Se Heterostructures Research Articles

Modulation of Charge Redistribution in Heterogeneous CoSe-Ni0.95Se Coupling with Ti3C2Tx MXene for Hydrazine-Assisted Water Splitting.

Integrating abundant dual sites of hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER) into one catalyst is extremely urgent toward energy-saving H2 production. Herein, CoSe-Ni0.95Se heterostructure coupling with Ti3C2Tx MXene (CoSe-Ni0.95Se/MXene) is fabricated on nickel foam (NF) to enhance the catalytic performance. The heterogeneous CoSe-Ni0.95Se and MXene coupling effect can change the coordination of Ni and Co, resulting in adjusted interfacial electronic field and enhanced electron transfer from Ni0.95Se to CoSe especially near MXene surface. Also, the appearance of MXene can anchor more active sites, thereby abundant nucleophilic CoSe and electrophilic Ni0.95Se are formed induced by the charge redistribution, which can tailor d-band center, moderate *H adsorption free energy (∆GH *) and facilitate adsorption/desorption for hydrazine intermediates, contributing to much enhanced HER and HzOR performance. For example, the low potentials of -160.8 and 116.1mV at 400 mA cm-2 are seen for HER and HzOR with long-term stability of 7 days. When assembled as overall hydrazine splitting (OHzS), a small cell voltage of 0.35V to drive 100 mA cm-2 is obtained. Such concept of integrating abundant nucleophilic and electrophilic dual sites and regulating their d-band centers can offer in-depth understandings to design efficient bifunctional HER and HzOR electrocatalysts.

Improved hydrogen generation integrated with methanol electrooxidation by manganese selenide/cobalt selenide heterostructure electrocatalyst

The electro-oxidation of mono-alcohol molecules to produce valuable products in combination with the formation of hydrogen is not an easy process. Herein, the manganese selenide/cobalt selenide hetero-nanoparticles embedded in nitrogen-doped carbon (namely MnSe/Co0.85Se@NC) are fabricated as high-performance catalysts by regulating electronic structures through heterointerface engineering. Experimental and theoretical results demonstrate that the formation of MnSe/Co0.85Se heterostructure will take charges from the Co0.85Se sites, which is advantageous to the adsorption of mono-alcohol molecules and thus makes Co0.85Se a high-performance electrocatalyst for mono-alcohol oxidation reactions (M−AOR). Notably, the activity order of M−AOR on the MnSe/Co0.85Se@NC electrode is methanol > ethanol > n-propanol > isopropanol. Furthermore, the charge transfer from Co0.85Se to MnSe occurs, resulting in a strong electronic interaction at the heterointerface of MnSe/Co0.85Se, giving it superior HER activity. Impressively, MnSe/Co0.85Se@NC can be used as a bifunctional catalyst for methanol-assisted water electrolysis in a two-electrode configuration, which only demands a cell potential of 1.49 V to obtain the 10 mA cm−2 current density, accompanying with valuable formate generation at the anode and hydrogen generation at the cathode. This tactic employing a heterogeneous electrocatalyst to produce high-value chemicals is considered of great importance in the development of new energy technology.

Modulating Electronic Structure by Etching Strategy to Construct NiSe2 /Ni0.85 Se Heterostructure for Urea-Assisted Hydrogen Evolution Reaction.

Exploring and developing novel strategies for constructing heterostructure electrocatalysts is still challenging for water electrolysis. Herein, a creative etching treatment strategy is adopted to construct NiSe2 /Ni0.85 Se heterostructure. The rich heterointerfaces between NiSe2 and Ni0.85 Se emerge strong electronic interaction, which easily induces the electron transfer from NiSe2 to Ni0.85 Se, and tunes the charge-state of NiSe2 and Ni0.85 Se. In the NiSe2 /Ni0.85 Se heterojunction nanomaterial, the higher charge-state Ni0.85 Se is capable of affording partial electrons to combine with hydrogen protons, inducing the rapid formation of H2 molecule. Accordingly, the lower charge-state NiSe2 in the NiSe2 /Ni0.85 Se heterojunction nanomaterial is more easily oxidized into high valence state Ni3+ during the oxygen evolution reaction (OER) process, which is beneficial to accelerate the mass/charge transferand enhancethe electrocatalytic activities towards OER. Theoretical calculations indicate that the heterointerfaces are conducive to modulating the electronic structure and optimizing the adsorption energy toward intermediate H* during the hydrogen evolution reaction (HER) process, leading to superior electrocatalytic activities. To expand the application of the NiSe2 /Ni0.85 Se-2h electrocatalyst, urea is served as the adjuvant to proceed with the energy-saving hydrogen production and pollutant degradation, and it is proven to be a brilliant strategy.

Interface engineering on super-hydrophilic amorphous/crystalline NiFe-based hydroxide/selenide heterostructure nanoflowers for accelerated industrial overall water splitting at high current density

Designing heterojunction catalysts with energy effects at the interface, particularly combining the surface structure advantages of super-hydrophilic interfaces with the high activity advantages of bimetal synergistic optimisation, is the key to developing economical and efficient industrial electrocatalytic water-splitting catalysts. In this study, a coupled nanoflower-like NiFe(OH)x/(Ni, Fe)Se heterostructure catalyst supported on Ni foam (NF) (NFSe@NFOH/NF) was designed and successfully prepared using hydrothermal and electrodeposition strategies. Owing to the electron interaction at the heterogeneous amorphous (NFOH)/crystalline (NFSe) interface and the bimetallic synergistic effect of Ni and Fe, the prepared NFSe@NFOH/NF exhibited excellent and stable oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalytic properties, with low overpotentials of 214/276 mV at 100 mA⋅cm−2 and 262/340 mV at 500 mA⋅cm−2. The assembled water electrolyser comprising NFSe@NFOH/NF || NFSe@NFOH/NF needed only small voltages of 1.73 and 1.85 V to yield current densities of 100 and 500 mA⋅cm−2, respectively. This study offers an innovative design idea for the rational adoption of interface engineering and amorphous–crystalline engineering techniques to construct catalysts with excellent catalytic activity and stability for electrocatalytic overall water splitting (EOWS) at a high current density, which further facilitates the advancement of sustainable energy technology in the future.

Charge Transfer Modulation in Vanadium-Doped WS2 /Bi2 O2 Se Heterostructures.

The field of photovoltaics is revolutionized in recent years by the development of two-dimensional (2D) type-II heterostructures. These heterostructures are made up of two different materials with different electronic properties, which allows for the capture of a broader spectrum of solar energy than traditional photovoltaic devices. In this study, the potential of vanadium (V)-doped WS2 is investigated, hereafter labeled V-WS2 , in combination with air-stable Bi2 O2 Se for use in high-performance photovoltaic devices. Various techniques are used to confirm the charge transfer of these heterostructures, including photoluminescence (PL) and Raman spectroscopy, along with Kelvin probe force microscopy (KPFM). The results show that the PL is quenched by 40%, 95%, and 97% for WS2 /Bi2 O2 Se, 0.4 at.% V-WS2 /Bi2 O2 Se, and 2at.% V-WS2 /Bi2 O2 Se, respectively, indicating a superior charge transfer in V-WS2 /Bi2 O2 Se compared to pristine WS2 /Bi2 O2 Se. The exciton binding energies for WS2 /Bi2 O2 Se, 0.4at.% V-WS2 /Bi2 O2 Se and 2 at.% V-WS2 /Bi2 O2 Se heterostructures are estimated to be ≈130, 100, and 80 meV, respectively, which is much lower than that for monolayer WS2 . These findings confirm that by incorporating V-doped WS2 , charge transfer in WS2 /Bi2 O2 Se heterostructures can be tuned, providing a novel light-harvesting technique for the development of the next generation of photovoltaic devices based on V-doped transition metal dichalcogenides (TMDCs)/Bi2 O2 Se.

Interface engineering of heterostructrured MoSe2/Co0.85Se nanoplate array as a highly efficient electrocatalyst for overall water splitting

Hollow nanoplate array of MoSe2/Co0.85Se heterostructure on nickel frame (MoSe2/Co0.85Se/NF) was prepared using metal-organic framework as a template via a process of dissolution–regrowth following by gas-phase selenization and annealing. 3D architecture of MoSe2/Co0.85Se heterostructure shows a significantly enhanced activity and durability as a bifunctional electrocatalyst for oxygen and hydrogen evolution reactions (OER and HER) in alkaline solution. A current density of 10 mA/cm2 can be delivered at an overpotential of 102 mV for HER and 229 mV for OER with a corresponding Tafel slope of only 35 mV/dec for HER and 48 mV/dec for OER, respectively. Density functional theory calculations revealed that MoSe2/Co0.85Se heterostructure will favor water dissociation, and the neutral adsorption energy of H∗ intermediate in MoSe2/Co0.85Se heterostructure can boost hydrogen evolution. OER measurements will cause surface reconstruction of MoSe2/Co0.85Se/NF and form a new heterostructure of CoO/Co2Mo3O8 in alkaline media. OER occurs at Co atoms on CoO/Co2Mo3O8 heterojunction interface, and the neighboring Mo atom will promote the formation of OOH∗ intermediate, leading to a fast OER kinetics. The superior HER and OER performance of MoSe2/Co0.85Se/NF can rival most of reported transition metal catalysts, holding great promise as advanced catalysts for water splitting in industrial scale.

Effects of chemical composition and vacant oxygen defects on the performance of Ni(OH)2–Ni0.85Se heterostructure nanowires as supercapacitor electrodes

The research focus of supercapacitors is the composition and structural design of electrode materials.

Synergetic design of N-doped defect-enriched porous carbon matrix with Co-Co0.85Se loading for water splitting

Developing robust and efficient non noble catalysts for water splitting is needed in the energy storage and application field. Constructing electronic structures to enhance the catalytic activity is always interesting and meaningful. Herein, electronic structures are simply synthesized through a rational design of Co-Co0.85Se heterostructures anchoring on the defective N-doped carbon matrix. Co anchoring on the defective N-doped carbon matrix is obtained from hydrothermal-carbonization process of pectin, melamine and cobalt chloride. Rational design of partial selenization can construct electronic structures to form Co-Co0.85Se heterostructures anchoring on the defective N-doped carbon matrix (Co-Co0.85Se-CN). The introduction of Co atoms induces the electron cloud redistribution of Co0.85Se, enhancing the electrocatalytic activity for water splitting. The defective N-doped carbon matrix provides plenty of catalytic sites and good conductivity for ions transition. Co-Co0.85Se-CN exhibits outstanding catalytic performance for hydrogen evolution reaction and oxygen evolution reaction. The Operando Raman spectroscopy demonstrates that the dual active centers of Co and Se atom, facilitating the catalytic process for water splitting. DFT calculation results reveal that the constructed electronic structures from Co and Co0.85Se-CN is good for the H* adsorption for HER. This work provides a facile synthetic strategy to construct electronic structures for water splitting.

A bidirectional electrocatalyst for enhancing Li2S nucleation and decomposition kinetics in lithium–sulfur batteries

Well-dispersed (NiCo)0.85Se nanoparticles embedded in Ti3C2nanosheets are developed. The Ti3C2/(NiCo)0.85Se heterostructure is demonstrated as a bidirectional electrocatalyst and endows Li–S batteries with an ultrastable lifespan.

A novel CuSe-Cu1.8Se heterostructure with hexahedral structure cathode material for aluminum batteries

Along with the energy consumption, clean energy such as secondary batteries are increasingly widely used in daily life. As a substitute for lithium-ion batteries, aluminum batteries have become a research hotspot because of environmental protection and lower price. However, as the research progresses, it is increasingly important to find a suitable cathode material for aluminum batteries. Therefore, we design a new Al battery by calcining Cu2O and Se powder at different temperatures in different mass ratios to obtain different phases. The CuSe-Cu1.8Se heterogeneous structure with hexahedral is obtained when the mass ratio of Cu2O and Se powder is 1:1 at 400 °C. Through electrochemical analysis, the CuSe-Cu1.8Se heterogeneous structure shows excellent electrochemical performance. At 1 A g−1, the charge and discharge specific capacity is 1440.4 mAh g−1 and 607.3 mAh g−1, respectively. The discharge specific capacity remains 185.8 mAh g−1 after 200 cycles. Moreover, the soft pack battery can still work normally after bending and shearing, showing incredible flexibility and safety. More importantly, the energy storage mechanism of reversible conversion Cu+/Cu2+ and Se2−/Se2+/Se4+ in CuSe-Cu1.8Se heterostructure is investigated by ex-situ XRD and XPS. It is believed that it can provide a new direction for the future development of aluminum batteries.

Constructing FeCoSe2/Co0.85Se heterostructure catalysts for efficient oxygen evolution

The slow kinetics and high cost of noble metal catalysts greatly hinder the oxygen evolution reaction (OER) in the application of large-scale oxygen production, as well as water splitting. In order to overcome this burgeoning issue, worldwide research efforts have been carried out to find alternative, and efficient electrocatalysts. Due to its cheap and abundant sources, FeCo-based materials are considered as better candidate electrocatalysts for OER. Herein, a nanocomposite catalyst consisting of FeCoSe2 nanoparticles and Co0.85Se nanosheets was synthesized via a one-pot hydrothermal method. The resultant FeCoSe2/Co0.85Se heterostructure catalysts can further used as a self-supported catalytic electrode to drive the OER, which exhibits the overpotential of 0.33 V at a current density of 10 mA cm−2 and Tafel slope of 50.8 mV dec−1. Raman spectroscopy was employed to explore the intrinsic active species of as-prepared hybrid catalyst during the OER process, and test result shows that metal selenides was acting as the precursor of the real reaction species. This work provides a possibility to develop cheap and effective OER electrocatalysts to replace the costly noble metal catalysts for OER in electrochemical devices.

The interface superconductivity of Bi2Se3/Fe–Se heterostructure

Bi2Se3/Fe–Se heterostructures on Si(100) substrates have been prepared by radio frequency magnetron sputtering technique. The thickness of FeSe2 film is an important factor for the properties of Bi2Se3/Fe–Se heterostructures. Our Bi2Se3/Fe–Se heterostructural samples showed ferromagnetism, which increase with increasing thickness of FeSe2 layer. However, when the FeSe2 layer is as thin as 20 nm, superconductivity could be observed through magnetization measurements, due to the existence of superconducting Fe–Se. Thus the Bi2Se3/Fe–Se heterostructure provides an approach to achieve both ferromagnetism and superconductivity simultaneously in interface, as well as to realize the interplay between a superconductor and a topological insulator.

Investigation of carrier transport mechanisms in the Cu–Zn–Se based hetero-structure grown by sputtering technique

In this paper, we present results of the electrical characterization of n-Si/p-Cu–Zn–Se hetero-structure. Sputtered film was found in Se-rich behavior with tetragonal polycrystalline nature along with (112) preferred orientation. The band gap energy for direct optical transitions was obtained as 2.65 eV. The results of the conductivity measurements indicated p-type behavior and carrier transport mechanism was modelled according to thermionic emission theory. Detailed electrical characterization of this structure was carried out with the help of temperature-dependent current–voltage measurements in the temperature range of 220–360 K, room temperature, and frequency-dependent capacitance–voltage and conductance-voltage measurements. The anomaly in current–voltage characteristics was related to barrier height inhomogeneity at the interface and modified by the assumption of Gaussian distribution of barrier height, in which mean barrier height and standard deviation at zero bias were found as 2.11 and 0.24 eV, respectively. Moreover, Richardson constant value was determined as 141.95 Acm−2K−2 by means of modified Richardson plot.

NiSe-Ni0.85 Se Heterostructure Nanoflake Arrays on Carbon Paper as Efficient Electrocatalysts for Overall Water Splitting.

Fabricating cost-effective, bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in basic media is critical for renewable energy generation. Here, NiSe/CP, Ni0.85 Se/CP, and NiSe-Ni0.85 Se/CP heterostructure catalysts with different phase constitutions are successfully prepared through in situ selenylation of a NiO nanoflake array oriented on carbon paper (CP) by tuning the original Ni/Se molar ratio of the raw materials. The relationship between the crystal phase component and electrocatalytic activity is systematically studied. Benefiting from the synergetic effect of the intrinsic metallic state, facile charge transport, abundant catalytic active sites, and multiple electrolyte transmission paths, the optimized NiSe-Ni0.85 Se/CP exhibits a remarkably higher catalytic activity for both the HER and OER than single-phase NiSe/CP and Ni0.85 Se/CP. A current density of 10 mA cm-2 at 1.62 V and a high stability can be obtained by using NiSe-Ni0.85 Se/CP as both the cathode and anode for overall water splitting under alkaline conditions. Density functional theory calculations confirm that H and OH- can be more easily adsorbed on NiSe-Ni0.85 Se than on NiSe and Ni0.85 Se. This study paves the way for enhancing the overall water splitting performance of nickel selenides by fabricating heterophase junctions using nickel selenides with different phases.

Size effect on I– V characteristics of low dimensional metal–semiconductor heterojunctions

Cu–Se heterostructures of diameter 20, 100 and 200 nm were synthesized by electrodeposition within the pores of anodic alumina membranes (AAM) via template synthesis. The morphology of heterostructures was characterized by scanning electron microscope (SEM). The collective I– V characteristics of heterojunctions were measured at room temperature (25 °C) and the characteristics were observed to be like those of resonating tunneling diodes (RTDs) and peak-to-valley current ratio was found to reduce with decreasing diameter of RTDs.

Effects of Rashba spin–orbit interaction on spin-dependent resonant tunneling in ZnSe/Zn 1−xMn xSe multilayer heterostructures

We investigate the effects of external electric field-induced Rashba spin–orbit interaction (SOI) on the spin-dependent resonant tunneling through ZnSe/Zn 1− x Mn x Se heterostructure with double paramagnetic layers in the presence of a magnetic field. Our investigations show a four-fold enhancement of the polarization of the spin-dependent current densities due to the electric field-induced Rashba SOI. These features could be used in the design and fabrication of spin-dependent microelectronic and optoelectronic devices.

Recent developments in the MOVPE growth of low H content ZnSe-based compounds and heterostructures

The origin of unintentional hydrogen (H) incorporation during metalorganic vapour phase epitaxy (MOVPE) of ZnSe-based compounds is reviewed and discussed. Hydrogen enters in MOVPE-grown ZnSe as a result of alkyls surface reactions, effectively passivating intentional nitrogen (N) acceptors in p-doped ZnSe during the fabrication of blue-light emitting diodes and laser diodes. The existence of a marked trade-off between the proclivity of common Se alkyls to incorporate H and their thermal stability is pointed out. Current strategies to overcome this process limitation are then described along with results achieved and technological drawbacks. The use of a novel class of VI-group alkyl precursors of the form R 2X 2 [where X=Se, S and R is an ethyl (Et) or methyl (Me) radical] is proposed as an alternative solution. These alkyls allow a reduction of H incorporation in ZnSe-based materials, whilst retaining the low temperatures required for the growth of device quality wide band-gap II–VI compounds. Dimethyldiselenide (Me 2Se 2) and diethyldisulphide (Et 2S 2) allow the pyrolytic MOVPE growth of Zn(S)Se compounds below 400 °C. Mass spectrometry fragmentation experiments performed on the alkyl molecular ions allowed to investigate their relative bond strengths and likely decomposition paths. The reduced thermal stability of these alkyls is attributed to a weakening of the XC bonds in the R 2X 2 molecule induced by the stronger XX bond. Secondary ion mass spectrometry (SIMS) analysis showed that as-grown ZnSe have [H]≈(1–3)×10 17 cm −3, i.e. among the lowest ever reported for MOVPE-grown layers. The functional validation of the new S and Se alkyls is completed by the structural and optical characterisation of Zn(S)Se-based heterostructures grown on (100)GaAs. High-resolution X-ray diffraction studies are presented along with cathodoluminescence (CL) measurements and compared to what reported in the literature. The epilayer structural properties compare well with that of molecular beam epitaxy and MOVPE grown Zn(S)Se heterostructures. CL spectra of ZnSe epilayers appear of good quality, with pronounced band-edge emissions and reduced deep level contributions. Specific emissions in the spectra of ZnS and ZnSe confirm the occurrence of several impurities in the layers, whose origin can be in part attributed to the yet insufficient purity of the novel alkyls.

MBE growth and luminescence properties of hybrid Al(Ga)Sb/InAs/Cd(Mg)Se heterostructures

We report for the first time on molecular beam epitaxial growth of new hybrid Al(Ga)Sb/InAs/Cd(Mg)Se heterostructures and studies of their structural, luminescence and transport properties. The structures demonstrate intense photoluminescence (PL) in both visible and infra-red spectral regions. The results of luminescence and structural measurements indicate the rather high structural quality of the À 3Â 5/À 2Â 6 interface. Theoretical estimations of band line-ups in these structures predict type II band alignment for the InAs/CdSe interface, which transforms to type I with increasing the Mg content in a CdMgSe alloy. A valence band offset as large as 1.6 eV is expected at the InAs/Cd(Mg)Se interface. The results of electron transport measurements along the interface are in good agreement with the theoretical estimation.

Structural, luminescent, and transport properties of hybrid AlAsSb/InAs/Cd(Mg)Se heterostructures grown by molecular beam epitaxy

The fabrication of new hybrid AlAsSb/InAs/Cd(Mg)Se heterostructures by molecular beam epitaxy and investigation of their structural, luminescent, and transport properties are reported for the first time. These structures show intense luminescence both in the infrared and in the visible regions of the spectrum. This factor, taken together with structural data, indicates a heterointerface of high quality between the III–V and II–VI layers. A theoretical estimate is made of the relative positions of energy bands in the proposed hybrid structures, indicating that the InAs/CdSe interface is a type-II heterojunction, whereas the InAs/Cd0.85Mg0.15Se interface is a type-I heterojunction with a large valence band offset ΔE v≈1.6 eV. The data obtained on the longitudinal electron transport at the InAs/Cd(Mg)Se heterointerface are in good agreement with the theoretical estimate.

Resonant electron tunneling in single quantum well heterostructure junction of electrodeposited metal semiconductor nanostructures using nuclear track filters

We report on resonant electron tunneling through a Cu–Se heterostructure junction grown electrochemically in the submicron size pores (0.8 μm) of a nuclear track filter (Polycarbonate). The prominent feature of negative differential resistance (NDR) has been observed in the current–voltage ( I– V) characteristic of the so-fabricated array of resonant tunneling diodes (RTDs) even at room temperature, along with a significant peak to valley current ratio (2.5) of the resonance. Tunneling structures of the nanofabricated RTDs around zero bias are also observed at room temperature. Our results show that the low cost and relatively easy electrodeposition method can be a very effective way to prepare resonant quantum tunneling devices, using the pores of nuclear track filters.