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1.
Nano Lett ; 2020 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-32048513

RESUMO

Pt-based alloy catalysts are promising candidates for fuel-cell applications, especially for cathodic oxygen reduction reaction (ORR) and anodic methanol oxidation reaction (MOR). The rational design of composition and morphology is crucial to promoting catalytic performances. Here, we report the synthesis of Pt-Co nanoframes via chemical etching of Co from solid rhombic dodecahedra. The obtained Pt-Co nanoframes exhibit excellent ORR mass activity in acidic electrolyte, which is as high as 0.40 A mgPt-1 initially and 0.34 A mgPt-1 after 10 000 potential cycles at 0.95 VRHE. Furthermore, their MOR mass activity in alkaline media is up to 4.28 A mgPt-1 and is 4-fold higher than that of commercial Pt/C catalyst. Experimental studies indicate that the weakened binding of intermediate carbonaceous poison contributes to the enhanced MOR behavior. More impressively, the Pt-Co nanoframes also demonstrate remarkable stability under long-term testing, which could be attributed to the negligible electrochemical Co dissolution.

2.
Chem Rev ; 120(2): 1184-1249, 2020 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-31580651

RESUMO

The surface and interfaces of heterogeneous catalysts are essential to their performance as they are often considered to be active sites for catalytic reactions. With the development of nanoscience, the ability to tune surface and interface of nanostructures has provided a versatile tool for the development and optimization of a heterogeneous catalyst. In this Review, we present the surface and interface control of nanoparticle catalysts in the context of oxygen reduction reaction (ORR), electrochemical CO2 reduction reaction (CO2 RR), and tandem catalysis in three sections. In the first section, we start with the activity of ORR on the nanoscale surface and then focus on the approaches to optimize the performance of Pt-based catalyst including using alloying, core-shell structure, and high surface area open structures. In the section of CO2 RR, where the surface composition of the catalysts plays a dominant role, we cover its reaction fundamentals and the performance of different nanosized metal catalysts. For tandem catalysis, where adjacent catalytic interfaces in a single nanostructure catalyze sequential reactions, we describe its concept and principle, catalyst synthesis methodology, and application in different reactions.

3.
Nano Lett ; 19(8): 5431-5436, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31287958

RESUMO

Direct methanol/ethanol alkaline fuel cells (DMAFCs/DEAFCs) represent an attractive mobile power generation technology. The methanol/ethanol oxidation reaction (MOR/EOR) often requires high-performance yet expensive Pt-based catalysts that may be easily poisoned. Herein, we report the development of PtCuNi tetrahedra electrocatalysts with optimized specific activity and mass activity for MOR and EOR. Our synthetic and structural characterizations show that these PtCuNi tetrahedra have Cu-rich core and PtNi-rich shell with tunable surface composition. Electrocatalytic studies demonstrate that Pt56Cu28Ni16 exhibits exceptional MOR and EOR specific activities of 14.0 ± 1.0 mA/cm2 and 11.2 ± 1.0 mA/cm2, respectively and record high mass activity of 7.0 ± 0.5 A/mgPt and 5.6 ± 0.6 A/mgPt, comparing favorably with the best MOR or EOR Pt alloy-based catalysts reported to date. Furthermore, we show that the unique core-shell tetrahedra configuration can also lead to considerably improved durability.

4.
Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi ; 32(11): 1421-1428, 2018 Nov 01.
Artigo em Chinês | MEDLINE | ID: mdl-30417618

RESUMO

Objective: To investigate the possibility of mitochondria-dependent apoptosis as a mechanism of early steroid-induced avascular necrosis of femoral head (SANFH) in rats and vitamin E as a possible prevention strategy. Methods: Seventy-two male Sprague Dawley rats were randomly divided into control group, model group, and intervention group, with 24 rats in each group. The rats in control group were not treated as normal control. The rats in model group and intervention group were established early SANFH models by lipopolysaccharide combined with methylprednisolone injection. At the same time, the rats in intervention group were injected with vitamin E (40 mg/kg) every day for 7 days. At 2, 4, and 8 weeks after the final injection, the bilateral femoral heads were harvested and observed by HE staining, TUNEL assay, immunohistochemical staining, and Western blot. The rate of empty lacunae, apoptotic index, and the expressions of Caspase-9, Caspase-3, and cytochrome-c (Cyt-c) proteins were calculated. Results: According to histological staining, there were significant differences in the rate of empty lacunae between intervention group and control group at 8 weeks ( P<0.05) and between intervention group and model group at 4 and 8 weeks ( P<0.05). The apoptotic index of intervention group was significantly lower than that of model group at each time point ( P<0.05). And there was significant difference between the intervention group and the control group at 8 weeks ( P<0.05). According to immunohistochemistry staining and Western blot, the expressions of Cyt-c, Caspase-9, and Caspase-3 all significantly decreased in intervention group than those in model group at each time point ( P<0.05); and the differences were significant between intervention group and control group at 8 weeks ( P<0.05). Conclusion: Vitamin E can delay the progression of early SANFH by reducing mitochondrial dependent osteocyte apoptosis.


Assuntos
Necrose da Cabeça do Fêmur , Vitamina E , Vitaminas , Animais , Apoptose , Modelos Animais de Doenças , Cabeça do Fêmur , Necrose da Cabeça do Fêmur/induzido quimicamente , Necrose da Cabeça do Fêmur/tratamento farmacológico , Glucocorticoides/efeitos adversos , Masculino , Metilprednisolona/efeitos adversos , Distribuição Aleatória , Ratos , Ratos Sprague-Dawley , Vitamina E/farmacologia , Vitaminas/farmacologia
5.
Nature ; 562(7726): 254-258, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-30283139

RESUMO

Two-dimensional (2D) materials, consisting of atomically thin crystal layers bound by the van der Waals force, have attracted much interest because of their potential in diverse technologies, including electronics, optoelectronics and catalysis1-10. In particular, solution-processable 2D semiconductor (such as MoS2) nanosheets are attractive building blocks for large-area thin-film electronics. In contrast to conventional zero- and one-dimensional nanostructures (quantum dots and nanowires, respectively), which are typically plagued by surface dangling bonds and associated trapping states, 2D nanosheets have dangling-bond-free surfaces. Thin films created by stacking multiple nanosheets have atomically clean van der Waals interfaces and thus promise excellent charge transport11-15. However, preparing high-quality solution-processable 2D semiconductor nanosheets remains a challenge. For example, MoS2 nanosheets and thin films produced using lithium intercalation and exfoliation are plagued by the presence of the metallic 1T phase and poor electrical performance (mobilities of about 0.3 square centimetres per volt per second and on/off ratios of less than 10)2,12, and materials produced by liquid exfoliation exhibit an intrinsically broad thickness distribution, which leads to poor film quality and unsatisfactory thin-film electrical performance (mobilities of about 0.4 square centimetres per volt per second and on/off ratios of about 100)14,16,17. Here we report a general approach to preparing highly uniform, solution-processable, phase-pure semiconducting nanosheets, which involves the electrochemical intercalation of quaternary ammonium molecules (such as tetraheptylammonium bromide) into 2D crystals, followed by a mild sonication and exfoliation process. By precisely controlling the intercalation chemistry, we obtained phase-pure, semiconducting 2H-MoS2 nanosheets with a narrow thickness distribution. These nanosheets were then further processed into high-performance thin-film transistors, with room-temperature mobilities of about 10 square centimetres per volt per second and on/off ratios of 106 that greatly exceed those obtained for previous solution-processed MoS2 thin-film transistors. The scalable fabrication of large-area arrays of thin-film transistors enabled the construction of functional logic gates and computational circuits, including an inverter, NAND, NOR, AND and XOR gates, and a logic half-adder. We also applied our approach to other 2D materials, including WSe2, Bi2Se3, NbSe2, In2Se3, Sb2Te3 and black phosphorus, demonstrating its potential for generating versatile solution-processable 2D materials.

6.
ACS Nano ; 12(8): 8697-8705, 2018 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-30028589

RESUMO

Pt-based alloys have shown great promise as cathodic catalysts for cost-effective proton-exchange membrane fuel cells. Post-synthesis treatment has been recognized as a critical step to improve the catalytic performance of Pt-based alloys. Here, we present the effects of catalyst processing on the catalytic behavior of Pt-Ni nanoframe electrocatalysts in oxygen reduction reaction. The Pt-Ni nanoframes were made by corroding the Ni-rich phase from solid rhombic dodecahedral particles. A total of three different corrosion procedures were compared. Among them, electrochemical corrosion led to the highest initial specific activity (1.35 mA cm-2 at 0.95 V versus reversible hydrogen electrode) by retaining more Ni in the nanoframes. However, the high activity gradually went down in a subsequent stability test due to continuous Ni loss and concomitant surface reconstruction. On the other hand, the best stability was achieved by a more-aggressive corrosion using oxidative nitric acid. Although the initial activity was compromised, this procedure imparted a less-defective surface, and thus, the specific activity dropped by only 7% over 30 000 potential cycles. These results indicate a delicate trade-off between the activity and stability of Pt-Ni nanoframe electrocatalysts. The obtained understanding of how to balance the activity-stability trade-off via catalyst processing can be generalized to other Pt-based alloys.

7.
ACS Cent Sci ; 4(5): 590-599, 2018 May 23.
Artigo em Inglês | MEDLINE | ID: mdl-29806005

RESUMO

The development of future sustainable energy technologies relies critically on our understanding of electrocatalytic reactions occurring at the electrode-electrolyte interfaces, and the identification of key reaction promoters and inhibitors. Here we present a systematic in situ nanoelectronic measurement of anionic surface adsorptions (sulfates, halides, and cyanides) on ultrathin platinum nanowires during active electrochemical processes, probing their competitive adsorption behavior with oxygenated species and correlating them to the electrokinetics of the oxygen reduction reaction (ORR). The competitive anionic adsorption features obtained from our studies provide fundamental insight into the surface poisoning of Pt-catalyzed ORR kinetics by various anionic species. Particularly, the unique nanoelectronic approach enables highly sensitive characterization of anionic adsorption and opens an efficient pathway to address the practical poisoning issue (at trace level contaminations) from a fundamental perspective. Through the identified nanoelectronic indicators, we further demonstrate that rationally designed competitive anionic adsorption may provide improved poisoning resistance, leading to performance (activity and lifetime) enhancement of energy conversion devices.

8.
Nano Lett ; 18(2): 798-804, 2018 02 14.
Artigo em Inglês | MEDLINE | ID: mdl-29272136

RESUMO

Doping with a transition metal was recently shown to greatly boost the activity and durability of PtNi/C octahedral nanoparticles (NPs) for the oxygen reduction reaction (ORR), but its specific roles remain unclear. By combining electrochemistry, ex situ and in situ spectroscopic techniques, density functional theory calculations, and a newly developed kinetic Monte Carlo model, we showed that Mo atoms are preferentially located on the vertex and edge sites of Mo-PtNi/C in the form of oxides, which are stable within the wide potential window of the electrochemical cycle. These surface Mo oxides stabilize adjacent Pt sites, hereby stabilizing the octahedral shape enriched with (111) facets, and lead to increased concentration of Ni in subsurface layers where they are protected against acid dissolution. Consequently, the favorable Pt3Ni(111) structure for the ORR is stabilized on the surface of PtNi/C NPs in acid against voltage cycling. Significantly, the unusual potential-dependent oxygen coverage trend on Mo-doped PtNi/C NPs as revealed by the surface-sensitive Δµ analysis suggests that the Mo dopants may also improve the ORR kinetics by modifying the coordination environments of Pt atoms on the surface. Our studies point out a possible way to stabilize the favorable shape and composition established on conceptual catalytic models in practical nanoscale catalysts.

9.
Science ; 356(6338): 599-604, 2017 05 12.
Artigo em Inglês | MEDLINE | ID: mdl-28495745

RESUMO

Nanostructured materials have shown extraordinary promise for electrochemical energy storage but are usually limited to electrodes with rather low mass loading (~1 milligram per square centimeter) because of the increasing ion diffusion limitations in thicker electrodes. We report the design of a three-dimensional (3D) holey-graphene/niobia (Nb2O5) composite for ultrahigh-rate energy storage at practical levels of mass loading (>10 milligrams per square centimeter). The highly interconnected graphene network in the 3D architecture provides excellent electron transport properties, and its hierarchical porous structure facilitates rapid ion transport. By systematically tailoring the porosity in the holey graphene backbone, charge transport in the composite architecture is optimized to deliver high areal capacity and high-rate capability at high mass loading, which represents a critical step forward toward practical applications.

10.
Science ; 354(6318): 1414-1419, 2016 12 16.
Artigo em Inglês | MEDLINE | ID: mdl-27856847

RESUMO

Improving the platinum (Pt) mass activity for the oxygen reduction reaction (ORR) requires optimization of both the specific activity and the electrochemically active surface area (ECSA). We found that solution-synthesized Pt/NiO core/shell nanowires can be converted into PtNi alloy nanowires through a thermal annealing process and then transformed into jagged Pt nanowires via electrochemical dealloying. The jagged nanowires exhibit an ECSA of 118 square meters per gram of Pt and a specific activity of 11.5 milliamperes per square centimeter for ORR (at 0.9 volts versus reversible hydrogen electrode), yielding a mass activity of 13.6 amperes per milligram of Pt, nearly double previously reported best values. Reactive molecular dynamics simulations suggest that highly stressed, undercoordinated rhombus-rich surface configurations of the jagged nanowires enhance ORR activity versus more relaxed surfaces.

11.
Chem Commun (Camb) ; 52(75): 11215-11218, 2016 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-27722573

RESUMO

Herein, we report a one-step synthesis method for octahedral Pt-Ni-Co ternary catalysts with tunable compositions and fixed shapes. Impressively, the composition optimized octahedral PtNi0.55Co0.1/C demonstrated a significant improvement in ORR activity compared to those of previously reported Pt-Ni-Co alloy octahedra, showing an outstanding specific activity of 5.05 mA cm-2 and a mass activity of 2.80 mA µgPt-1, which are around 20.2 times and 14.7 times higher than those of the commercial Pt/C catalyst (0.25 mA cm-2 and 0.19 mA µgPt-1).

12.
ACS Appl Mater Interfaces ; 8(40): 26769-26774, 2016 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-27635786

RESUMO

An efficient non-noble metal catalyst for the oxygen reduction reaction (ORR) is of great importance for the fabrication of cost-effective fuel cells. Nitrogen-doped carbons with various transition metal co-dopants have emerged as attractive candidates to replace the expensive platinum catalysts. Here we report the preparation of various copper- and nitrogen-doped carbon materials as highly efficient ORR catalysts by pyrolyzing porphyrin based metal organic frameworks and investigate the effects of air impurities during the thermal carbonization process. Our results indicate that the introduction of air impurities can significantly improve ORR activity in nitrogen-doped carbon and the addition of copper co-dopant further enhances the ORR activity to exceed that of platinum. Systematic structural characterization and electrochemical studies demonstrate that the air-impurity-treated samples show considerably higher surface area and electron transfer numbers, suggesting that the partial etching of the carbon by air leads to increased porosity and accessibility to highly active ORR sites. Our study represents the first example of using air or oxygen impurities to tailor the ORR activity of metal and nitrogen co-doped carbon materials and open up a new avenue to engineer the catalytic activity of these materials.

13.
J Am Chem Soc ; 137(50): 15672-5, 2015 Dec 23.
Artigo em Inglês | MEDLINE | ID: mdl-26636882

RESUMO

We have developed an efficient strategy for the production of stable ß-palladium hydride (PdH0.43) nanocrystals with controllable shapes and remarkable stability. The as-synthesized PdH0.43 nanocrystals showed impressive stability in air at room temperature for over 10 months, which has enabled the investigation of their catalytic property for the first time. The prepared PdH0.43 nanocrystals served as highly efficient catalysts in the oxidation of methanol, showing higher activity than their Pd counterparts. These studies opened a door for further exploration of ß-palladium hydride-based nanomaterials as a new class of promising catalytic materials and beyond.

14.
Science ; 348(6240): 1230-4, 2015 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-26068847

RESUMO

Bimetallic platinum-nickel (Pt-Ni) nanostructures represent an emerging class of electrocatalysts for oxygen reduction reaction (ORR) in fuel cells, but practical applications have been limited by catalytic activity and durability. We surface-doped Pt3Ni octahedra supported on carbon with transition metals, termed M-Pt3Ni/C, where M is vanadium, chromium, manganese, iron, cobalt, molybdenum (Mo), tungsten, or rhenium. The Mo-Pt3Ni/C showed the best ORR performance, with a specific activity of 10.3 mA/cm(2) and mass activity of 6.98 A/mg(Pt), which are 81- and 73-fold enhancements compared with the commercial Pt/C catalyst (0.127 mA/cm(2) and 0.096 A/mg(Pt)). Theoretical calculations suggest that Mo prefers subsurface positions near the particle edges in vacuum and surface vertex/edge sites in oxidizing conditions, where it enhances both the performance and the stability of the Pt3Ni catalyst.

15.
Nano Lett ; 14(7): 3887-94, 2014 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-24873775

RESUMO

Structural defects/grain boundaries in metallic materials can exhibit unusual chemical reactivity and play important roles in catalysis. Bulk polycrystalline materials possess many structural defects, which is, however, usually inaccessible to solution reactants and hardly useful for practical catalytic reactions. Typical metallic nanocrystals usually exhibit well-defined crystalline structure with few defects/grain boundaries. Here, we report the design of ultrafine wavy nanowires (WNWs) with a high density of accessible structural defects/grain boundaries as highly active catalytic hot spots. We show that rhodium WNWs can be readily synthesized with controllable number of structural defects and demonstrate the number of structural defects can fundamentally determine their catalytic activity in selective oxidation of benzyl alcohol by O2, with the catalytic activity increasing with the number of structural defects. X-ray photoelectron spectroscopy (XPS) and cyclic voltammograms (CVs) studies demonstrate that the structural defects can significantly alter the chemical state of the Rh WNWs to modulate their catalytic activity. Lastly, our systematic studies further demonstrate that the concept of defect engineering in WNWs for improved catalytic performance is general and can be readily extended to other similar systems, including palladium and iridium WNWs.

16.
Chem Commun (Camb) ; 47(13): 4019-21, 2011 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-21347472

RESUMO

Nanocomposites composed of nanoparticles of iron oxide and aluminium oxide (Fe(2)O(3)-Al(2)O(3)) with a unique structure show a remarkable catalytic performance in Fischer-Tropsch synthesis (FTS), compared with the traditional iron-based catalyst.


Assuntos
Óxido de Alumínio/química , Compostos Férricos/química , Nanopartículas/química , Catálise
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