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1.
ACS Appl Mater Interfaces ; 14(6): 7731-7740, 2022 Feb 16.
Artigo em Inglês | MEDLINE | ID: mdl-35128928

RESUMO

Electrochemical CO2 reduction (ECR) promises the replacement of fossil fuels as the source of feedstock chemicals and seasonal storage of renewable energy. While much progress has been made in catalyst development and electrochemical reactor design, few studies have addressed the effect of catalyst integration on device performance. Using a microfluidic gas diffusion electrolyzer, we systematically studied the effect of thickness and the morphology of electron beam (EB) and magnetron-sputtered (MS) Cu catalyst coatings on ECR performance. We observed that EB-Cu outperforms MS-Cu in current density, selectivity, and energy efficiency, with 400 nm thick catalyst coatings performing the best. The superior performance of EB-Cu catalysts is assigned to their faceted surface morphology and sharper Cu/gas diffusion layer interface, which increases their hydrophobicity. Tests in a large-scale zero-gap electrolyzer yielded similar product selectivity distributions with an ethylene Faradaic efficiency of 39% at 200 mA/cm2, demonstrating the scalability for industrial ECR applications.

2.
J Chem Phys ; 155(11): 114702, 2021 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-34551531

RESUMO

Cu-based catalysts currently offer the most promising route to actively and selectively produce value-added chemicals via electrochemical reduction of CO2 (eCO2R); yet further improvements are required for their wide-scale deployment in carbon mitigation efforts. Here, we systematically investigate a family of dilute Cu-based alloys to explore their viability as active and selective catalysts for eCO2R through a combined theoretical-experimental approach. Using a quantum-classical modeling approach that accounts for dynamic solvation effects, we assess the stability and activity of model single-atom catalysts under eCO2R conditions. Our calculations identify that the presence of eCO2R intermediates, such as CO*, H*, and OH*, may dynamically influence the local catalyst surface composition. Additionally, we identify through binding energy descriptors of the CO*, CHO*, and OCCO* dimer intermediates that certain elements, such as group 13 elements (B, Al, and Ga), enhance the selectivity of C2+ species relative to pure Cu by facilitating CO dimerization. The theoretical work is corroborated by preliminary testing of eCO2R activity and selectivity of candidate dilute Cu-based alloy catalyst films prepared by electron beam evaporation in a zero-gap gas diffusion electrode-based reactor. Of all studied alloys, dilute CuAl was found to be the most active and selective toward C2+ products like ethylene, consistent with the theoretical predictions. We attribute the improved performance of dilute CuAl alloys to more favorable dimerization reaction energetics of bound CO species relative to that on pure Cu. In a broader context, the results presented here demonstrate the power of our simulation framework in terms of rational catalyst design.

3.
ACS Appl Mater Interfaces ; 9(38): 32424-32429, 2017 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-28901138

RESUMO

Previously, the solution-based cation exchange reaction has been extensively studied for the synthesis of the complex heteroepitaxial nanocolloidals. Here, we demonstrated that the strain induced selective phase segregation technique can also be applied to large size nanowires in a well-studied CdS/Cu2S system, leading to the formation of superlattice nanowire structure with a simple solution-based cation exchange reaction. This structural evolution is driven by the distinct interface formation energy at different CdS facets as indicated by ab initio calculation. Because of the energy filtering effect, the superlattice nanowire shows an enhanced thermopower without significant decrease of the electrical conductivity. This study provides a promising low-cost solution process to produce superlattice nanostructures for practical thermoelectric applications.

4.
Sci Rep ; 7(1): 8323, 2017 08 16.
Artigo em Inglês | MEDLINE | ID: mdl-28814808

RESUMO

Electronic properties of two-dimensional (2D) MoS2 semiconductors can be modulated by introducing specific defects. One important type of defect in 2D layered materials is known as rotational stacking fault (RSF), but the coexistence of multiple RSFs with different rotational angles was not directly observed in freestanding 2D MoS2 before. In this report, we demonstrate the coexistence of three RSFs with three different rotational angles in a freestanding bilayer MoS2 sheet as directly observed using an aberration-corrected transmission electron microscope (TEM). Our analyses show that these RSFs originate from cracks and dislocations within the bilayer MoS2. First-principles calculations indicate that RSFs with different rotational angles change the electronic structures of bilayer MoS2 and produce two new symmetries in their bandgaps and offset crystal momentums. Therefore, employing RSFs and their coexistence is a promising route in defect engineering of MoS2 to fabricate suitable devices for electronics, optoelectronics, and energy conversion.

5.
Nanoscale ; 9(35): 12830-12834, 2017 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-28702619

RESUMO

By utilizing the interaction between inorganic species and organic surfactants, the ordered layered mesostructures were generated for the synthesis of the one-dimensional oxide nanomaterials. The oxide nanomaterial products which evolved from the above layered structures were demonstrated as ultrathin (less than 2 nm) one-dimensional structures with superior catalytic performance. The synthetic method based on layered structures can be extended to prepare other one-dimensional oxide nanomaterials with the same ultrathin structures.

6.
Nanoscale ; 8(48): 19994-20000, 2016 Dec 08.
Artigo em Inglês | MEDLINE | ID: mdl-27858031

RESUMO

A rational integration of 1D metallic nanotubes and oxide nanoparticles has been demonstrated as a viable strategy for the production of both highly stable and efficient anodes for lithium ion batteries. We encapsulated copper oxide (CuO) nanoparticles in ultra-long metallic copper nanotubes with engineered interspaces, and explored their electrochemical properties. Such a hierarchical architecture provides three important features: (i) a continuous nanoscale metallic Cu shell to minimize electronic/ionic transmitting impedance; (ii) a unique quasi-one-dimensional structure with a large aspect ratio to reduce self-aggregation; (iii) free space for volume expansion of CuO nanoparticles and stable solid-electrolyte interphase (SEI) formation. The anode materials with such hierarchical structures have high specific capacity (around 600 mA h g-1 at a current density of 0.1 A g-1), excellent cycling stability (over 94% capacity retention after 200 cycles) and superb reversible capacity of 175 mA h g-1 at a high charging rate of 15 A g-1.

7.
ACS Appl Mater Interfaces ; 7(30): 16802-12, 2015 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-26186078

RESUMO

Electrode design in nanoscale is expected to contribute significantly in constructing an enhanced electrochemical platform for a superb sensor. In this work, we present a facile synthesis of new fashioned heteronanostructure that is composed of one-dimensional Cu nanowires (NWs) and epitaxially grown two-dimensional Cu2O nanosheets (NSs). This hierarchical architecture is quite attractive in molecules detection for three unique characteristics: (1) the three-dimensional hierarchical architecture provides large specific surface areas for more active catalytic sites and easy accessibility for the target molecules; (2) the high-quality heterojunction with minimal lattice mismatch between the built-in current collector (Cu core) and active medium (Cu2O shell) considerably promotes the electron transport; (3) the adequate free space between branches and anisotropic NWs can accommodate a large volume change to avoid collapse or distortion during the reduplicative operation processes under applied potentials. The above three proposed advantages have been addressed in the fabricated Cu@Cu2O NS-NW-based superb glucose sensors, where a successful integration of ultrahigh sensitivity (1420 µA mM(-1) cm(-2)), low limit of detection (40 nM), and fast response (within 0.1 s) has been realized. Furthermore, the durability and reproducibility of such devices made by branched core-shell nanowires were investigated to prove viability of the proposed structures. This achievement in current work demonstrates an innovative strategy for nanoscale electrode design and application in molecular detection.


Assuntos
Técnicas Biossensoriais/instrumentação , Condutometria/instrumentação , Glucose/análise , Nanopartículas Metálicas/química , Microeletrodos , Nanofios/química , Cobre/química , Desenho de Equipamento , Análise de Falha de Equipamento , Glucose/química , Nanopartículas Metálicas/ultraestrutura , Nanofios/ultraestrutura , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
8.
Chemistry ; 20(36): 11439-44, 2014 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-25059762

RESUMO

Fluorine-doped hierarchical porous single-crystal rutile TiO(2) nanorods have been synthesized through a silica template method, in which F(-) ions acts as both n-type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F-doped porous single crystals displays a remarkably enhanced solar-to-hydrogen conversion efficiency (≈0.35 % at -0.33 V vs. Ag/AgCl) under 100 mW cm(-2) of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO(2) single crystals.


Assuntos
Flúor/química , Nanotubos/química , Titânio/química , Água/química , Cristalização , Técnicas Eletroquímicas , Nanotubos/ultraestrutura , Fotólise , Porosidade
9.
Science ; 343(6177): 1339-43, 2014 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-24578531

RESUMO

Control of structure at the atomic level can precisely and effectively tune catalytic properties of materials, enabling enhancement in both activity and durability. We synthesized a highly active and durable class of electrocatalysts by exploiting the structural evolution of platinum-nickel (Pt-Ni) bimetallic nanocrystals. The starting material, crystalline PtNi3 polyhedra, transforms in solution by interior erosion into Pt3Ni nanoframes with surfaces that offer three-dimensional molecular accessibility. The edges of the Pt-rich PtNi3 polyhedra are maintained in the final Pt3Ni nanoframes. Both the interior and exterior catalytic surfaces of this open-framework structure are composed of the nanosegregated Pt-skin structure, which exhibits enhanced oxygen reduction reaction (ORR) activity. The Pt3Ni nanoframe catalysts achieved a factor of 36 enhancement in mass activity and a factor of 22 enhancement in specific activity, respectively, for this reaction (relative to state-of-the-art platinum-carbon catalysts) during prolonged exposure to reaction conditions.

10.
ACS Appl Mater Interfaces ; 6(3): 2118-24, 2014 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-24409807

RESUMO

The preparation of nitrogen-doped TiO2/graphene nanohybrids and their application as counter electrode for dye-sensitized solar cell (DSSC) are presented. These nanohybrids are prepared by self-assembly of pyrene modified H2Ti3O7 nanosheets and graphene in aqueous medium via π-π stacking interactions, followed by thermal calcination at different temperatures in ammonia atmosphere to afford nitrogen-doped TiO2/graphene nanohybrids. H2Ti3O7 nanosheets were synthesized from TiOSO4·xH2O by a hydrothermal reaction at 150 °C for 48 h. The microstructure of the obtained mixed-phase nanohybrids was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transforms infrared spectroscopy (FTIR). Moreover, the performances of the as-prepared nanohybrids as counter electrode materials for DSSC was investigated, and the results indicated that the nanohybrids prepared at higher nitridation temperature would lead to higher short-circuit current density than those prepared at lower nitridation temperature, indicating that it can be utilized as a low-cost alternative to Pt for DSSCs and other applications.

11.
Nanoscale ; 6(1): 195-8, 2014 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-24241480

RESUMO

Hierarchical branched Cu2O nanowires were synthesized under mild conditions and exhibit remarkable performance for photocatalytic H2 generation from water. The obtained results open appealing perspectives for converting solar energy into storable chemical energy.


Assuntos
Cobre/química , Hidrogênio/química , Nanoestruturas/química , Nanofios/química , Catálise , Luz , Oxirredução , Energia Solar , Água/química
12.
Nat Nanotechnol ; 6(9): 568-72, 2011 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-21857684

RESUMO

Semiconductor nanowires are promising for photovoltaic applications, but, so far, nanowire-based solar cells have had lower efficiencies than planar cells made from the same materials, even allowing for the generally lower light absorption of nanowires. It is not clear, therefore, if the benefits of the nanowire structure, including better charge collection and transport and the possibility of enhanced absorption through light trapping, can outweigh the reductions in performance caused by recombination at the surface of the nanowires and at p-n junctions. Here, we fabricate core-shell nanowire solar cells with open-circuit voltage and fill factor values superior to those reported for equivalent planar cells, and an energy conversion efficiency of ∼5.4%, which is comparable to that of equivalent planar cells despite low light absorption levels. The device is made using a low-temperature solution-based cation exchange reaction that creates a heteroepitaxial junction between a single-crystalline CdS core and single-crystalline Cu2S shell. We integrate multiple cells on single nanowires in both series and parallel configurations for high output voltages and currents, respectively. The ability to produce efficient nanowire-based solar cells with a solution-based process and Earth-abundant elements could significantly reduce fabrication costs relative to existing high-temperature bulk material approaches.

13.
Nat Chem ; 3(5): 372-6, 2011 May.
Artigo em Inglês | MEDLINE | ID: mdl-21505495

RESUMO

Supported catalysts are widely used in industry and can be optimized by tuning the composition and interface of the metal nanoparticles and oxide supports. Rational design of metal-metal oxide interfaces in nanostructured catalysts is critical to achieve better reaction activities and selectivities. We introduce here a new class of nanocrystal tandem catalysts that have multiple metal-metal oxide interfaces for the catalysis of sequential reactions. We utilized a nanocrystal bilayer structure formed by assembling platinum and cerium oxide nanocube monolayers of less than 10 nm on a silica substrate. The two distinct metal-metal oxide interfaces, CeO(2)-Pt and Pt-SiO(2), can be used to catalyse two distinct sequential reactions. The CeO(2)-Pt interface catalysed methanol decomposition to produce CO and H(2), which were subsequently used for ethylene hydroformylation catalysed by the nearby Pt-SiO(2) interface. Consequently, propanal was produced selectively from methanol and ethylene on the nanocrystal bilayer tandem catalyst. This new concept of nanocrystal tandem catalysis represents a powerful approach towards designing high-performance, multifunctional nanostructured catalysts.


Assuntos
Nanopartículas , Catálise , Cério/química , Microscopia Eletrônica de Transmissão , Platina/química , Dióxido de Silício/química
14.
Nano Lett ; 10(10): 4279-83, 2010 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-20839780

RESUMO

This work investigated the thermoelectric properties of thin silicon membranes that have been decorated with high density of nanoscopic holes. These "holey silicon" (HS) structures were fabricated by either nanosphere or block-copolymer lithography, both of which are scalable for practical device application. By reducing the pitch of the hexagonal holey pattern down to 55 nm with 35% porosity, the thermal conductivity of HS is consistently reduced by 2 orders of magnitude and approaches the amorphous limit. With a ZT value of ∼0.4 at room temperature, the thermoelectric performance of HS is comparable with the best value recorded in silicon nanowire system.

15.
Angew Chem Int Ed Engl ; 48(26): 4816-9, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-19472253

RESUMO

The music of the spheres: Transition-metal phosphate colloidal spheres with one metal (Mn, Fe, Co, Ni, and Cu; see picture) or more than one metal (such as Fe-Ni, Co-Cu, Fe-Co-Cu, Fe-Co-Ni-Cu, Mn-Fe-Co-Ni-Cu, and Mn-Fe-Co-Ni-Cu-Zn) were synthesized in solution at low temperature. Porous and hollow iron phosphate spheres were prepared by adjusting the pH value of the reaction.


Assuntos
Metais/química , Fosfatos/química , Elementos de Transição/química , Coloides , Concentração de Íons de Hidrogênio , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Tamanho da Partícula
16.
Nano Lett ; 9(3): 1260-4, 2009 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-19206219

RESUMO

Sub-2-nm (down to one-unit cell) uniform oxide nanocrystals and highly ordered superstructures were obtained in one step using oleylamine and oleic acid as capping and structure directing agents. The cooperative nature of the nanocrystal growth and assembly resulted in mesoscopic one-dimensional ribbon-like superstructures made of these ultrathin nanocrystals. The process reported here is general and can be readily extended to the production of many other transition metal (TiO2, ZnO, Nb2O5) and rare earth oxide (Eu2O3, Sm2O3, Er2O3, Y2O3, Tb2O3, and Yb2O3) systems.

17.
Chem Commun (Camb) ; (32): 3741-3, 2008 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-18685762

RESUMO

Monodisperse CeO(2) nanocrystals and superlattice-like colloidal particles have been successfully synthesized in ethanol-water mixed solvent by adopting a one-pot approach using icosahedral (NH(4))(2)Ce(NO(3))(6) as precursor.

18.
Nano Lett ; 8(7): 2041-4, 2008 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-18537294

RESUMO

Ultrathin single crystal Au nanowires with diameter of approximately 1.6 nm and length of few micrometers were synthesized with high yield by simply mixing HAuCl 4 and oleylamine at room temperature. High resolution transmission electron microscopy studies revealed that all of these nanowires are single crystalline and grew along the [111] direction. The valency evolution of the gold species during the synthesis was studied by X-ray photoelectron spectroscopy, which showed a clear Au (3+) --> Au (+) --> Au stepwise reduction at different reaction stages. Small angle X-ray scattering and small-angle X-ray diffraction suggest mesostructure formation upon HAuCl 4 and oleylamine mixing. The slow in situ reduction of this mesostructure leads to the formation of ultrathin nanowires in solution. This novel nanowire growth mechanism relies on cooperative interaction, organization, and reaction between inorganic precursor salts and oleylamine.

19.
Inorg Chem ; 47(2): 543-7, 2008 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-18088117

RESUMO

In this paper, a description of the process by which two kinds of surfactants with relative long or short alkyl chains are introduced onto the surface of Ag nanocrystals, which contribute to the formation of tunable and anisotropic "covalent bonds" between two Ag nanocrystals, is given. By altering the lengths of the short alkyl chains, the sizes and structures of the as-obtained supercrystals as well as the exposed crystal planes of the interior nanocrystals can be tuned. This strategy may further enrich the "chemical bond" categories of artificial atoms and serve as the base for the discovery of more functional superstructures.

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