Showing papers on "Oxide published in 2017"
TL;DR: A simple scalable method is demonstrated to obtain graphene-based membranes with limited swelling, which exhibit 97% rejection for NaCl and decrease exponentially with decreasing sieve size, but water transport is weakly affected.
Abstract: Ion permeation and selectivity of graphene oxide membranes with sub-nm channels dramatically alters with the change in interlayer distance due to dehydration effects whereas permeation of water molecules remains largely unaffected. Graphene oxide membranes show exceptional molecular permeation properties, with promise for many applications1,2,3,4,5. However, their use in ion sieving and desalination technologies is limited by a permeation cutoff of ∼9 A (ref. 4), which is larger than the diameters of hydrated ions of common salts4,6. The cutoff is determined by the interlayer spacing (d) of ∼13.5 A, typical for graphene oxide laminates that swell in water2,4. Achieving smaller d for the laminates immersed in water has proved to be a challenge. Here, we describe how to control d by physical confinement and achieve accurate and tunable ion sieving. Membranes with d from ∼9.8 A to 6.4 A are demonstrated, providing a sieve size smaller than the diameters of hydrated ions. In this regime, ion permeation is found to be thermally activated with energy barriers of ∼10–100 kJ mol–1 depending on d. Importantly, permeation rates decrease exponentially with decreasing sieve size but water transport is weakly affected (by a factor of <2). The latter is attributed to a low barrier for the entry of water molecules and large slip lengths inside graphene capillaries. Building on these findings, we demonstrate a simple scalable method to obtain graphene-based membranes with limited swelling, which exhibit 97% rejection for NaCl.
1,297 citations
TL;DR: Here, cationic control of the interlayer spacing of graphene oxide membranes with ångström precision is demonstrated using K+, Na+, Ca2+, Li+ or Mg2+ ions, suggesting that other ions could be used to produce a wider range of interlayer spacings.
Abstract: Graphene oxide membranes-partially oxidized, stacked sheets of graphene-can provide ultrathin, high-flux and energy-efficient membranes for precise ionic and molecular sieving in aqueous solution. These materials have shown potential in a variety of applications, including water desalination and purification, gas and ion separation, biosensors, proton conductors, lithium-based batteries and super-capacitors. Unlike the pores of carbon nanotube membranes, which have fixed sizes, the pores of graphene oxide membranes-that is, the interlayer spacing between graphene oxide sheets (a sheet is a single flake inside the membrane)-are of variable size. Furthermore, it is difficult to reduce the interlayer spacing sufficiently to exclude small ions and to maintain this spacing against the tendency of graphene oxide membranes to swell when immersed in aqueous solution. These challenges hinder the potential ion filtration applications of graphene oxide membranes. Here we demonstrate cationic control of the interlayer spacing of graphene oxide membranes with angstrom precision using K+, Na+, Ca2+, Li+ or Mg2+ ions. Moreover, membrane spacings controlled by one type of cation can efficiently and selectively exclude other cations that have larger hydrated volumes. First-principles calculations and ultraviolet absorption spectroscopy reveal that the location of the most stable cation adsorption is where oxide groups and aromatic rings coexist. Previous density functional theory computations show that other cations (Fe2+, Co2+, Cu2+, Cd2+, Cr2+ and Pb2+) should have a much stronger cation-π interaction with the graphene sheet than Na+ has, suggesting that other ions could be used to produce a wider range of interlayer spacings.
1,082 citations
TL;DR: A facile solution reduction method using NaBH4 as a reductant is developed to prepare iron-cobalt oxide nanosheets (Fex Coy -ONSs) with a large specific surface area, ultrathin thickness, and, importantly, abundant oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H2 O onto nearby Co3+ sites.
Abstract: Electrochemical water splitting is a promising method for storing light/electrical energy in the form of H2 fuel; however, it is limited by the sluggish anodic oxygen evolution reaction (OER). To improve the accessibility of H2 production, it is necessary to develop an efficient OER catalyst with large surface area, abundant active sites, and good stability, through a low-cost fabrication route. Herein, a facile solution reduction method using NaBH4 as a reductant is developed to prepare iron-cobalt oxide nanosheets (FexCoy-ONSs) with a large specific surface area (up to 261.1 m2 g−1), ultrathin thickness (1.2 nm), and, importantly, abundant oxygen vacancies. The mass activity of Fe1Co1-ONS measured at an overpotential of 350 mV reaches up to 54.9 A g−1, while its Tafel slope is 36.8 mV dec−1; both of which are superior to those of commercial RuO2, crystalline Fe1Co1-ONP, and most reported OER catalysts. The excellent OER catalytic activity of Fe1Co1-ONS can be attributed to its specific structure, e.g., ultrathin nanosheets that could facilitate mass diffusion/transport of OH− ions and provide more active sites for OER catalysis, and oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H2O onto nearby Co3+ sites.
1,058 citations
TL;DR: In this paper, the influence of different solvents on the structure and electrical properties of graphene oxide was studied by using modified hummers method in which different from conventional hummer's method.
886 citations
TL;DR: In this paper, the authors focus on the significant advances in tailored nanostructures of noble metal-metal oxide nanohybrids and highlight the improvement in performance in the representative solar energy conversion applications.
Abstract: The controlled synthesis of nanohybrids composed of noble metals (Au, Ag, Pt and Pd, as well as AuAg alloy) and metal oxides (ZnO, TiO2, Cu2O and CeO2) have received considerable attention for applications in photocatalysis, solar cells, drug delivery, surface enhanced Raman spectroscopy and many other important areas. The overall architecture of nanocomposites is one of the most important factors dictating the physical properties of nanohybrids. Noble metals can be coupled to metal oxides to yield diversified nanostructures, including noble metal decorated-metal oxide nanoparticles (NPs), nanoarrays, noble metal/metal oxide core/shell, noble metal/metal oxide yolk/shell and Janus noble metal–metal oxide nanostructures. In this review, we focus on the significant advances in tailored nanostructures of noble metal–metal oxide nanohybrids. The improvement in performance in the representative solar energy conversion applications including photocatalytic degradation of organic pollutants, photocatalytic hydrogen generation, photocatalytic CO2 reduction, dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are discussed. Finally, we conclude with a perspective on the future direction and prospects of these controllable nanohybrid materials.
756 citations
TL;DR: Graphene oxide-based aerogels with carefully tailored properties are developed to enable efficient solar steam generation under one-sun illumination.
Abstract: Graphene oxide-based aerogels with carefully tailored properties are developed to enable efficient solar steam generation. Aerogels, with inherent porous structures, are excellent thermal insulators and provide channels for water supply and vapor escape. With enhanced absorption and hydrophilicity by incorporation of carbon nanotubes and sodium alginate, the resulting aerogels can enable efficient (≈83%) solar steam generation under one-sun illumination.
751 citations
TL;DR: A better understanding of the complex reaction network is provided, the capability of manipulating structure and combination of metal and oxide at the interface in tuning selectivity is grasped, and the key descriptors to control the activity and, in particular, the selectivity of catalysts are identified.
Abstract: The chemical transformation of CO2 not only mitigates the anthropogenic CO2 emission into the Earth’s atmosphere but also produces carbon compounds that can be used as precursors for the production of chemicals and fuels. The activation and conversion of CO2 can be achieved on multifunctional catalytic sites available at the metal/oxide interface by taking advantage of the synergy between the metal nanoparticles and oxide support. Herein, we look at the recent progress in mechanistic studies of CO2 hydrogenation to C1 (CO, CH3OH, and CH4) compounds on metal/oxide catalysts. On this basis, we are able to provide a better understanding of the complex reaction network, grasp the capability of manipulating structure and combination of metal and oxide at the interface in tuning selectivity, and identify the key descriptors to control the activity and, in particular, the selectivity of catalysts. Finally, we also discuss challenges and future research opportunities for tuning the selective conversion of CO2 on ...
685 citations
10 Jan 2017
TL;DR: In this article, a modified Hummers method was used to synthesize reduced graphite oxide (rGO), which was then used as a precursor for graphene synthesis by thermal reduction processes.
Abstract: Over the span of years, improvements over various synthesis methods of graphene are constantly pursued to provide safer and more effective alternatives. Though the extraction of graphene through Hummers method is one of the oldest techniques yet it is one of the most suitable methods for the formation of bulk graphene. Graphene can be obtained in the form of reduced Graphite oxide, sometimes also referred as Graphene oxide. The effectiveness of this oxidation process can be evaluated by the magnitude of carbon/oxygen ratio of the obtained graphene. Here, graphene oxide (GO) was prepared by oxidizing the purified natural flake graphite (NFG) by a modified Hummers method. The attempts have been made to synthesize GO having few layers by using a modified Hummers method where the amount of NaNO3 has been decreased, and the amount of KMnO4 is increased. The reaction has been performed in a 9:1 (by volume) mixture of H2SO4/H3PO4. This modification is successful in increasing the reaction yield and reducing the toxic gas evolution while using a varied proportion of KMnO4 and H2SO4 as those required by Hummers method. A new component of K2S2O8 has been introduced to the reaction system to maintain the pH value. Reduced graphene oxide (rGO) was thereafter extracted by thermal modification of GO. Here, GO has been used as a precursor for graphene synthesis by thermal reduction processes. The results of FTIR and Raman spectroscopy analysis show that the NFG when oxidized by strong oxidants like KMnO4 and NaNO3, introduced oxygen atoms into the graphite layers and formed bonds like C=O, C-H, COOH and C-O-C with the carbon atoms in the graphite layers. The structure and morphology of both GO and rGO were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy, Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).
665 citations
TL;DR: Graphene oxide and its composites have attracted widespread attentions as novel adsorbents for the adsorption of various heavy metal contaminants as mentioned in this paper, because of the unique physicochemical characteristics, they might become an excellent and most potential adsorbent.
629 citations
TL;DR: The enhanced precision of top-down nanofabrication is used to prepare controlled and precisely tunable model systems that allow us to quantify the efficiency and spatial extent of hydrogen spillover on both reducible and nonreducible supports.
Abstract: The mechanism of hydrogen spillover is described using a precisely nanofabricated model system, explaining why it is slower on an aluminum oxide catalyst support than on a titanium oxide catalyst support.
533 citations
TL;DR: In this paper, the authors consider an additional aspect related to the formation of a metal/oxide interface, which can be realized when small metal nanoparticles are deposited on the surface of an oxide support or when a nanostructured oxide, either a nanoparticle or a thin film, is grown on a metal.
Abstract: Reducibility is an essential characteristic of oxide catalysts in oxidation reactions following the Mars–van Krevelen mechanism. A typical descriptor of the reducibility of an oxide is the cost of formation of an oxygen vacancy, which measures the tendency of the oxide to lose oxygen or to donate it to an adsorbed species with consequent change in the surface composition, from MnOm to MnOm–x. The oxide reducibility, however, can be modified in various ways: for instance, by doping and/or nanostructuring. In this review we consider an additional aspect, related to the formation of a metal/oxide interface. This can be realized when small metal nanoparticles are deposited on the surface of an oxide support or when a nanostructured oxide, either a nanoparticle or a thin film, is grown on a metal. In the past decade, both theory and experiment indicate a particularly high reactivity of the oxygen atoms at the boundary region between a metal and an oxide. Oxygen atoms can be removed from interface sites at much...
TL;DR: A direct stepwise method for converting methane into methanol with high selectivity over a copper-containing zeolite, based on partial oxidation with water, involving methane oxidation at CuII oxide active centers, followed by CuI reoxidation by water with concurrent formation of hydrogen.
Abstract: Direct functionalization of methane in natural gas remains a key challenge. We present a direct stepwise method for converting methane into methanol with high selectivity (~97%) over a copper-containing zeolite, based on partial oxidation with water. The activation in helium at 673 kelvin (K), followed by consecutive catalyst exposures to 7 bars of methane and then water at 473 K, consistently produced 0.204 mole of CH3OH per mole of copper in zeolite. Isotopic labeling confirmed water as the source of oxygen to regenerate the zeolite active centers and renders methanol desorption energetically favorable. On the basis of in situ x-ray absorption spectroscopy, infrared spectroscopy, and density functional theory calculations, we propose a mechanism involving methane oxidation at CuII oxide active centers, followed by CuI reoxidation by water with concurrent formation of hydrogen.
TL;DR: In this article, the authors used room-temperature liquid metals as a reaction environment for the synthesis of oxide nanomaterials with low dimensionality, which can be used to create 2D materials that were previously inaccessible with preexisting methods.
Abstract: Two-dimensional (2D) oxides have a wide variety of applications in electronics and other technologies. However, many oxides are not easy to synthesize as 2D materials through conventional methods. We used nontoxic eutectic gallium-based alloys as a reaction solvent and co-alloyed desired metals into the melt. On the basis of thermodynamic considerations, we predicted the composition of the self-limiting interfacial oxide. We isolated the surface oxide as a 2D layer, either on substrates or in suspension. This enabled us to produce extremely thin subnanometer layers of HfO2, Al2O3, and Gd2O3. The liquid metal–based reaction route can be used to create 2D materials that were previously inaccessible with preexisting methods. The work introduces room-temperature liquid metals as a reaction environment for the synthesis of oxide nanomaterials with low dimensionality.
TL;DR: In this article, the authors have studied the synthesis methods, characterization and the possible mechanism for green reduction, especially by ascorbic acid, which could possibly motivate the researcher worldwide to innovate new green methods for mass scale production of graphene based materials.
TL;DR: In this article, a solvent-based epoxy coatings filled with graphene oxide nanosheets (GO) was developed to enhance the corrosion protection of mild steel substrates.
TL;DR: Through the NH3 atmosphere annealing of a graphene oxide precursor containing trace amounts of Ru, this work has synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium, providing a route for the design of efficient ORR single-atom catalysts.
Abstract: The cathodic oxygen reduction reaction (ORR) is essential in the electrochemical energy conversion of fuel cells. Here, through the NH3 atmosphere annealing of a graphene oxide (GO) precursor containing trace amounts of Ru, we have synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium. The Ru/nitrogen-doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO4, together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. X-ray adsorption fine structure analysis and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy are performed and indicate that the chemical structure of Ru is predominantly composed of isolated Ru atoms coordinated with nitrogen atoms on the graphene substrate. Furthermor...
TL;DR: In this article, the synthesis of carbonaceous materials from a metal organic framework (MIL-100), organic linker and N-precursor was comprehensively investigated, and the structures of the products were characterized.
Abstract: The synthesis of carbonaceous materials from a metal organic framework (MIL-100), organic linker and N-precursor was comprehensively investigated, and the structures of the products were characterized. It was found that simple pyrolysis of mixed MIL-100 (Fe)/dicyandiamide (DCDA) could produce nitrogen-doped graphene (N-graphene). The N-graphene showed excellent performances in peroxymonosulfate (PMS) activation, which were superior to those of counterparts of graphene, iron(II, III) oxide, manganese(IV) oxide and cobalt(II, III) oxide. With PMS activation, N-graphene exhibited efficient catalytic degradation of various organic pollutants such as phenol, 2,4,6-trichlorophenol (TCP), sulfachloropyridazine (SCP) and p-hydroxybenzoic acid (PHBA). Electron paramagnetic resonance (EPR) spectroscopy and radical quenching tests were employed to investigate the PMS activation and organic degradation processes. It was found that singlet oxygen (1O2) was mainly produced during the activation of PMS by N-graphene, and contributed to the catalytic oxidation instead of sulfate and/or hydroxyl radicals. These findings provide new insights into PMS activation by metal-free carbon catalysis.
TL;DR: Indium-oxide (In2O3) nanobelts coated by a 5-nm-thick carbon layer provide an enhanced photocatalytic reduction of CO2 to CO andCH4, yielding CO and CH4 evolution rates of 126.6 and 27.9 μmol h-1, respectively, with water as reductant and Pt as co-catalyst.
Abstract: Indium-oxide (In2O3) nanobelts coated by a 5-nm-thick carbon layer provide an enhanced photocatalytic reduction of CO2 to CO and CH4, yielding CO and CH4 evolution rates of 126.6 and 27.9 μmol h–1, respectively, with water as reductant and Pt as co-catalyst. The carbon coat promotes the absorption of visible light, improves the separation of photoinduced electron–hole pairs, increases the chemisorption of CO2, makes more protons from water splitting participate in CO2 reduction, and thereby facilitates the photocatalytic reduction of CO2 to CO and CH4.
TL;DR: It is shown that amorphous CP can be used as general synthesis precursors of highly complex mixed metal oxide shells and can be applied to produce ternary and quaternary metal oxide onions with tunable size and composition.
Abstract: Metal-organic frameworks (MOFs) or coordination polymers (CPs) have been used as precursors for synthesis of materials. Unlike crystalline MOF, amorphous CP is nonspecific to metal cation species, therefore its composition can be tuned easily. Here, it is shown that amorphous CP can be used as general synthesis precursors of highly complex mixed metal oxide shells. As a proof of concept, NiCo coordination polymer spheres are first synthesized and subsequently transformed into seven-layered NiCo oxide onions by rapid thermal oxidation. This approach is very versatile and can be applied to produce ternary and quaternary metal oxide onions with tunable size and composition. The NiCo oxide onions exhibit exceptional charge storage capability in aqueous electrolyte with high specific capacitance (≈1900 F g-1 at 2 A g-1 ), good rate capability, and ultrahigh cycling stability (93.6% retention over 20 000 cycles). A hybrid supercapacitor against graphene/multishelled mesoporous carbon sphere shows a high energy density of 52.6 Wh kg-1 at a power density of 1604 W kg-1 (based on active materials weight), as well as remarkable cycling stability.
TL;DR: Investigating the electrocatalytic activity of ultrathin (diameter ∼20 nm) 5-fold twinned copper nanowires (Cu NWs) for CO2 reduction suggests that product selectivity on Cu NWs is highly dependent on morphological features and that hydrocarbon selectivity can be manipulated by structural evolution or the prevention thereof.
Abstract: Copper is uniquely active for the electrocatalytic reduction of carbon dioxide (CO2) to products beyond carbon monoxide, such as methane (CH4) and ethylene (C2H4). Therefore, understanding selectivity trends for CO2 electrocatalysis on copper surfaces is critical for developing more efficient catalysts for CO2 conversion to higher order products. Herein, we investigate the electrocatalytic activity of ultrathin (diameter ∼20 nm) 5-fold twinned copper nanowires (Cu NWs) for CO2 reduction. These Cu NW catalysts were found to exhibit high CH4 selectivity over other carbon products, reaching 55% Faradaic efficiency (FE) at -1.25 V versus reversible hydrogen electrode while other products were produced with less than 5% FE. This selectivity was found to be sensitive to morphological changes in the nanowire catalyst observed over the course of electrolysis. Wrapping the wires with graphene oxide was found to be a successful strategy for preserving both the morphology and reaction selectivity of the Cu NWs. These results suggest that product selectivity on Cu NWs is highly dependent on morphological features and that hydrocarbon selectivity can be manipulated by structural evolution or the prevention thereof.
TL;DR: The reduction protocol in this study allowed to achieve the highest conductivity values reported so far for the aqueous reduction of graphene oxide mediated by sodium borohydride, reflected in the dramatic change in the structural stability of the rGO nanofoams produced by freeze-drying.
Abstract: The electrical conductivity of reduced graphene oxide (rGO) obtained from graphene oxide (GO) using sodium borohydride (NaBH4) as a reducing agent has been investigated as a function of time (2 min to 24 h) and temperature (20 °C to 80 °C). Using a 300 mM aqueous NaBH4 solution at 80 °C, reduction of GO occurred to a large extent during the first 10 min, which yielded a conductivity increase of 5 orders of magnitude to 10 S m-1. During the residual 1400 min of reaction, the reduction rate decreased significantly, eventually resulting in a rGO conductivity of 1500 S m-1. High resolution XPS measurements showed that C/O increased from 2.2 for the GO to 6.9 for the rGO at the longest reaction times, due to the elimination of oxygen. The steep increase in conductivity recorded during the first 8-12 min of reaction was mainly due to the reduction of C-O (e.g., hydroxyl and epoxy) groups, suggesting the preferential attack of the reducing agent on C-O rather than C[double bond, length as m-dash]O groups. In addition, the specular variation of the percentage content of C-O bond functionalities with the sum of Csp2 and Csp3 indicated that the reduction of epoxy or hydroxyl groups had a greater impact on the restoration of the conductive nature of the graphite structure in rGO. These findings were reflected in the dramatic change in the structural stability of the rGO nanofoams produced by freeze-drying. The reduction protocol in this study allowed to achieve the highest conductivity values reported so far for the aqueous reduction of graphene oxide mediated by sodium borohydride. The 4-probe sheet resistivity approach used to measure the electrical conductivity is also, for the first time, presented in detail for filtrate sheet assemblies' of stacked GO/rGO sheets.
TL;DR: It is found that these holey oxide nanosheets exhibit strong mechanical stability inherited from graphene oxide, displaying minimal structural changes during lithiation/delithiation processes, and could open up opportunities in many energy storage and conversion systems.
Abstract: Transition metal oxide nanomaterials are promising electrodes for alkali-ion batteries owing to their distinct reaction mechanism, abundant active sites and shortened ion diffusion distance. However, detailed conversion reaction processes in terms of the oxidation state evolution and chemical/mechanical stability of the electrodes are still poorly understood. Herein we explore a general synthetic strategy for versatile synthesis of various holey transition metal oxide nanosheets with adjustable hole sizes that enable greatly enhanced alkali-ion storage properties. We employ in-situ transmission electron microscopy and operando X-ray absorption structures to study the mechanical properties, morphology evolution and oxidation state changes during electrochemical processes. We find that these holey oxide nanosheets exhibit strong mechanical stability inherited from graphene oxide, displaying minimal structural changes during lithiation/delithiation processes. These holey oxide nanosheets represent a promising material platform for in-situ probing the electrochemical processes, and could open up opportunities in many energy storage and conversion systems.
TL;DR: By engineering strain into cobalt oxide, the authors transform a once poor hydrogen evolution catalyst into one that is competitive with the state of the art.
Abstract: Designing high-performance and cost-effective electrocatalysts toward oxygen evolution and hydrogen evolution reactions in water-alkali electrolyzers is pivotal for large-scale and sustainable hydrogen production. Earth-abundant transition metal oxide-based catalysts are particularly active for oxygen evolution reaction; however, they are generally considered inactive toward hydrogen evolution reaction. Here, we show that strain engineering of the outermost surface of cobalt(II) oxide nanorods can turn them into efficient electrocatalysts for the hydrogen evolution reaction. They are competitive with the best electrocatalysts for this reaction in alkaline media so far. Our theoretical and experimental results demonstrate that the tensile strain strongly couples the atomic, electronic structure properties and the activity of the cobalt(II) oxide surface, which results in the creation of a large quantity of oxygen vacancies that facilitate water dissociation, and fine tunes the electronic structure to weaken hydrogen adsorption toward the optimum region.
TL;DR: In this article, a new bifunctional oxygen electrode based on nitrogen-doped carbon nanotubes decorated by spinel CuCo2O4 quantum dots was proposed, outperforming the benchmark of state-of-the-art noble metal catalysts.
Abstract: The large-scale production of metal–air batteries, an appealing solution for next-generation energy storage, requires low-cost, earth-abundant, and efficient oxygen electrode materials, yet insights into active catalyst structures and synergistic reactivity remain largely unknown. Here, a new bifunctional oxygen electrode based on nitrogen-doped carbon nanotubes decorated by spinel CuCo2O4 quantum dots (CuCo2O4/N-CNTs) is reported, outperforming the benchmark of state-of-the-art noble metal catalysts. Combining spectroscopic characterization and electrochemical studies, a prominent synergetic effect between CuCo2O4 and N-doped carbon nanotubes is uncovered: the high conductivity, large active surface area, and increase in the number of catalytic sites induced by Cu doping (i.e., Cu2+ and CuN) can be beneficial to the overall electrocatalytic activities. Remarkably, the native flexibility of CuCo2O4/N-CNTs allows its direct use as reversible oxygen electrodes in Zn–air batteries either with liquid alkaline electrolyte or in the all-solid-state configuration. The prepared devices demonstrate excellent discharging/charging performance, large energy density (83.83 mW cm−2 in liquid state, 1.86 W g−1 in all-solid-state), and long lifetime (48 h in liquid state, 9 h in all-solid-state), holding great promise in the practical application of rechargeable metal–air batteries and other fuel cells.
TL;DR: In this paper, a flexible, free-standing MoS2-reduced graphene oxide (MG) film with a 3D porous structure is fabricated via a facile spontaneous self-assembly process and subsequent freeze-drying.
Abstract: Flexible freestanding electrodes are highly desired to realize wearable/flexible batteries as required for the design and production of flexible electronic devices. Here, the excellent electrochemical performance and inherent flexibility of atomically thin 2D MoS2 along with the self-assembly properties of liquid crystalline graphene oxide (LCGO) dispersion are exploited to fabricate a porous anode for high-performance lithium ion batteries. Flexible, free-standing MoS2-reduced graphene oxide (MG) film with a 3D porous structure is fabricated via a facile spontaneous self-assembly process and subsequent freeze-drying. This is the first report of a one-pot self-assembly, gelation, and subsequent reduction of MoS2/LCGO composite to form a flexible, high performance electrode for charge storage. The gelation process occurs directly in the mixed dispersion of MoS2 and LCGO nanosheets at a low temperature (70 °C) and normal atmosphere (1 atm). The MG film with 75 wt% of MoS2 exhibits a high reversible capacity of 800 mAh g-1 at a current density of 100 mA g-1. It also demonstrates excellent rate capability, and excellent cycling stability with no capacity drop over 500 charge/discharge cycles at a current density of 400 mA g-1.
TL;DR: In this article, a mixture of concentrated H2SO4/H3PO4 and ascorbic acid was used to produce reduced graphene oxide, which was then used for graphite powder synthesis.
Abstract: In this work, graphene oxide was synthesized by treating graphite powder with KMnO4 and a mixture of concentrated H2SO4/H3PO4 and reduced with ascorbic acid to produce reduced graphene oxide. The e...
TL;DR: It is proposed that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy, which would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.
Abstract: Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO2RR). Using in situ ambient pressure X-ray photoelectron spectroscopy and quasi in situ electron energy-loss spectroscopy in a transmission electron microscope, we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts but no residual copper oxide. On the basis of these findings in combination with density functional theory simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO2RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.
TL;DR: In this paper, a simple layer-by-layer procedure is used to construct a sandwiched vein-membrane interlayer of thickness 2 µm and areal density 0.104 mg cm−2 by loading MnO2 nanoparticles and graphene oxide (GO) sheets on superaligned carbon nanotube films.
Abstract: Ultrathin MnO2/graphene oxide/carbon nanotube (G/M@CNT) interlayers are developed as efficient polysulfide-trapping shields for high-performance Li–S batteries. A simple layer-by-layer procedure is used to construct a sandwiched vein–membrane interlayer of thickness 2 µm and areal density 0.104 mg cm−2 by loading MnO2 nanoparticles and graphene oxide (GO) sheets on superaligned carbon nanotube films. The G/M@CNT interlayer provides a physical shield against both polysulfide shuttling and chemical adsorption of polysulfides by MnO2 nanoparticles and GO sheets. The synergetic effect of the G/M@CNT interlayer enables the production of Li–S cells with high sulfur loadings (60–80 wt%), a low capacity decay rate (−0.029% per cycle over 2500 cycles at 1 C), high rate performance (747 mA h g−1 at a charge rate of 10 C), and a low self-discharge rate with high capacity retention (93.0% after 20 d rest). Electrochemical impedance spectroscopy, cyclic voltammetry, and scanning electron microscopy observations of the Li anodes after cycling confirm the polysulfide-trapping ability of the G/M@CNT interlayer and show its potential in developing high-performance Li–S batteries.
TL;DR: In this article, a green and facile protocol of thermal treatment of graphene oxide (GO) with urea was adopted to synthesize nitrogen-doped graphene (NG-Urea-air) at a low temperature (350°C) in the static air.
TL;DR: In this paper, a conformal coating of 2 nm sulfur (S) onto reduced graphene oxide (rGO) nanocomposite is proposed to reduce the interface resistance and stress/strain of Li-S batteries.
Abstract: Safety and the polysulfide shuttle reaction are two major challenges for liquid electrolyte lithium–sulfur (Li–S) batteries. Although use of solid-state electrolytes can overcome these two challenges, it also brings new challenges by increasing the interface resistance and stress/strain. In this work, the interface resistance and stress/strain of sulfur cathodes are significantly reduced by conformal coating ≈2 nm sulfur (S) onto reduced graphene oxide (rGO). An Li–S full cell consisting of an rGO@S-Li10GeP2S12-acetylene black (AB) composite cathode is evaluated. At 60 °C, the all-solid-state Li–S cell demonstrates a similar electrochemical performance as in liquid organic electrolyte, with high rate capacities of 1525.6, 1384.5, 1336.3, 903.2, 502.6, and 204.7 mA h g−1 at 0.05, 0.1, 0.5, 1.0, 2.0, and 5.0 C, respectively. It can maintain a high and reversible capacity of 830 mA h g−1 at 1.0 C for 750 cycles. The uniform distribution of the rGO@S nanocomposite in the Li10GeP2S12-AB matrix generates uniform volume changes during lithiation/delithiation, significantly reducing the stress/strain, thus extending the cycle life. Minimization of the stress/strain of solid cells is the key for a long cycle life of all-solid-state Li–S batteries.