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1.
ACS Nano ; 2020 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-32031780

RESUMO

Wafer-scale monocrystalline two-dimensional (2D) materials can theoretically be grown by seamless coalescence of individual domains into a large single crystal. Here we present a concise study of the coalescence behavior of crystalline 2D films using a combination of complementary in situ methods. Direct observation of overlayer growth from the atomic to the millimeter scale and under model- and industrially relevant growth conditions reveals the influence of the film-substrate interaction on the crystallinity of the 2D film. In the case of weakly interacting substrates, the coalescence behavior is dictated by the inherent growth kinetics of the 2D film. It is shown that the merging of coaligned domains leads to a distinct modification of the growth dynamics through the formation of fast-growing high-energy edges. The latter can be traced down to a reduced kink-creation energy at the interface between well-aligned domains. In the case of strongly interacting substrates, the lattice mismatch between film and substrate induces a pronounced moiré corrugation that determines the growth and coalescence behavior. It furthermore imposes additional criteria for seamless coalescence and determines the structure of grain boundaries. The experimental findings, obtained here for the case of graphene, are confirmed by theory-based growth simulations and can be generalized to other 2D materials that show 3- or 6-fold symmetry. Based on the gained understanding of the relation between film-substrate interaction, shape evolution, and coalescence behavior, conditions for seamless coalescence and, thus, for the optimization of large-scale production of monocrystalline 2D materials are established.

2.
Adv Mater ; 32(6): e1906193, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31894628

RESUMO

Reversible exsolution and dissolution of metal nanoparticles in perovskite has been investigated as an efficient strategy to improve CO2 electrolysis performance. However, fundamental understanding with regard to the reversible exsolution and dissolution of metal nanoparticles in perovskite is still scarce. Herein, in situ exsolution and dissolution of CoFe alloy nanoparticles in Co-doped Sr2 Fe1.5 Mo0.5 O6-δ (SFMC) revealed by in situ X-ray diffraction, scanning transmission electron microscopy, environmental scanning electron microscopy, and density functional theory calculations are reported. Under a reducing atmosphere, facile exsolution of Co promotes reduction of the Fe cation to generate CoFe alloy nanoparticles in SFMC, accompanied by structure transformation from double perovskite to layered perovskite at 800 °C. Under an oxidizing atmosphere, spherical CoFe alloy nanoparticles are first oxidized to flat CoFeOx nanosheets, and then dissolved into the bulk with structure evolution from layered perovskite back to double perovskite. Electrochemically, CO2 electrolysis performance can be retrieved during 12 redox cycles due to the regenerative ability of the CoFe alloy nanoparticles. The anchoring of the CoFe alloy nanoparticles in SFMC perovskite via reduction shows enhanced CO2 electrolysis performance and stability compared with the parent SFMC perovskite.

3.
Artigo em Inglês | MEDLINE | ID: mdl-31944516

RESUMO

The electrochemical CO2 reduction reaction (CO2 RR) to give C1 (formate and CO) products is one of the most techno-economically achievable strategies for alleviating CO2 emissions. Now, it is demonstrated that the SnOx shell in Sn2.7 Cu catalyst with a hierarchical Sn-Cu core can be reconstructed in situ under cathodic potentials of CO2 RR. The resulting Sn2.7 Cu catalyst achieves a high current density of 406.7±14.4 mA cm-2 with C1 Faradaic efficiency of 98.0±0.9 % at -0.70 V vs. RHE, and remains stable at 243.1±19.2 mA cm-2 with a C1 Faradaic efficiency of 99.0±0.5 % for 40 h at -0.55 V vs. RHE. DFT calculations indicate that the reconstructed Sn/SnOx interface facilitates formic acid production by optimizing binding of the reaction intermediate HCOO* while promotes Faradaic efficiency of C1 products by suppressing the competitive hydrogen evolution reaction, resulting in high Faradaic efficiency, current density, and stability of CO2 RR at low overpotentials.

4.
Artigo em Inglês | MEDLINE | ID: mdl-31960561

RESUMO

Despite significant progress achieved in Fischer-Tropsch synthesis (FTS) technology, the selectivity control remains a challenge in syngas conversion. Herein, we demonstrate that zinc ion-exchanged ZSM-5 steers syngas conversion toward ethane with a selectivity in hydrocarbons (excluding CO 2 ) reaching as high as 87% at 20% CO conversion. NMR spectroscopy, X-ray absorption spectroscopy and X-ray fluorescence indicate that the selective pathway toward ethane is likely attributed to the Zn sites grafted within the ZSM-5 pores. Quasi-in-situ solid state NMR detects C 2 species of acetyl [-COCH 3 ] bonding with an oxygen, ethyl [-CH 2 CH 3 ] bonding with a Zn site, and epoxyethane molecules adsorbing on a Zn site and a Brønsted acid site of the catalyst, respectively. These could provide some insights to C-C bond formation during ethane formation. Interestingly, this selective reaction pathway toward ethane appears to be general, because a series of other Zn 2+ ion-exchanged aluminosilicate zeolites with different topologies e.g. SSZ-13, MCM-22, ZSM-12 all give predominantly ethane. By contrast, a physical mixture of ZnO-ZSM-5 favors formation of hydrocarbons beyond C 3+ . These results provide an important guidance for tuning the product selectivity in syngas conversion.

6.
J Chem Phys ; 151(21): 214704, 2019 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-31822092

RESUMO

Under the oxidizing condition, the cheap metal component of bimetallic catalysts often segregates to the surface and forms oxide nanoclusters (NCs) supported on the metal surface, which exhibit unique structures and catalytic properties drastically different from the corresponding bulk materials. Here, density functional theory calculations are employed to describe the atomic and electronic structures of a series of triangular FeOx NCs confined on Pt(111) with the size ranging from ∼0.3 nm to ∼2.2 nm, which behave differently from the FeO film reported previously. The lattice of supported FeOx NCs on Pt(111) is found to vary not only with the NC size but also with the Fe/O ratio or the edge termination. Owing to a strong FeOx-Pt interaction, the heterogeneous distribution of local atomic and electronic structures of Fe across the FeOx NC is observed, though most of Fe atoms are positioned at the threefold hollow site of Pt(111). Our study not only sheds light on the catalytically active sites of supported FeOx NCs but also provides guidance for the design of highly active and stable oxide nanocatalysts under reactive environment.

7.
Adv Sci (Weinh) ; 6(23): 1902147, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31832329

RESUMO

With the relentless development of smart and miniaturized electronics, the worldwide thirst for microscale electrochemical energy storage devices with form factors is launching a new era of competition. Herein, the first prototype planar sodium-ion microcapacitors (NIMCs) are constructed based on the interdigital microelectrodes of urchin-like sodium titanate as faradaic anode and nanoporous activated graphene as non-faradaic cathode along with high-voltage ionogel electrolyte on a single flexible substrate. By effectively coupling with battery-type anode and capacitor-type cathode, the resultant all-solid-state NIMCs working at 3.5 V exhibit a high volumetric energy density of 37.1 mWh cm-3 and an ultralow self-discharge rate of 44 h from V max to 0.6 V max, both of which surpass most reported hybrid micro-supercapacitors. Through tuning graphene layer covered on the top surface of interdigital microelectrodes, the NIMCs unveil remarkably enhanced power density, owing to the establishment of favorable multidirectional fast ion diffusion pathways that significantly reduce the charge transfer resistance. Meanwhile, the as-fabricated NIMCs present excellent mechanical flexibility without capacitance fade under repeated deformation, and electrochemical stability at a high temperature of 80 °C because of using nonflammable ionogel electrolyte and in-plane geometry. Therefore, these flexible planar NIMCs with multidirectional ion diffusion pathways hold tremendous potential for microelectronics.

8.
J Am Chem Soc ; 141(45): 18318-18324, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31644275

RESUMO

A large amount of zeolite structures are still not synthetically available or not available in the form of aluminosilicate currently. Despite significant progress in the development of predictive concepts for zeolite synthesis, accessing some of these new materials is still challenging. One example is the IWR structure as well. Despite successful synthesis of Ge-based IWR zeolites, direct synthesis of aluminosilicate IWR zeolite is still not successful. In this report we show how a suitable organic structure directing agent (OSDA), through modeling of an OSDA/zeolite cage interaction, could access directly the aluminum-containing IWR structure (denoted as COE-6), which might allow access to new classes of materials and thus open opportunities in valuable chemical applications. The experimental results reveal that the COE-6 zeolites with a SiO2/Al2O3 ratio as low as 30 could be obtained. Very interestingly, the COE-6 zeolite has much higher hydrothermal and thermal stabilities than those of the conventional Ge-Al-IWR zeolite. In methanol-to-propylene (MTP) reaction, the COE-6 zeolite exhibits excellent selectivity for propylene, offering a potential catalyst for MTP reaction in the future.

9.
Adv Mater ; 31(50): e1902044, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31483546

RESUMO

High-performance uncooled photodetectors operating in the long-wavelength infrared and terahertz regimes are highly demanded in the military and civilian fields. Photothermoelectric (PTE) detectors, which combine photothermal and thermoelectric conversion processes, can realize ultra-broadband photodetection without the requirement of a cooling unit and external bias. In the last few decades, the responsivity and speed of PTE-based photodetectors have made impressive progress with the discovery of novel thermoelectric materials and the development of nanophotonics. In particular, by introducing hot-carrier transport into low-dimensional material-based PTE detectors, the response time has been successfully pushed down to the picosecond level. Furthermore, with the assistance of surface plasmon, antenna, and phonon absorption, the responsivity of PTE detectors can be significantly enhanced. Beyond the photodetection, PTE effect can also be utilized to probe exotic physical phenomena in spintronics and valleytronics. Herein, recent advances in PTE detectors are summarized, and some potential strategies to further improve the performance are proposed.

10.
Adv Mater ; 31(41): e1903470, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31441152

RESUMO

Simultaneously achieving high Faradaic efficiency, current density, and stability at low overpotentials is essential for industrial applications of electrochemical CO2 reduction reaction (CO2 RR). However, great challenges still remain in this catalytic process. Herein, a synergistic catalysis strategy is presented to improve CO2 RR performance by anchoring Fe-N sites with cobalt phthalocyanine (denoted as CoPc©Fe-N-C). The potential window of CO Faradaic efficiency above 90% is significantly broadened from 0.18 V over Fe-N-C alone to 0.71 V over CoPc©Fe-N-C while the onset potential of CO2 RR over both catalysts is as low as -0.13 V versus reversible hydrogen electrode. What is more, the maximum CO current density is increased ten times with significantly enhanced stability. Density functional theory calculations suggest that anchored cobalt phthalocyanine promotes the CO desorption and suppresses the competitive hydrogen evolution reaction over Fe-N sites, while the *COOH formation remains almost unchanged, thus demonstrating unprecedented synergistic effect toward CO2 RR.

11.
Adv Mater ; 31(50): e1901996, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31390100

RESUMO

The unique electronic and structural properties of 2D materials have triggered wide research interest in catalysis. The lattice of 2D materials and the interface between 2D covers and other substrates provide intriguing confinement environments for active sites, which has stimulated a rising area of "confinement catalysis with 2D materials." Fundamental understanding of confinement catalysis with 2D materials will favor the rational design of high-performance 2D nanocatalysts. Confinement catalysis with 2D materials has found extensive applications in energy-related reaction processes, especially in the conversion of small energy-related molecules such as O2 , CH4 , CO, CO2 , H2 O, and CH3 OH. Two representative strategies, i.e., 2D lattice-confined single atoms and 2D cover-confined metals, have been applied to construct 2D confinement catalytic systems with superior catalytic activity and stability. Herein, the recent advances in the design, applications, and structure-performance analysis of two 2D confinement catalytic systems are summarized. The different routes for tuning the electronic states of 2D confinement catalysts are highlighted and perspectives on confinement catalysis with 2D materials toward energy conversion and utilization in the future are provided.

12.
Angew Chem Int Ed Engl ; 58(45): 16043-16046, 2019 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-31468666

RESUMO

Oxidative dehydrogenation of ethane (ODE) is limited by the facile deep oxidation and potential safety hazards. Now, electrochemical ODE reaction is incorporated into the anode of a solid oxide electrolysis cell, utilizing the oxygen species generated at anode to catalytically convert ethane. By infiltrating γ-Al2 O3 onto the surface of La0.6 Sr0.4 Co0.2 Fe0.8 O3-δ -Sm0.2 Ce0.8 O2-δ (LSCF-SDC) anode, the ethylene selectivity reaches as high as 92.5 %, while the highest ethane conversion is up to 29.1 % at 600 °C with optimized current and ethane flow rate. Density functional theory calculations and in situ X-ray photoelectron spectroscopy characterizations reveal that the Al2 O3 /LSCF interfaces effectively reduce the amount of adsorbed oxygen species, leading to improved ethylene selectivity and stability, and that the formation of Al-O-Fe alters the electronic structure of interfacial Fe center with increased density of state around Fermi level and downshift of the empty band, which enhances ethane adsorption and conversion.

13.
Adv Mater ; 31(50): e1902033, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31282069

RESUMO

High-temperature CO2 electrolysis in solid-oxide electrolysis cells (SOECs) could greatly assist in the reduction of CO2 emissions by electrochemically converting CO2 to valuable fuels through effective electrothermal activation of the stable CO bond. If powered by renewable energy resources, it could also provide an advanced energy-storage method for their intermittent output. Compared to low-temperature electrochemical CO2 reduction, CO2 electrolysis in SOECs at high temperature exhibits higher current density and energy efficiency and has thus attracted much recent attention. The history of its development and its fundamental mechanisms, cathode materials, oxygen-ion-conducting electrolyte materials, and anode materials are highlighted. Electrode, electrolyte, and electrode-electrolyte interface degradation issues are comprehensively summarized. Fuel-assisted SOECs with low-cost fuels applied to the anode to decrease the overpotential and electricity consumption are introduced. Furthermore, the challenges and prospects for future research into high-temperature CO2 electrolysis in SOECs are included.

14.
Angew Chem Int Ed Engl ; 58(35): 12043-12048, 2019 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-31192496

RESUMO

Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO2 catalysts with porous Al2 O3 overlayers coated by atomic layer deposition (ALD). 27 Al magic angle spinning NMR analysis showed that Al2 O3 overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al3+ sites capable of strongly interacting with adjacent surface PdOx phases on supported Pd particles. Consequently, Al2 O3 -decorated Pd/SiO2 catalysts exhibit active and stable PdOx and Pd-PdOx structures to efficiently catalyze methane combustion between 200 and 850 °C. These results reveal the unique structural characteristics of Al2 O3 overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.

15.
Adv Mater ; 31(50): e1900583, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31222810

RESUMO

The rapid development and further modularization of miniaturized and self-powered electronic systems have substantially stimulated the urgent demand for microscale electrochemical energy storage devices, e.g., microbatteries (MBs) and micro-supercapacitors (MSCs). Recently, planar MBs and MSCs, composed of isolated thin-film microelectrodes with extremely short ionic diffusion path and free of separator on a single substrate, have become particularly attractive because they can be directly integrated with microelectronic devices on the same side of one single substrate to act as a standalone microsized power source or complement miniaturized energy-harvesting units. The development of and recent advances in planar MBs and MSCs from the fundamentals and design principle to the fabrication methods of 2D and 3D planar microdevices in both in-plane and stacked geometries are highlighted. Additonally, a comprehensive analysis of the primary aspects that eventually affect the performance metrics of microscale energy storage devices, such as electrode materials, electrolyte, device architecture, and microfabrication techniques are presented. The technical challenges and prospective solutions for high-energy-density planar MBs and MSCs with multifunctionalities are proposed.

16.
Angew Chem Int Ed Engl ; 58(22): 7400-7404, 2019 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-30945413

RESUMO

Despite significant efforts towards the direct conversion of syngas into liquid fuels, the selectivity remains a challenge, particularly with regard to high-quality gasoline with a high octane number and a low content of aromatic compounds. Herein, we show that zeolites with 1D ten-membered-ring (10-MR) channel structures such as SAPO-11 and ZSM-22 in combination with zinc- and manganese-based metal oxides (Zna Mnb Ox ) enable the selective synthesis of gasoline-range hydrocarbons C5 -C11 directly from syngas. The gasoline selectivity reached 76.7 % among hydrocarbons, with only 2.3 % CH4 at 20.3 % CO conversion. The ratio of isoparaffins to n-paraffins was as high as 15, and the research octane number was estimated to be 92. Furthermore, the content of aromatic compounds in the gasoline was as low as 16 %. The composition and structure of Zna Mnb Ox play an important role in determining the overall activity. This process constitutes a potential technology for the one-step synthesis of environmentally friendly gasoline with a high octane number from a variety of carbon resources via syngas.

17.
Nat Commun ; 10(1): 1340, 2019 03 22.
Artigo em Inglês | MEDLINE | ID: mdl-30902984

RESUMO

Geometric or electronic confinement of guests inside nanoporous hosts promises to deliver unusual catalytic or opto-electronic functionality from existing materials but is challenging to obtain particularly using metastable hosts, such as metal-organic frameworks (MOFs). Reagents (e.g. precursor) may be too large for impregnation and synthesis conditions may also destroy the hosts. Here we use thermodynamic Pourbaix diagrams (favorable redox and pH conditions) to describe a general method for metal-compound guest synthesis by rationally selecting reaction agents and conditions. Specifically we demonstrate a MOF-confined RuO2 catalyst (RuO2@MOF-808-P) with exceptionally high catalytic CO oxidation below 150 °C as compared to the conventionally made SiO2-supported RuO2 (RuO2/SiO2). This can be caused by weaker interactions between CO/O and the MOF-encapsulated RuO2 surface thus avoiding adsorption-induced catalytic surface passivation. We further describe applications of the Pourbaix-enabled guest synthesis (PEGS) strategy with tutorial examples for the general synthesis of arbitrary guests (e.g. metals, oxides, hydroxides, sulfides).

18.
Ultramicroscopy ; 200: 105-110, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30851711

RESUMO

Photoemission electron microscopy (PEEM) is a powerful surface technique for dynamic imaging of surface processes while PEEM studies have been performed under ultrahigh vacuum or high vacuum conditions. Here we report on a near ambient pressure PEEM (NAP-PEEM) instrument, which enables high resolution PEEM imaging in near ambient pressure (> 1 mbar) gases over a wide temperature range (150 - 1200 K). Installed with an electron gun near ambient pressure low energy electron microscopy (NAP-LEEM) can be achieved as well. The success of this new NAP-PEEM/LEEM instrument relies on the following key design concepts. First, a two-stage accelerating electric field consisting of a low field region between sample and intermediate electrode ("nozzle") and a high field between nozzle and objective lens. Second, a three-stage differential pumping system allowing a near ambient pressure atmosphere at the sample surface while ultrahigh vacuum maintained in the imaging lens systems. Third, a unique NAP cell with gas inlet/outlet, light illumination, sample cooling/heating, and precise sample positioning. The new technique will have important applications in surface catalysis, thin film growth, and energy conversion devices under nearly realistic working conditions.

19.
Angew Chem Int Ed Engl ; 58(14): 4617-4621, 2019 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-30737877

RESUMO

The oxygen evolution reaction (OER) is a sluggish electrocatalytic reaction in solid oxide electrolysis cells (SOECs) at high temperatures (600-850 °C). Perovskite oxide has been widely investigated for catalyzing the OER; however, the formation of cation-enriched secondary phases at the oxide/oxide interface blocks the active sites and decreases OER performance. Herein, we show that the Au/yttria-stabilized zirconia (YSZ) interface possesses much higher OER activity than the lanthanum strontium manganite/YSZ anode. Electrochemical characterization and density functional theory calculations suggest that the Au/YSZ interface provides a favorable path for OER by triggering interfacial oxygen spillover from the YSZ to the Au surface. In situ X-ray photoelectron spectroscopy results confirm the existence of spillover oxygen on the Au surface. This study demonstrates that the Au/YSZ interface possesses excellent catalytic activity for OER at high temperatures in SOECs.

20.
Phys Chem Chem Phys ; 21(6): 3287-3293, 2019 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-30681681

RESUMO

A comparative study of the adsorption and desorption processes of methanol in two kinds of nanochannels (i.e. MCM-41 and SWNTs) is performed by in situ continuous-flow laser-hyperpolarized 129Xe NMR. The high sensitivity and short acquisition time of hyperpolarized 129Xe allow for probing the molecular dynamics in a confined geometry under real working conditions. Hyperpolarized 129Xe NMR spectra indicate that the methanol adsorption behavior in nanochannels is determined by the characters of adsorption sites and that the methanol adsorption rate in the nanochannels of SWNTs is faster than in MCM-41. The experimental data shown in this work also indicate that there is a change in gas phase 129Xe NMR signal intensity during the adsorption and desorption of methanol in SWNTs. This may be because there is a strong depolarization of hyperpolarized 129Xe in SWNTs.

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