Showing papers by "Xiang Qi published in 2017"

Environmentally Robust Black Phosphorus Nanosheets in Solution: Application for Self-Powered Photodetector

Abstract: Large-size 2D black phosphorus (BP) nanosheets have been successfully synthesized by a facile liquid exfoliation method. The as-prepared BP nanosheets are used to fabricate electrodes for a self-powered photodetector and exhibit preferable photoresponse activity as well as environmental robustness. Photoelectrochemical (PEC) tests demonstrate that the current density of BP nanosheets can reach up to 265 nA cm−2 under light irradiation, while the dark current densities fluctuate near 1 nA cm−2 in 0.1 M KOH. UV–vis and Raman spectra are carried out and confirm the inherent optical and physical properties of BP nanosheets. In addition, the cycle stability measurement exhibits no detectable distinction after processing 50 and 100 cycles, while an excellent on/off behavior is still preserved even after one month. Furthermore, the PEC performance of BP nanosheets-based photodetector is evaluated in various KOH concentrations, which demonstrates that the as-prepared BP nanosheets may have a great potential application in self-powered photodetector. It is anticipated that the present work can provide fundamental acknowledgement of the performance of a PEC-type BP nanosheets-based photodetector, offering extendable availabilities for 2D BP-based heterostructures to construct high-performance PEC devices.

Few-Layer Black Phosphorus Nanosheets as Electrocatalysts for Highly Efficient Oxygen Evolution Reaction

Abstract: Black phosphorus (BP) is a new rediscovered layered material, which has attracted enormous interests in the field of electrocatalysis. Recent investigations reveal that bulk BP is a promising electrocatalyst for oxygen evolution reactions (OER), whereas its bulk crystal structure restricts sufficient active sites for achieving highly efficient OER catalytic performances. Toward this end, few-layer BP nanosheets prepared by facile liquid exfoliation are applied as electrocatalysts and exhibit preferable electrocatalytic OER activity in association with structural robustness; subsequently, the dependence of current density and applied bias potential on the concentration of OH− has also been uncovered. Most importantly, we are aware that reduction in the thickness of BP nanosheets would generate extra active sites from the ultrathin planar structure and complimenting to the electrocatalytic activities. It is further anticipated that the current work might provide further implementation about the OER performance of BP nanosheets, thereby, offering extendable availabilities for BP-based electrocatalysts in constructing high-performance OER devices.

A black/red phosphorus hybrid as an electrode material for high-performance Li-ion batteries and supercapacitors

Abstract: A single elemental hybrid composed of black phosphorus (BP) and red phosphorus (RP) is synthesized via a feasible sonochemical method. BP and RP can construct a new single elemental heterostructure. This kind of structure with an excellent interfacial contact between BP and RP would be beneficial to electron transfer and exhibits a superior electrochemical performance. Compared with the sole RP, the as-prepared BP/RP hybrid exhibits enhanced electrochemical performances as an electrode material for both lithium-ion batteries and supercapacitors. For lithium-ion battery applications, the BP/RP hybrid provides a high cycling performance with an initial discharge capacity of 2449 mA h g−1 and a reversible capacity of 491 mA h g−1 after 100 cycles. For supercapacitor applications, the specific capacitance of the BP/RP hybrid achieves a high value up to about 60.1 F g−1 and a long cycling life with a capacity retention of 83.3% after 2000 cycles. The present study demonstrates that the BP/RP hybrid has potential for application as an electrode with high performances in electrochemical energy-storage devices.

Present Perspectives of Advanced Characterization Techniques in TiO2-Based Photocatalysts

Abstract: TiO2 is the most investigated photocatalyst because of its nontoxicity, low cost, chemical stability, and strong photooxidative ability. Because of the morphology- and structure-dependent photocatalytic properties of TiO2, accurate characterization of the crystal and electronic structures of TiO2-based materials and their performance during the photocatalytic process is crucial not only for understanding the photocatalytic mechanism but also for providing experimental guidelines as well as a theoretical framework for the synthesis of high performance photocatalysts. In this review, we focused on the advanced characterization techniques that are utilized in the studies on the TiO2 structures and photocatalytic performance of TiO2 and TiO2-based materials. It is therefore anticipated that this review can provide a novel perspective to understand the fundamental aspects of photocatalysis and inspire the development of new photocatalysts with superior performances.

Temperature-Dependent Raman Responses of the Vapor-Deposited Tin Selenide Ultrathin Flakes

Abstract: Tin selenide (SnSe) is a newly emerging layered material. SnSe with low dimensionality has been reported as an appealing material with a diverse range of applications such as rechargeable lithium-ion batteries, memory switching devices, solar energy conversion, thermoelectric energy conversion, and near-infrared optoelectronic devices. Here we synthesized SnSe ultrathin flakes on SiO2/Si substrates through simple vapor deposition route and investigated its temperature-dependent Raman spectroscopy behavior with 532, 633, and 785 nm excitation wavelengths. It was found that the Ag2, Ag3, and B3g modes soften as temperature increases from 98 to 298 K under all wavelengths. Our results revealed anharmonic phonon properties of SnSe, and they will benefit the advanced study of its thermal properties. This approach will also have large application in characterizing the optical, electronic, and thermal properties of other novel layered materials. Moreover, our results can be utilized to measure the temperature of...

Hydrothermal synthesis of NiSe2 nanosheets on carbon cloths for photoelectrochemical hydrogen generation

Abstract: Two-dimensional NiSe2 nanosheets arrange on three-dimensional carbon cloths (CC) have been synthesized through a facile two-step hydrothermal process. The as-prepared NiSe2/CC photoelectrode demonstrates outstanding photoelectrochamical (PEC) performance. Subsequently, a series of characterization techniques including X-ray diffraction and Raman spectra are carried out and confirm a well crystalline NiSe2/CC. Additional morphological and microstructural tests depict large-scale NiSe2 nanosheets are uniformly aligned on the basement of conductive carbon cloth. The PEC measurements show the steady photocurrent density can be effectively raised from 10 to 600 μA/cm2 when bias potential increases from 0 to 0.5 V, which is proposed to be attributed to the adequate exposure of active sites and reduction of surface contact resistance provided by carbon cloth. The structure and performances of hydrothermal synthesized NiSe2/CC suggest promising applications in the field of PEC hydrogen production.

Mixed-dimensional TiO2 nanoparticles with MoSe2 nanosheets for photochemical hydrogen generation

Abstract: Novel TiO2/MoSe2 catalyst has been synthesized via a hydrothermal method. The morphologies, microstructures and optical properties were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, UV–Vis absorption spectroscopy, the result show that a large quantity of MoSe2 nanosheets (NSs) were obtained from MoSe2 bulks by lithium intercalatation way and TiO2 nanoparticles has been grown on the NSs successfully. According to the photoelectrochemical measurements, the TiO2/MoSe2 hybrid nanostructures show the photocurrent density of 15 μA/cm2, which is much higher than bare TiO2 of 8 μA/cm2 and bare MoSe2 of 10 μA/cm2. It is proposed that type-II heteroshtucture of TiO2/MoSe2 can efficiently promote photocatalytic activity.

Voltage-on-Type RTP Pockels Cell for Q-switch of an Er:YAG Laser at 1,617 nm

Abstract: We report a resonantly diode-pumped electro-optic Q-switched Er:YAG laser operating at 1,617 nm using a voltage-on-type rubidium titanyl phosphate (RTP) Pockels cell as the modulator. The Er:YAG laser operates at a very stable Q-switching mode with a per pulse energy yield of 1.5 mJ and a pulse duration of 114 ns at 1 kHz PRF under an incident pump power of 21.6 W.

Stable Q-switched operation of a resonantly diode pumped Er:YAG laser at 1617 and 1645 nm by Cr2+:ZnSe crystal

Abstract: Using Cr2+:ZnSe as the saturable absorber, stable passively Q-switched operation of the Er:YAG laser at 1617 and 1645nm with per-pulse energy higher than 200μJ can be achieved by controlling the output coupling ratios. The result indicates that the Cr2+:ZnSe crystal could be a robust nonlinear optical modulator for ∼1.6μm pulsed laser.