2D/2D Heterostructures:Rational Design for Advanced Batteries and Electrocatalysis

Two-dimensional/two-dimensional(2D/2D)heterostructures consisting of two or more 2D building blocks possess intriguing electronic features at the nanosized interfacial regions,endowing the possibility for effectively modulating the confinement,and transport of charge carriers,excitons,photons,phonons,etc.to bring about a wide range of extraordinary physical,chemical,thermal,and/or mechanical properties.By rational design and synthesis of 2D/2D heterostructures,electrochemical properties for advanced batteries and electrocatalysis can be well regulated to meet some practical requirements.In this review,a summary on the commonly employed synthetic strategies for 2D/2D heterostructures is first given,followed by a comprehensive review on recent progress for their applications in batteries and various electrocatalysis reactions.Finally,a critical outlook on the current challenges and promising solutions is presented,which is expected to offer some insightful ideas on the design principles of advanced 2D-based nanomaterials to address the current challenges in sustainable energy storages and green fuel generations.

Mixed‑Dimensional Assembly Strategy to Construct Reduced Graphene Oxide/Carbon Foams Heterostructures for Microwave Absorption,Anti‑Corrosion and Thermal Insulation

Considering the serious electromagnetic wave(EMW)pollution problems and complex application condition,there is a pressing need to amalgamate multiple functionalities within a single substance.However,the effective integration of diverse functions into designed EMW absorption materials still faces the huge challenges.Herein,reduced graphene oxide/carbon foams(RGO/CFs)with two-dimensional/three-dimensional(2D/3D)van der Waals(vdWs)heterostructures were meticulously engineered and synthesized utilizing an efficient methodology involving freeze-drying,immersing absorption,secondary freeze-drying,followed by carbonization treatment.Thanks to their excellent linkage effect of amplified dielectric loss and optimized impedance matching,the designed 2D/3D RGO/CFs vdWs heterostructures demonstrated commendable EMW absorption performances,achieving a broad absorption bandwidth of 6.2 GHz and a reflection loss of-50.58 dB with the low matching thicknesses.Furthermore,the obtained 2D/3D RGO/CFs vdWs heterostructures also displayed the significant radar stealth properties,good corrosion resistance performances as well as outstanding thermal insulation capabilities,displaying the great potential in complex and variable environments.Accordingly,this work not only demonstrated a straightforward method for fabricating 2D/3D vdWs heterostructures,but also outlined a powerful mixeddimensional assembly strategy for engineering multifunctional foams for electromagnetic protection,aerospace and other complex conditions.

Recent Progress in the Fabrication, Properties, and Devices of Heterostructures Based on 2D Materials

With a large number of researches being conducted on two?dimen?sional(2D) materials, their unique properties in optics, electrics, mechanics, and magnetics have attracted increasing attention. Accordingly, the idea of combining distinct functional 2D materials into heterostructures naturally emerged that pro?vides unprecedented platforms for exploring new physics that are not accessible in a single 2D material or 3D heterostructures. Along with the rapid development of controllable, scalable, and programmed synthesis techniques of high?quality 2D heterostructures, various heterostructure devices with extraordinary performance have been designed and fabricated, including tunneling transistors, photodetectors, and spintronic devices. In this review, we present a summary of the latest progresses in fabrications, properties, and applications of di erent types of 2D heterostruc?tures, followed by the discussions on present challenges and perspectives of further investigations.

Alternately aligned 2D heterostructures enabled by dspacing accessible,highly periodic accordion-like graphene oxide frameworks

Two-dimensional(2D)heterostructures hold great promise in designing integrated materials,while the current synthesis strategies still confront challenges for multilayer heterostructure construction and scale-up production.Here we report a generalized host-guest strategy based on nonexfoliated layered graphene oxide(LGO)to construct graphene-based heterostructures that consist of multilayered,alternately aligned graphene and metal oxide nanosheets.The 2D-aligned GOs and open interlayer spaces make LGO an ideal platform to create periodic 2D host frameworks.Polyetheramine oligomers covalently bond the adjacent GOs.The extended chain conformation endows the resulting accordionlike GO frameworks with high structural stability,periodicity and enlarged interlayer space.Owing to the high affinity of the open and well-arranged 2D channels toward guest precursors,a variety of high-quality heterostructures can be synthesized.Furthermore,a variety of exfoliated,ultrathin metal oxide nanosheets can also be prepared by removing the graphene skeleton.The flexible interlayer chemistry presented in this study paves a way toward the synthesis of a large family of graphene-inorganic/organic 2D heterostructures.

Trimetallic synergistic optimization of 0D NiCoFe-P QDs anchoring on 2D porous carbon for efficient electrocatalysis and high-energy supercapacitor

Developing multi-functional and low-cost noble-metal-free catalysts such as transition metal phosphides(TMPs)to replace noble-metal is of practical significance for energy conversion and storage.However,the low-durability and the agglomeration phenomenon during the electrochemical process limit their practical applications.Herein,using metal–organic frameworks(MOFs)as the precursor and a combined strategy of gradient temperature calcination and thermal phosphorization,a 0D/2D heterostructure of NiCoFe-P quantum dots(QDs)anchored on porous carbon was successfully developed as highly efficient electrode materials for overall water splitting and supercapacitors.Owing to this distinctive 0D/2D heterostructure and the synergistic effect of multi-metallic TMPs,the NiCoFe-P/C exhibits excellent electrocatalytic activity and durability of HER(87 mV at 10 mA cm^(-2))and OER(257 mV at 100 mA cm^(-2))in the KOH electrolyte.When NiCoFe-P/C is used as the two electrodes of electrolyzed water,only 1.55 V can drive the current density to 10 m A cm^(-2).At the same time,our NiCoFe-P/C possessed extraordinary property for charge storage.In particular,an ultra-high energy density of 100.8 Wh kg^(-1) was achieved at a power density of 900.0 W kg^(-1) for our assembled hybrid supercapacitor device NiCoFe-P/C(2:1)//activated carbon(AC).This work may open a potential way for the design of 0D/2D hybrid multifunctional nanomaterials based on TMPs QDs.

Interface engineering of 2D NiFe LDH/NiFeS heterostructure for highly efficient 5-hydroxymethylfurfural electrooxidation

The electrochemical oxidation of 5-hydroxymethylfurfural(HMF)to valuable chemicals is an efficient way to upgrade biomass molecules and replace traditional catalytic synthesis.It is crucial to develop efficient and low-cost earth-abundant electrocatalysts to enhance catalytic performance of HMF oxidation.Herein,a new type of two-dimensional(2D)hybrid arrays consisting of Ni Fe layered double hydroxides(LDH)nanosheets and bimetallic sulfide(Ni Fe S)is constructed via interface engineering for efficient electrocatalytic oxidation of HMF to 2,5-furandicarboxylic acid(FDCA).The preparation process of 2D Ni Fe LDH/NiFeS with ultrathin heterostructure involves in anchoring a Co-based metal-organic framework(Co MOF)as template onto the carbon cloth(CC)via in-situ growth,formation of NiFe LDH on the surface of Co MOF and subsequent partial sulfidation.The electrocatalyst of Ni Fe LDH/Ni Fe S exhibits outstanding performance towards HMF oxidation,about 98.5%yield for FDCA and 97.2%Faraday efficiency(FE)in the alkaline electrolyte with 10 mmol/L HMF,as well as excellent stability retaining 90.1%FE for FDCA after six cycles test.Moreover,even at an HMF concentration of 100 mmol/L,the yield and FE for FDCA remain high at 83.6%and 93.6%,respectively.These findings highlight that 2D heterostructure containing abundant interfaces between Ni Fe LDH nanosheets and Ni Fe S can enhance the intrinsic activity of LDH and thus promote the oxidation reaction kinetics.Additionally,the synergistic effect of the bimetallic Ni Fe compounds also improved the selectivity of HMF conversion to FDCA.Our present work demonstrates that constructing 2D ultrathin heterostructure of Ni Fe LDH/Ni Fe S is a facile strategy via interface engineering to enhance the intrinsic activity of LDH electrocatalysts,which would open new avenues toward low-cost and advanced 2D nanocatalysts for sustainable energy conversion and electrochemical valorization of biomass derivatives.

Nanoscale phase management of the 2D/3D heterostructure toward efficient perovskite solar cells

The stabilization of the formamidinium lead iodide(FAPbI_(3))structure is pivotal for the development of efficient photovoltaic devices.Employing two-dimensional(2D)layers to passivate the threedimensional(3D)perovskite is essential for maintaining the a-phase of FAPbI_(3) and enhancing the power conversion efficiency(PCE)of perovskite solar cells(PSCs).However,the role of bulky ligands in the phase management of 2D perovskites,crucial for the stabilization of FAPbI_(3),has not yet been elucidated.In this study,we synthesized nanoscale 2D perovskite capping crusts with<n>=1 and 2 Ruddlesden-Popper(RP)perovskite layers,respectively,which form a type-Ⅱ 2D/3D heterostructure.This heterostructure stabilizes the a-phase of FAPbI_(3),and facilitates ultrafast carrier extraction from the 3D perovskite network to transport contact layer.We introduced tri-fluorinated ligands to mitigate defects caused by the halide vacancies and uncoordinated Pb^(2+)ions,thereby reducing nonradiative carrier recombination and extending carrier lifetime.The films produced were incorporated into PSCs that not only achieved a PCE of 25.39%but also maintained 95%of their initial efficiency after 2000 h of continuous light exposure without encapsulation.These findings underscore the effectiveness of a phase-pure 2D/3D heterostructure-terminated film in inhibiting phase transitions passivating the iodide anion vacancy defects,facilitating the charge carrier extraction,and boosting the performance of optoelectronic devices.

Tailoring lithium intercalation pathway in 2D van der Waals heterostructure for high-speed edge-contacted floating-gate transistor and artificial synapses

Local phase transition in transition metal dichalcogenides (TMDCs) by lithiumintercalation enables the fabrication of high-quality contact interfaces in twodimensional(2D) electronic devices. However, controlling the intercalation oflithium is hitherto challenging in vertically stacked van der Waalsheterostructures (vdWHs) due to the random diffusion of lithium ions in thehetero-interface, which hinders their application for contact engineering of 2DvdWHs devices. Herein, a strategy to restrict the lithium intercalation pathwayin vdWHs is developed by using surface-permeation assisted intercalationwhile sealing all edges, based on which a high-performance edge-contact MoS_(2)vdWHs floating-gate transistor is demonstrated. Our method avoids intercalationfrom edges that are prone to be random but intentionally promotes lithiumintercalation from the top surface. The derived MoS_(2) floating-gatetransistor exhibits improved interface quality and significantly reduced subthresholdswing (SS) from >600 to 100 mV dec^(–1). In addition, ultrafast program/erase performance together with well-distinguished 32 memory statesare demonstrated, making it a promising candidate for low-power artificialsynapses. The study on controlling the lithium intercalation pathways in 2DvdWHs offers a viable route toward high-performance 2D electronics for memoryand neuromorphic computing purposes.

Allying interfacial engineering of 2D carbon nanosheet-,graphene-,and graphdiyne-based heterostructured electrocatalysts toward hydrogen evolution and overall water splitting

Electrochemical hydrogen evolution reaction(HER)and overall water splitting(OWS)for renewable energy generation have recently become a highly promising and sustainable strategy to tackle energy crisis and global warming arising from our overreliance on fossil fuels.Previously,tremendous research breakthroughs have been made in 2D carbon-based heterostructured electrocatalysts in this field.Such heterostructures are distinguished by their remarkable electrical conductivity,exposed active sites,and mechanical stability.Herein,with fundamental mechanisms of electrocatalytic OWS summarized,our review critically emphasized on state-of-the-art 2D carbon nanosheet-,graphene-,and graphdiyne-based heterostructured electrocatalysts in HER and OWS since 2018.Particularly,the three emerging carbonaceous substrates tend to be incorporated with metal carbides,phosphides,dichalcogenides,nitrides,oxides,nanoparticles,single atom catalysts,or layered double hydroxides.Meanwhile,fascinating structural engineering and facile synthesis strategies were also unraveled to establish the structure-activity relationship,which will enlighten future electrocatalyst developments toward ameliorated HER and OWS activities.Additionally,computational results from density functional theory simulations were highlighted as well to better comprehend the synergistic effects within the heterostructures.Finally,current stages and future recommendations of this brand-new electrocatalyst type were concluded and discussed for advanced catalyst designs and future practical applications.

Facile fabrication of ZnIn2S4/SnS2 3D heterostructure for efficient visible-light photocatalytic reduction of Cr（Ⅵ）

Photocatalytic method has been intensively explored for Cr(VI)reduction owing to its efficient and environmentally friendly natures.In order to obtain a high efficiency in practical application,efficient photocatalysts need to be developed.Here,ZnIn2S4/SnS2 with a three-dimensional(3D)heterostructure was prepared by a hydrothermal method and its photocatalytic performance in Cr(VI)reduction was investigated.When the mass ratio of SnS2 to ZnIn2S4 is 1:10,the ZnIn2S4/SnS2 composite exhibits the highest photocatalytic activity with 100%efficiency for Cr(VI)(50 mg/L)reduction within 70 min under visible-light irradiation,which is much higher than those of pure ZnIn2S4 and SnS2.The enhanced charge separation and the light absorption have been confirmed from the photoluminescence and UV-vis absorption spectra to be the two reasons for the increased activity towards photocatalytic Cr(VI)reduction.In addition,after three cycles of testing,no obvious degradation is observed with the 3D heterostructured ZnIn2S4/SnS2,which maintains a good photocatalytic stability.

Synthesis of two-dimensional/one-dimensional heterostructures with tunable width

Two-dimensional/one-dimensional(2D/1D)heterostructures as a new type of heterostructure have been studied for their unusual properties and promising applications in electronic and optoelectronic devices.However,the studies of 2D/1D heterostructures are mainly focused on vertical heterostructures,such as MoS_(2) nanosheet-carbon nanotubes.The research on lateral 2D/1D heterostructures with a tunable width of 1D material is still scarce.In this study,bidirectional flow chemical vapor deposition(CVD)was used to accurately control the width of the WS_(2)/WSe2(WS_(2)/MoS_(2))heterostructures by controlling reacting time.WSe2 and MoS_(2) with different widths were epitaxially grown at the edge of WS_(2),respectively.Optical microscope,atomic force microscope(AFM),and scanning electron microscope(SEM)images show the morphology and width of the heterostructures.These results show that the width of the heterostructures can be as low as 10 nm by using this method.The interface of the heterostructure is clear and smooth,which is suitable for application.This report offers a new method for the growth of 1D nanowires,and lays the foundation for the future study of the physical and chemical properties of 2D/1D lateral heterostructures.

Nonlinear optics of two-dimensional heterostructures

Two-dimensional (2D) materials exhibit exceptionally strong nonlinear optical responses, benefiting from their reduced dimensionality, relaxed phase-matching requirements, and enhanced light-matter interaction. With additional degrees of freedom in the modulation of the physical properties by stacking 2D layers together, nonlinear optics of 2D heterostructures becomes increasingly fascinating. In this perspective, we provide a brief overview of recent advances in the field of nonlinear optics of 2D heterostructures, with a particular focus on their remarkable capabilities in characterization and modulation. Given the recent advances and the emergence of novel heterostructures, combined with innovative tuning knobs and advanced nonlinear optical techniques, we anticipate deeper insights into the underlying mechanisms and more associated applications in this rapidly evolving field.

Recent advances in 2D organic−inorganic heterostructures for electronics and optoelectronics

Two‐dimensional(2D)materials show outstanding properties such as dangling bond‐free surfaces,strong in‐plane while weak out‐of‐plane bonding,layer‐dependent electronic structures,and tunable electronic and optoelectronic properties,making them promising for numerous applications.Integrating 2D inorganics with organic materials to make van der Waals heterostructures at the 2D thickness limit has created new platforms for fabricating on‐demand multifunctional devices.To further broaden the limited choices of 2D inorganic‐based heterostructures,a wide range of available 2D organic materials with tunable properties have opened new opportunities for designing large numbers of heterostructures with 2D inorganic materials.This review aims to attract the attention of researchers toward this emerging 2D organic−inorganic field.We first highlight recent progress in organic−inorganic heterostructures and their synthesis and then discuss their potential applications,such as field‐effect transistors,photodetectors,solar cells,and neuromorphic computing devices.In the end,we present a summary of challenges and opportunities in this field.

MoS_(2)/Si tunnel diodes based on comprehensive transfer technique

Due to the pristine interface of the 2D/3D face-tunneling heterostructure with an ultra-sharp doping profile, the 2D/3D tunneling field-effect transistor(TFET) is considered as one of the most promising low-power devices that can simultaneously obtain low off-state current(IOFF), high on-state current(ION) and steep subthreshold swing(SS). As a key element for the 2D/3D TFET, the intensive exploration of the tunnel diode based on the 2D/3D heterostructure is in urgent need.The transfer technique composed of the exfoliation and the release process is currently the most common approach to fabricating the 2D/3D heterostructures. However, the well-established transfer technique of the 2D materials is still unavailable.Only a small part of the irregular films can usually be obtained by mechanical exfoliation, while the choice of the chemical exfoliation may lead to the contamination of the 2D material films by the ions in the chemical etchants. Moreover, the deformation of the 2D material in the transfer process due to its soft nature also leads to the nonuniformity of the transferred film,which is one of the main reasons for the presence of the wrinkles and the stacks in the transferred film. Thus, the large-scale fabrication of the high-quality 2D/3D tunnel diodes is limited. In this article, a comprehensive transfer technique that can mend up the shortages mentioned above with the aid of the water and the thermal release tape(TRT) is proposed. Based on the method we proposed, the MoS_(2)/Si tunnel diode is experimentally demonstrated and the transferred monolayer MoS_(2) film with the relatively high crystal quality is confirmed by atomic force microscopy(AFM), scanning electron microscopy(SEM), and Raman characterizations. Besides, the prominent negative differential resistance(NDR) effect is observed at room temperature, which verifies the relatively high quality of the MoS_(2)/Si heterojunction. The bilayer MoS_(2)/Si tunnel diode is also experimentally fabricated by repeating the transfer process we proposed, followed by the specific analysis of the electrical characteristics. This study shows the advantages of the transfer technique we proposed and indicates the great application foreground of the fabricated 2D/3D heterostructure for ultralow-power tunneling devices.

Alternating nanolayers as lithiophilic scaffolds for Li-metal anode

Nanostructured scaffolds offer promising opportunities in enabling dendrite-free long-cycle life Li metal anode.The rational design and controllable synthesis of scaffolding architectures are imperative for development of rechargeable Li metal batteries.In this study,we explore the fabrication and application of a tin monoxide/graphene hybrid architecture as a lithiophilic host for high-performance Li metal anode.Using a polymer-assisted sonochemical synthesis route,we tuned the thickness of SnO nanolayers and the nanostructure of alternatively stacking thin SnO nanosheet/graphene(SnO-NS/G) heterostructure.Offering abundant nucleation sites,fast ion transport tunnels,and 3D-conductivity,the unique 2D-2D architecture enables stable lithium plating-stripping cycling with low nucleation overpotential and high coulombic efficiency(CE).Hosted by SnO-NS/G scaffold,the resulting Li metal anode exhibits stable cycling over 200 cycles at 0.5 mA cm^(-2)(2 mAh).Full cell pairing high-mass-loading cathode LiCoO_(2)(LCO)(12 mg cm^(-2)) with SnO-NS/G hosted Li metal anode delivers high energy density of 402 Wh kg^(-1) and stable cyclability of over 100 cycles.We elucidate the structure-property relationship between nanolayer thickness and Li-metal plating behaviors,giving new insight on structuring 2D-nanomaterials with ideal architectures for stable lithium metal batteries.

Atomically constructing a van der Waals heterostructure of CrTe_(2)/Bi_(2)Te_(3) by molecular beam epitaxy

A 2D heterostructure with proximity coupling of magnetism and topology can provide enthralling prospects for hosting new quantum states and exotic properties that are relevant to next-generation spintronic devices.Here,we synthesize a delicate van der Waals(vdW)heterostructure of CrTe_(2)/Bi_(2)Te_(3) at the atomic scale via molecular beam epitaxy.Low-temperature scanning tunneling microscopy/spectroscopy measurements are utilized to characterize the geometric and electronic properties of the CrTe_(2)/Bi_(2)Te_(3) heterostructure with a compressed vdW gap.Detailed structural analysis reveals complex interfacial structures with diversiform step heights and intriguing moirépatterns.The formation of the interface is ascribed to the embedded characteristics of CrTe_(2) and Bi_(2)Te_(3) by sharing Te atomic layer upon interfacing,showing intercoupled features of electronic structure for CrTe_(2) and Bi_(2)Te_(3).Our study demonstrates a possible approach to construct artificial heterostructures with different types of ordered states,which may be of use for achieving tunable interfacial Dzyaloshinsky–Moriya interactions and tailoring the functional building blocks in low dimensions.

Opto-valleytronics in the 2D van der Waals heterostructure

The development of information processing devices with minimum carbon emission is crucial in this information age. One of the approaches to tackle this challenge is by using valleys (local extremum points in the momentum space) to encode the information instead of charges. The valley information in some material such as monolayer transition metal dichalcogenide (TMD) can be controlled by using circularly polarized light. This opens a new field called opto-valleytronics. In this article, we first review the valley physics in monolayer TMD and two-dimensional (2D) heterostructure composed of monolayer TMD and other materials. Such 2D heterostructure has been shown to exhibit interesting phenomena such as interlayer exciton, magnetic proximity effect, and spin-orbit proximity effect, which is beneficial for opto-valleytronics application. We then review some of the optical valley control methods that have been used in the monolayer TMD and the 2D heterostructure. Finally, a summary and outlook of the 2D heterostructure opto-valleytronics are given.

A prospective future towards bio/medical technology and bioelectronics based on 2D vdWs heterostructures

Nano-biotechnology research has become extremely important due to the possibilities in manipulation and characterization of biological molecules through nanodevices.Nanomaterials exhibit exciting electrical,optoelectronic,magnetic,mechanical and chemical properties that can be exploited to develop efficient biosensors or bio-probes.Those unique properties in nanomaterials can also be used in bioimaging and cancer therapeutics,where biomolecules influence the inherent properties in nanomaterials.Effective manipulation of nanomaterial properties can lead to many breakthroughs in nanotechnology applications.Nowadays,2D nanomaterials have emerged as viable materials for nanotechnology.Large cross-section area and functional availability of 2D or 1D quantum limit in these nanomaterials allow greater flexibility and better nanodevice performance.2D nanomaterials enable advanced bioelectronics to be more easily integrated due to their atomic thickness,biocompatibility,mechanical flexibility and conformity.Furthermore,with the development of 2D material heterostructures,enhanced material properties can be obtained which can directly influence bio-nanotechnology applications.This article firstly reviews the development of various types of 2D heterostructures in a wide variety of nano-biotechnology applications.Furthermore,future 2D heterostructure scopes in bioimaging,nanomedicine,bio-markers/therapy and bioelectronics are discussed.This paper can be an avenue for providing a wide scope for 2D van der Waals(vdWs)heterostructures in bio-and medical fields.

Optoelectronics based on 2D TMDs and heterostructures

2D materials including graphene and TMDs have proven interesting physical properties and promising optoelectronic applications.We reviewed the growth,characterization and optoelectronics based on 2D TMDs and their heterostructures,and demonstrated their unique and high quality of performances.For example,we observed the large mobility,fast response and high photo-responsivity in Mo S;,WS;and WSe;phototransistors,as well as the novel performances in vd W heterostructures such as the strong interlayer coupling,am-bipolar and rectifying behaviour,and the obvious photovoltaic effect.It is being possible that 2D family materials could play an increasingly important role in the future nano- and opto-electronics,more even than traditional semiconductors such as silicon.

Two-dimensional heterostructure promoted infrared photodetection devices

It is a rapidly developed subject in expanding the fundamental properties and application of two-dimensional(2D)materials.The weak van der Waals interaction in 2D materials inspired researchers to explore 2D heterostructures(2DHs)based broadband photodetectors in the far-infrared(IR)and middle-IR regions with high response and high detectivity.This review focuses on the strategy and motivation of designing 2DHs based high-performance IR photodetectors,which provides a wide view of this field and new expectation for advanced photodetectors.First,the photocarriers'generation mechanism and frequently employed device structures are presented.Then,the 2DHs are divided into semimetal/semiconductor 2DHs,semiconductor/semiconductor 2DHs,and multidimensional semi-2DHs;the advantages,motivation,mechanism,recent progress,and outlook are discussed.Finally,the challenges for next-generation photodetectors are described for this rapidly developing field.