Showing papers by "Yury Gogotsi published in 2015"
TL;DR: In this article, density functional theory is used to predict the existence of two new families of 2D ordered, carbides (MXenes), where M′ layers sandwich M″ carbide layers.
Abstract: The higher the chemical diversity and structural complexity of two-dimensional (2D) materials, the higher the likelihood they possess unique and useful properties. Herein, density functional theory (DFT) is used to predict the existence of two new families of 2D ordered, carbides (MXenes), M′2M″C2 and M′2M″2C3, where M′ and M″ are two different early transition metals. In these solids, M′ layers sandwich M″ carbide layers. By synthesizing Mo2TiC2Tx, Mo2Ti2C3Tx, and Cr2TiC2Tx (where T is a surface termination), we validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2D flakes’ chemical and electrochemical properties. The latter was proven by showing quite different electrochemical behavior of Mo2TiC2Tx and Ti3C2Tx. This work further expands the family of 2D materials, offering additional choices of structures, chemistries, and ultimately useful properties.
1,167 citations
TL;DR: Free-standing and flexible sandwich-like MXene/carbon nanotube (CNT) paper, composed of alternating MXene and CNT layers, is fabricated using a simple filtration method, and exhibits high volumetric capacitances, good rate performances, and excellent cycling stability when employed as electrodes in supercapacitors.
Abstract: Dr. M.-Q. Zhao, C. E. Ren, Z. Ling, M. R. Lukatskaya, C. F. Zhang, K. L. Van Aken, Prof. M. W. Barsoum, Prof. Y. Gogotsi Department of Materials Science and Engineering and A. J. Drexel Nanomaterials Institute Drexel University 3141 Chestnut Street , Philadelphia , PA 19104 , USA E-mail: gogotsi@drexel.edu Z. Ling Carbon Research Laboratory Liaoning Key Lab for Energy Materials and Chemical Engineering State Key Lab of Fine Chemicals Dalian University of Technology Dalian 116024 , China C. F. Zhang State Key Laboratory of Chemical Engineering East China University of Science and Technology Shanghai 200237 , China
1,074 citations
TL;DR: Freestanding, flexible paper is produced that exhibits high capacity and excellent stability when used as the electrode for Li-ion batteries and capacitors.
Abstract: 2D Nb2CTx MXene flakes are produced using an amine-assisted delamination process. Upon mixing with carbon nanotubes and filtration, freestanding, flexible paper is produced. The latter exhibits high capacity and excellent stability when used as the electrode for Li-ion batteries and capacitors.
688 citations
TL;DR: Micrometer-thick MXene membranes demonstrated ultrafast water flux of 37.4 L/(Bar·h·m(2)) and differential sieving of salts depending on both the hydration radius and charge of the ions.
Abstract: Nanometer-thin sheets of 2D Ti3C2Tx (MXene) have been assembled into freestanding or supported membranes for the charge- and size-selective rejection of ions and molecules. MXene membranes with controllable thicknesses ranging from hundreds of nanometers to several micrometers exhibited flexibility, high mechanical strength, hydrophilic surfaces, and electrical conductivity that render them promising for separation applications. Micrometer-thick MXene membranes demonstrated ultrafast water flux of 37.4 L/(Bar·h·m2) and differential sieving of salts depending on both the hydration radius and charge of the ions. Cations with a larger charge and hydration radii smaller than the interlayer spacing of MXene (∼6 A) demonstrate an order of magnitude slower permeation compared to single-charged cations. Our findings may open a door for developing efficient and highly selective separation membranes from 2D carbides.
661 citations
TL;DR: A simple, one-step mechano-chemical process to exfoliate and functionalize h-BN into highly water-dispersible, few-layer h-bn containing amino groups is presented.
Abstract: The poor dispersibility of 2D hexagonal boron nitride in water currently limits its exfoliation and applications. Here, the authors present a one-step mechano-chemical process to achieve unprecedented colloidal concentrations, which permits fabrication of ultralight aerogels and freestanding membranes.
621 citations
TL;DR: The use of selective extraction of one or more elements from the precursor materials releases 2D structures that in turn will result in expanding the world of nanomaterials in general and 2D materials in particular, generating new materials that cannot be produced by other means.
Abstract: CONSPECTUS: Two-dimensional (2D) materials have attracted much attention in the past decade. They offer high specific surface area, as well as electronic structure and properties that differ from their bulk counterparts due to the low dimensionality. Graphene is the best known and the most studied 2D material, but metal oxides and hydroxides (including clays), dichalcogenides, boron nitride (BN), and other materials that are one or several atoms thick are receiving increasing attention. They may deliver a combination of properties that cannot be provided by other materials. The most common synthesis approach in general is by reacting different elements or compounds to form a new compound. However, this approach does not necessarily work well for low-dimensional structures, since it favors formation of energetically preferred 3D (bulk) solids. Many 2D materials are produced by exfoliation of van der Waals solids, such as graphite or MoS2, breaking large particles into 2D layers. However, these approaches are not universal; for example, 2D transition metal carbides cannot be produced by any of them. An alternative but less studied way of material synthesis is the selective extraction process, which is based on the difference in reactivity and stability between the different components (elements or structural units) of the original material. It can be achieved using thermal, chemical, or electrochemical processes. Many 2D materials have been synthesized using selective extraction, such as graphene from SiC, transition metal oxides (TMO) from layered 3D salts, and transition metal carbides or carbonitrides (MXenes) from MAX phases. Selective extraction synthesis is critically important when the bonds between the building blocks of the material are too strong (e.g., in carbides) to be broken mechanically in order to form nanostructures. Unlike extractive metallurgy, where the extracted metal is the goal of the process, selective extraction of one or more elements from the precursor materials releases 2D structures. In this Account, in addition to graphene and TMO, we focused on MXenes as an example for the use of selective extraction synthesis to produce novel 2D materials. About 10 new carbides and carbonitrides of transition metals have been produced by this method in the past 3 years. They offer an unusual combination of metallic conductivity and hydrophilicity and show very attractive electrochemical properties. We hope that this Account will encourage researchers to extend the use of selective extraction to other layered material systems that in turn will result in expanding the world of nanomaterials in general and 2D materials in particular, generating new materials that cannot be produced by other means.
533 citations
TL;DR: The field of supercapacitors (electrochemical capacitors) is constantly evolving and the global motivation is to create devices that possess a significant energy density without compromising the power density as mentioned in this paper.
Abstract: The field of supercapacitors (electrochemical capacitors) is constantly evolving. The global motivation is to create devices that possess a significant energy density without compromising the power density. To achieve this goal, new materials must be discovered and complex electrode architectures developed.
463 citations
TL;DR: This work investigated the electrochemical behavior of 2D vanadium carbide, V2C, from the MXene family, and investigated the mechanism of Na intercalation by XRD and achieved capacitance of ∼100 F/g at 0.2 mV/s.
Abstract: Ion capacitors store energy through intercalation of cations into an electrode at a faster rate than in batteries and within a larger potential window. These devices reach a higher energy density compared to electrochemical double layer capacitor. Li-ion capacitors are already produced commercially, but the development of Na-ion capacitors is hindered by lack of materials that would allow fast intercalation of Na-ions. Here we investigated the electrochemical behavior of 2D vanadium carbide, V2C, from the MXene family. We investigated the mechanism of Na intercalation by XRD and achieved capacitance of ∼100 F/g at 0.2 mV/s. We assembled a full cell with hard carbon as negative electrode, a known anode material for Na ion batteries, and achieved capacity of 50 mAh/g with a maximum cell voltage of 3.5 V.
351 citations
TL;DR: In this article, the deformation of 2D Ti3C2Tx (MXene) electrode materials at various states-of-charge with a variety of cations (Li, Na, K, Cs, Mg, Ca, Ba, and three tetra-alkylammonium cations) during cycling by electrochemical quartz-crystal admittance was analyzed.
Abstract: Fast ion adsorption processes in supercapacitors enable quick storage/delivery of significant amounts of energy, while ion intercalation in battery materials leads to even larger amounts of energy stored, but at substantially lower rates due to diffusional limitations. Intercalation of ions into the recently discovered 2D Ti3C2Tx (MXene) occurs with a very high rate and leads to high capacitance, posing a paradox. Herein, by characterizing the mechanical deformations of MXene electrode materials at various states-of-charge with a variety of cations (Li, Na, K, Cs, Mg, Ca, Ba, and three tetraalkylammonium cations) during cycling by electrochemical quartz-crystal admittance (EQCA, quartz-crystal microbalance with dissipation monitoring) combined with in situ electronic conductance and electrochemical impedance, light is shone on this paradox. Based on this work, it appears that the capacitive paradox stems from cationic insertion, accompanied by significant deformation of the MXene particles, that occurs so rapidly so as to resemble 2D ion adsorption at solid-liquid interfaces. The latter is greatly facilitated by the presence of water molecules between the MXene sheets.
274 citations
TL;DR: The unique properties of 2D materials, such as graphene or transition metal dichalcogenides, have been attracting much attention in the past decade, and metallically conductive and even superconducting transition metal carbides are entering the game.
Abstract: The unique properties of 2D materials, such as graphene or transition metal dichalcogenides, have been attracting much attention in the past decade. Now, metallically conductive and even superconducting transition metal carbides are entering the game.
266 citations
TL;DR: The aerogels exhibit up to 52% reversible magnetic field-induced strain and strain-dependent electrical resistance that can be used to monitor the degree of compression/stretching of the material and are an ultralight magnetic elastomer with potential applications in self-sensing soft actuators, microsensors, microswitches, and environmental remediation.
Abstract: Three-dimensional (3D) graphene aerogels (GA) show promise for applications in supercapacitors, electrode materials, gas sensors, and oil absorption due to their high porosity, mechanical strength, and electrical conductivity. However, the control, actuation, and response properties of graphene aerogels have not been well studied. In this paper, we synthesized 3D graphene aerogels decorated with Fe3O4 nanoparticles (Fe3O4/GA) by self-assembly of graphene with simultaneous decoration by Fe3O4 nanoparticles using a modified hydrothermal reduction process. The aerogels exhibit up to 52% reversible magnetic field-induced strain and strain-dependent electrical resistance that can be used to monitor the degree of compression/stretching of the material. The density of Fe3O4/GA is only about 5.8 mg cm(-3), making it an ultralight magnetic elastomer with potential applications in self-sensing soft actuators, microsensors, microswitches, and environmental remediation.
TL;DR: In this paper, an effective method to expand the operating potential window (OPW) of electrochemical capacitors based on formulating the ionic-liquid (IL) electrolytes is reported.
Abstract: An effective method to expand the operating potential window (OPW) of electrochemical capacitors based on formulating the ionic-liquid (IL) electrolytes is reported. Using model electrochemical cells based on two identical onion-like carbon (OLC) electrodes and two different IL electrolytes and their mixtures, it was shown that the asymmetric behavior of the electrolyte cation and anion toward the two electrodes limits the OPW of the cell and therefore its energy density. Also, a general solution to this problem is proposed by formulating the IL electrolyte mixtures to balance the capacitance of electrodes in a symmetric supercapacitor.
TL;DR: The mechanical properties of two-dimensional titanium carbides were investigated in this study using classical molecular dynamics and it is found that the structure of the simulated samples is preserved during the deformation process.
Abstract: Two-dimensional materials beyond graphene are attracting much attention Recently discovered 2D carbides and nitrides (MXenes) have shown very attractive electrical and electrochemical properties, but their mechanical properties have not been characterized yet There are neither experimental measurements reported in the literature nor predictions of strength or fracture modes for single-layer MXenes The mechanical properties of two-dimensional titanium carbides were investigated in this study using classical molecular dynamics Young's modulus was calculated from the linear part of strain-stress curves obtained under tensile deformation of the samples Strain-rate effects were observed for all Tin+1Cn samples From the radial distribution function, it is found that the structure of the simulated samples is preserved during the deformation process Calculated values of the elastic constants are in good agreement with published DFT data
TL;DR: In this article, two-dimensional transition metal carbides (MXenes) were used as anode for Li-ion batteries to achieve a reversible capacity of 6.7 mAh/cm2 after 50 cycles.
TL;DR: • Advantages of nanodiamond in polymer composites: superior mechanical properties, nanometer size, and fully available surface as discussed by the authors, which can be used to construct polymeric composites.
TL;DR: Kimwipes as mentioned in this paper is a foldable supercapacitor electrode using a macroporous cellulose fiber network, Kimwipes ®, as the scaffold through a simple dip-absorption-polymerization method.
TL;DR: It was demonstrated that higher mass densities could be used without increasing energy for pumping when using oxidized active material, and the surface chemistry of the active material in a flow electrode effects the electrical and pumping energy requirements of a FCDI system.
Abstract: Flow electrode deionization (FCDI) is an emerging area for continuous and scalable deionization, but the electrochemical and flow properties of the flow electrode need to be improved to minimize energy consumption. Chemical oxidation of granular activated carbon (AC) was examined here to study the role of surface heteroatoms on rheology and electrochemical performance of a flow electrode (carbon slurry) for deionization processes. Moreover, it was demonstrated that higher mass densities could be used without increasing energy for pumping when using oxidized active material. High mass-loaded flow electrodes (28% carbon content) based on oxidized AC displayed similar viscosities (∼21 Pa s) to lower mass-loaded flow electrodes (20% carbon content) based on nonoxidized AC. The 40% increased mass loading (from 20% to 28%) resulted in a 25% increase in flow electrode gravimetric capacitance (from 65 to 83 F g–1) without sacrificing flowability (viscosity). The electrical energy required to remove ∼18% of the io...
TL;DR: In this article, natural fiber welded yarns embedded with porous carbon materials are described for applications as electrodes in textile electrochemical capacitors, which are subsequently knitted into full fabrics on industrial knitting machines.
Abstract: Natural fiber welded (NFW) yarns embedded with porous carbon materials are described for applications as electrodes in textile electrochemical capacitors. With this fabrication technique, many kinds of carbons can be embedded into cellulose based yarns and subsequently knitted into full fabrics on industrial knitting machines. Yarns welded with carbon and stainless steel have device capacitances as high as 37 mF cm-1, one of the highest reported values for carbon-based yarns. The versatility of this technique to weld any commercially available cellulose yarn with any micro- or nanocarbon means properties can be tuned for specific applications. Most importantly, it is found that despite having full flexibility, increased strength, and good electrochemical performance, not all of the electrode yarns are suitable for knitting. Therefore, it is recommended that all works reporting on fiber/yarn capacitors for wearables attempt processing into full fabrics.
TL;DR: In this paper, atomic force microscopy was used to monitor the macroscopic deformation in a delaminated Ti3C2 paper electrode in situ, during charge/discharge in a variety of aqueous electrolytes to examine the effect of the cation intercalation on the electrochemical behavior and mechanical response.
TL;DR: The research described here combines classical aspects of electrochemistry, colloidal science, material science, fluid mechanics, and rheology to describe ion and charge percolation, adsorption of ions, and redox charge storage processes in suspension electrodes.
Abstract: Suspension or semi-solid electrodes have recently gained increased attention for large-scale applications such as grid energy storage, capacitive water deionization, and wastewater treatment. A suspension electrode is a multiphase material system comprised of an active (charge storing) material suspended in ionic solution (electrolyte). Gravimetrically, the electrolyte is the majority component and aids in physical transport of the active material. This principle enables, for the first time, scalability of electrochemical energy storage devices (supercapacitors and batteries) previously limited to small and medium scale applications. This critical review describes the ongoing material challenges encompassing suspension-based systems. The research described here combines classical aspects of electrochemistry, colloidal science, material science, fluid mechanics, and rheology to describe ion and charge percolation, adsorption of ions, and redox charge storage processes in suspension electrodes. This review summarizes the growing inventory of material systems, methods and practices used to characterize suspension electrodes, and describes universal material system properties (rheological, electrical, and electrochemical) that are pivotal in the design of high performing systems. A discussion of the primary challenges and future research directions is included.
TL;DR: In this article, two graphene-like carbide derived carbons (CDC-Gs) were produced by chlorination of SiC nanosheets obtained by magnesio-thermal reduction at moderate temperature of silica/graphene oxide nanocomposites.
TL;DR: Electrochemically and selectively extract Ti from the MAX phase Ti2SC to form carbon/sulfur (C/S) nanolaminates at room temperature, suggesting that electrochemical etching can be a powerful method to selectively extract the "M" elements from theMAX phases, to produce "AX" layered structures, that cannot be made otherwise.
Abstract: Herein we electrochemically and selectively extract Ti from the MAX phase Ti2SC to form carbon/sulfur (C/S) nanolaminates at room temperature. The products are composed of multi-layers of C/S flakes, with predominantly amorphous and some graphene-like structures. Covalent bonding between C and S is observed in the nanolaminates, which render the latter promising candidates as electrode materials for Li-S batteries. We also show that it is possible to extract Ti from other MAX phases, such as Ti3AlC2 , Ti3SnC2 , and Ti2GeC, suggesting that electrochemical etching can be a powerful method to selectively extract the “M” elements from the MAX phases, to produce “AX” layered structures, that cannot be made otherwise. The latter hold promise for a variety of applications, such as energy storage, catalysis, etc.
TL;DR: The high capacitance and long cycle life were ascribed to the short diffusional paths, uniform PANI coating, and tight confinement of the PANI in the inner pores of the tire-derived carbon through π-π interactions, which minimized the degradation ofThe PANI upon cycling.
Abstract: Recycling hazardous wastes to produce value-added products is becoming essential for the sustainable progress of our society. Herein, highly porous carbon (1625 m2/g–1) is synthesized using waste tires as the precursor and used as supercapacitor electrode. The narrow pore size distribution (PSD) and high surface area led to a good charge storage capacity, especially when used as a three-dimensional nanoscaffold to polymerize polyaniline (PANI/TC). The composite film was highly flexible, conductive and exhibited a capacitance of 480 F/g–1 at 1 mV/s–1 with excellent capacitance retention up to 98% after 10,000 charge/discharge cycles. The high capacitance and long cycle life were ascribed to the short diffusional paths, uniform PANI coating and tight confinement of the PANI in the inner pores of the tire-derived carbon via - interactions, which minimized the degradation of the PANI upon cycling. Here, we anticipate that the same strategy can be applied to deposit other pseudocapacitive materials with low-cost TC to achieve even higher electrochemical performance and longer cycle life, a key challenge for redox active polymers.
TL;DR: In this paper, carbon spheres (CS) were wrapped by highly conductive reduced graphene oxide sheets (rGO) to address the issues of rapid charge percolation in flowable electrodes.
TL;DR: In this paper, the authors demonstrate the application of nuclear magnetic resonance (NMR) spectroscopy and pair distribution function (PDF) analysis as new tools to probe the local structures of porous carbons.
Abstract: The structural characterization of nanoporous carbons is a challenging task as they generally lack long-range order and can exhibit diverse local structures Such characterization represents an important step toward understanding and improving the properties and functionality of porous carbons, yet few experimental techniques have been developed for this purpose Here we demonstrate the application of nuclear magnetic resonance (NMR) spectroscopy and pair distribution function (PDF) analysis as new tools to probe the local structures of porous carbons, alongside more conventional Raman spectroscopy Together, the PDFs and the Raman spectra allow the local chemical bonding to be probed, with the bonding becoming more ordered for carbide-derived carbons (CDCs) synthesized at higher temperatures The ring currents induced in the NMR experiment (and thus the observed NMR chemical shifts for adsorbed species) are strongly dependent on the size of the aromatic carbon domains We exploit this property and use co
14 Jan 2015
TL;DR: In this paper, the authors report the preparation of nanometer-sized carbon electrodes and their use as substrates for the immobilization of single gold nanoparticles (AuNPs).
Abstract: Electrochemical experiments at individual metal nanoparticles (NPs) can provide new insights into their electrocatalytic behavior. In this Communication, we report the preparation of nanometer-sized carbon electrodes and their use as substrates for the immobilization of single gold NPs (AuNPs). In addition to its very small size, the surface of a carbon nanoelectrode is catalytically inert, which makes it an excellent substrate for studying electrocatalytic reactions. The activity of single AuNPs towards the hydrogen evolution reaction was investigated and compared to that of low-atomicity gold clusters. Three approaches to attaching AuNPs to either chemically modified or bare carbon nanoelectrodes, and the effects of immobilization on hydrogen adsorption and catalytic behavior of AuNPs are discussed. The developed methodology should be useful for studying the effects of NP size, geometry, and surface attachment on the electrocatalytic activity.
TL;DR: This study reports an investigation of hydroquinone (HQ) as a multielectron organic redox molecule to enhance the performance of flowable electrodes and observed a twofold increase in capacitance under flow conditions compared to that of previous studies.
Abstract: This study reports an investigation of hydroquinone (HQ) as a multielectron organic redox molecule to enhance the performance of flowable electrodes. Two different methods to produce high-performance pseudocapacitive flowable electrodes were investigated for electrochemical flow capacitors. First, HQ molecules were deposited on carbon spheres (CSs) by a self-assembly approach using various HQ loadings. In the second approach, HQ was used as a redox-mediating agent in the electrolyte. Flowable electrodes composed of HQ showed a capacitance of 342 F g−1, which is >200 % higher than that of flowable electrodes based on nontreated CSs (160 F g−1), and outperformed (in gravimetric performance) many reported film electrodes. A similar trend in capacitance was observed if HQ was used as a redox agent in the electrolyte; however, its poor cycle life restricted further consideration. In addition, a twofold increase in capacitance was observed under flow conditions compared to that of previous studies.
TL;DR: In this paper, a K+ preintercalated hydrogenated MoO3 (KyMoO3−x) with enhanced conductivity and widened interlayer gaps was reported.
TL;DR: Carbon is the most versatile material, and virtually any combination of mechanical, optical, electrical, and chemical properties can be achieved with carbon by controlling its structure and surface chemistry as mentioned in this paper.
Abstract: Carbon, with its variety of allotropes and forms, is the most versatile material, and virtually any combination of mechanical, optical, electrical, and chemical properties can be achieved with carbon by controlling its structure and surface chemistry. The goal of this article is to help readers appreciate the variety of carbon nanomaterials and to describe some engineering applications of the most important of these. Many different materials are needed to meet a variety of performance requirements, but they can all be built of carbon. Considering the example of supercapacitor electrodes, zero- and one-dimensional nanoparticles, such as carbon onions and nanotubes, respectively, deliver very high power because of fast ion sorption/desorption on their outer surfaces. Two-dimensional (2D) graphene offers higher charge/discharge rates than porous carbons and a high volumetric energy density. Three-dimensional porous activated, carbide-derived, and templated carbon networks, with high surface areas and porosities in the angstrom or nanometer range, can provide high energy densities if the pore size is matched with the electrolyte ion size. Finally, carbon-based nanostructures further expand the range of available nanomaterials: Recently discovered 2D transition-metal carbides (MXenes) have already grown into a family with close to 20 members in about four years and challenge graphene in some applications.
TL;DR: The results suggest that the graphene-RTIL interfacial structure is bistable in which the EDL structure at any intermediate potential can be described by the combination of two extreme-potential structures whose proportions vary depending on the polarity and magnitude of the applied potential.
Abstract: It is well known that room temperature ionic liquids (RTILs) often adopt a charge-separated layered structure, i.e. with alternating cation- and anion-rich layers, at electrified interfaces. However, the dynamic response of the layered structure to temporal variations in applied potential is not well understood. We used in situ, real-time x-ray reflectivity to study the potential-dependent electric double layer (EDL) structure of an imidazolium-based RTIL on charged epitaxial graphene during potential cycling as a function of temperature. The results suggest that the graphene–RTIL interfacial structure is bistable in which the EDL structure at any intermediate potential can be described by the combination of two extreme-potential structures whose proportions vary depending on the polarity and magnitude of the applied potential. This picture is supported by the EDL structures obtained by fully atomistic molecular dynamics simulations at various static potentials. The potential-driven transition between the two structures is characterized by an increasing width but with an approximately fixed hysteresis magnitude as a function of temperature. The results are consistent with the coexistence of distinct anion- and cation-adsorbed structures separated by an energy barrier (∼0.15 eV).