Triple Heterostructures Research Articles

Construction of triple heterogeneous interfaces optimizing electronic structure with B-doped amorphous CoP deposited on crystalline Cu2S/Ni3S2 nanosheets to enhance water electrolysis

Triple heterostructure electrocatalysts CoPB@Cu2S/Ni3S2 with optimized electronic structure and geometry, showing competitive catalytic performance for the HER and OER.

Paradigm metallothermic-sulfidation-carbonization constructing ZIFs-derived TMSs@Graphene/CNx heterostructures for high-capacity and long-life energy storage

Enhancing electrochemical activity and structural stability of transition metal sulfides (TMSs) are critical for improving the capacity output and retention of TMSs-based batteries. Here, we report a new paradigmatic approach for fabricating TMSs/C composites, adopting a metallothermic-sulfidation-carbonization strategy (2TM + CS2 = 2TMS + C) based on zeolitic imidazolate frameworks (ZIFs) to synchronously construct a compact TMSs@Graphene/CNx triple heterostructure. The obtained structure features crystalline TMSs nanoparticles wrapped by few-layer graphene and totally embedded within porous carbonized polyhedral frameworks. All three nanocomponents of TMSs@Graphene/CNx are connected via chemical bonding of S−C and TM−C, forming a chemical cross-linked nanostructure. Such structure design bears intrinsic advantages in improving the volumetric-efficiency for accommodating TMSs and electrical properties, enabling promising electrochemical performance in lithium- and sodium-ion storage. As a representative, the ZnS@Graphene/CNx electrode exhibits a high capacity of 891.5 mAh g−1 and an excellent retention of 80 % after 1000 cycles in lithium-ion batteries. More notably, this general metallothermic-sulfidation-carbonization mechanism can be applicable to all ZIFs, defining a new ZIFs-derived TMSs/C heterostructures.

Constructing Bi2O3/BiOIO3 triple heterojunction doped with Yb3+ ions as accelerating charge carriers transfer channel to enhance photocatalytic activity

Yb3+- Bi2O3/BiOIO3 heterojunction photocatalyst was successfully prepared by EG assisted hydrothermal method and calcination method. Bi2O3 has a variety of crystal structure. Doped different proportion of Yb3+ will lead to lattice phase transition of Bi2O3. When the amount of Yb3+ doped in the complex is 1 mol%, the two crystal phases of Bi2O3 coexist. α-Bi2O3, β-Bi2O3 and BiOIO3 are compounded in pairs to form a triple heterostructure, which constructs a unique electron transmission channel and promotes the separation of photogenerated carriers. At the same time, Yb3+ has unique electronic transition characteristics, effectively broadening the spectral response range of Yb3+- Bi2O3/BiOIO3 photocatalyst, which can respond to 850–1100 nm near-infrared light. The photocatalytic activity is greatly improved. Due to its optimized performance, the best efficiency of Yb3+-Bi2O3/BiOIO3 triple heterojunction photocatalyst to remove gaseous Hg0 under visible light can reach 76.73%, which is much higher than its pure component. Finally, the possible mechanism of photocatalysis is proposed, which provides a new idea for the construction of high-performance photocatalysts.

Lithiothermic‐Synchronous Construction of Mo‐Li2S‐Graphene Nanocomposites for High‐Energy Li2S//SiC Battery

AbstractReducing the activation barrier and stabilizing the sulfur species of Li2S cathodes can ultimately enhance cell efficiency and the cycle life of S‐based Li‐ion batteries (LIBs). Here, a unique synchronous synthesis method is established that can simultaneously construct Li2S encapsulated in conductive protective layers, and accordingly propose a coordination effect of catalysis and domain restriction for Li2S cathodes. Typically, based on the lithiothermic reaction of 8Li + MoS2 + CS2 = 4Li2S + Mo + C, the obtained composite features abundant Mo nanocrystals embedded in crystalline Li2S matrices and then wrapped by few‐layer graphene. Notably, all three components derived from lithiothermic reaction are linked by the chemical bonding of MoS and CS, forming a compact Mo‐Li2S‐graphene triple heterostructure. Systematic studies reveal an unprecedented relevancy between charge overpotential and catalytic activation of Mo‐Li2S‐graphene, whereas a low activation potential of 2.43 V is achieved. Further studies disclose the relationship between cycle stability and confinement effect of core‐shell structure, whereas the improved confinement efficiency for polysulfides enables an excellent cycle life for the Li‐S battery. Moreover, the Mo‐Li2S‐graphene cathode demonstrates promising application for LIB, where the Mo‐Li2S‐graphene//SiC battery shows a high capacity of 764 mAh g−1 and outstanding cycle stability.

Construction, structure and photocatalysis of janus nanofiber modified by g-C3N4 nanosheets heterostructure photocatalysts

The construction of photocatalyst with gradient band structure is guided by the principle of band gap engineering. Rational structural design is advanced and applied to construct a new-typed peculiarly structural and functional carbon-based [TiO2/C]//[Bi2WO6/C] Janus nanofiber modified by g-C3N4 nanosheets heterostructure photocatalyst (denoted as TB-JgHP). The flexible carbon-based [TiO2/C]//[Bi2WO6/C] Janus nanofiber with one side responding to ultraviolet light and the other capturing visible light is fabricated by conjugate electrospinning, and then g-C3N4 nanosheets are uniformly grown in-situ on the surface of the Janus nanofibers by using gas-solid reaction via gasification of urea. The optimized TB-JgHP possesses remarkable hydrogen evolution efficiency (17.48 mmol h−1 g−1) and methylene blue degradation rate (99.2%) under simulated sunlight illumination for 100 min, demonstrating prominent dual-functional characteristics. The enhanced photocatalytic performance benefits from the unique Janus structure as well as the synergistic effects among the triple heterostructures of TiO2 and Bi2WO6, g-C3N4 and TiO2, g-C3N4 and Bi2WO6. The formation of gradient band structure among heterostructures is more conducive to the multi-step separation of photo-induced electron-hole pairs and more effective absorption of light. Further, flexible self-standing carbon-based photocatalysts not only have outstanding electron transport performance, but also are easy to separate from solution with preeminent recyclable stability. Based on a series of characterization techniques, it is further proved that TB-JgHP has higher carrier separation efficiency than the counterpart contrast samples. The formation mechanism of TB-JgHP is proposed, and the construction technique is established. The design philosophy and construction technique presented in this work pave a new avenue for research and development of other heterostructure photocatalysts.

Triple VTe2/graphene/VTe2 heterostructures as perspective magnetic tunnel junctions

New perspective 1.4 nm thick spin-polarized triple heterostructures based on graphene sandwiched between two vanadium ditelluride monolayers (VTe2/graphene/VTe2) were studied using ab initio DFT technique. Both possible trigonal prismatic (H-VTe2) and octahedral (T-VTe2) VTe2 phases were considered to design and study graphene-based heterostructures. It was shown that the interaction with graphene changes the electronic structure of 2D T-VTe2 from metallic to half-metallic, making T phase perspective to be used for magnetic tunnel junctions. The electronic subsystem of graphene fragment is slightly hole doped. Calculated tunnel magnetoresistance ratio for the favorable heterostructure configuration estimated within the Julliere model is 220%, which opens a way to use VTe2/graphene/VTe2 as prospective magnetic tunnel junction in novel spintronic nanodevices based on tunnel magnetic resistance and spin transfer torque effects.

Transition of hexagonal to square sheets of Co3O4 in a triple heterostructure of Co3O4/MnO2/GO for high performance supercapacitor electrode

Cobalt oxide and manganese oxides are promising electrode materials amongst the transition metal oxides (TMOs) for pseudocapacitors. The lack of reversibility and deterioration of capacitance at higher current densities is major flaw in Co3O4 as an electrode for supercapacitor while MnO2 suffers from low electrical conductivity and poor cycling stability. It is inevitable to bridge the performance gap between these two TMOs to obtain a high performance supercapacitor based on environmental benign and earth abundant materials. Herein, we fabricated a hybrid triple heterostructure high-performing supercapacitor based on hexagonal sheets of Co3O4, MnO2 nanowires and graphene oxide (GO) to form a composite structure of Co3O4/MnO2/GO by all hydrothermal synthesis route. The Co3O4 square sheets serves as an excellent backbone with good mechanical adhesion with the current collector providing a rapid electronic transfer channel while the integrated nanostructure of MnO2 NW/GO permits more electrolyte ions to penetrate capably into the hybrid structure and allows effective utilization of more active surface areas. A triple heterostructured device exhibits a high areal capacitance of 3087 mF cm−2 at 10 mV s−1 scan rate along with the exceptional rate capability and cycling stability having capacitance retention of ∼170% after 5000 charge/discharge cycles. The TMOs based pseudocapacitor with the conducting scaffolds anchoring based on graphene derivatives like this will pave an encouraging alternatives for next generation energy storage devices.

In situ synthesis of Ag@Ag3PO4/MWCNT triples hetero-photocatalyst for degradation of malachite green

The Ag@Ag3PO4/MWCNT triple heterostructure nanocomposites were facilely fabricated by an in-situ reduction method. The multi-walled carbon nanotube (MWCNT) was fully enwrapped by Ag@Ag3PO4 nanocrystals with an average diameter of 200nm. Ag@Ag3PO4/MWCNT hetero-photocatalyst showed strong absorbance in the visible regions. Compared with Ag@Ag3PO4, Ag@Ag3PO4/MWCNT hetero-photocatalyst exhibited significantly higher photocatalytic activities under the irradiation of visible light for the photodegradation of malachite green (MG), as the MWCNT could facilitate charge transfer and suppress the recombination of electron–hole pairs. This study provided an invaluable methodology for designing and fabrication of highly efficient visible-light-driven photocatalysts for catalytic and new energy applications.

In Situ Fabrication of Ag/Ag3PO4/Graphene Triple Heterostructure Visible‐Light Photocatalyst through Graphene‐Assisted Reduction Strategy

AbstractThe design and architecture of the nanoheterostructure composites was a key aim of material scientists owing to the central role of the composites in the improvement in photogenerated charge separation and quantum efficiency. The Ag/Ag3PO4/graphene triple heterostructure composites were fabricated in situ by the redox reaction between Ag+ and graphene. The structural evolution of these heterostructures was characterized by using XRD and TEM. The XPS and surface photovoltage spectroscopy revealed the photogenerated electron–hole pair’s transmission process within the composites. The Ag/Ag3PO4/graphene triple heterostructure could improve the charge separation rate under visible‐light irradiation. Simultaneously, the photocorrosion phenomenon can be inhibited effectively by the triple heterostructure, which leads to the high structural stability for photocatalysis. Graphene’s fine adsorption performance for O2 and organic pollutants is also an important factor in improving the photocatalytic efficiency. Thus, the novel Ag/Ag3PO4/graphene triple heterostructure demonstrates improved photocatalytic activity and structural stability under visible‐light irradiation. This facile and straightforward method has promising applications in the fabrication of different graphene‐based heterostructure photocatalyses.

Development of MgZnO-ZnO-AlGaN heterostructures for ultraviolet light emitting applications

We report on the fabrication and characterization of an ultraviolet (UV) light-emitting diode (LED) based on a p-n junction MgZnO/ZnO/AlGaN/GaN semiconductor triple-heterostructure (THS). Radio-frequency (RF) plasma-assisted molecular-beam epitaxy (MBE) has been employed to grow individual epitaxial layers of ZnO, MgxZn1−xO, and the complete heterostructure on c-plane GaN/sapphire templates. Various growth strategies have been used to optimize the quality of the ZnO layers as well as to precisely control the composition of the MgxZn1−xO compound. Cross-sectional transmission electron microscopy (TEM) study shows the excellent crystalline quality of the pseudomorphically grown ZnO active region of the device. A strong electroluminescence (EL) emission associated with ZnO excitonic transition was observed up to 650 K. The results shown in this paper strongly suggest the viability of RF plasma-assisted MBE in the development of next-generation UV emitters using ZnO-based materials.

Mg Zn O ∕ Al Ga N heterostructure light-emitting diodes

We report on p–n junction light-emitting diodes fabricated from MgZnO∕ZnO∕AlGaN∕GaN triple heterostructures. Energy band diagrams of the light-emitting diode structure incorporating piezoelectric and spontaneous polarization fields were simulated, revealing a strong hole confinement near the n-ZnO∕p-AlGaN interface with a hole sheet density as large as 1.82×1013cm−2 for strained structures. The measured current–voltage (IV) characteristics of the triple heterostructure p–n junctions have rectifying characteristics with a turn-on voltage of ∼3.2V. Electron-beam-induced current measurements confirmed the presence of a p–n junction located at the n-ZnO∕p-AlGaN interface. Strong optical emission was observed at ∼390nm as expected for excitonic optical transitions in these structures. Experimental spectral dependence of the photocurrent confirmed the excitonic origin of the optical transition at 390nm. Light emission was measured up to 650K, providing additional confirmation of the excitonic nature of the optical transitions in the devices.