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1.
Nanotechnology ; 31(34): 345704, 2020 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-32375140

RESUMO

Two-dimensional transition metal dichalcogenide (2D TMDs) alloys, consisting of three or more elements, offer a luxury variety of chemical and physical properties through elemental ratio alteration, thus may provide ideal candidate with tunable band gap for specific electrical applications. In this work, we demonstrate a high-quality layered MoSe2xTe2-2x (x = 0 ∼ 1) alloy synthesized via one-step chemical vapor transport method for high-performance electronic and optoelectronic transistors. Our characterizations reveal the obtained ternary alloy forming high-quality single crystal layers with 2H phase. Interestingly, the electronic transistors fabricated on MoSe2xTe2-2x thin layers (6 ∼ 7 layers) display an anomalous transition from ambipolar to n-type in conductive characteristics with the increase of substitution x value. The subsequent photoelectrical measurements exhibit that high on-off ratio for every ratio (x = 0.18, 0.38, 0.67, 0.83) with optical band gap in the range of 1.6 eV and 1.1 eV (near infrared). The optimized MoSe0.37Te1.63-based transistor can achieve up to ∼107 I on/I off and 105 I ph/I dark ratio, 100 mA W-1 photo-responsivity and 2.38% external quantum efficiency with high photoresponsivity. Thus, such ternary MoSe2xTe2-2x alloys may pose a great potential for 2D-based electronic and photoelectronic applications.

2.
J Phys Chem Lett ; : 1746-1752, 2020 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-32048849

RESUMO

Recent years have witnessed various in-depth research efforts on self-reconstruction behavior toward electrocatalysis. Tracking the phase transformation and evolution of true active sites is of great significance for the development of self-reconstructed electrocatalysts. Here, the optimized atomic sulfur-doped bismuth nanobelt (S-Bi) is fabricated via an electrochemical self-reconstruction evolved from Bi2S3. Advanced technologies have demonstrated that the nonmetallic S atoms have been doped into the lattice Bi frame, leading to the reconstruction of local electronic structure of Bi. The as-prepared S-Bi nanobelt exhibits a remarkable NH3 generation rate of 10.28 µg h-1 mg-1 and Faradaic efficiency of 10.48%. Density functional theory calculations prove that the S doping can significantly lower the energy barrier of the rate-determining step and enlarge the N≡N bond for further dissociation toward N2 fixation. This work not only establishes insights into the evolution process of electrochemically derived self-reconstruction but also unravels the root of the N2 reduction reaction mechanism associated with the atomic nonmetal dopants.

3.
ACS Nano ; 14(1): 835-841, 2020 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-31860270

RESUMO

Two-dimensional layered transition-metal telluride can build stable metallic, metastable metallic, or semimetallic polymorphic crystal structures with enormous technological and scientific applications. Herein the hexagonal structures of zirconium ditelluride (ZrTe2) and ZrTe2(1-x)Se2x (0 ≤ x ≤ 1) single crystals were selectively synthesized through the chemical vapor transport method. The electronic band structures were systematically studied through angle-resolved photoemission spectroscopy (ARPES) combined with first-principles density functional theory (DFT) calculations. The ARPES results suggested a clear electronic phase transition from a semimetal to a semiconductor in ZrTe2(1-x)Se2x with the x value changing. Compared with pristine ZrTe2, the valence band splitting in ZrTe2(1-x)Se2x decreased at the Γ point due to the reduction of the spin-orbit interaction, whereas an indirect band gap opened in the vicinity of the Fermi level with the increase in Se concentration. Our DFT calculations further confirmed that the substituted Se atoms on Te sites could affect the band structure of ZrTe2 to induce a distinct transition from semimetal to semiconductor, suggesting their high potential for valleytronics applications.

4.
Adv Mater ; 31(48): e1903841, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31621970

RESUMO

A titanium carbide (Ti3 C2 Tx ) MXene is employed as an efficient solid support to host a nitrogen (N) and sulfur (S) coordinated ruthenium single atom (RuSA ) catalyst, which displays superior activity toward the hydrogen evolution reaction (HER). X-ray absorption fine structure spectroscopy and aberration corrected scanning transmission electron microscopy reveal the atomic dispersion of Ru on the Ti3 C2 Tx MXene support and the successful coordination of RuSA with the N and S species on the Ti3 C2 Tx MXene. The resultant RuSA -N-S-Ti3 C2 Tx catalyst exhibits a low overpotential of 76 mV to achieve the current density of 10 mA cm-2 . Furthermore, it is shown that integrating the RuSA -N-S-Ti3 C2 Tx catalyst on n+ np+ -Si photocathode enables photoelectrochemical hydrogen production with exceptionally high photocurrent density of 37.6 mA cm-2 that is higher than the reported precious Pt and other noble metals catalysts coupled to Si photocathodes. Density functional theory calculations suggest that RuSA coordinated with N and S sites on the Ti3 C2 Tx MXene support is the origin of this enhanced HER activity. This work would extend the possibility of using the MXene family as a solid support for the rational design of various single atom catalysts.

5.
J Phys Chem Lett ; 10(20): 6081-6087, 2019 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-31539474

RESUMO

Rationally designing cheap and efficient electrocatalysts at the atomic level is highly desirable for the hydrogen evolution reaction (HER). Here, we demonstrate a metallic MoS2 electrocatalyst decorated with platinum single atoms. When combined with electron microscopy observations, our synchrotron X-ray characterizations and theoretical calculations clearly reveal that the doped Pt atoms bond to S atoms on the surface of MoS2. Notably, these Pt single atoms serve as critical active centers for the HER through capturing H+ from the solution. The optimized Pt-MoS2 catalysts achieve significantly enhanced HER performance due to the single-atom coordination effect. This finding is expected to facilitate further realization of hybridized catalysts through the monatomic riveting strategy.

6.
ACS Nano ; 13(10): 11733-11740, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31525961

RESUMO

Molybdenum disulfide (MoS2) has attracted much attention as a promising alternative to Pt-based catalysts for highly efficient hydrogen generation. However, it suffers sluggish kinetics for driving the hydrogen evolution reaction (HER) process because of inert basal planes, especially in alkaline solution. Here, we show a combination of heteroatom doping and phase transformation strategies to engineer the in-plane structure of MoS2, that trigger their catalytic activities. Systematic characterizations are performed with advanced aberration-corrected microscopy and X-ray techniques, indicating that an as-designed MoS2 catalyst has a distorted zigzag-chain superlattice in metallic phase, while its in-plane structure was engineered via the incorporation of cobalt and oxygen species. The optimal Co, O dual-doped metallic phase molybdenum disulfide (1T-MoS2) electrocatalyst shows a significantly enhanced HER activity with a low overpotential of 113 mV at 10 mA cm-2 and corresponding small Tafel slope of 50 mV dec-1, accompanied by the robust stability in alkaline media. The calculated turnover frequency is higher than 6.65 H2 s-1 at an overpotential of 200 mV. More in-depth insights from the first-principle calculations illustrate that the water dissociation as a rate-determining step was largely accelerated by the in-plane Co-O-Mo species and fast electron transfer of the catalyst. Benefiting from ingenious design and fine identifications, this work provides a fundamental understanding of the relationships among heteroatom doping, phase transformation, and performance for MoS2-based catalysts.

7.
Angew Chem Int Ed Engl ; 58(35): 12252-12257, 2019 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-31245890

RESUMO

Common-metal-based single-atom catalysts (SACs) are quite difficult to design due to the complex synthesis processes required. Herein, we report a single-atom nickel iodide (SANi-I) electrocatalyst with atomically dispersed non-metal iodine atoms. The SANi-I is prepared via a simple calcination step in a vacuum-sealed ampoule and subsequent cyclic voltammetry activation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and synchrotron-based X-ray absorption spectroscopy are applied to confirm the atomic-level dispersion of iodine atoms and detailed structure of SANi-I. Single iodine atoms are found to be isolated by oxygen atoms. The SANi-I is structural stable and shows exceptional electrocatalytic activity for the hydrogen evolution reaction (HER). In situ Raman spectroscopy reveals that the hydrogen adatom (Hads ) is adsorbed by a single iodine atom, forming the I-Hads intermediate, which promotes the HER process.

8.
Nat Commun ; 10(1): 2840, 2019 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-31253761

RESUMO

The design of efficient and stable photocatalysts for robust CO2 reduction without sacrifice reagent or extra photosensitizer is still challenging. Herein, a single-atom catalyst of isolated single atom cobalt incorporated into Bi3O4Br atomic layers is successfully prepared. The cobalt single atoms in the Bi3O4Br favors the charge transition, carrier separation, CO2 adsorption and activation. It can lower the CO2 activation energy barrier through stabilizing the COOH* intermediates and tune the rate-limiting step from the formation of adsorbed intermediate COOH* to be CO* desorption. Taking advantage of cobalt single atoms and two-dimensional ultrathin Bi3O4Br atomic layers, the optimized catalyst can perform light-driven CO2 reduction with a selective CO formation rate of 107.1 µmol g-1 h-1, roughly 4 and 32 times higher than that of atomic layer Bi3O4Br and bulk Bi3O4Br, respectively.

9.
Adv Mater ; 31(32): e1902709, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31194268

RESUMO

Electrochemical nitrogen reduction reaction (NRR) under ambient conditions provides an avenue to produce carbon-free hydrogen carriers. However, the selectivity and activity of NRR are still hindered by the sluggish reaction kinetics. Nitrogen Vacancies on transition metal nitrides are considered as one of the most ideal active sites for NRR by virtue of their unique vacancy properties such as appropriate adsorption energy to dinitrogen molecule. However, their catalytic performance is usually limited by the unstable feature. Herein, a new 2D layered W2 N3 nanosheet is prepared and the nitrogen vacancies are demonstrated to be active for electrochemical NRR with a steady ammonia production rate of 11.66 ± 0.98 µg h-1 mgcata -1 (3.80 ± 0.32 × 10-11 mol cm-2 s-1 ) and Faradaic efficiency of 11.67 ± 0.93% at -0.2 V versus reversible hydrogen electrode for 12 cycles (24 h). A series of ex situ synchrotron-based characterizations prove that the nitrogen vacancies on 2D W2 N3 are stable by virtue of the high valence state of tungsten atoms and 2D confinement effect. Density function theory calculations suggest that nitrogen vacancies on W2 N3 can provide an electron-deficient environment which not only facilitates nitrogen adsorption, but also lowers the thermodynamic limiting potential of NRR.

10.
J Am Chem Soc ; 141(19): 7807-7814, 2019 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-31038309

RESUMO

Nitrogen fixation in a simulated natural environment (i.e., near ambient pressure, room temperature, pure water, and incident light) would provide a desirable approach to future nitrogen conversion. As the N≡N triple bond has a thermodynamically high cleavage energy, nitrogen reduction under such mild conditions typically undergoes associative alternating or distal pathways rather than following a dissociative mechanism. Here, we report that surface plasmon can supply sufficient energy to activate N2 through a dissociative mechanism in the presence of water and incident light, as evidenced by in situ synchrotron radiation-based infrared spectroscopy and near ambient pressure X-ray photoelectron spectroscopy. Theoretical simulation indicates that the electric field enhanced by surface plasmon, together with plasmonic hot electrons and interfacial hybridization, may play a critical role in N≡N dissociation. Specifically, AuRu core-antenna nanostructures with broadened light adsorption cross section and active sites achieve an ammonia production rate of 101.4 µmol g-1 h-1 without any sacrificial agent at room temperature and 2 atm pressure. This work highlights the significance of surface plasmon to activation of inert molecules, serving as a promising platform for developing novel catalytic systems.

11.
Chemistry ; 25(41): 9670-9677, 2019 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-31069880

RESUMO

As photocatalysis technology could transform renewable and clean solar energy into green hydrogen (H2 ) energy through solar water splitting, it is regarded as the "Holy Grail" in chemistry field in the 21st century. Unfortunately, the bottleneck of this technique still lies in the exploration of highly active, cost-effective, and robust photocatalysts. This work reports the design and synthesis of a novel zeolitic imidazole framework (ZIF) coupled Zn0.8 Cd0.2 S hetero-structured photocatalyst for high-performance visible-light-induced H2 production. State-of-the-art characterizations and theoretical computations disclose that the interfacial electronic interaction between ZIF and Zn0.8 Cd0.2 S, the high distribution of Zn0.8 Cd0.2 S on ZIF, and the atomically dispersed coordinately unsaturated Co sites in ZIF synergistically arouse the significantly improved visible-light photocatalytic H2 production performance.

12.
Nanoscale ; 11(17): 8304-8309, 2019 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-30982842

RESUMO

The rapid consumption of non-renewable fossil fuels and the relevant critical environmental issues have significantly boosted the demand for clean, renewable and carbon-free energy sources. The conversion of solar energy into green hydrogen (H2) via photocatalytic water splitting stands out as a promising, cost-effective and environmentally friendly technology. However, the realization of large-scale solar-driven photocatalytic H2 production relies on the development of inexpensive, efficient and stable photocatalysts. Here, for the first time, we report the fabrication of Zn0.8Cd0.2S (ZCS) nanoparticles (NPs) dispersed Co-based metal-organic layers (CMLs) using an easy self-assembly approach. The as-synthesized ZCS/CML composite shows a remarkable visible-light-induced H2-production activity of 18 102 µmol h-1 g-1, 492% higher than that of pure ZCS. A series of advanced characterization studies, e.g., synchrotron-based X-ray absorption near edge structure and time-resolved photoluminescence spectroscopy, disclose that the strong electronic interaction between ZCS and CML and the abundant reactive sites on the CML lead to the significantly improved photocatalytic H2-production activity. Our contribution not only demonstrates the application of CML as an earth-abundant support and promoter to tremendously boost photocatalytic H2 production without noble-metal co-catalysts, but also sheds light on the tailored design and synthesis of metal-organic-layer based materials for energy conversion and storage.

13.
Adv Mater ; 31(19): e1900592, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30907474

RESUMO

High-performance bifunctional oxygen electrocatalysis constitutes the key technique for the widespread application of clean and sustainable energy through electrochemical devices such as rechargeable Zn-air batteries. Single-atom electrocatalysts with maximum atom efficiency are highly considered as an alternative of the present noble-metal-based electrocatalysts. However, the fabrication of transition metal single-atoms is very challenging, requiring extensive attempts of precursors with novel design principles. Herein, an all-covalently constructed cobalt-coordinated framework porphyrin with graphene hybridization is innovatively designed and prepared as the pyrolysis precursor to fabricate single-atom Co-Nx -C electrocatalysts. Excellent electrochemical performances are realized for both bifunctional oxygen electrocatalysis and rechargeable Zn-air batteries with regard to reduced overpotentials, improved kinetics, and prolonged cycling stability comparable with noble-metal-based electrocatalysts. Design principles from multiple scales are proposed and rationalized with detailed mechanism investigation. This work not only provides a novel precursor for the fabrication of high-performance single-atom electrocatalysts, but also inspires further attempts to develop advanced materials and emerging applications.

14.
Adv Mater ; 31(8): e1805127, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30633404

RESUMO

Unravelling the intrinsic mechanism of electrocatalytic oxygen evolution reaction (OER) by use of heterogeneous catalysts is highly desirable to develop related energy conversion technologies. Albeit dynamic self-reconstruction of the catalysts during OER is extensively observed, it is still highly challenging to operando probe the reconstruction and precisely identify the true catalytically active components. Here, a new class of OER precatalyst, cobalt oxychloride (Co2 (OH)3 Cl) with unique features that allow a gradual phase reconstruction during OER due to the etching of lattice anion is demonstrated. The reconstruction continuously boosts OER activities. The reconstruction-derived component delivers remarkable performance in both alkaline and neutral electrolytes. Operando synchrotron radiation-based X-ray spectroscopic characterization together with density functional theory calculations discloses that the etching of lattice Cl- serves as the key to trigger the reconstruction and the boosted catalytic performance roots in the atomic-level coordinatively unsaturated sites (CUS). This work establishes fundamental understanding on the OER mechanism associated with self-reconstruction of heterogeneous catalysts.

15.
Small ; 14(50): e1803811, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30394689

RESUMO

The emerging phosphate species on the surface or near-surface of electrode materials are versatile and have an intriguing ability for dramatically enhanced electrochemical performance. Unfortunately, the distribution/dispersion of phosphate species still keeps at levels on the exterior not within the interior surface of materials, and the micro-/nanoscale tuning is commonly rarely concerned and its function remains poorly understood. Herein, for the first time, well-dispersed phosphate species up to 70% mass ratio implanted within Ni-doped CoP nanowire matrix are presented via an efficient low-temperature phosphorization strategy. The resultant nanohybrids possess kinetics-favorable open frameworks with abundant mesopores and a high degree covalency in the chemical bonds, thus leading to rapid mass transport/charge transfer and enhanced redox reaction kinetics. Remarkably, the phosphate species feature superwettability toward water and strong affinity for OH- in the electrolyte, evidenced by the shortened distance and reduced adsorption energy between the OH- and the nuclear Co atoms on the nanohybrids as revealed by density functional theory calculations. As such, the nanohybrids exhibit an ultrahigh specific capacity of 250 mAh g-1 even at 50 A g-1 . This work presents a deeper understanding of the dispersion and role of phosphate species for supercapacitors and other energy-related storage/conversion devices.

16.
Adv Mater ; 30(51): e1805655, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30357972

RESUMO

2D transition metal nitrides, especially nitrogen-rich tungsten nitrides (Wx Ny , y > x), such as W3 N4 and W2 N3 , have a great potential for the hydrogen evolution reaction (HER) since the catalytic activity is largely enhanced by the abundant WN bonding. However, the rational synthesis of 2D nitrogen-rich tungsten nitrides is challenging due to the large formation energy of WN bonding. Herein, ultrathin 2D hexagonal-W2 N3 (h-W2 N3 ) flakes are synthesized at atmospheric pressure via a salt-templated method. The formation energy of h-W2 N3 can be dramatically decreased owing to the strong interaction and domain matching epitaxy between KCl and h-W2 N3 . 2D h-W2 N3 demonstrates an excellent catalytic activity for cathodic HER with an onset potential of -30.8 mV as well as an overpotential of -98.2 mV for 10 mA cm-2 .

17.
Adv Mater ; 30(51): e1803477, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30368920

RESUMO

The development of stable and efficient hydrogen evolution reaction (HER) catalysts is essential for the production of hydrogen as a clean energy resource. A combination of experiment and theory demonstrates that the normally inert basal planes of 2D layers of MoS2 can be made highly catalytically active for the HER when alloyed with rhenium (Re). The presence of Re at the ≈50% level converts the material to a stable distorted tetragonal (DT) structure that shows enhanced HER activity as compared to most of the MoS2 -based catalysts reported in the literature. More importantly, this new alloy catalyst shows much better stability over time and cycling than lithiated 1T-MoS2 . Density functional theory calculations find that the role of Re is only to stabilize the DT structure, while catalysis occurs primarily in local Mo-rich DT configurations, where the HER catalytic activity is very close to that in Pt. The study provides a new strategy to improve the overall HER performance of MoS2 -based materials via chemical doping.

18.
Chemistry ; 24(69): 18398-18402, 2018 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-30102805

RESUMO

Metal-containing nanocrystals with well-designed surface structures represent a class of model systems for revealing the fundamental physical and chemical processes involved in heterogeneous catalysis. Herein it is shown how surface modification can be utilized as an efficient strategy for controlling the surface electronic state of catalysts and, thus, for tuning their catalytic activity. As model catalysts, the Pd-tetrahedron-TiO2 nanostructures, modified on the surface with different foreign atoms, showed a varied activity in the catalytic decomposition of formic acid towards H2 production. The catalytic activity increases with a reduction in the work function of modified atoms; this reduction can be well explained by a surface polarization mechanism. In this hybrid system, the difference in the work functions of Pd and modified atoms results in surface polarization on the Pd surface and, thus, in the tuning of its charge state. Together with the Schottky junction between TiO2 and metals, the tuned charge state enables the promotion of catalytic efficiency in the catalytic decomposition of formic acid to H2 and CO2 .

19.
J Am Chem Soc ; 140(30): 9434-9443, 2018 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-29975522

RESUMO

Photocatalysis may provide an intriguing approach to nitrogen fixation, which relies on the transfer of photoexcited electrons to the ultrastable N≡N bond. Upon N2 chemisorption at active sites (e.g., surface defects), the N2 molecules have yet to receive energetic electrons toward efficient activation and dissociation, often forming a bottleneck. Herein, we report that the bottleneck can be well tackled by refining the defect states in photocatalysts via doping. As a proof of concept, W18O49 ultrathin nanowires are employed as a model material for subtle Mo doping, in which the coordinatively unsaturated (CUS) metal atoms with oxygen defects serve as the sites for N2 chemisorption and electron transfer. The doped low-valence Mo species play multiple roles in facilitating N2 activation and dissociation by refining the defect states of W18O49: (1) polarizing the chemisorbed N2 molecules and facilitating the electron transfer from CUS sites to N2 adsorbates, which enables the N≡N bond to be more feasible for dissociation through proton coupling; (2) elevating defect-band center toward the Fermi level, which preserves the energy of photoexcited electrons for N2 reduction. As a result, the 1 mol % Mo-doped W18O49 sample achieves an ammonia production rate of 195.5 µmol gcat-1 h-1, 7-fold higher than that of pristine W18O49. In pure water, the catalyst demonstrates an apparent quantum efficiency of 0.33% at 400 nm and a solar-to-ammonia efficiency of 0.028% under simulated AM 1.5 G light irradiation. This work provides fresh insights into the design of photocatalyst lattice for N2 fixation and reaffirms the versatility of subtle electronic structure modulation in tuning catalytic activity.

20.
Chem Commun (Camb) ; 54(60): 8379-8382, 2018 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-29998261

RESUMO

In this work, few-layer SnS2 nanosheets confined in a nitrogen-doped graphene sheet composite (SnS2/NGS) are successfully synthesized via a facile thermal decomposition method. SnS2/NGS demonstrates sufficient nitrogen-doping and full graphene encapsulation. When evaluated as an anode material for lithium/sodium-ion batteries, it exhibits an excellent electrochemical performance.

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