nanogenerator can only output alternating current and the output current density is quite small (0.01-0.1 A m −2 ), [5] which limits its widespread applications. [6] Recently, the vertical movement between the metal and semiconducting polymer has been demonstrated to output intermittent current peaks with low current density (2.7-62.4 µA cm −2 ), [7] where the metal contacts with polymer periodically. On the other hand, the microscale direct current generator based on sliding between metal tip and semiconductor has been demonstrated, [8] where the mechanism was ascribed to the triboelectric effect. However, the mechanism of triboelectric effect is confusing, [9] as the fundamental physical mechanism of the charge transfer process during friction is not solved. [6,10] Herein, we have demonstrated a macroscale direct-current generator through a moving van der Waals Schottky diode by dynamically moving graphene or metal film over Si or GaAs substrates. The mechanism of the moving Schottky diode generator is based on the built-in electric field separation of the diffusing carriers emitted by the appearance and disappearance of the depletion layer in moving Schottky diode. The working lifetime and flexibility can be properly improved by choosing graphene as the metal material, which is outstanding not only because of its high conductive but also the high mechanical physical properties. [11,12] Actually, static graphene/semiconductor van der Waals heterostructure-based solar cells, [13] self-driven photodetectors, [14] and water flow nanogenerator [15] have been proposed. Compared with metal, graphene film has the unique advantage of high flexibility and durability, which promises the graphene film/ silicon moving Schottky diode generator working well after 10 000 runs back and forth. The persistent direct-current generating ability firmly demonstrates that the physical mechanism of the moving Schottky diode generator is not caused by the triboelectricity. Instead, we uniquely propose that the dynamic disappearance and establishment of Schottky junction during the movement between graphene/metal and semiconductors is the origin of the direct current output. The proposed mechanism is self-consistent and can well explain the systematic experiments presented herein. This moving Schottky diode direct-current generator can light up a blue light-emitting diode (LED) and a flexible graphene wristband is demonstrated for the first time. Under the guidance of the mechanism, we achieved a currentdensity output up of ≈40 A m −2 through minimizing the contact Traditionally, Schottky diodes are used statically in the electronic information industry while dynamic or moving Schottky diode-based applications are rarely explored. Herein, a novel Schottky diode named "moving Schottky diode generator" is designed, which can convert mechanical energy into electrical energy by means of lateral movement between the graphene/metal film and semiconductor. The mechanism is based on the built-in electric field separation of the diffusing carr...
Recently, several reports have demonstrated that a moving droplet of seawater or ionic solution over monolayer graphene produces an electric power of about 19 nW, and this has been suggested to be a result of the pseudocapacitive effect between graphene and the liquid droplet. Here, we show that the change in the triboelectrification-induced pseudocapacitance between the water droplet and monolayer graphene on polytetrafluoroethylene (PTFE) results in a large power output of about 1.9 μW, which is about 100 times larger than that presented in previous research. During the graphene transfer process, a very strong negative triboelectric potential is generated on the surface of the PTFE. Positive and negative charge accumulation, respectively, occurs on the bottom and the top surfaces of graphene due to the triboelectric potential, and the negative charges that accumulate on the top surface of graphene are driven forward by the moving droplet, charging and discharging at the front and rear of the droplet.
Tailoring molybdenum selenide electrocatalysts with tunable phase and morphology is of great importance for advancement of hydrogen evolution reaction (HER). In this work, phase- and morphology-modulated N-doped MoSe /TiC-C shell/core arrays through a facile hydrothermal and postannealing treatment strategy are reported. Highly conductive TiC-C nanorod arrays serve as the backbone for MoSe nanosheets to form high-quality MoSe /TiC-C shell/core arrays. Impressively, continuous phase modulation of MoSe is realized on the MoSe /TiC-C arrays. Except for the pure 1T-MoSe and 2H-MoSe , mixed (1T-2H)-MoSe nanosheets are achieved in the N-MoSe by N doping and demonstrated by spherical aberration electron microscope. Plausible mechanism of phase transformation and different doping sites of N atom are proposed via theoretical calculation. The much smaller energy barrier, longer HSe bond length, and diminished bandgap endow N-MoSe /TiC-C arrays with substantially superior HER performance compared to 1T and 2H phase counterparts. Impressively, the designed N-MoSe /TiC-C arrays exhibit a low overpotential of 137 mV at a large current density of 100 mA cm , and a small Tafel slope of 32 mV dec . Our results pave the way to unravel the enhancement mechanism of HER on 2D transition metal dichalcogenides by N doping.
As ynergistic Nd oping plus PO 4 3À intercalation strategy is used to induce high conversion (ca. 41 %) of 2H-MoS 2 into 1T-MoS 2 ,which is muchhigher than single Ndoping (ca. 28 %) or single PO 4 3À intercalation (ca. 10 %). Ascattering mechanism is proposed to illustrate the synergistic phase transformation from the 2H to the 1T phase,w hich was confirmed by synchrotron radiation and spherical aberration TEM. To further enhance reaction kinetics,t he designed (N,PO 4 3À )-MoS 2 nanosheets are combined with conductive vertical graphene (VG) skeleton forming binder-free arrays for high-efficiency hydrogen evolution reaction (HER). Owing to the decreased band gap,l ower d-band center,a nd smaller hydrogen adsorption/desorption energy,t he designed (N,PO 4 3À )-MoS 2 /VGe lectrode shows excellent HER performance with al ower Tafel slope and overpotential than N-MoS 2 /VG, PO 4 3À -MoS 2 /VGc ounterparts,a nd other Mo-base catalysts in the literature.
Two-dimensional (2D) atomic crystals, especially graphene, have received much attention. However, the main shortcoming of graphene is its zero band gap. Silicon carbide, composed of silicon and carbon, is a typical wurtzite compound semiconductor, with more than 250 alloy types. Herein, we give some evidence of the solution exfoliation of 2D SiC nanoflakes with thickness down to 0.5–1.5 nm. Transmission electron microscopy (TEM) and X-ray diffraction characterizations reveal that graphitic (0001)/(0001̅) SiC most possibly has been formed by sonication of wurtzite SiC. Graphene, which is also produced in this process, naturally forms the ultrathin substrate facilitating the TEM characterization of 2D SiC. The mechanism of this exfoliation process should be related to the surface reconstruction of wurtzite SiC into graphitic SiC. Photoluminescence spectra show a strong light-emitting ability and a quantum-confinement-induced emission peak at 373 nm for these ultrathin SiC nanosheets.
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