Huiqiao Li

Achieving Uniform Monolayer Transition Metal Dichalcogenides Film on Silicon Wafer via Silanization Treatment: A Typical Study on WS2

A silanization reaction is employed to improve the dispersion of precursors on a silicon wafer for a large-size uniform transition metal dichalcogenide (TMD) film synthesis and to achieve a highly crystalline monolayer WS2 film up to 1 cm2 . The novel strategy is also verified for the synthesis of WSe2 and MoS2 uniform films, suggesting universality for TMD film fabrication.

Tunneling Diode Based on WSe2/SnS2 Heterostructure Incorporating High Detectivity and Responsivity

van der Waals (vdW) heterostructures based on atomically thin 2D materials have led to a new era in next-generation optoelectronics due to their tailored energy band alignments and ultrathin morphological features, especially in photodetectors. However, these photodetectors often show an inevitable compromise between photodetectivity and photoresponsivity with one high and the other low. Herein, a highly sensitive WSe2 /SnS2 photodiode is constructed on BN thin film by exfoliating each material and manually stacking them. The WSe2 /SnS2 vdW heterostructure shows ultralow dark currents resulting from the depletion region at the junction and high direct tunneling current when illuminated, which is confirmed by the energy band structures and electrical characteristics fitted with direct tunneling. Thus, the distinctive WSe2 /SnS2 vdW heterostructure exhibits both ultrahigh photodetectivity of 1.29 × 1013 Jones (Iph /Idark ratio of ≈106 ) and photoresponsivity of 244 A W-1 at a reverse bias under the illumination of 550 nm light (3.77 mW cm-2 ).

Strain Driven Spectral Broadening of Pb Ion Exchanged CdS Nanowires

Broad visible photodetectors based on individual Pb ion exchanged CdS nanowires are reported. They are prepared via an ion exchange reaction initiated on the surface of CdS nanowires with a further diffusion of ionic reactants. The broadening of the response spectrum is relative to electronic band structure transition caused by the tensile strain in the lattice.

Facile synthesis and electrochemical properties of nanoflake VN for supercapacitors

Vanadium nitrides (VN) have drawn much attention due to their large negative potential window, high electronic conductivity and fast reversible redox reaction. The electrochemical performances of VN are affected by their morphology and specific surface area, which depend deeply on the synthesis method. Herein, a large-sized nanoflake V2O5 xerogel is synthesized by a hydrothermal method followed by freeze drying, and then the nanoflake V2O5 xerogel is thermally treated for various times under NH3 atmosphere to study the nitriding process. The results show that the nanoflake V2O5 xerogel is reduced to nanoflake V2O3 before being completely transformed into nanoflake VN. The nanoflake VN demonstrate superior capacitive performance than the nanoflake V2O5 xerogel and intermediate V2O3, which arises from higher intrinsic conductivity.

Controllable Hydrogen Generation from Water

Hydrogen has been considered as a promising alternative to unsustainable fossil fuels for a long time. It produces water and electricity when combined with oxygen in a fuel cell, without the noxious pollutants that accompany the burning of most fossil fuels. Currently, most hydrogen is produced from fossil resources by steam reforming, which consumes a lot of energy and is accompanied by serious CO2 emissions. [1a, b] To realize a hydrogen-based economy, hydrogen must be produced in an efficient and sustainable manner. Splitting water with solar energy should be the best way for hydrogen generation. In the past years, sunlight-induced water splitting has received considerable attention. However, challenges facing this process are: (1) a visible-light photocatalyst is needed; (2) the speed of hydrogen generation is slow; (3) hydrogen generation is not controllable; and (4) the generated hydrogen has to be stored with complex technology and can not be directly applied in energy conversion devices, such as a fuel cell. Certainly, a solar cell with a particular potential (higher than 1.23 V) can also be directly employed to split water into hydrogen and oxygen by the electrolysis reaction. Nevertheless, the performance of solar cells is based on the weather and therefore cannot provide a controllable manner of hydrogen generation. Another route for splitting water is the direct chemical reaction between water and a metal, in which the metal, such as Li or Mg, may also be synthesized from sea water (or a salt solution) by solar energy. In this way, solar energy is first converted into chemical energy through metal production. When the hydrogen fuel is needed, the metal is used to generate hydrogen from water. Although some metal–water direct chemical reactions can produce a large amount of hydrogen in a short time, they are too intense to be controlled. A case in point is the chemical reaction between lithium and water. This reaction can be summarized as:

Highly reversible sodium storage in a GeP5/C composite anode with large capacity and low voltage

Sodium ion batteries (SIBs) are considered to be a promising alternative to lithium ion batteries because of the high abundance of sodium. However, the scarcities of suitable anode materials severely hamper the development of SIBs. Here, we synthesized a GeP5/C composite with binary sodium-reactive components on a large scale. Theoretically, it can promise a capacity of 1888 mA h g−1 or 6891 mA h cm−3, which is the best record in anodes for SIBs reported so far. In practice, the GeP5/C showed a low potential of ≈0.4 V vs. Na+/Na with a smooth charge/discharge profile. It delivered a large reversible capacity of 1250 mA h g−1 with a first coulombic efficiency of 93%. Electrochemical-mechanism studies suggested that the formation of a GeP5 phase endowed a high first coulombic efficiency and synergetic effect between the sodiation of Ge and P. This effect smoothly leveled the multistep plateaus and effectively reduced the polarization between charge/discharge. When applied to a full cell by coupling a Na3V2(PO4)3/C cathode, the assembled Na3V2(PO4)3//GeP5 full cell showed a large capacity of 800 mA h g−1 with a high average output voltage of 2.65 V. The excellent sodium-storage performances of GeP5/C will ensure commercial utilization in future SIBs.

Multi-heteroatom self-doped porous carbon derived from swim bladders for large capacitance supercapacitors

Multi-heteroatom self-doped porous carbon was synthesized via carbonization and activation of amino-acid-rich swim bladders and used for high-performance supercapacitors. The effects of different activation temperatures on the pore structure and composition of the carbon were investigated by TEM, Raman, XPS and nitrogen sorption analyses. With increasing temperature, the pore size broadens and the amount of doped heteroatoms decreases. The obtained materials have a high surface area of up to 3068 m2 g−1 with nitrogen, oxygen and sulfur multi-heteroatom doping. Carbon activated at 550 °C shows the highest capacitance of 410 F g−1 and excellent cyclic stability during 10 000 cycles due to the high surface area and multi-heteroatom doping. The outstanding performance makes this material promising for supercapacitors.

Layer Structured Materials for Advanced Energy Storage and Conversion

Owing to the strong in-plane chemical bonds and weak van der Waals force between adjacent layers, investigations of layer structured materials have long been the hotspots in energy-related fields. The intrinsic large interlayer space endows them capabilities of guest ion intercalation, fast ion diffusion, and swift charge transfer along the channels. Meanwhile, the well-maintained in-plane integrity contributes to exceptional mechanical properties. This anisotropic structural feature is also conducive to effective chemical combination, exfoliation, or self-assembly into various nanoarchitectures, accompanied by the introduction of defects, lattice strains, and phase transformation. This review starts with a brief introduction of typical layered materials and their crystal structures, then the structural characteristics and structure oriented unique applications in batteries, capacitors, catalysis, flexible devices, etc., are highlighted. It is surprising to observe that layered materials possess: (1) high reactivity, high reversibility, and enhanced performance via forming additional chemical bonds in alkali-metal ion batteries; (2) facile phase modulation, great feasibility for in-plane/sandwich device design, and cation intercalation enabled high capacitance in supercapacitors; (3) promoted structural diversity, effective strain engineering, and capabilities to function as ideal supporting materials/templates in electrocatalysis field. Finally, the future prospects and challenges faced by layered materials are also outlined.

A novel rechargeable Li–AgO battery with hybrid electrolytes

Nanoscaled AgO with high purity was synthesized by a chemical oxidation method. It can perform well as the cathode material in the proposed Li-AgO battery which coupled a Li metal anode and employed an aqueous//LISICON//nonaqueous electrolyte. The assembled Li-AgO cell demonstrated both a higher energy density and a superior power performance than its predecessors.

One-step synthesis of p-type GaSe nanoribbons and their excellent performance in photodetectors and phototransistors

High quality p-type GaSe nanoribbons were synthesized through a one-step thermal deposition process and their optoelectronic characteristics and device applications have been systematically explored. The steady-state CL study reveals the presence of two emission bands and the trap relevant emission at 710 nm is more intense at low temperatures. The GaSe nanoribbon-based photodetectors reflect an excellent spectral responsivity (Rλ) of 31.1 A W−1, external quantum efficiency (EQE) of 11 046% and a detectivity (D*) of 3.29 × 1010 Jones. In addition, under illumination, the phototransistors have shown quadrupled mobility up to 0.12 cm2 V−1 s−1 in comparison with the value (0.03 cm2 V−1 s−1) measured in darkness, attributed to a joint effect of increased photo-generated carriers and the reduced Schottky barrier. The success in one-step synthesis of high quality p-type GaSe nanoribbons and the detailed exploration of the optoelectronic properties strongly support their future practical applications.