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1.
Due to the unique advantages of Pt, it plays an important role in fuel cells and microelectronics. Considering the fact that Pt is an expensive metal, a major challenging point nowadays is how to realize efficient utilization of Pt. In this paper, a cost‐effective atomic layer deposition (ALD) process with a low N2 filling step is introduced for realizing well‐defined Pt nanotube arrays in anodic alumina nano‐porous templates. Compared to the conventional ALD growth of Pt, much fewer ALD cycles and a shorter precursor pulsing time are required, which originates from the low N2 filling step. To achieve similar Pt nanotubes, about half cycles and 10% Pt precursor pulsing time is needed using our ALD process. Meanwhile, the Pt nanotube array is explored as a current collector for supercapacitors based on core/shell Pt/MnO2 nanotubes. This nanotube‐based electrode exhibits high gravimetric and areal specific capacitance (810 Fg?1 and 75 mF cm?2 at a scan rate of 5 mV s?1) as well as an excellent rate capability (68% capacitance retention from 2 to 100 Ag?1). Additionally, a negligible capacitance loss is observed after 8000 cycles of random charging‐discharging from 2 to 100 Ag?1.  相似文献   

2.
Electrocatalytic hydrogen evolution reaction (HER) is an efficient way to generate hydrogen fuel for the storage of renewable energy. Currently, the widely used Pt‐based catalysts suffer from high costs and limited electrochemical stability; therefore, developing an efficient alternative catalyst is very urgent. Herein, one pot hydrothermal synthesis is reported of amorphous ruthenium‐sulfide (RuSx) nanoparticles (NPs) supported on sulfur‐doped graphene oxide (GO). The as‐obtained composite serves as a Pt‐like HER electrocatalyst. Achieving a current density of ?10 mA cm?2 only requires a small overpotential (?31, ?46, and ?58 mV in acidic, neutral, and alkaline electrolyte, respectively) with high durability. The isolated Ru active site inducing Volmer–Heyrovsky mechanism in the RuSx NPs is demonstrated by the Tafel analysis and X‐ray absorption spectroscopy characterization. Theoretical simulation indicates the isolated Ru site exhibits Pt‐like Gibbs free energy of hydrogen adsorption (?0.21 eV) therefore generating high intrinsic HER activity. Moreover, the strong bonding between the RuSx and S–GO, as well as pH tolerance of RuSx are believed to contribute to the high stability. This work shows a new insight for amorphous materials and provides alternative opportunities in designing advanced electrocatalysts with low‐cost for HER in the hydrogen economy.  相似文献   

3.
A long‐range ordered organic/inorganic material is synthesized from a bis‐silane, (EtO)3Si? (CH2)3? NHCONH? C6H4? NHCONH? (CH2)3? Si(OEt)3. This crosslinked sol–gel solid exhibits a supramolecular organization via intermolecular hydrogen bonding interactions between urea groups (? NHCONH? ) and covalent siloxane bonding, ?Si? O? Si?. Time‐resolved in situ X‐ray measurements (coupling small‐ and wide‐angle X‐ray scattering techniques) are performed to follow the different steps involved in the synthetic process. A new mechanism based on the crystallization of the hydrolyzed species followed by their polycondensation in solid state is proposed.  相似文献   

4.
Perfect platinum (Pt) nanocubes with high density have been synthesized by controlled reduction of hexachloroplatinic acid in the presence of H2SO4 and HCl, employing a pair of low-resistivity fastened silicon (FS) wafers at room temperature. The presence of the additive charges (induced by prior etching of the silicon surface with HF to remove any SiO2 layer) between the interfaces of the FS surface results in a high charge density and facilitates fast deposition of Pt nanoparticles via electroless plating. The charge density, stirring time, and homogeneity of the aqueous solution influenced the geometrical shapes of the Pt nanoparticles. The parameters were finely tuned in order to control the nucleation and growth rates and obtain perfect Pt nanocubes. The perfect Pt nanocubes were single crystalline with exposed {100} facets. Per equivalent Pt surface areas, the perfect Pt nanocubes showed enhanced catalytic activity relative to truncated Pt nanocubes or spherical Pt nanoparticles for the electrooxidation of liquid feed fuels such as methanol and ethanol. Moreover, there a strong correlation was observed between the optical, electrical, thermal, magnetic, and catalytic properties of the perfect Pt nanocubes which should lead to a variety of technological applications of these materials.  相似文献   

5.
In this paper, post‐treatments, including reflowing treatment, passivation treatment, and ultrasonic treatment for tinplates with different coating mass, are discussed, and surface characteristics brought by the post‐treatments have also been investigated by grazing incidence X‐ray diffraction and X‐ray photoelectron spectroscopy. Grazing incidence X‐ray diffraction results show the amount of highest iron and FeSn2 and lowest tin on tinplate with a coating mass of 1.1 g ? m?2, indicating the poor surface coverage of steel substrate. The amount of lowest iron and tin‐iron alloy and highest tin on tinplate with a coating mass of 11.2 g ? m?2 indicates the best surface coverage of tinplate among the four test samples. X‐ray photoelectron spectroscopy depth analysis shows that the sample with coating mass of 1.1 g ? m?2 has a higher amount of iron atomic concentration, which decreases sharply as the coating mass increases, indicating the poor surface coverage by lower coating mass.  相似文献   

6.
It is an ongoing challenge to fabricate nonprecious oxygen reduction reaction (ORR) catalysts that can be comparable to or exceed the efficiency of platinum. A highly active non‐platinum self‐supporting Fe?N/C catalyst has been developed through the pyrolysis of a new type of precursor of iron coordination complex, in which 1,4‐bis(1H‐1,3,7,8–tetraazacyclopenta(1)phenanthren‐2‐yl)benzene (btcpb) functions as a ligand complexing Fe(II) ions. The optimal catalyst pyrolyzed at 700 °C (Fe?N/C?700) shows the best ORR activity with a half‐wave potential (E1/2) of 840 mV versus reversible hydrogen electrode (RHE) in 0.1 m KOH, which is more positive than that of commercial Pt/C (E1/2: 835 mV vs RHE). Additionally, the Fe?N/C?700 catalyst also exhibits high ORR activity in 0.1 m HClO4 with the onset potential and E1/2 comparable to those of the Pt/C catalyst. Notably, the Fe?N/C?700 catalyst displays superior durability (9.8 mV loss in 0.1 m KOH and 23.6 mV loss in 0.1 m HClO4 for E1/2 after 8000 cycles) and better tolerance to methanol than Pt/C. Furthermore, the Fe?N/C?700 catalyst can be used for fabricating the air electrode in Zn–air battery with a specific capacity of 727 mA hg?1 at 5 mA cm?2 and a negligible voltage loss after continuous operation for 110 h.  相似文献   

7.
Due to its electronic structure, similar to platinum, molybdenum carbides (Mo2C) hold great promise as a cost‐effective catalyst platform. However, the realization of high‐performance Mo2C catalysts is still limited because controlling their particle size and catalytic activity is challenging with current synthesis methods. Here, the synthesis of ultrafine β‐Mo2C nanoparticles with narrow size distribution (2.5 ± 0.7 nm) and high mass loading (up to 27.5 wt%) on graphene substrate using a giant Mo‐based polyoxomolybdate cluster, Mo132 ((NH4)42[Mo132O372(CH3COO)30(H2O)72]·10CH3COONH4·300H2O) is demonstrated. Moreover, a nitrogen‐containing polymeric binder (polyethyleneimine) is used to create Mo? N bonds between Mo2C nanoparticles and nitrogen‐doped graphene layers, which significantly enhance the catalytic activity of Mo2C for the hydrogen evolution reaction, as is revealed by X‐ray photoelectron spectroscopy and density functional theory calculations. The optimal Mo2C catalyst shows a large exchange current density of 1.19 mA cm?2, a high turnover frequency of 0.70 s?1 as well as excellent durability. The demonstrated new strategy opens up the possibility of developing practical platinum substitutes based on Mo2C for various catalytic applications.  相似文献   

8.
Here a multifunctional nanoplatform (upconversion nanoparticles (UCNPs)‐platinum(IV) (Pt(IV))?ZnFe2O4, denoted as UCPZ) is designed for collaborative cancer treatment, including photodynamic therapy (PDT), chemotherapy, and Fenton reaction. In the system, the UCNPs triggered by near‐infrared light can convert low energy photons to high energy ones, which act as the UV–vis source to simultaneously mediate the PDT effect and Fenton's reaction of ZnFe2O4 nanoparticles. Meanwhile, the Pt(IV) prodrugs can be reduced to high virulent Pt(II) by glutathione in the cancer cells, which can bond to DNA and inhibit the copy of DNA. The synergistic therapeutic effect is verified in vitro and in vivo results. The cleavage of Pt(IV) from UCNPs during the reduction process can shift the larger UCPZ nanoparticles (NPs) to the smaller ones, which promotes the enhanced permeability and retention (EPR) and deep tumor penetration. In addition, due to the inherent upconversion luminescence (UCL) and the doped Yb3+ and Fe3+ in UCPZ, this system can serve as a multimodality bioimaging contrast agent, covering UCL, X‐ray computed tomography, magnetic resonance imaging, and photoacoustic. A smart all‐in‐one imaging‐guided diagnosis and treatment system is realized, which should have a potential value in the treatment of tumor.  相似文献   

9.
LiV3O8 nanorods with controlled size are successfully synthesized using a nonionic triblock surfactant Pluronic‐F127 as the structure directing agent. X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques are used to characterize the samples. It is observed that the nanorods with a length of 4–8 µm and diameter of 0.5–1.0 µm distribute uniformly. The resultant LiV3O8 nanorods show much better performance as cathode materials in lithium‐ion batteries than normal LiV3O8 nanoparticles, which is associated with the their unique micro–nano‐like structure that can not only facilitate fast lithium ion transport, but also withstand erosion from electrolytes. The high discharge capacity (292.0 mAh g?1 at 100 mA g?1), high rate capability (138.4 mAh g?1 at 6.4 A g?1), and long lifespan (capacity retention of 80.5% after 500 cycles) suggest the potential use of LiV3O8 nanorods as alternative cathode materials for high‐power and long‐life lithium ion batteries. In particular, the synthetic strategy may open new routes toward the facile fabrication of nanostructured vanadium‐based compounds for energy storage applications.  相似文献   

10.
The development of manganese dioxide as the cathode for aqueous Zn‐ion battery (ZIB) is limited by the rapid capacity fading and material dissolution. Here, a highly reversible aqueous ZIB using graphene scroll‐coated α‐MnO2 as the cathode is proposed. The graphene scroll is uniformly coated on the MnO2 nanowire with an average width of 5 nm, which increases the electrical conductivity of the MnO2 nanowire and relieves the dissolution of the cathode material during cycling. An energy density of 406.6 Wh kg?1 (382.2 mA h g?1) at 0.3 A g?1 can be reached, which is the highest specific energy value among all the cathode materials for aqueous Zn‐ion battery so far, and good long‐term cycling stability with 94% capacity retention after 3000 cycles at 3 A g?1 are achieved. Meanwhile, a two‐step intercalation mechanism that Zn ions first insert into the layers and then the tunnels of MnO2 framework is proved by in situ X‐ray diffraction, galvanostatic intermittent titration technique, and X‐ray photoelectron spectroscopy characterizations. The graphene scroll‐coated metallic oxide strategy can also bring intensive interests for other energy storage systems.  相似文献   

11.
Mesoporous and amorphous ZnSnO3 nanocubes of ~37 nm size coated with a thin porous carbon layer have been prepared using monodisperse ZnSn(OH)6 as the active precursor and low‐temperature synthesized polydopamine as the carbon precursor. The small single nanocubes cross‐link with each other to form a continuous conductive framework and interconnected porous channels with macropores of 74 nm width. Because of its multi‐featured nanostructure, this material exhibits greatly enhanced integration of reversible alloying/de‐alloying (i.e., transformation of Li4.4Sn and LiZn to Sn and Zn) and conversion (i.e., oxidation of Sn and Zn to ZnSnO3) reaction processes with an extremely high capacity of 1060 mA h g?1 for up to 100 cycles. A high reversible capacity of 650 and 380 mA h g?1 can also be delivered at rates of 2 and 3 A g?1, respectively. This excellent electrochemical performance is attributed to the small particle size, well‐developed mesoporosity, the amorphous nature of the ZnSnO3 and the continuous conductive framework produced by the interconnected carbon layers.  相似文献   

12.
Carbon‐supported nickel selenide (Ni0.85Se/C) hollow nanowires are prepared from carbon‐coated selenium nanowires via a self‐templating hydrothermal method, by first dissolving selenium in the Se/C nanowires in hydrazine, allowing it to diffuse out of the carbon layer, and then reacting with nickel ions into Ni0.85Se nanoplates on the outer surface of the carbon. Ni0.85Se/C hollow nanowires are employed as anode materials for sodium‐ion batteries, and their electrochemical performance is evaluated via the cyclic voltammetry and electrochemical impedance spectroscopy combined with ex situ X‐ray photoelectron spectroscopy and X‐ray diffraction measurements. It is found that Ni0.85Se/C hollow nanowires exhibit greatly enhanced cycle stability and rate capability as compared to Ni0.85Se nanoparticles, with a reversible capacity around 390 mA h g?1 (the theoretical capacity is 416 mA h g?1) at the rate of 0.2 C and 97% capacity retention after 100 cycles. When the current rate is raised to 5 C, they still deliver capacity of 219 mA h g?1. The synthetic methodology introduced here is general and can easily be applied to building similar structures for other metal selenides in the future.  相似文献   

13.
A fundamental understanding of the interplay between ligand‐removal kinetics and metal aggregation during the formation of platinum nanoparticles (NPs) in atomic layer deposition of Pt on TiO2 nanopowder using trimethyl(methylcyclo‐pentadienyl)platinum(IV) as the precursor and O2 as the coreactant is presented. The growth follows a pathway from single atoms to NPs as a function of the oxygen exposure (PO2 × time). The growth kinetics is modeled by accounting for the autocatalytic combustion of the precursor ligands via a variant of the Finke–Watzky two‐step model. Even at relatively high oxygen exposures (<120 mbar s) little to no Pt is deposited after the first cycle and most of the Pt is atomically dispersed. Increasing the oxygen exposure above 120 mbar s results in a rapid increase in the Pt loading, which saturates at exposures >> 120 mbar s. The deposition of more Pt leads to the formation of NPs that can be as large as 6 nm. Crucially, high PO2 (≥5 mbar) hinders metal aggregation, thus leading to narrow particle size distributions. The results show that ALD of Pt NPs is reproducible across small and large surface areas if the precursor ligands are removed at high PO2.  相似文献   

14.
Conventional cathodes of Li‐ion batteries mainly operate through an insertion–extraction process involving transition metal redox. These cathodes will not be able to meet the increasing requirements until lithium‐rich layered oxides emerge with beyond‐capacity performance. Nevertheless, in‐depth understanding of the evolution of crystal and excess capacity delivered by Li‐rich layered oxides is insufficient. Herein, various in situ technologies such as X‐ray diffraction and Raman spectroscopy are employed for a typical material Li1.2Ni0.2Mn0.6O2, directly visualizing O?? O? (peroxo oxygen dimers) bonding mostly along the c‐axis and demonstrating the reversible O2?/O? redox process. Additionally, the formation of the peroxo O? O bond is calculated via density functional theory, and the corresponding O? O bond length of ≈1.3 Å matches well with the in situ Raman results. These findings enrich the oxygen chemistry in layered oxides and open opportunities to design high‐performance positive electrodes for lithium‐ion batteries.  相似文献   

15.
Tin dioxide (SnO2) has attracted much attention in lithium‐ion batteries (LIBs) due to its abundant source, low cost, and high theoretical capacity. However, the large volume variation, irreversible conversion reaction limit its further practical application in next‐generation LIBs. Here, a novel solvent‐free approach to construct uniform metal–organic framework (MOF) shell‐derived carbon confined SnO2/Co (SnO2/Co@C) nanocubes via a two‐step heat treatment is developed. In particular, MOF‐coated CoSnO3 hollow nanocubes are for the first time synthesized as the intermediate product by an extremely simple thermal solid‐phase reaction, which is further developed as a general strategy to successfully obtain other uniform MOF‐coated metal oxides. The as‐synthesized SnO2/Co@C nanocubes, when tested as LIB anodes, exhibit a highly reversible discharge capacity of 800 mAh g?1 after 100 cycles at 200 mA g?1 and excellent cycling stability with a retained capacity of 400 mAh g?1 after 1800 cycles at 5 A g?1. The experimental analyses demonstrate that these excellent performances are mainly ascribed to the delicate structure and a synergistic effect between Co and SnO2. This facile synthetic approach will greatly contribute to the development of functional metal oxide‐based and MOF‐assisted nanostructures in many frontier applications.  相似文献   

16.
Preventing the aggregation of nanosized electrode materials is a key point to fully utilize the advantage of the high capacity. In this work, a facile and low‐cost surface solvation treatment is developed to synthesize Fe2VO4 hierarchical porous microparticles, which efficiently prevents the aggregation of the Fe2VO4 primary nanoparticles. The reaction between alcohol molecules and surface hydroxy groups is confirmed by density functional theory calculations and Fourier transform infrared spectroscopy. The electrochemical mechanism of Fe2VO4 as lithium‐ion battery anode is characterized by in situ X‐ray diffraction for the first time. This electrode material is capable of delivering a high reversible discharge capacity of 799 mA h g?1 at 0.5 A g?1 with a high initial coulombic efficiency of 79%, and the capacity retention is 78% after 500 cycles. Moreover, a remarkable reversible discharge capacity of 679 mA h g?1 is achieved at 5 A g?1. Furthermore, when tested as sodium‐ion battery anode, a high reversible capacity of 382 mA h g?1 can be delivered at the current density of 1 A g?1, which still retains at 229 mA h g?1 after 1000 cycles. The superior electrochemical performance makes it a potential anode material for high‐rate and long‐life lithium/sodium‐ion batteries.  相似文献   

17.
Herein, a new type of cobalt encapsulated nitrogen‐doped carbon (Co@NC) nanostructure employing ZnxCo1?x(C3H4N2) metal–organic framework (MOF) as precursor is developed, by a simple, ecofriendly, solvent‐free approach that utilizes a mechanochemical coordination self‐assembly strategy. Possible evolution of ZnxCo1?x(C3H4N2) MOF structures and their conversion to Co@NC nanostructures is established from an X‐ray diffraction technique and transmission electron microscopy analysis, which reveal that MOF‐derived Co@NC core–shell nanostructures are well ordered and highly crystalline in nature. Co@NC–MOF core–shell nanostructures show excellent catalytic activity for the oxygen reduction reaction (ORR), with onset potential of 0.97 V and half‐wave potential of 0.88 V versus relative hydrogen electrode in alkaline electrolyte, and excellent durability with zero degradation after 5000 potential cycles; whereas under similar experimental conditions, the commonly utilized Pt/C electrocatalyst degrades. The Co@NC–MOF electrocatalyst also shows excellent tolerance to methanol, unlike the Pt/C electrocatalyst. X‐ray photoelectron spectroscopy (XPS) analysis shows the presence of ORR active pyridinic‐N and graphitic‐N species, along with CoNx? Cy and Co? Nx ORR active (M–N–C) sites. Enhanced electron transfer kinetics from nitrogen‐doped carbon shell to core Co nanoparticles, the existence of M–N–C active sites, and protective NC shells are responsible for high ORR activity and durability of the Co@NC–MOF electrocatalyst.  相似文献   

18.
Na‐ion batteries (NIBs) are ideal candidates for solving the problem of large‐scale energy storage, due to the worldwide sodium resource, but the efforts in exploring and synthesizing low‐cost and eco‐friendly anode materials with convenient technologies and low‐cost raw materials are still insufficient. Herein, with the assistance of a simple calcination method and common raw materials, the environmentally friendly and nontoxic N‐doped C@Zn3B2O6 composite is directly synthesized and proved to be a potential anode material for NIBs. The composite demonstrates a high reversible charge capacity of 446.2 mAh g?1 and a safe and suitable average voltage of 0.69 V, together with application potential in full cells (discharge capacity of 98.4 mAh g?1 and long cycle performance of 300 cycles at 1000 mA g?1). In addition, the sodium‐ion storage mechanism of N‐doped C@Zn3B2O6 is subsequently studied through air‐insulated ex situ characterizations of X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and Fourier‐transform infrared (FT‐IR) spectroscopy, and is found to be rather different from previous reports on borate anode materials for NIBs and lithium‐ion batteries. The reaction mechanism is deduced and proposed as: Zn3B2O6 + 6Na+ + 6e? ? 3Zn + B2O3 ? 3Na2O, which indicates that the generated boracic phase is electrochemically active and participates in the later discharge/charge progress.  相似文献   

19.
The realization of large‐scale solar hydrogen (H2) production relies on the development of high‐performance and low‐cost photocatalysts driven by sunlight. Recently, cocatalysts have demonstrated immense potential in enhancing the activity and stability of photocatalysts. Hence, the rational design of highly active and inexpensive cocatalysts is of great significance. Here, a facile method is reported to synthesize Ni@C core–shell nanoparticles as a highly active cocatalyst. After merging Ni@C cocatalyst with CdS nanorod (NR), a tremendously enhanced visible‐light photocatalytic H2‐production performance of 76.1 mmol g?1 h?1 is achieved, accompanied with an outstanding quantum efficiency of 31.2% at 420 nm. The state‐of‐art characterizations (e.g., synchrotron‐based X‐ray absorption near edge structure) and theoretical calculations strongly support the presence of pronounced nanoconfinement effect in Ni@C core–shell nanoparticles, which leads to controlled Ni core size, intimate interfacial contact and rapid charge transfer, optimized electronic structure, and protection against chemical corrosion. Hence, the combination of nanoconfined Ni@C with CdS nanorod leads to significantly improved photocatalytic activity and stability. This work not only for the first time demonstrates the great potential of using highly active and inexpensive Ni@C core–shell structure to replace expensive Pt in photocatalysis but also opens new avenues for synthesizing cocatalyst/photocatalyst hybridized systems with excellent performance by introducing nanoconfinement effect.  相似文献   

20.
Maximizing activity of Pt catalysts toward methanol oxidation reaction (MOR) together with minimized poisoning of adsorbed CO during MOR still remains a big challenge. In the present work, uniform and well‐distributed Pt nanoparticles (NPs) grown on an atomic carbon layer, that is in situ formed by means of dry‐etching of silicon carbide nanoparticles (SiC NPs) with CCl4 gas, are explored as potential catalysts for MOR. Significantly, as‐synthesized catalysts exhibit remarkably higher MOR catalytic activity (e.g., 647.63 mA mg?1 at a peak potential of 0.85 V vs RHE) and much improved anti‐CO poisoning ability than the commercial Pt/C catalysts, Pt/carbon nanotubes, and Pt/graphene catalysts. Moreover, the amount of expensive Pt is a few times lower than that of the commercial and reported catalyst systems. As confirmed from density functional theory (DFT) calculations and X‐ray absorption fine structure (XAFS) measurements, such high performance is due to reduced adsorption energy of CO on the Pt NPs and an increased amount of adsorbed energy OH species that remove adsorbed CO fast and efficiently. Therefore, these catalysts can be utilized for the development of large‐scale and industry‐orientated direct methanol fuel cells.  相似文献   

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