Zhongzhou Cheng

Tungsten Oxide@Polypyrrole Core–Shell Nanowire Arrays as Novel Negative Electrodes for Asymmetric Supercapacitors

Among active pseudocapacitive materials, polypyrrole (PPy) is a promising electrode material in electrochemical capacitors. PPy-based materials research has thus far focused on its electrochemical performance as a positive electrode rather than as a negative electrode for asymmetric supercapacitors (ASCs). Here high-performance electrochemical supercapacitors are designed with tungsten oxide@PPy (WO3 @PPy) core-shell nanowire arrays and Co(OH)2 nanowires grown on carbon fibers. The WO3 @PPy core-shell nanowire electrode exhibits a high capacitance (253 mF/cm2) in negative potentials (-1.0-0.0 V). The ASCs packaged with CF-Co(OH)2 as a positive electrode and CF-WO3 @PPy as a negative electrode display a high volumetric capacitance up to 2.865 F/cm3 based on volume of the device, an energy density of 1.02 mWh/cm3 , and very good stability performance. These findings promote the application of PPy-based nanostructures as advanced negative electrodes for ASCs.

van der Waals epitaxial ultrathin two-dimensional nonlayered semiconductor for highly efficient flexible optoelectronic devices.

Despite great progress in synthesis and application of graphene-like materials, it remains a considerable challenge to prepare two-dimensional (2D) nanostructures of nonlayered materials that may bring us surprising physical and chemical properties. Here, we propose a general strategy for the growth of 2D nonlayered materials by van der Waals epitaxy (vdWE) growth with two conditions: (1) the nonlayered materials satisfy 2D anisotropic growth and (2) the growth is implemented on the van der Waals substrates. Large-scale ultrathin 2D Pb(1-x)Sn(x)Se nanoplates (∼15-45 nm) have been produced on mica sheets by applying this strategy. Benefiting from the 2D geometry of Pb(1-x)Sn(x)Se nanoplates and the flexibility of mica sheet, flexible photodetectors that exhibit fast, reversible, and stable photoresponse and broad spectra detection ranging from UV to infrared light (375, 473, 632, 800, and 980 nm) are in situ fabricated based on Pb(1-x)Sn(x)Se nanoplates. We anticipate that more nonlayered materials will be developed into 2D nanostructures through vdWE, enabling the exploitation of novel electronic and optoelectronic devices.

Au plasmonics in a WS2-Au-CuInS2 photocatalyst for significantly enhanced hydrogen generation

Promoting the activities of photocatalysts is still the critical challenge in H2 generation area. Here, a Au plasmon enhanced photocatalyst of WS2-Au-CuInS2 is developed by inserting Au nanoparticles between WS2 nanotubes and CuInS2 (CIS) nanoparticles. Due to the localized surface plasmonic resonance properties from Au nanoparticles, WS2-Au-CIS shows the best performance as compared to Au-CIS, CIS, WS2-CIS, CIS-Au, WS2-Au, and WS2-CIS-Au. The surface plasmonic resonance effects dramatically intensify the absorption of visible light and help to inject hot electrons into the semiconductors. Our findings open up an efficient method to optimize the type-II structures for photocatalytic water splitting.

Efficient Catalysis of Hydrogen Evolution Reaction from WS2(1−x)P2x Nanoribbons

The rational design of Earth abundant electrocatalysts for efficiently catalyzing hydrogen evolution reaction (HER) is believed to lead to the generation of carbon neutral energy carrier. Owing to their fascinating chemical and physical properties, transition metal dichalcogenides (TMDs) are widely studied for this purpose. Of particular note is that doping by foreign atom can bring the advent of electronic perturbation, which affects the intrinsic catalytic property. Hence, through doping, the catalytic activity of such materials could be boosted. A rational synthesis approach that enables phosphorous atom to be doped into WS2 without inducing phase impurity to form WS2(1-x) P2x nanoribbon (NRs) is herein reported. It is found that the WS2(1-x) P2x NRs exhibit considerably enhanced HER performance, requiring only -98 mV versus reversible hydrogen electrode to achieve a current density of -10 mA cm-2 . Such a high performance can be attributed to the ease of H-atom adsorption and desorption due to intrinsically tuned WS2 , and partial formation of NRs, a morphology wherein the exposure of active edges is more pronounced. This finding can provide a fertile ground for subsequent works aiming at tuning intrinsic catalytic activity of TMDs.

Highly sensitive photodetectors based on hybrid 2D-0D SnS2-copper indium sulfide quantum dots

Both high speed and efficiency of photoelectric conversion are essential for photodetectors. As an emerging layered metal dichalcogenide (LMD), tin disulfide owns intrinsic faster photodetection ability than most other LMDs but poor light absorption and low photoelectric conversion efficiency. We develop an efficient method to enhance its performance by constructing a SnS2-copper indium sulfide hybrid structure. As a result, the responsivity reaches 630 A/W, six times stronger than pristine SnS2 and much higher than most other LMDs photodetectors. Additionally, the photocurrents are enhanced by more than 1 order of magnitude. Our work may open up a pathway to improve the performance of photodetectors based on LMDs.

Efficient CoO nanowire array photocatalysts for H2 generation

CoO nanowire arrays for efficient water-splitting were fabricated via a facile hydrothermal and subsequent annealing method. The CoO nanowire is composed of assembled CoO nanoparticles and the particle size can be controlled by annealing temperatures. CoO nanowire array exhibits advantages of easy fabrication, recyclability, and high stability. The origin of the difference of photocatalytic activity among CoO bulk, CoO nanowires annealed under different temperatures, can be contributed to remarkable shift in the position of the band edge due to different CoO particle sizes. Our finding may provide an avenue in design and fabrication of Co-based nanosturctures for practical applications.

Surface plasmon resonance enhanced light absorption of Au decorated composition-tuned ZnO/ZnxCd1−xSeyTe1−y core/shell nanowires for efficient H2 production

Efficient solar-to-hydrogen photoelectrodes need harvest sunlight to capacity and improve the separation efficiency of charge carriers for chemical reactions in water. Herein, we demonstrate the merits of type-II heterostructures with component controllable quaternary shells (ZnxCd1−xSeyTe1−y) and the surface plasmon resonance of Au nanoparticles to satisfy photocatalytic requirements. Our ZnO/ZnxCd1−xSeyTe1−y/Au nanostructures display a broad absorption edge from UV to NIR (Near Infrared) and high charge separation efficiency. The finite element method simulation and UV-vis-NIR diffuse reflectance spectroscopy confirm the enhanced absorption of visible light. Furthermore, these ZnO/ZnxCd1−xSeyTe1−y/Au heterostructures show remarkable hydrogen-production ability from water, suggesting a type of photocatalytic paradigm for H2 production.

Carbon dots decorated vertical SnS2 nanosheets for efficient photocatalytic oxygen evolution

Metal sulfides are highly desirable materials for photocatalytic water splitting because of their appropriate energy bands. However, the poor stability under light illumination in water hinders their wide applications. Here, two-dimensional SnS2 nanosheets, along with carbon dots of the size around 10 nm, are uniformly grown on fluorine doped tin oxide glasses with a layer of nickel nanoparticles. Significantly, strong light absorption and enhanced photocurrent density are achieved after integration of SnS2 nanosheets with carbon dots. Notably, the rate of oxygen evolution reached up to 1.1 mmol g−1 h−1 under simulated sunlight irradiation featuring a good stability.

Efficient Photocatalytic Hydrogen Evolution via Band Alignment Tailoring: Controllable Transition from Type-I to Type-II

Considering the sizable band gap and wide spectrum response of tin disulfide (SnS2 ), ultrathin SnS2 nanosheets are utilized as solar-driven photocatalyst for water splitting. Designing a heterostructure based on SnS2 is believed to boost their catalytic performance. Unfortunately, it has been quite challenging to explore a material with suitable band alignment using SnS2 nanomaterials for photocatalytic hydrogen generation. Herein, a new strategy is used to systematically tailor the band alignment in SnS2 based heterostructure to realize efficient H2 production under sunlight. A Type-I to Type-II band alignment transition is demonstrated via introducing an interlayer of Ce2 S3 , a potential photocatalyst for H2 evolution, between SnS2 and CeO2 . Subsequently, this heterostructure demonstrates tunability in light absorption, charge transfer kinetics, and material stability. The optimized heterostructure (SnS2 -Ce2 S3 -CeO2 ) exhibits an incredibly strong light absorption ranging from deep UV to infrared light. Significantly, it also shows superior hydrogen generation with the rate of 240 µmol g-1 h-1 under the illumination of simulated sunlight with a very good stability.

High‐Yield Production of Monolayer FePS3 Quantum Sheets via Chemical Exfoliation for Efficient Photocatalytic Hydrogen Evolution

2D layered transition metal phosphorus trichalcogenides (MPX3 ) possess higher in-plane stiffness and lower cleavage energies than graphite. This allows them to be exfoliated down to the atomic thickness. However, a rational exfoliation route has to be sought to achieve surface-active and uniform individual layers. Herein, monolayered FePS3 quantum sheets (QSs) are systematically obtained, whose diameters range from 4-8 nm, through exfoliation of the bulk in hydrazine solution. These QSs exhibit a widened bandgap of 2.18 eV as compared to the bulk (1.60 eV) FePS3 . Benefitting from the monolayer feature, FePS3 QSs demonstrate a substantially accelerated photocatalytic H2 generation rate, which is up to three times higher than the bulk counterpart. This study presents a facile way, for the first time, of producing uniform monolayer FePS3 QSs and opens up new avenues for designing other low-dimensional materials based on MPX3 .