首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
This paper reviews new approaches to size‐controlled silicon‐nanocrystal synthesis. These approaches allow narrowing of the size distribution of the nanocrystals compared with those obtained by conventional synthesis processes such as ion implantation into SiO2 or phase separation of sub‐stoichiometric SiOx layers. This size control is realized by different approaches to introducing a superlattice‐like structure into the synthesis process, by velocity selection of silicon aerosols, or by the use of electron lithography and subsequent oxidation processes. Nanocrystals between 2 and 20 nm in size with a full width at half maximum of the size distribution of 1 nm can be synthesized and area densities above 1012 cm–2 can be achieved. The role of surface passivation is elucidated by comparing Si/SiO2 layers with superlattices of fully passivated silicon nanocrystals within a SiO2 matrix. The demands on silicon nanocrystals for various applications such as non‐volatile memories or light‐emitting devices are discussed for different size‐controlled nanocrystal synthesis approaches.  相似文献   

2.
Exploring highly efficient electrocatalysts is greatly important for the widespread uptake of the fuel cells. However, many newly generated nanocrystals with attractive nanostructures often have extremely limited surface area or large particle‐size, which leads them to display limited electrocatalytic performance. Herein, a novel anode catalyst of hollow and porous Pd3Pt half‐shells with rich “active sites” is synthesized by using urea as a guiding surfactant. It is identified that the formation of Pd3Pt half‐shells involves the combination of bubble guiding, in situ deposition of particles and bubble burst. The obtained Pd3Pt half‐shells demonstrate a rich edge area with abundant exposed active sites and surface defects, indicating great potential for the electrocatalysis. When used as an electrocatalyst, the Pd3Pt half‐shells exhibit remarkably improved electrocatalytic performance for formic acid oxidation (FAO), where it promotes the dehydrogenation process of FAO by suppressing the formation of poisonous species COads via the electronic effect and ensemble effect.  相似文献   

3.
Plasmon‐based photothermal therapy is one of the most intriguing applications of noble metal nanostructures. The photothermal conversion efficiency is an essential parameter in practically realizing this application. The effects of the plasmon resonance wavelength, particle volume, shell coating, and assembly on the photothermal conversion efficiencies of Au nanocrystals are systematically studied by directly measuring the temperature of Au nanocrystal solutions with a thermocouple and analyzed on the basis of energy balance. The temperature of Au nanocrystal solutions reaches the maximum at ~75°C when the plasmon resonance wavelength of Au nanocrystals is equal to the illumination laser wavelength. For Au nanocrystals with similar shapes, the larger the nanocrystal, the smaller the photothermal conversion efficiency becomes. The photothermal conversion can also be controlled by shell coating and assembly through the change in the plasmon resonance energy of Au nanocrystals. Moreover, coating Au nanocrystals with semiconductor materials that have band gap energies smaller than the illumination laser energy can improve the photothermal conversion efficiency owing to the presence of an additional light absorption channel.  相似文献   

4.
Lithium–sulfur batteries (LSBs) have shown great potential for application in high‐density energy storage systems. However, the performance of LSBs is hindered by the shuttle effect and sluggish reaction kinetics of lithium polysulfides (LiPSs). Herein, heterostructual Nb2O5 nanocrystals/reduced graphene oxide (Nb2O5/RGO) composites are introduced into LSBs through separator modification for boosting the electrochemical performance. The Nb2O5/RGO heterostructures are designed as chemical trappers and conversion accelerators of LiPSs. Originating from the strong chemical interactions between Nb2O5 and LiPSs as well as the superior catalytic nature of Nb2O5, the Nb2O5/RGO nanocomposite possesses high trapping efficiency and efficient electrocatalytic activity to long‐chain LiPSs. The effective regulation of LiPSs conversion enables the LSBs enhanced redox kinetics and suppressed shuttle effect. Moreover, the Nb2O5/RGO nanocomposite has abundant sulfophilic sites and defective interfaces, which are beneficial for the nucleation and growth of Li2S, as evidenced by analysis of the cycled separators. As a result, LSBs with the Nb2O5/RGO‐modified separators exhibit excellent rate capability (816 mAh g?1 at 3 A g?1) and cyclic performance (628 mAh g?1 after 500 cycles). Remarkably, high specific capacity and stable cycling performance are demonstrated even at an elevated temperature of 50 °C or with higher sulfur loadings.  相似文献   

5.
Selectively exposing active surfaces and judiciously tuning the near‐surface composition of electrode materials represent two prominent means of promoting electrocatalytic performance. Here, a new class of Pt3Fe zigzag‐like nanowires (Pt‐skin Pt3Fe z‐NWs) with stable high‐index facets (HIFs) and nanosegregated Pt‐skin structure is reported, which are capable of substantially boosting electrocatalysis in fuel cells. These unique structural features endow the Pt‐skin Pt3Fe z‐NWs with a mass activity of 2.11 A mg?1 and a specifc activity of 4.34 mA cm?2 for the oxygen reduction reaction (ORR) at 0.9 V versus reversible hydrogen electrode, which are the highest in all reported PtFe‐based ORR catalysts. Density function theory calculations reveal a combination of exposed HIFs and formation of Pt‐skin structure, leading to an optimal oxygen adsorption energy due to the ligand and strain effects, which is responsible for the much enhanced ORR activities. In contrast to previously reported HIFs‐based catalysts, the Pt‐skin Pt3Fe z‐NWs maintain ultrahigh durability with little activity decay and negligible structure transformation after 50 000 potential cycles. Overcoming a key technical barrier in electrocatalysis, this work successfully extends the nanosegregated Pt‐skin structure to nanocatalysts with HIFs, heralding the exciting prospects of high‐effcient Pt‐based catalysts in fuel cells.  相似文献   

6.
The development of active and durable bifunctional electrocatalysts for overall water splitting is mandatory for renewable energy conversion. This study reports a general method for controllable synthesis of a class of IrM (M = Co, Ni, CoNi) multimetallic porous hollow nanocrystals (PHNCs), through etching Ir‐based, multimetallic, solid nanocrystals using Fe3+ ions, as catalysts for boosting overall water splitting. The Ir‐based multimetallic PHNCs show transition‐metal‐dependent bifunctional electrocatalytic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic electrolyte, with IrCo and IrCoNi PHNCs being the best for HER and OER, respectively. First‐principles calculations reveal a ligand effect, induced by alloying Ir with 3d transition metals, can weaken the adsorption energy of oxygen intermediates, which is the key to realizing much‐enhanced OER activity. The IrCoNi PHNCs are highly efficient in overall‐water‐splitting catalysis by showing a low cell voltage of only 1.56 V at a current density of 2 mA cm?2, and only 8 mV of polarization‐curve shift after a 1000‐cycle durability test in 0.5 m H2SO4 solution. This work highlights a potentially powerful strategy toward the general synthesis of novel, multimetallic, PHNCs as highly active and durable bifunctional electrocatalysts for high‐performance electrochemical overall‐water‐splitting devices.  相似文献   

7.
Nanocrystals made of Pt–Ir alloys are fascinating catalysts towards the oxygen reduction reaction (ORR), but the lack of control over their surface atomic structures hinders further optimization of their catalytic performance. Here we report, for the first time, a class of highly active and durable ORR catalysts based on Pd@Pt–Ir nanocrystals with well-controlled facets. With an average of 1.6 atomic layers of a Pt4Ir alloy on the surface, the nanocrystals can be made in cubic, octahedral, and icosahedral shapes to present Pt–Ir {1 0 0}, {1 1 1}, and {1 1 1} plus twin boundaries, respectively. The Pd@Pt–Ir nanocrystals exhibit not only facet-dependent catalytic properties but also substantially enhanced ORR activity and durability relative to a commercial Pt/C and their Pd@Pt counterparts. Among them, the Pd@Pt–Ir icosahedra deliver the best performance, with a mass activity of 1.88 A·mg−1Pt at 0.9 V, which is almost 15 times that of the commercial Pt/C. Our density functional theory (DFT) calculations attribute the high activity of the Pd@Pt–Ir nanocrystals, and the facet dependence of these activities, to easier protonation of O* and OH* under relevant OH* coverages, relative to the corresponding energetics on clean Pd@Pt surfaces. The DFT calculations also indicate that incorporating Ir atoms into the Pt lattice destabilizes OH–OH interactions on the surface, thereby raising the oxidation potential of Pt and greatly improving the catalytic durability.  相似文献   

8.
Most electrocatalysts for the ethanol oxidation reaction suffer from extremely limited operational durability and poor selectivity toward the C?C bond cleavage. In spite of tremendous efforts over the past several decades, little progress has been made in this regard. This study reports the remarkable promoting effect of Ni(OH)2 on Pd nanocrystals for electrocatalytic ethanol oxidation reaction in alkaline solution. A hybrid electrocatalyst consisting of intimately mixed nanosized Pd particles, defective Ni(OH)2 nanoflakes, and a graphene support is prepared via a two‐step solution method. The optimal product exhibits a high mass‐specific peak current of >1500 mA mg?1Pd, and excellent operational durability forms both cycling and chronoamperometric measurements in alkaline solution. Most impressively, this hybrid catalyst retains a mass‐specific current of 440 mA mg?1 even after 20 000 s of chronoamperometric testing, and its original activity can be regenerated via simple cyclic voltammetry cycles in clean KOH. This great catalyst durability is understood based on both CO stripping and in situ attenuated total reflection infrared experiments suggesting that the presence of Ni(OH)2 alleviates the poisoning of Pd nanocrystals by carbonaceous intermediates. The incorporation of Ni(OH)2 also markedly shifts the reaction selectivity from the originally predominant C2 pathway toward the more desirable C1 pathway, even at room temperature.  相似文献   

9.
Humidity sensors are essential components in wearable electronics for monitoring of environmental condition and physical state. In this work, a unique humidity sensing layer composed of nitrogen‐doped reduced graphene oxide (nRGO) fiber on colorless polyimide film is proposed. Ultralong graphene oxide (GO) fibers are synthesized by solution assembly of large GO sheets assisted by lyotropic liquid crystal behavior. Chemical modification by nitrogen‐doping is carried out under thermal annealing in H2(4%)/N2(96%) ambient to obtain highly conductive nRGO fiber. Very small (≈2 nm) Pt nanoparticles are tightly anchored on the surface of the nRGO fiber as water dissociation catalysts by an optical sintering process. As a result, nRGO fiber can effectively detect wide humidity levels in the range of 6.1–66.4% relative humidity (RH). Furthermore, a 1.36‐fold higher sensitivity (4.51%) at 66.4% RH is achieved using a Pt functionalized nRGO fiber (i.e., Pt‐nRGO fiber) compared with the sensitivity (3.53% at 66.4% RH) of pure nRGO fiber. Real‐time and portable humidity sensing characteristics are successfully demonstrated toward exhaled breath using Pt‐nRGO fiber integrated on a portable sensing module. The Pt‐nRGO fiber with high sensitivity and wide range of humidity detection levels offers a new sensing platform for wearable humidity sensors.  相似文献   

10.
To reveal how the size effect and strain effect synergistically regulate the mass activity (MA) and specific activity (SA) of Pt alloy nanocrystal catalysts in oxygen reduction reaction (ORR), remains to be difficult due to the highly entangled factors. In this work, six ternary PtCoCu catalysts with sequentially changed composition, size, and compression strain are prepared. It is found that the smaller the alloy particles, the higher the electrochemical active surface area (ECSA) and MA values, that is, the particle size plays a decisive role in the size of the ECSA and MA. While, along alloy size decrease, the intrinsic activity SA first increases, then remains unchanged, and finally rapidly increases again. This detailed analysis shows that for the alloys above 4 nm, it is the surface coordination number that decides the SA, while for those below 4 nm, it is the well-regulated compression strain that determines the SA. Particularly, Pt47Co26Cu27 demonstrates the MA of 1.19 A mgPt−1 and SA of 1.48 mA cm−2, being 7.9 and 6.4 times those of commercial Pt/C respectively, representing an especially superior ORR catalyst.  相似文献   

11.
A reduced graphene oxide (RGO)-NiFe2O4 nanocomposite was synthesized by a simple one step hydrothermal approach and its application in the electrocatalytic oxidation of hydrazine was demonstrated. The as-synthesized nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Thermogravimetric analysis, Field emission-scanning electron microscopy (FE-SEM), and Transmission electron microscopy (TEM). The FE-SEM and TEM image analyses revealed that the NiFe2O4 nanoparticles were uniformly distributed on the RGO sheets with a diameter and length of ∼10 and ∼100 nm, respectively. The XPS analysis confirmed the ionic states of Ni and Fe to be Ni3+ and Ni2+, and Fe2+ and Fe3+, respectively. Further, the electrochemical activity of the RGO-NiFe2O4 nanocomposite was investigated by studying the oxidation of hydrazine. The RGO-NiFe2O4 modified glassy carbon electrode (GCE) showed an outstanding electrocatalytic activity towards the oxidation of hydrazine as compared to the NiFe2O4 and RGO modified electrodes. The enhanced electrocatalytic activity is due to the synergistic effect between RGO and NiFe2O4. Using amperometry, the lowest detection limit of 200 nM was achieved with the RGO-NiFe2O4 modified GCE. Therefore, the RGO-NiFe2O4 modified GCE can be used for the electrochemical oxidation of hydrazine.  相似文献   

12.
The surface structure‐controlled synthesis of noble metal nanocrystals (NCs) bounded by high‐index facets has become a hot research topic due to their potential to significantly improve catalytic performance. This study reports the preparation of monodisperse Au–Pd alloy NCs with systematic shape evolution from rhombic dodecahedral (RD) to trisoctahedral (TOH), and hexoctahedral (HOH) structures by varying the concentration of surfactant in the surfactant‐mediated synthesis. The as‐prepared three kinds of alloy NCs possess almost the same size and composition as each other. It is suggested that the surfactant containing long‐chain octadecyltrimethyl ammonium (OTA+) ions plays a key role in the formation of high index facets, and the crystal growth kinetics may also have an effect on the formation of different nanocrystal morphologies. In addition, the catalytic activities of these NCs are evaluated by structure‐sensitive reactions, including ethanol electro‐oxidation and the catalytic reduction of 4‐nitrophenol (4‐NPh). These three types of Au–Pd alloy NCs exhibit different catalytic selectivities towards these two reactions. The catalytic activities toward electro‐oxidation of ethanol are in the order of HOH > RD > TOH, which follows the order of their corresponding surface energies. However, the activities toward catalytic reduction of 4‐NPh are in the order of RD > TOH > HOH, which should be related to the local structure of the surfaces.  相似文献   

13.
Dye‐sensitized solar cells (DSCs) are promising alternatives to conventional silicon devices because of their simple fabrication procedure, low cost, and high efficiency. Platinum is generally used as a superior counter electrode (CE) material, but the disadvantages such as high cost and low abundance greatly restrict the large‐scale application of DSCs. An efficient and sustainable way to overcome the limited supply of Pt is the development of high‐efficiency Pt‐free CE materials, which should possess both high electrical conductivity and superior electrocatalytic activity simultaneously. Herein, for the first time, a two‐step strategy to synthesize ruthenium dioxide (RuO2) nanocrystals is reported, and it is shown that RuO2 catalysts exhibit promising electrocatalytic activity towards triiodide reduction, which results in comparable energy conversion efficiency to that of conventional Pt CEs. More importantly, by virtue of first‐principles calculations, the catalytic mechanism of electrocatalysis for triiodide reduction on various CEs is investigated systematically and it is found that the electrochemical triiodide reduction reaction on RuO2 catalyst surfaces can be enhanced significantly, owing to the ideal combination of good electrocatalytic activity and high electrical conductivity.  相似文献   

14.
Electrocatalytic hydrogen evolution reaction (HER) in alkaline media is important for hydrogen economy but suffers from sluggish reaction kinetics due to a large water dissociation energy barrier. Herein, Pt5P2 nanocrystals anchoring on amorphous nickel phosphate nanorods as a high-performance interfacial electrocatalyst system (Pt5P2 NCs/a-NiPi) for the alkaline HER are demonstrated. At the unique polycrystalline/amorphous interface with abundant defects, strong electronic interaction, and optimized intermediate adsorption strength, water dissociation is accelerated over abundant oxophilic Ni sites of amorphous NiPi, while hydride coupling is promoted on the adjacent electron-rich Pt sites of Pt5P2. Meanwhile, the ultra-small-sized Pt5P2 nanocrystals and amorphous NiPi nanorods maximize the density of interfacial active sites for the Volmer–Tafel reaction. Pt5P2 NCs/a-NiPi exhibits small overpotentials of merely 9 and 41 mV at −10 and −100 mA cm−2 in 1 M KOH, respectively. Notably, Pt5P2 NCs/a-NiPi exhibits an unprecedentedly high mass activity (MA) of 14.9 mA µgPt−1 at an overpotential of 70 mV, which is 80 times higher than that of Pt/C and represents the highest MA of reported Pt-based electrocatalysts for the alkaline HER. This work demonstrates a phosphorization and interfacing strategy for promoting Pt utilization and in-depth mechanistic insights for the alkaline HER.  相似文献   

15.
采用油胺为还原剂和稳定剂,通过晶种生长法制备了Au-Pt海胆状纳米结构,研究了各种合成条件对产物结构及形貌的影响。结果表明,空气气氛下不能合成Au-Pt双金属杂聚体结构;Pt(acac)2和H2PtCl6·6H2O两种Pt前体对于产物形貌没有明显影响;强极性的1-十八烯参与合成反应时不易得到海胆状的双金属结构;不同Au/Pt配比对产物形貌影响的研究指出,Au-Pt海胆状杂聚体结构的形成是因为后还原的Pt会倾向性地沉积到先还原成核的Au纳米颗粒的特定表面。一锅法合成得到了AuPt合金结构,表明后还原的Pt以Au为晶种,在小尺寸效应作用下使颗粒发生纳米尺度的原子扩散形成了带浓度梯度的AuPt合金。  相似文献   

16.
A facile approach for the synthesis of Au‐ and Pt‐decorated CuInS2 nanocrystals (CIS NCs) as sensitizer materials on the top of MoS2 bilayers is demonstrated. A single surfactant (oleylamine) is used to prepare such heterostructured noble metal decorated CIS NCs from the pristine CIS. Such a feasible way to synthesize heterostructured noble metal decorated CIS NCs from the single surfactant can stimulate the development of the functionalized heterostructured NCs in large scale for practical applications such as solar cells and photodetectors. Photodetectors based on MoS2 bilayers with the synthesized nanocrystals display enhanced photocurrent, almost 20–40 times higher responsivity and the On/Off ratio is enlarged one order of magnitude compared with the pristine MoS2 bilayers‐based photodetectors. Remarkably, by using Pt‐ or Au‐decorated CIS NCs, the photocurrent enhancement of MoS2 photodetectors can be tuned between blue (405 nm) to green (532 nm). The strategy described here acts as a perspective to significantly improve the performance of MoS2‐based photodetectors with the controllable absorption wavelengths in the visible light range, showing the feasibility of the possible color detection.  相似文献   

17.
PbSe nanorods and branched nanorods can be grown using binary Au/Fe3O4 nanoparticles as seeds, as reported by Swihart, Zeng, Prasad, and co‐workers on p. 1889. PbSe nucleates on the Au portion of the seed particle and grows anisotropically as one or more straight or branched nanorods. The background images show PbSe nanorods (top), and ternary Fe3O4–Au–PbSe hybrid nanocrystals (bottom). High‐resolution TEM images show Fe3O4(purple)–Au(gold)–PbSe (green) ternary nanocrystals. A ball‐and‐stick cartoon model illustrates the approximate size of these structures relative to the individual atoms.  相似文献   

18.
It is promising for AuNPs/RGO composites to be exploited for hydrogen evolution reaction (HER), due to the collaborative effects between the electrocatalytic Au nanoparticles (AuNPs) and conductive reduced graphene oxide (RGO). In this work, we used a simple way to decorate AuNPs onto the RGO surface by one pot in situ reduction both HAuCl4 and GO, for which the controlled average size of AuNPs (2.7, 11.5 and 45.7 nm) is adjusting with the mass ratio of HAuCl4 and GO. The obtained materials, AuNPs/RGO composites, show excellent electrocatalytic activity for the HER that critical dependence on the particle size of AuNPs. The results show that AuNPs/RGO with AuNPs size of 11.5 nm exhibits superior electrochemical activity: low onset potential of 0.029 V versus the reversible hydrogen electrode as well as a small Tafel slope of 86 mV per decade.  相似文献   

19.
MnO2/reduced graphene oxide(RGO) composites were synthesized by a facile and effective polymer-assisted chemical reduction method. The synthetic MnO2/RGO composites have a uniform surface distribution and large coverage of MnO2 nanoparticles onto graphene, which were characterized with scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and cyclic voltammetry. The synthetic MnO2/RGO composites were studied with respect to its electrocatalytic activity toward the reduction of oxygen in alkaline media and were found to possess a good electrocatalytic activity toward the four-electron reduction of oxygen.  相似文献   

20.
Intimately coupled carbon/transition‐metal‐based hierarchical nanostructures are one of most interesting electrode materials for boosting energy conversion and storage applications owing to the strong synergistic effect between the two components and appealing structural stability. Herein, a universal method is reported for making hierarchical hollow carbon nanospheres (HCSs) with intimately coupled ultrathin carbon nanosheets and Mo‐based nanocrystals. The in situ and confined reaction of the synthetic strategy can not only allow the aggregation of the nanocrystals to be impeded, but also endows extremely intimate coupled interaction between the conductive carbon nanosheets and the nanocrystals MoM (M = P, S, C and O). As a proof of concept, the as‐prepared MoP/C HCSs exhibit extraordinary hydrogen evolution reaction electrocatalytic activity with small overpotential and robust durability in both acidic and alkaline solutions. In addition, the unique sheet‐on‐sheet MoS2/C HCSs as an anode demonstrate high capacity, great rate capabilities, and long‐term cycles for sodium‐ion batteries (SIBs). The capacity can be maintained at 410 mA h g?1 even after 1000 cycles even at a high current density of 4 A g?1, one of the best reported values for MoS2‐based electrode materials for SIBs. The present work highlights the importance of designing and fabricating functional strongly coupled hybrid materials for enhancing energy conversion and storage applications.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号