Dirac heterointerfaces of the few-layer graphene and layered tetradymite, Sb₂Te₃ (which coincidently have excellent thermoelectric properties) are not well understood. In this work, using the first-principles density-functional theory calculations, we investigate the detailed atomic and electronic structure of these Dirac heterointerfaces of graphene and Sb₂Te₃ and further re-examine the effect of finite temperature on the electronic band structures using a phenomenological temperature-broadening model based on Fermi-Dirac statistics. We then proceed to understand the underlying charge redistribution process in this Dirac heterointerfaces and through solving the Boltzmann transport equation, we present the theoretical evidence of electron-hole asymmetry in its electrical conductivity as a consequence of this charge redistribution mechanism. We finally propose that the hexagonal-stacked Dirac heterointerfaces are useful as efficient p-n junction building blocks in the next-generation thermoelectric devices where the electron-hole asymmetry promotes the thermoelectric transport by "hot" excited charge carriers.

Ferromagnetic-Antiferromagnetic Coupling by Distortion of Fe/Mn Oxygen Octahedrons in (BiFeO3 )m (La0.7 Sr0.3 MnO3 )n Superlattices

Interface enhanced magnetism attracts much attention due to its potential use in exploring novel structure devices. Nevertheless, the magnetic behavior at interfaces has not been quantitatively determined. In this study, abnormal magnetic moment reduction is observed in La_0.7 Sr_0.3 MnO₃ (LSMO)/BiFeO₃ (BFO) superlattices, which is induced by ferromagnetic (FM)/antiferromagnetic (AFM) coupling in the interface. With reduced repetition of the superlattice's unit cell [(LSMO)_n /(BFO)_n ]_60/n (n = 1, 2, 5, 10) on a SrTiO₃ substrate, magnetic moment reduction from 25.5 emu cc^-1 ([(LSMO)₁₀ /(BFO)₁₀ ]₆ ) to 1.5 emu cc^-1 ([(LSMO)₁ /(BFO)₁ ]₆₀ ) is obtained. Ab initio simulations show that due to the different magnetic domain formation energies, the magnetic moment orientation tends to be paramagnetic in the FM/AFM interface. The work focuses on the magnetic domain formation energy and provides a pathway to construct artificial heterostructures that can be an effective way to tune the magnetic moment orientation and control the magnetization of ultrathin films.

Chestnut-Like TiO2@α-Fe2O3 Core-Shell Nanostructures with Abundant Interfaces for Efficient and Ultralong Life Lithium-Ion Storage

Transition metal oxides caused much attention owing to the scientific interests and potential applications in energy storage systems. In this study, a free-standing three-dimensional (3D) chestnut-like TiO₂@α-Fe₂O₃ core-shell nanostructure (TFN) is rationally synthesized and utilized as a carbon-free electrode for lithium-ion batteries (LIBs). Two new interfaces between anatase TiO₂ and α-Fe₂O₃ are observed and supposed to provide synergistic effect. The TiO₂ microsphere framework significantly improves the mechanical stability, while the α-Fe₂O₃ provides large capacity. The abundant boundary structures offer the possibility for interfacial lithium storage and electron transport. The as-prepared TFN delivers a high capacity of 820 mAh g^-1 even after 1000 continuous cycles with a Coulombic efficiency of ca. 99% at a current of 500 mA g^-1, which is better than the works reported previously. A thin gel-like SEI (solid electrolyte interphase) film and Fe⁰ phase yielded during charge/discharge cycling have been confirmed which makes it possible to alleviate the volumetric change and enhance the electronic conductivity. This confirmation is helpful for understanding the mechanism of lithium-ion storage in α-Fe₂O₃-based materials. The as-prepared free-standing TFN with excellent stability and high capacity can be an appropriate candidate for carbon-free anode material in LIBs.

Control of the Metal-Insulator Transition at Complex Oxide Heterointerfaces through Visible Light

The coupling of the localized surface plasmon resonance of Au nanoparticles is utilized to deliver a visible-light stimulus to control conduction at the LaAlO3 /SrTiO3 interface. A giant photoresponse and the controllable metal-insulator transition are characterized at this heterointerface. This study paves a new route to optical control of the functionality at the heterointerfaces.

Enhanced Structural and Magnetic Coupling in a Mesocrystal-Assisted Nanocomposite

Benefiting from the advances made in well-controlled materials synthesis techniques, nanocomposites have drawn considerable attention due to their enthralling physics and functionalities. In this work, we report a new heteroepitaxial mesocrystal-perovskite nanocomposite, (NiFe2O4)0.33:(La0.67Ca0.33MnO3)0.67. Elaborate structural studies revealed that tiny NiFe2O4 nanocrystals aggregate into ordered octahedral mesocrystal arrays with {111} facets together with a concomitant structural phase transition of the La0.67Ca0.33MnO3 matrix upon postannealing process. Combined magnetic and X-ray absorption spectroscopic measurements show significant enhancement in the magnetic properties at room temperature due to the structural evolution of magnetic NiFe2O4 and the consequent magnetic coupling at the heterointerfaces mediating via well connected octahedrons of Mn-O6 in La0.67Ca0.33MnO3 and (Ni,Fe)-O6 in NiFe2O4. This work demonstrates an approach to manipulate the exciting physical properties of material systems by integrating desired functionalities of the constituents via synthesis of a self-assembled mesocrystal embedded nanocomposite system.

Layer-Resolved Cation Diffusion and Stoichiometry at the LaAlO3/SrTiO3 Heterointerface Probed by X-ray Photoemission Experiments and Site Occupancy Modeling

The layer-resolved cation occupancy for different conducting and insulating interfaces of LaAlO3 (LAO) thin films on SrTiO3 (STO) has been determined by angle-resoled X-ray photoelectron spectroscopy (AR-XPS). Three STO interfaces with LAO have been considered, namely, a conducting interface with a 5 unit cell (u.c.) LAO layer, an insulating interface with a 5 u.c. LAO layer, and an insulating interface with a 3 u.c. LAO layer. Considering inelastic and elastic scattering processes in the transport approximation, the core-level signal attenuation has been modeled on the basis of Monte Carlo calculations of the electron trajectories across the heterostructures. Different effects involving cation stoichiometry and diffusion through the interface have been considered to interpret data. Beyond a mere abrupt interface modeling, the LaAlO3/SrTiO3 heterojunction is shown to host cation diffusion processes within 3-4 unit cells in the bulk layer, along with a clear Sr substoichiometry, an issue so far virtually neglected in the analysis of these systems. The present results show the capability of the AR-XPS modeling to explore element-sensitive properties at the oxide interfaces, matching and completing the information that can be provided by probes based on electron microscopy or X-ray scattering.