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1.
A critical bottleneck limiting the performance of rechargeable zinc–air batteries lies in the inefficient bifunctional electrocatalysts for the oxygen reduction and evolution reactions at the air electrodes. Hybridizing transition‐metal oxides with functional graphene materials has shown great advantages due to their catalytic synergism. However, both the mediocre catalytic activity of metal oxides and the restricted 2D mass/charge transfer of graphene render these hybrid catalysts inefficient. Here, an effective strategy combining anion substitution, defect engineering, and the dopant effect to address the above two critical issues is shown. This strategy is demonstrated on a hybrid catalyst consisting of sulfur‐deficient cobalt oxysulfide single crystals and nitrogen‐doped graphene nanomeshes (CoO0.87S0.13/GN). The defect chemistries of both oxygen‐vacancy‐rich, nonstoichiometric cobalt oxysulfides and edge‐nitrogen‐rich graphene nanomeshes lead to a remarkable improvement in electrocatalytic performance, where CoO0.87S0.13/GN exhibits strongly comparable catalytic activity to and much better stability than the best‐known benchmark noble‐metal catalysts. In application to quasi‐solid‐state zinc–air batteries, CoO0.87S0.13/GN as a freestanding catalyst assembly benefits from both structural integrity and enhanced charge transfer to achieve efficient and very stable cycling operation over 300 cycles with a low discharge–charge voltage gap of 0.77 V at 20 mA cm?2 under ambient conditions.  相似文献   

2.
Nitrogen‐doped graphene (NG) with wrinkled and bubble‐like texture is fabricated by a thermal treatment. Especially, a novel sonication‐assisted pretreatment with nitric acid is used to further oxidize graphene oxide and its binding with melamine molecules. There are many bubble‐like nanoflakes with a dimension of about 10 nm appeared on the undulated graphene nanosheets. The bubble‐like texture provides more active sites for effective ion transport and reversible capacitive behavior. The specific surface area of NG (5.03 at% N) can reach up to 438.7 m2 g?1, and the NG electrode demonstrates high specific capacitance (481 F g?1 at 1 A g?1, four times higher than reduced graphene oxide electrode (127.5 F g?1)), superior cycle stability (the capacitance retention of 98.9% in 2 m KOH and 99.2% in 1 m H2SO4 after 8000 cycles), and excellent energy density (42.8 Wh kg?1 at power density of 500 W kg?1 in 2 m KOH aqueous electrolyte). The results indicate the potential use of NG as graphene‐based electrode material for energy storage devices.  相似文献   

3.
The molecular dipole moment plays a significant role in governing important phenomena like molecular interactions, molecular configuration, and charge transfer, which are important in several electronic, electrochemical, and optoelectronic systems. Here, the effect of the change in the dipole moment of a tethered molecule on the carrier properties of (functionalized) trilayer graphene—a stack of three layers of sp2‐hybridized carbon atoms—is demonstrated. It is shown that, due to the high carrier confinement and large quantum capacitance, the trans‐to‐cis isomerisation of ‘covalently attached’ azobenzene molecules, with a change in dipole moment of 3D, leads to the generation of a high effective gating voltage. Consequently, 6 units of holes are produced per azobenzene molecule (hole density increases by 440 000 holes μm?2). Based on Raman and X‐ray photoelectron spectroscopy data, a model is outlined for outer‐layer, azobenzene‐functionalized trilayer graphene with current modulation in the inner sp2 matrix. Here, 0.097 V are applied by the isomerisation of the functionalized azobenzene. Further, the large measured quantum capacitance of 72.5 μF cm?2 justifies the large Dirac point in the heavily doped system. The mechanism defining the effect of dipole modulation of covalently tethered molecules on graphene will enable future sensors and molecular‐machine interfaces with graphene.  相似文献   

4.
To date, graphene‐based electric double layer supercapacitors have not shown the remarkable specific capacitance as theoretically predicted. An efficient strategy toward boosting the overall capacitance is to endow graphene with pseudocapacitance. Herein, molecules of hydrolyzed polyimide (HPI) are used to functionalize N‐doped graphene (NG) via π–π interaction and the resulting enhanced electrochemical energy storage is reported. These aromatic molecules in monolayer form on graphene contribute strong pseudocapacitance. Paper‐like NG films with different areal mass loadings ranging from 0.5 to 4.8 mg cm?2 are prepared for supercapacitor electrodes. It is shown that the gravimetric capacitance can be increased by 50–60% after the surface functionalization by HPI molecules. A high specific capacitance of 553 F g?1 at 5 mV s?1 is achieved by the HPI‐NG film with a graphene mass loading of 0.5 mg cm?2 in H2SO4 aqueous electrolyte. For the HPI‐NG film with highest mass loading, the gravimetric specific capacitance drops to 340 F g?1 while the areal specific capacitance reaches a high value of 1.7 F cm?2. HPI‐NG films are also tested in Li2SO4 aqueous electrolyte, over an extended voltage window of 1.6 V. High specific energy densities up to 40 Wh kg?1 are achieved with the Li2SO4 electrolyte.  相似文献   

5.
The interaction of Tat‐conjugated PEGylated CdSe/ZnS quantum dots (QD) with the amphiphilic disulfonated aluminium phthalocyanine photosensitiser is investigated in aqueous solution and in a human breast cancer cell line. In aqueous solution, the QDs and phthalocyanine form stable nanocomposites. Using steady‐state and time‐resolved fluorescence measurements combined with singlet oxygen detection, efficient Förster resonance energy transfer (FRET) is observed with the QDs acting as donors, and the phthalocyanine photosensitiser, which mediates production of singlet oxygen, as acceptors. In cells, the Tat‐conjugated QDs localise in lysosomes and the QD fluorescence lifetimes are close to values observed in aqueous solution. Strong FRET‐induced quenching of the QD lifetime is observed in cells incubated with the nanocomposites using fluorescence lifetime imaging microscopy (FLIM). Using excitation of the QDs at wavelengths where phthalocyanine absorption is negligible, FRET‐induced release of QDs from endo/lysosomes is confirmed using confocal imaging and FLIM, which is attributed to photooxidative damage to the endo/lysosomal membranes mediated by the phthalocyanine acceptor.  相似文献   

6.
Catalysts with low‐cost, high activity and stability toward oxygen reduction reaction (ORR) are extremely desirable, but its development still remains a great challenge. Here, a novel magnetically separable hybrid of multimetal oxide, cobalt ferrite (CoFe2O4), anchored on nitrogen‐doped reduced graphene oxide (CoFe2O4/NG) is prepared via a facile solvothermal method followed by calcination at 500 °C. The structure of CoFe2O4/NG and the interaction of both components are analyzed by several techniques. The possible formation of Co/Fe N interaction in the CoFe2O4/NG catalyst is found. As a result, the well‐combination of CoFe2O4 nanoparticles with NG and its improved crystallinity lead to a synergistic and efficient catalyst with high performance to ORR through a four‐electron‐transfer process in alkaline medium. The CoFe2O4/NG exhibits particularly comparable catalytic activity as commercial Pt/C catalyst, and superior stability against methanol oxidation and CO poisoning. Meanwhile, it has been proved that both nitrogen doping and the spinel structure of CoFe2O4 can have a significant contribution to the catalytic activity by contrast experiments. Multimetal oxide hybrid demonstrates better catalysis to ORR than a single metal oxide hybrid. All results make the low‐cost and magnetically separable CoFe2O4/NG a promising alternative for costly platinum‐based ORR catalyst in fuel cells and metal‐air batteries.  相似文献   

7.
Development of high‐performance and low‐cost nonprecious metal electrocatalysts is critical for eco‐friendly hydrogen production through electrolysis. Herein, a novel nanoflower‐like electrocatalyst comprising few‐layer nitrogen‐doped graphene‐encapsulated nickel–copper alloy directly on a porous nitrogen‐doped graphic carbon framework (denoted as Nix Cuy @ NG‐NC) is successfully synthesized using a facile and scalable method through calcinating the carbon, copper, and nickel hydroxy carbonate composite under inert atmosphere. The introduction of Cu can effectively modulate the morphologies and hydrogen evolution reaction (HER) performance. Moreover, the calcination temperature is an important factor to tune the thickness of graphene layers of the Nix Cuy @ NG‐NC composites and the associated electrocatalytic performance. Due to the collective effects including unique porous flowered architecture and the synergetic effect between the bimetallic alloy core and graphene shell, the Ni3Cu1@ NG‐NC electrocatalyst obtained under optimized conditions exhibits highly efficient and ultrastable activity toward HER in harsh environments, i.e., a low overpotential of 122 mV to achieve a current density of 10 mA cm?2 with a low Tafel slope of 84.2 mV dec?1 in alkaline media, and a low overpotential of 95 mV to achieve a current density of 10 mA cm?2 with a low Tafel slope of 77.1 mV dec?1 in acidic electrolyte.  相似文献   

8.
Two‐dimensional (2D) in‐plane p–n junctions with a continuous interface have great potential in next‐generation devices. To date, the general fabrication strategies rely on lateral epitaxial growth of p‐ and n‐type 2D semiconductors. An in‐plane p–n junction is fabricated with homogeneous monolayer Te at the step edge on graphene/6H‐SiC(0001). Scanning tunneling spectroscopy reveals that Te on the terrace of trilayer graphene is p‐type, and it is n‐type on monolayer graphene. Atomic‐resolution images demonstrate the continuous lattice of the junction, and mappings of the electronic states visualize the type‐II band bending across the space‐charge region of 6.2 nm with a build‐in field of 4 × 105 V cm?1. The reported strategy can be extended to other 2D semiconductors on patternable substrates for designed fabrication of in‐plane junctions.  相似文献   

9.
A new strategy is reported to achieve high‐mobility, low‐off‐current, and operationally stable solution‐processable metal‐oxide thin‐film transistors (TFTs) using a corrugated heterojunction channel structure. The corrugated heterojunction channel, having alternating thin‐indium‐tin‐zinc‐oxide (ITZO)/indium‐gallium‐zinc‐oxide (IGZO) and thick‐ITZO/IGZO film regions, enables the accumulated electron concentration to be tuned in the TFT off‐ and on‐states via charge modulation at the vertical regions of the heterojunction. The ITZO/IGZO TFTs with optimized corrugated structure exhibit a maximum field‐effect mobility >50 cm2 V?1 s?1 with an on/off current ratio of >108 and good operational stability (threshold voltage shift <1 V for a positive‐gate‐bias stress of 10 ks, without passivation). To exploit the underlying conduction mechanism of the corrugated heterojunction TFTs, a physical model is implemented by using a variety of chemical, structural, and electrical characterization tools and Technology Computer‐Aided Design simulations. The physical model reveals that efficient charge manipulation is possible via the corrugated structure, by inducing an extremely high carrier concentration at the nanoscale vertical channel regions, enabling low off‐currents and high on‐currents depending on the applied gate bias.  相似文献   

10.
Lithium–sulfur (Li–S) batteries have arousing interest because of their high theoretical energy density. However, they often suffer from sluggish conversion of lithium polysulfides (LiPS) during the charge/discharge process. Single nickel (Ni) atoms on nitrogen‐doped graphene (Ni@NG) with Ni–N4 structure are prepared and introduced to modify the separators of Li–S batteries. The oxidized Ni sites of the Ni–N4 structure act as polysulfide traps, efficiently accommodating polysulfide ion electrons by forming strong Sx 2????Ni? N bonding. Additionally, charge transfer between the LiPS and oxidized Ni sites endows the LiPS on Ni@NG with low free energy and decomposition energy barrier in an electrochemical process, accelerating the kinetic conversion of LiPS during the charge/discharge process. Furthermore, the large binding energy of LiPS on Ni@NG also shows its ability to immobilize the LiPS and further suppresses the undesirable shuttle effect. Therefore, a Li–S battery based on a Ni@NG modified separator exhibits excellent rate performance and stable cycling life with only 0.06% capacity decay per cycle. It affords fresh insights for developing single‐atom catalysts to accelerate the kinetic conversion of LiPS for highly stable Li–S batteries.  相似文献   

11.
A novel zinc phthalocyanine containing eight carboxyl groups was synthesized and utilized as a co-adsorbent with lutein for dye-sensitized solar cells enhance the photoelectric conversion efficiency. The effects of various phthalocyanine/lutein mole ratios on the performances of the fabricated solar cells were investigated. The results showed that zinc octacarboxylic phthalocyanine aggregation decreased with the increasing lutein/phthalocyanine mole ratios and zinc octacarboxylic phthalocyanine fluorescence was strongly quenched due to energy transfer from the phthalocyanine to the excited lutein. The photoelectric conversion efficiency reached its maximum when zinc octacarboxylic phthalocyanine/lutein mole ratio was 4:1. Moreover, the charge-transfer resistances and electron lifetimes at the TiO2/dye/electrolyte interface also showed great dependency on the phthalocyanine/lutein mole ratios by electrochemical impedance spectroscopy. The density-functional theory calculation of zinc phthalocyanine suggests that the electronic cloud density distribution move from the phthalocyanine ring framework toward the anchoring carboxylic group and further to the conduction band of TiO2, which results in efficient electron transfer.  相似文献   

12.
A wafer‐scale patterning method for solution‐processed graphene electrodes, named the transfer‐and‐reverse stamping method, is universally applicable for fabricating source/drain electrodes of n‐ and p‐type organic field‐effect transistors with excellent performance. The patterning method begins with transferring a highly uniform reduced graphene oxide thin film, which is pre‐prepared on a glass substrate, onto hydrophobic silanized (rigid/flexible) substrates. Patterns of the as‐prepared reduced graphene oxide films are then formed by modulating the surface energy of the films and selectively delaminating the films using an oxygen‐plasma‐treated elastomeric stamp with patterns. Reduced graphene oxide patterns with various sizes and shapes can be readily formed onto an entire wafer. Also, they can serve as the source/drain electrodes for benchmark n‐ and p‐type organic field‐effect transistors with enhanced performance, compared to those using conventional metal electrodes. These results demonstrate the general utility of this technique. Furthermore, this simple, inexpensive, and scalable electrode‐patterning‐technique leads to assembling organic complementary circuits onto a flexible substrate successfully.  相似文献   

13.
Under development for next‐generation wearable electronics are flexible, knittable, and wearable energy‐storage devices with high energy density that can be integrated into textiles. Herein, knittable fiber‐shaped zinc–air batteries with high volumetric energy density (36.1 mWh cm?3) are fabricated via a facile and continuous method with low‐cost materials. Furthermore, a high‐yield method is developed to prepare the key component of the fiber‐shaped zinc–air battery, i.e., a bifunctional catalyst composed of atomically thin layer‐by‐layer mesoporous Co3O4/nitrogen‐doped reduced graphene oxide (N‐rGO) nanosheets. Benefiting from the high surface area, mesoporous structure, and strong synergetic effect between the Co3O4 and N‐rGO nanosheets, the bifunctional catalyst exhibits high activity and superior durability for oxygen reduction and evolution reactions. Compared to a fiber‐shaped zinc–air battery using state‐of‐the‐art Pt/C + RuO2 catalysts, the battery based on these Co3O4/N‐rGO nanosheets demonstrates enhanced and stable electrochemical performance, even under severe deformation. Such batteries, for the first time, can be successfully knitted into clothes without short circuits under external forces and can power various electronic devices and even charge a cellphone.  相似文献   

14.
Halide perovskites have high light absorption coefficients, long charge carrier diffusion lengths, intense photoluminescence, and slow rates of non‐radiative charge recombination. Thus, they are attractive photoactive materials for developing high‐performance optoelectronic devices. These devices are also cheap and easy to be fabricated. To realize the optimal performances of halide perovskite‐based optoelectronic devices (HPODs), perovskite photoactive layers should work effectively with other functional materials such as electrodes, interfacial layers and encapsulating films. Conventional two‐dimensional (2D) materials are promising candidates for this purpose because of their unique structures and/or interesting optoelectronic properties. Here, we comprehensively summarize the recent advancements in the applications of conventional 2D materials for halide perovskite‐based photodetectors, solar cells and light‐emitting diodes. The examples of these 2D materials are graphene and its derivatives, mono‐ and few‐layer transition metal dichalcogenides (TMDs), graphdiyne and metal nanosheets, etc. The research related to 2D nanostructured perovskites and 2D Ruddlesden–Popper perovskites as efficient and stable photoactive layers is also outlined. The syntheses, functions and working mechanisms of relevant 2D materials are introduced, and the challenges to achieving practical applications of HPODs using 2D materials are also discussed.  相似文献   

15.
Fabrication and characterization of heterojunction solar cells of tetracyanoquinodimethane (TCNQ)/copper phthalocyanine (CuPc) and zinc phthalocyanine (ZnPc) were carried out. The light-induced charge separation with charge transfer was investigated by light-induced current density and optical absorption. In both cases of the TCNQ/CuPc and TCNQ/ZnPc solar cells, the TCNQ thin film worked for strong electron-accepting layer as n-type semiconductor. These behaviors would be originated in charge transfer of excited electron from CuPc and ZnPc to TCNQ. The photovoltaic mechanism was discussed on the basis of the experimental results.  相似文献   

16.
Bismuth is a promising anode material for state‐of‐the‐art rechargeable batteries due to its high theoretical volumetric capacity and relatively low working potential. However, its charge storage mechanism is unclear, hindering further improvement of the cell performance. Here, using in situ transmission electron microscopy and X‐ray diffraction techniques as well as theoretical analysis, it is found that a large anisotropic volume expansion of 142% occurs along the z‐axis largely due to the alloy reaction during sodiation, significantly reducing the electrochemical performance of bismuth electrodes. To address this problem, ultrathin few‐layer bismuthene with a large aspect ratio is rationally synthesized, and can relieve the expansion strain along the z‐axis. A free‐standing bismuthene/graphene composite electrode with tunable thickness achieves a strikingly stable and high areal sodium storage capacity of 12.1 mAh cm?2, which greatly exceeds that of most reported electrode materials. The clarification of the charge storage mechanism and the superior areal capacity achieved should facilitate the development of bismuth‐based high‐performance anodes for practical electrochemical energy‐storage applications.  相似文献   

17.
Graphene is a promising candidate material for high‐speed and ultra‐broadband photodetectors. However, graphene‐based photodetectors suffer from low photoreponsivity and Ilight/Idark ratios due to their negligible‐gap nature and small optical absorption. Here, a new type of graphene/InAs nanowire (NW) vertically stacked heterojunction infrared photodetector is reported, with a large photoresponsivity of 0.5 AW?1 and Ilight/Idark ratio of 5 × 102, while the photoresponsivity and Ilight/Idark ratio of graphene infrared photodetectors are 0.1 mAW?1 and 1, respectively. The Fermi level (EF ) of graphene can be widely tuned by the gate voltage owing to its 2D nature. As a result, the back‐gated bias can modulate the Schottky barrier (SB) height at the interface between graphene and InAs NWs. Simulations further demonstrate the rectification behavior of graphene/InAs NW heterojunctions and the tunable SB controls charge transport across the vertically stacked heterostructure. The results address key challenges for graphene‐based infrared detectors, and are promising for the development of graphene electronic and optoelectronic applications.  相似文献   

18.
Visible‐light‐driven conversion of CO2 into chemical fuels is an intriguing approach to address the energy and environmental challenges. In principle, light harvesting and catalytic reactions can be both optimized by combining the merits of homogeneous and heterogeneous photocatalysts; however, the efficiency of charge transfer between light absorbers and catalytic sites is often too low to limit the overall photocatalytic performance. In this communication, it is reported that the single‐atom Co sites coordinated on the partially oxidized graphene nanosheets can serve as a highly active and durable heterogeneous catalyst for CO2 conversion, wherein the graphene bridges homogeneous light absorbers with single‐atom catalytic sites for the efficient transfer of photoexcited electrons. As a result, the turnover number for CO production reaches a high value of 678 with an unprecedented turnover frequency of 3.77 min?1, superior to those obtained with the state‐of‐the‐art heterogeneous photocatalysts. This work provides fresh insights into the design of catalytic sites toward photocatalytic CO2 conversion from the angle of single‐atom catalysis and highlights the role of charge kinetics in bridging the gap between heterogeneous and homogeneous photocatalysts.  相似文献   

19.
Conjugated‐polyelectrolyte (CPE)‐functionalized reduced graphene oxide (rGO) sheets are synthesized for the first time by taking advantage of a specially designed CPE, PFVSO3, with a planar backbone and charged sulfonate and oligo(ethylene glycol) side chains to assist the hydrazine‐mediated reduction of graphene oxide (GO) in aqueous solution. The resulting CPE‐functionalized rGO (PFVSO3‐rGO) shows excellent solubility and stability in a variety of polar solvents, including water, ethanol, methanol, dimethyl sulfoxide, and dimethyl formamide. The morphology of PFVSO3‐rGO is studied by atomic force microscopy, X‐ray diffraction, and transmission electron microscopy, which reveal a sandwich‐like nanostructure. Within this nanostructure, the backbones of PFVSO3 stack onto the basal plane of rGO sheets via strong π–π interactions, while the charged hydrophilic side chains of PFVSO3 prevent the rGO sheets from aggregating via electrostatic and steric repulsions, thus leading to the solubility and stability of PFVSO3‐rGO in polar solvents. Optoelectronic studies show that the presence of PFVSO3 within rGO induces photoinduced charge transfer and p‐doping of rGO. As a result, the electrical conductivity of PFVSO3‐rGO is not only much better than that of GO, but also than that of the unmodified rGO.  相似文献   

20.
Semiconducting polymers with π‐conjugated electronic structures have potential application in the large‐scale printable fabrication of high‐performance electronic and optoelectronic devices. However, owing to their poor environmental stability and high‐cost synthesis, polymer semiconductors possess limited device implementation. Here, an approach for constructing a π‐conjugated polymer/graphene composite material to circumvent these limitations is provided, and then this material is patterned into 1D arrays. Driven by the π–π interaction, several‐layer polymers can be adsorbed onto the graphene planes. The low consumption of the high‐cost semiconductor polymers and the mass production of graphene contribute to the low‐cost fabrication of the π‐conjugated polymer/graphene composite materials. Based on the π‐conjugated system, a reduced π–π stacking distance between graphene and the polymer can be achieved, yielding enhanced charge‐transport properties. Owing to the incorporation of graphene, the composite material shows improved thermal stability. More generally, it is believed that the construction of the π‐conjugated composite shows clear possibility of integrating organic molecules and 2D materials into microstructure arrays for property‐by‐design fabrication of functional devices with large area, low cost, and high efficiency.  相似文献   

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