Carbon Overlayer Research Articles

Magnetization Reversal and Domain Nucleation in Ultra-Thin Co/Re(0001) Capped by Graphitic C

By using X-ray magnetic circular dichroism-photoemission electron microscopy, we study the magnetic behavior of ultra-thin Co on Re(0001) covered by a single layer of graphitic carbon. The carbon overlayer is lithographically fabricated via electron-stimulated dissociative adsorption of CO and subsequent annealing to 650 K. Graphitization is found to induce perpendicular magnetic anisotropy in cobalt at a thickness in the range 4-5 atomic layers, where out-of-plane domains separated by chiral Neél type walls are observed. The graphitic overlayer efficiently protects Co from oxidation upon exposure to ambient conditions, leaving its magnetic structure completely unaffected. The magnetic response of the Co film to an external field is imaged in situ across the hysteresis loop, allowing a quantitative analysis of the field-dependent domain area and structure. Our observations pinpoint the influence of the step morphology on the local magnetic behavior. Moreover, below the saturation field, the domains with chiral walls evolve into nanometric-sized magnetic structures resembling skyrmionic bubbles for applied fields <;20 G.

Mesoporous, nitrogen-doped, graphitized carbon nanosheets embedded with cobalt nanoparticles for efficient oxygen electroreduction

Nitrogen-doped graphitized carbon nanosheets embedded with crystalline cobalt nanoparticles are facilely synthesized with the aid of melamine-containing hydrogen-bonded organic frameworks (HOF). Experimentally, HOF microrods with an in situ polymerized dopamine (DA) overlayer are coordinated with Co2+ cations and used as a precursor. After pyrolyzing the Co@DA-HOF precursor, irregular sheet-like carbons comprising a large number of Co nanoparticles as well as abundant mesopores are obtained (Co@MPC-T). The thermal decomposition of melamine-containing HOF microrods during high-temperature pyrolysis helps generate the abundant porous structures in the resulting catalyst samples. Thus, synthesized Co@MPC-T catalysts display an apparent ORR activity, and the one pyrolyzed at 800 °C is determined to show the highest ORR catalytic activity among the series, with a half-wave potential of + 0.796 V, a diffusion-limiting current density of 5.492 mA cm−2 at + 0.200 V and a kinetic current of 51.40 mA cm−2 that is even two times higher than the 20.10 mA cm−2 for commercial Pt/C catalyst. Moreover, benefiting from the protection of graphitized carbon overlayer, Co@MPC-800 shows a substantially higher operation stability as well as superior tolerance to fuel crossover, as compared with the commercial Pt/C catalyst. The remarkable ORR performance of Co@MPC-800 highlights the high potential of graphitized two-dimensional carbon composites with nonprecious transition metal nanoparticles in electrocatalysis.

Stimulated CO Dissociation and Surface Graphitization by Microfocused X-ray and Electron Beams

The irradiation with photons or electrons can dramatically influence the chemical stability of a molecule, either free or adsorbed on a surface, inducing its fragmentation or desorption. We revisit here the exostimulated dissociation of CO, a prototypical case, choosing hcp thin cobalt films as model support. Intense, microfocused soft X-rays or electron beams are used to locally stimulate CO dissociation. Fast-XPS gives direct access to the adsorbates’ chemical state and coverage during irradiation, enabling the kinetics of the process to be monitored in real time. The energy-dependent cross sections for photon and electron stimulated molecular dissociation and desorption are estimated for a fixed initial CO coverage of 1/3 ML. In the soft X-ray regime, the desorption channel always prevails over dissociation and is significantly enhanced above the O K edge. The relative dissociation probability increases steadily with increasing photon energy, reaching 30% at 780 eV. Furthermore, we show that low energy electrons in the range 50 to 200 eV dissociate CO more efficiently than X-rays. The prolonged irradiation of the Co surface in CO ambient is found to produce a continuous increase of the carbon coverage, initially promoting the formation of carbides and subsequently accumulating sp2 carbon on the surface. Far from being a detrimental effect, the CO stimulated dissociation can be exploited to lithographically graft carbon-rich microscopic patterns on Co, with resolution well into the nanometer scale. A brief thermal treatment following irradiation results in the formation of a graphitic carbon overlayer, which effectively protects Co from oxidation upon exposure to ambient conditions, preserving its out-of-plane magnetic anisotropy and domain configuration.

Protective Carbon Overlayers from 2,3-Naphthalenediol Pyrolysis on Mesoporous SiO₂ and Al₂O₃ Analyzed by Solid-State NMR.

Hydrothermally stable carbon overlayers can protect mesoporous oxides (SiO2 and Al2O3) from hydrolysis during aqueous-phase catalysis. Overlayers made at 800 °C by pyrolysis of 2,3-naphthalenediol deposited out of acetone solution were analyzed by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Power absorption due to sample conductivity was prevented by diluting the sample in nonconductive and background-free tricalcium phosphate. While pyrolysis on SiO2 produced a predominantly aromatic carbon film, at least 15% of nonaromatic carbon (sp3-hybridized C as well as C=O) was observed on γ-Al2O3. These species were not derived from residual solvent, according to spectra of the same material treated at 400 °C. The sp3-hybridized C exhibited weak couplings to hydrogen, short spin-lattice relaxation times, and unusually large shift anisotropies, which are characteristics of tetrahedral carbon with high concentrations of unpaired electrons. Moderate heat treatment at 400 °C on SiO2 and Al2O3 resulted in yellow-brown and nearly black samples, respectively, but the darker color on Al2O3 did not correspond to more extensive carbonization. Aromatic carbon bonded to hydrogen remained predominant and the peaks of naphthalenediol were still recognizable; however, some of the chemical shifts differed by up to 5 ppm, indicating significant differences in local structure. On SiO2, additional sharp peaks were detected and attributed to 1/3 of the 2,3-naphthalene molecules undergoing fast, nearly isotropic motions.

Boosting lithium-ion storage performance by synergistically coupling Zn0.76Co0.24S with N-/S-doped carbon and carbon nanofiber

In this work, we combine the preparation approach of bimetal-organic-framework and electrospinning technique to obtain Zn0.76Co0.24S nanoclusters with N-/S-doped carbon overlayer embedded in the interconnected one-dimensional (1D) carbon fibers (Zn0.76Co0.24S@C@CNF). Benefiting from the synergistic effect among Zn0.76Co0.24S, N-/S-doped carbon overlayer and carbon nanofiber, the Zn0.76Co0.24S@C@CNF anode exhibits large reversible capacities of 1113 mAh g−1 after 250 cycles at 0.1 A g−1 and 672 mAh g−1 after 500 cycles at 1 A g−1 for lithium ion batteries. The boosted lithium-ion storage performances of the Zn0.76Co0.24S@C@CNF anode are mainly due to the synergistic role of the two different metal sulfides reacting with lithium ions at discrepant voltages, N-/S-doped carbon coating supplying more active sites, and the interconnected 1D conductive nanofibers providing stable electrode structure, efficient transport route for electrons as well as fast lithium diffusion.

Interfacial Phenomena at the Junction of Conductive Carbon with Pseudocapacitive Metal Oxides and Polymers: Implications for Electrochemical Capacitors

The technological push to dramatically shorten the charge/discharge times of electrochemical energy-storage (EES) devices while still providing significant energy content requires rethinking how we design and assemble EES, from the choice of particular types of charge-storing materials to how those materials are spatially translated into a high-performance, yet still practical, electrode architecture. Materials that exhibit “pseudocapacitance,” with fast faradaic charge-storage mechanisms that mimic the current–voltage characteristics of a conventional capacitor, promise to satisfy both energy and power needs when incorporated into electrochemical capacitor (EC) devices. The poor electronic conductivity of most pseudocapacative materials (e.g., manganese oxides, MnOx) dictates that they must be integrated with a better electronic conductor, typically porous, nanostructured carbons, in order to minimize ohmic losses and to reasonably utilize innate faradaic capacity. The past decade has seen great advancements in the development of new electrode architectures that incorporate oxides or polymers at carbon substrates, accompanied by promising electrochemical results. Yet our experience with such multifunctional materials shows that we may still be “leaving on the table” too much energy and power performance, due to suboptimal electronic/chemical/physical interactions at the junction of carbon (with its semimetal character) and nanoscale overlayers of pseudocapacitive materials (often semiconductors or hopping conductors). In order to explore these fundamental questions, we step back from the complexity of 3D electrode architectures to planar electrode configurations that otherwise mimic the material characteristics of practical electrode structures. Carbon films prepared by chemical vapor deposition (CVD) that are based on the pyrolysis of benzene and related monomers serve as model substrates on which we deposit pseudocapacitive metal oxides and electroactive polymers. The resulting 2D interfaces are characterized by classical electroanalytical methods to determine fundamental properties such as electron-transfer kinetics. In conjunction with electrochemical characterization, we apply surface-sensitive techniques such as photoelectron spectroscopy and scanning probe microscopy to query electronic, chemical, and physical structure as those properties are tuned by variations in synthesis/deposition of each phase: carbon and pseudocapacitive coating. Lessons learned from these model 2D interfaces are readily applied to the redesign of practical 3D electrode structures in next-generation electrochemical capacitors and batteries.

Modulating the CO methanation activity of Ni catalyst by nitrogen doped carbon

Nitrogen doping has been proved to be an effective way to modify the properties of graphene and other carbon materials. Herein, we explore a composite with nitrogen doped carbon overlayers wrapping SiC substrate as a support for Ni (Ni/CN-SiC) and evaluate its effects on the methanation activity. The results show that both the activity and stability of Ni are enhanced. Characterization with STEM, XRD, XPS, Raman and H2-TPR indicates that nitrogen doping generates more defects in the carbon overlayers, which benefit the dispersion of Ni. Furthermore, the reduction of Ni is facilitated.

PVD-Deposited Micro-SOFC Model Systems

In order to lower the operating temperatures, an important branch of SOFC-related research is dedicated to finding new electrolyte materials to use instead of yttria-stabilized zirconia (YSZ), such as doped ceria or perovskites.[1] In conventional cells, these are around 1073–1273 K,[2] which is too high for mobile applications. Another option is to reduce the electrolyte thickness to the low micrometer range – creating so-called anode-supported SOFCs.[3] However, this temperature could be lowered even further by reducing the thickness of the electrolyte layer to the 100 nm range. To prepare the latter, physical vapor deposition (PVD) methods, such as magnetron sputtering, leading to dense, pinhole-free thin films, are ideal. If, additionally, also the anode and cathode materials are kept thin, lower masses of the whole cells result, creating so-called micro-SOFCs. Thus, less energy would be required for operation, rendering Micro-SOFCs economically efficient as they could also exhibit increased lifetimes. As preliminary tests of the feasibility of such thin film layers, model anodes and anode/electrolyte systems were prepared. As electrolyte material, YSZ was used, with the anode component consisting of a 1:1 nickel/copper alloy. The latter allows to potentially substitute the conventionally used nickel, which is an ideal catalyst for graphite growth.[4] The presence of copper has already been shown to inhibit carbon formation during operation.[5] The YSZ and NiCu thin films, as well as the NiCu/YSZ bilayer, were deposited via magnetron sputtering on heated silicon and sodium chloride single crystals (873 K) to allow for the creation of well-crystallized and -ordered specimens. The latter are ideally suited for various spectroscopic and microscopic experiments. The stability of the samples in a methane atmosphere at elevated temperatures was further investigated.[6] X-ray photoelectron spectroscopy (XPS) indicates that minor carbon deposition occurs on YSZ (primarily consisting of sp3 species) upon treatment in methane at 1073 K. Both NiCu and NiCu/YSZ, in contrast, featured a very thick, strongly graphitic carbon overlayer. Elemental maps (STEM-EDX) reveal that, while the NiCu particles are rather homogeneous in the as-grown state, they form a core-shell structure upon reductive treatment in CH4- the particles consist of a nickel-rich core and a copper-rich outer layer. This shell also features variations in composition. While on those parts of the shell where the Ni/Cu ratio is about 3.5 to 5, carbon is deposited (also featuring carbon nanotubes), those with Ni/Cu ratios of about 0.5 do not exhibit any carbon overlayer at all. This suggests that the copper alloy indeed inhibits carbon growth. However, Ni/Cu ratios lower than 1:1 are required. According to DFT calculations, copper segregation is energetically favored and has been shown to occur in hydrogen.[5,8] Hence, it should be possible to generate the carbon-inhibiting core/shell structure starting from the 1:1 alloy by means of a pre-treatment in hydrogen at higher temperatures. [1] Marinha, D.; Dessemond, L.; Djurado, E. Curr. Inorg. Chem. 2013, 3,2–22 [2] Atkinson, A.; Barnett, S.; Gorte, R. J.; Irvine, J. T. S.; McEvoy, A. J.; Mogensen, M.; Singhal, S. C.; Vohs, J. Nat. Mater. 2004, 3,17–27 [3] Verbraeken, M. Master’s Thesis, University of Twente, 2005 [4] Toebe, M. L.; Bitter, J. H.; van Dillen, A. J.; de Jong, K. P. Catal. Today 2002, 76,33–42 [5] Kim, H.; Lu, C.; Worrell, W. L.; Vohs, J. M.; Gorte, R. J. J. Electrochem. Soc. 2002, 149,A247–A250 [6] Götsch, T.; Schachinger, T.; Stöger-Pollach, M.; Kaindl, R.; Penner, S. Appl. Surf. Sci. 2017, 402,1–11 [7] Götsch, T.; Wallisch, W.; Stöger-Pollach, M.; Klötzer, B.; Penner, S. AIP Adv. 2016, 6 (2),025119 [8] Wolfbeisser, A.; Kovács, G.; Kozlov, S. M.; Föttinger, K.; Bernardi, J.; Klötzer, B.; Neymann, K. M.; Rupprechter, G. Catal. Today 2017,283, 134–143 Figure 1:STEM-EDX map of the NiCu/YSZ sample after methane treatment shows that the carbon deposition does not occur for those surfaces of the core/shell particles that have a Ni/Cu ratio of about 0.5 (marked by blue arrows). Figure 1

Bimetal-Organic-Framework Derivation of Ball-Cactus-Like Ni-Sn-P@C-CNT as Long-Cycle Anode for Lithium Ion Battery.

Metal phosphides are a new class of potential high-capacity anodes for lithium ion batteries, but their short cycle life is the critical problem to hinder its practical application. A unique ball-cactus-like microsphere of carbon coated NiP2 /Ni3 Sn4 with deep-rooted carbon nanotubes (Ni-Sn-P@C-CNT) is demonstrated in this work to solve this problem. Bimetal-organic-frameworks (BMOFs, Ni-Sn-BTC, BTC refers to 1,3,5-benzenetricarboxylic acid) are formed by a two-step uniform microwave-assisted irradiation approach and used as the precursor to grow Ni-Sn@C-CNT, Ni-Sn-P@C-CNT, yolk-shell Ni-Sn@C, and Ni-Sn-P@C. The uniform carbon overlayer is formed by the decomposition of organic ligands from MOFs and small CNTs are deeply rooted in Ni-Sn-P@C microsphere due to the in situ catalysis effect of Ni-Sn. Among these potential anode materials, the Ni-Sn-P@C-CNT is found to be a promising anode with best electrochemical properties. It exhibits a large reversible capacity of 704 mA h g-1 after 200 cycles at 100 mA g-1 and excellent high-rate cycling performance (a stable capacity of 504 mA h g-1 retained after 800 cycles at 1 A g-1 ). These good electrochemical properties are mainly ascribed to the unique 3D mesoporous structure design along with dual active components showing synergistic electrochemical activity within different voltage windows.

Ethene to Graphene: Surface Catalyzed Chemical Pathways, Intermediates, and Assembly

Diverse technologies from catalyst coking to graphene synthesis entail hydrocarbon dehydrogenation and condensation reactions on metals and assembly into carbon overlayers. Imperative to gaining control over these processes, through thermal steering of the formation of polyaryl intermediates and the controlled prevention of coking, is the exploration and elucidation of the detailed reaction scheme that starts with adsorbed hydrocarbons and culminates with the formation of extended graphene. Here we use scanning tunneling microscopy, high-resolution electron energy loss and thermal desorption spectroscopies, in combination with theoretical simulations to uncover the hierarchy of pathways and intermediates underlying the catalyzed evolution of ethene adsorbed on Rh(111) to form graphene. These investigations allow formulation of a reaction scheme whereby, upon heating, adsorbed ethene evolves via coupling reactions to form segmented one-dimensional polyaromatic hydrocarbons (1D-PAH). Further heating leads t...

Characteristics of elemental carbon overlayers over hematite electrodes prepared by electrodeposition with organic acid additives

We report that inducing elemental carbon overlayers on hematite electrodes is a universal case that can be achieved by electrodeposition with addition of a wide range of organic acid following by thermal treatment. The thickness of elemental carbon ovrelayers directly affects the photocurrent density of as-obtained samples, which can be adjusted by selection of organic acid and electrodeposition pH. An optimal carbon overlayer of approximately 2–5nm enhanced a 10 times higher photocurrent density (2.0mA/cm2 at 0.4VSCE) in comparison with those without carbon overlayers. While carbon overlayers were effective in passivating surface states, a capacitor was formed at the hematite/carbon overlayer interface upon illumination for 90min. Our results clearly demonstrated the characteristics of effective carbon overlayers include (i) passivating surface states to reduce the onset photocurrent potential, (ii) injecting additional charges to enhance the photocurrent plateau, and (iii) the durability to sustain a long period of sunlight illumination.

Carbon Nanotubes Rooted in Porous Ternary Metal Sulfide@N/S‐Doped Carbon Dodecahedron: Bimetal‐Organic‐Frameworks Derivation and Electrochemical Application for High‐Capacity and Long‐Life Lithium‐Ion Batteries

Lithium ion battery is the predominant power source for portable electronic devices, electrical vehicles, and back‐up electricity storage units for clean and renewable energies. High‐capacity and long‐life electrode materials are essential for the next‐generation Li‐ion battery with high energy density. Here bimetal‐organic‐frameworks synthesis of Co0.4Zn0.19S@N and S codoped carbon dodecahedron is shown with rooted carbon nanotubes (Co‐Zn‐S@N‐S‐C‐CNT) for high‐performance Li‐ion battery application. Benefiting from the synergetic effect of two metal sulfide species for Li‐storage at different voltages, mesoporous dodecahedron structure, N and S codoped carbon overlayer and deep‐rooted CNTs network, the product exhibits a larger‐than‐theoretical reversible Li‐storage capacity of 941 mAh g−1 after 250 cycles at 100 mA g−1 and excellent high‐rate capability (734, 591, 505 mAh g−1 after 500 cycles at large current densities of 1, 2, and 5 A g−1 , respectively).

Greatly Enhanced Stability of Supported Copper Nanocatalyst with a Thin Nitrogen‐Doped Carbon Overlayer for Transfer Dehydrogenation

AbstractIn the present study, we report a facile synthetic approach for supported copper nanocatalysts with a thin nitrogen‐doped carbon (CN) overlayer. This Cu@CN catalyst was directly generated by a thermal decomposition of Cu‐Al layered double hydroxide (CuAl‐LDH)/melamine hybrid precursor, and employed in the liquid‐phase transfer dehydrogenation of primary aliphatic alcohols. The strategy was found to be useful for the formation of a very thin in situ formed CN overlayer of 0.5–0.7 nm in thickness on copper nanoparticles of about 8.5 nm in diameter. Compared with uncoated copper‐based catalyst derived from pristine CuAl‐LDH, as‐fabricated Cu@CN catalyst showed significantly enhanced catalytic activity, which was attributed to the surface cooperative effect among strong Lewis base sites originating from the CN layer, well‐dispersed Cu0 nanoparticles and Cu+ species, thereby greatly promoting the activation of hydroxyl group in primary aliphatic alcohols and the following abstraction and transfer of hydrogen. Most importantly, the thin CN overlayer could successfully stabilize copper nanoparticles, thus preventing the leaching and the growth of copper species over the course of the reaction. This work offers a new strategy for fabricating cost‐effective, highly efficient and extremely stable supported copper catalysts for the transfer dehydrogenation of primary aliphatic alcohols.

Atomic Scale Interface Manipulation, Structural Engineering, and Their Impact on Ultrathin Carbon Films in Controlling Wear, Friction, and Corrosion.

Reducing friction, wear, and corrosion of diverse materials/devices using <2 nm thick protective carbon films remains challenging, which limits the developments of many technologies, such as magnetic data storage systems. Here, we present a novel approach based on atomic scale interface manipulation to engineer and control the friction, wear, corrosion, and structural characteristics of 0.7-1.7 nm carbon-based films on CoCrPt:oxide-based magnetic media. We demonstrate that when an atomically thin (∼0.5 nm) chromium nitride (CrNx) layer is sandwiched between the magnetic media and an ultrathin carbon overlayer (1.2 nm), it modifies the film-substrate interface, creates various types of interfacial bonding, increases the interfacial adhesion, and tunes the structure of carbon in terms of its sp(3) bonding. These contribute to its remarkable functional properties, such as stable and lowest coefficient of friction (∼0.15-0.2), highest wear resistance and better corrosion resistance despite being only ∼1.7 nm thick, surpassing those of ∼2.7 nm thick current commercial carbon overcoat (COC) and other overcoats in this work. While this approach has direct implications for advancing current magnetic storage technology with its ultralow thickness, it can also be applied to advance the protective and barrier capabilities of other ultrathin materials for associated technologies.

Electrochemical deposition of Ni on F-doped SnO2 substrate and its post-annealing for use as current collector of dye-sensitized solar cell

Current collector is an important part of nanostructured dye-sensitized solar cells (DSSCs), which reduces ohmic loss. In the present work, Ni current collector was electrochemically deposited on fluorine-doped tin oxide (FTO) for use as current collector of DSSC. The adhesion of Ni to FTO was improved by post-annealing in ambient atmosphere. A new method was proposed to prevent Ni coating from oxidation during annealing. According to this method, a carbon over-layer was applied on Ni coating, which protected Ni from oxidation. Visual inspection and X-ray diffraction (XRD) results showed the effectiveness of this method in protection of Ni coating from oxidation. Furthermore, the effect of current collector on photovoltaic performance of DSSCs was investigated using current density-voltage curve measurement and electrochemical impedance spectroscopy methods. It was observed that post-annealing in ambient atmosphere, under protection of carbon over-layer, improves both the adhesion of Ni current collector to FTO and the photovoltaic performance of DSSC. However, Ni oxidation during post-annealing of Ni current collector, without carbon over-layer, significantly decreased the photovoltaic parameters of DSSC. The above observations were explained by considering the series resistance of DSSC.

Carbon-Coated MnMoO4 Nanorod for High-Performance Lithium-Ion Batteries

Molybdenum oxysalt is a promising electrode candidate for lithium ion battery due to its flexible composition structure and large Li-storage capacity. An unprecedented MnMoO4 with a carbon overlayer is synthesized by room-temperature reaction of manganese salt and molybdate, followed hydrothermal treatment with glucose. The rod-like MnMoO4@C exhibits excellent electrochemical performance as an anode for rechargeable lithium ion batteries. A large reversible capacity of 1050mAhg−1 can be retained after 200 cycles at a current density of 100mAg−1. The improved lithium storage performance is attributed to the presence of electrically-conductive carbon coating, which can improve the lithium transportation and alleviate the large volume change of ternary metal oxide during repetitive cycling.

The role of carbon overlayers on Pt-based catalysts for H2-cleanup by CO-PROX

In this work, we analyze the effect of the activation method on the catalytic activity of Pt-based catalysts supported on alumina in the PROX reaction. For this, model Pt/Al2O3 catalysts with variable amounts of acetic acid were prepared and their thermal evolution studied by FTIR spectroscopy. From the analysis of the nature of the platinum surface upon acetic acid decomposition and the gas phase evolved products, we have demonstrated the formation of partially hydrogenated carbon overlayers that tailor the activity of Pt-based catalysts in the PROX reaction.

Controllable synthesis of carbon-coated Sn⿿SnO2⿿carbon-nanofiber membrane as advanced binder-free anode for lithium-ion batteries

A carbon-coated composite consisting of Sn, SnO2, and porous carbon-nanofiber membrane (Sn⿿SnO2⿿CNF@C) was successfully prepared via electrospinning followed by carbonization and low-temperature hydrothermal treatment. The thickness of the carbon overlayer formed by using sucrose as the carbon source could be well controlled by adjusting the sucrose concentration. The three-dimensional (3D) nanofiber network structure allowed the Sn⿿SnO2⿿CNF@C membrane to be used directly as an anode in lithium-ion batteries without adding any polymer binders or electrical conductors. The composite electrodes of this material exhibited a high discharge capacity of 712.2mAhg⿿1 at a high current density of 0.8Ag⿿1 after 200 cycles, as well as good cycling stability and excellent rate capability, which can be ascribed to the improved electrochemical properties of the Sn⿿SnO2 particles provided by the protective carbon coating and the 3D carbon nanofiber membrane. The composite can thus be widely used as an advanced binder-free anode material in high-current rechargeable lithium-ion batteries and extended to the fabrication of flexible electrodes.

Preparation of cribriform sheet-like carbon-coated zinc oxide with improved electrochemical performance

Cribriform sheet-like carbon-coated ZnO are prepared using pyrrole as the carbon source. It is found that a sheet-like precursor will form when polymerizing pyrrole in the presence of ZnO particles. After the carbonization of precursor, cribriform sheet-like carbon-coated ZnO can be obtained. Morphology and structure analysis of as-prepared carbon-coated ZnO is conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The carbon overlayer not only present a barrier layer on the surface of the ZnO particles, which keeps relative high discharge capacity by inhibiting the active materials in electrode from dissolving into electrolyte, but also modify the surface status of ZnO particles so as to obtain more uniform current distribution and improved conductivity. As a result, when evaluated as an anode material for Zn/Ni cell, carbon-coated ZnO exhibit a more stable cycle performance than bare ZnO electrode.

One-pot synthesis of carbon coated Fe3O4 nanosheets with superior lithium storage capability

Large-scale flat Fe3O4 nanosheets coated by an amorphous carbon overlayer (denoted as Fe3O4@C NSs) was prepared via a simple one-pot solution method. When evaluated as an electrode for LIBs, the as-prepared Fe3O4@C NSs hybrids exhibit highly enhanced lithium storage properties.