Showing papers by "Yury Gogotsi published in 2014"
TL;DR: Electrochemical measurements can distinguish between different types of energy storage materials and their underlying mechanisms, used to recover power in cars and electric mass transit vehicles that would otherwise lose braking energy as heat.
Abstract: Electrochemical measurements can distinguish between different types of energy storage materials and their underlying mechanisms.
4,394 citations
TL;DR: In this article, a new family of two-dimensional early transition metal carbides and carbonitrides, called MXenes, was discovered and a detailed outlook for future research on MXenes is also presented.
Abstract: Recently a new, large family of two-dimensional (2D) early transition metal carbides and carbonitrides, called MXenes, was discovered. MXenes are produced by selective etching of the A element from the MAX phases, which are metallically conductive, layered solids connected by strong metallic, ionic, and covalent bonds, such as Ti2AlC, Ti3AlC2, and Ta4AlC3. MXenes combine the metallic conductivity of transition metal carbides with the hydrophilic nature of their hydroxyl or oxygen terminated surfaces. In essence, they behave as “conductive clays”. This article reviews progress—both experimental and theoretical—on their synthesis, structure, properties, intercalation, delamination, and potential applications. MXenes are expected to be good candidates for a host of applications. They have already shown promising performance in electrochemical energy storage systems. A detailed outlook for future research on MXenes is also presented.
3,973 citations
TL;DR: This capacitance report reports a method of producing two-dimensional titanium carbide ‘clay’ using a solution of lithium fluoride and hydrochloric acid that offers a much faster route to film production as well as the avoidance of handling hazardous concentrated hydrofluoric acid.
Abstract: Safe and powerful energy storage devices are becoming increasingly important. Charging times of seconds to minutes, with power densities exceeding those of batteries, can in principle be provided by electrochemical capacitors--in particular, pseudocapacitors. Recent research has focused mainly on improving the gravimetric performance of the electrodes of such systems, but for portable electronics and vehicles volume is at a premium. The best volumetric capacitances of carbon-based electrodes are around 300 farads per cubic centimetre; hydrated ruthenium oxide can reach capacitances of 1,000 to 1,500 farads per cubic centimetre with great cyclability, but only in thin films. Recently, electrodes made of two-dimensional titanium carbide (Ti3C2, a member of the 'MXene' family), produced by etching aluminium from titanium aluminium carbide (Ti3AlC2, a 'MAX' phase) in concentrated hydrofluoric acid, have been shown to have volumetric capacitances of over 300 farads per cubic centimetre. Here we report a method of producing this material using a solution of lithium fluoride and hydrochloric acid. The resulting hydrophilic material swells in volume when hydrated, and can be shaped like clay and dried into a highly conductive solid or rolled into films tens of micrometres thick. Additive-free films of this titanium carbide 'clay' have volumetric capacitances of up to 900 farads per cubic centimetre, with excellent cyclability and rate performances. This capacitance is almost twice that of our previous report, and our synthetic method also offers a much faster route to film production as well as the avoidance of handling hazardous concentrated hydrofluoric acid.
3,783 citations
TL;DR: This first report (to the authors' knowledge) on MXene composites of any kind, shows that adding polymer binders/spacers between atomically thin MXenes layers or reinforcing polymers with MXenes results in composite films that have excellent flexibility, good tensile and compressive strengths, and electrical conductivity that can be adjusted over a wide range.
Abstract: MXenes, a new family of 2D materials, combine hydrophilic surfaces with metallic conductivity Delamination of MXene produces single-layer nanosheets with thickness of about a nanometer and lateral size of the order of micrometers The high aspect ratio of delaminated MXene renders it promising nanofiller in multifunctional polymer nanocomposites Herein, Ti 3 C 2 T x MXene was mixed with either a charged polydiallyldimethylammonium chloride (PDDA) or an electrically neutral polyvinyl alcohol (PVA) to produce Ti 3 C 2 T x /polymer composites The as-fabricated composites are flexible and have electrical conductivities as high as 22 × 10 4 S/m in the case of the Ti 3 C 2 T x /PVA composite film and 24 × 10 5 S/m for pure Ti 3 C 2 T x films The tensile strength of the Ti 3 C 2 T x /PVA composites was significantly enhanced compared with pure Ti 3 C 2 T x or PVA films The intercalation and confinement of the polymer between the MXene flakes not only increased flexibility but also enhanced cationic intercalation, offering an impressive volumetric capacitance of ∼530 F/cm 3 for MXene/PVA-KOH composite film at 2 mV/s To our knowledge, this study is a first, but crucial, step in exploring the potential of using MXenes in polymer-based multifunctional nanocomposites for a host of applications, such as structural components, energy storage devices, wearable electronics, electrochemical actuators, and radiofrequency shielding, to name a few
1,545 citations
TL;DR: In this article, the authors reviewed the recent advances in fabrication of materials and devices and provided a critical analysis of reported performances of micro-supercapacitors, including intrinsic properties of electrode materials and electrolyte, architectural design of the device and fabrication methods.
Abstract: Miniaturized energy storage is essential for the continuous development and further miniaturization of electronic devices. Electrochemical capacitors (ECs), also called supercapacitors, are energy storage devices with a high power density, fast charge and discharge rates, and long service life. Small-scale supercapacitors, or micro-supercapacitors, can be integrated with microelectronic devices to work as stand-alone power sources or as efficient energy storage units complementing batteries and energy harvesters, leading to wider use of these devices in many industries. In recent years, the research in this field has rapidly advanced and micro-supercapacitors with improved storage capacity and power density have been developed. The important factors affecting the performance of micro-supercapacitors are the intrinsic properties of electrode materials and electrolyte, architectural design of the device and the fabrication methods. This paper reviews the recent advances in fabrication of materials and devices and provides a critical analysis of reported performances of micro-supercapacitors.
1,118 citations
TL;DR: L lithiated oxygen terminated MXenes surfaces are able to adsorb additional Li beyond a monolayer, providing a mechanism to substantially increase capacity, as observed mainly in delaminated MXenes and confirmed by DFT calculations and XAS.
Abstract: A combination of density functional theory (DFT) calculations and experiments is used to shed light on the relation between surface structure and Li-ion storage capacities of the following functionalized two-dimensional (2D) transition-metal carbides or MXenes: Sc2C, Ti2C, Ti3C2, V2C, Cr2C, and Nb2C The Li-ion storage capacities are found to strongly depend on the nature of the surface functional groups, with O groups exhibiting the highest theoretical Li-ion storage capacities MXene surfaces can be initially covered with OH groups, removable by high-temperature treatment or by reactions in the first lithiation cycle This was verified by annealing f-Nb2C and f-Ti3C2 at 673 and 773 K in vacuum for 40 h and in situ X-ray adsorption spectroscopy (XAS) and Li capacity measurements for the first lithiation/delithiation cycle of f-Ti3C2 The high-temperature removal of water and OH was confirmed using X-ray diffraction and inelastic neutron scattering The voltage profile and X-ray adsorption near edge struc
1,070 citations
TL;DR: Compared to materials currently used in high-rate Li and Na ion battery anodes, MXene shows promise in increasing overall battery performance and is predicted by first-principles density functional calculations.
Abstract: Two-dimensional (2-D) materials are capable of handling high rates of charge in batteries since metal ions do not need to diffuse in a 3-D lattice structure. However, graphene, which is the most well-studied 2-D material, is known to have no Li capacity. Here, adsorption of Li, as well as Na, K, and Ca, on Ti3C2, one representative MXene, is predicted by first-principles density functional calculations. In our study, we observed that these alkali atoms exhibit different adsorption energies depending on the coverage. The adsorption energies of Na, K, and Ca decrease as coverage increases, while Li shows little sensitivity to variance in coverage. This observed relationship between adsorption energies and coverage of alkali ions on Ti3C2 can be explained by their effective ionic radii. A larger effective ionic radius increases interaction between alkali atoms, thus lower coverage is obtained. Our calculated capacities for Li, Na, K, and Ca on Ti3C2 are 447.8, 351.8, 191.8, and 319.8 mAh/g, respectively. Com...
1,053 citations
TL;DR: In this article, the authors describe MXenes, early transition metal carbides or carbonitrides resulting from the selective removal of the A element from ternary carbides called MAX phases like Ti2AlC, Ti3AlC2, or Ta4AlC3.
Abstract: Review: MXenes: early transition metal carbides or carbonitrides resulting from the selective removal of the A element from ternary carbides called MAX phases like Ti2AlC, Ti3AlC2, or Ta4AlC3; 70 refs.
1,026 citations
TL;DR: This work reports on the fabrication of ∼1 × 1 cm2 Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC 2 films, in aqueous HF or NH4HF2, and opens the door for the use of MXenes in electronic, photonic, and sensing applications.
Abstract: Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of ∼1 × 1 cm2 Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC2 films, in aqueous HF or NH4HF2. Films that were about 19 nm thick, etched with NH4HF2, transmit ∼90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to ∼100 K. Below 100 K, the films’ resistivity increases with decreasing temperature and they exhibit negative magnetoresistance—both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications.
1,015 citations
TL;DR: In this paper, a class of two-dimensional transition-metal carbides, called MXene nanosheets, are predicted to serve as highperforming anodes for non-lithium-ion batteries by combined first-principles simulations and experimental measurements.
Abstract: Rechargeable non-lithium-ion (Na+, K+, Mg2+, Ca2+, and Al3+) batteries have attracted great attention as emerging low-cost and high energy-density technologies for large-scale renewable energy storage applications. However, the development of these batteries is hindered by the limited choice of high-performance electrode materials. In this work, MXene nanosheets, a class of two-dimensional transition-metal carbides, are predicted to serve as high-performing anodes for non-lithium-ion batteries by combined first-principles simulations and experimental measurements. Both O-terminated and bare MXenes are shown to be promising anode materials with high capacities and good rate capabilities, while bare MXenes show better performance. Our experiments clearly demonstrate the feasibility of Na- and K-ion intercalation into terminated MXenes. Moreover, stable multilayer adsorption is predicted for Mg and Al, which significantly increases their theoretical capacities. We also show that O-terminated MXenes can decom...
764 citations
TL;DR: It is shown that heating 2D Ti3C2 in air results in TiO2 nanocrystals enmeshed in thin sheets of disordered graphitic carbon structures that can handle extremely high cycling rates when tested as anodes in lithium ion batteries.
TL;DR: In this paper, the adsorption and photocatalytic decomposition of organic molecules in aqueous environments containing Ti3C2Tx, a representative of the MXene family, was reported.
Abstract: Recently a large family of two-dimensional (2D) layered early transition metal carbides and carbonitrides – labelled MXene – possessing metallic conductivity and hydrophilic surfaces was discovered. Herein we report on the adsorption and photocatalytic decomposition of organic molecules in aqueous environments containing Ti3C2Tx, a representative of the MXene family. This material possesses excellent adsorption toward cationic dyes, best described by a Freundlich isotherm. We also found that the material may undergo structural changes in aqueous media.
TL;DR: In this article, the authors provide an overview and perspective on the field of textile energy storage with a specific emphasis on devices made from textiles or made as a fabric themselves. And the focus is on coated, fibre, woven as well as knitted supercapacitors and batteries.
Abstract: Research on flexible and wearable electronics has been gaining momentum in recent years, ranging in use from medical to military and everyday consumer applications. Yet to date, textile electronics still lack integrated energy storage solutions. This paper provides an overview and perspective on the field of textile energy storage with a specific emphasis on devices made from textiles or made as a fabric themselves. While other types of flexible energy storage devices are discussed, the focus is on coated, fibre, woven as well as knitted supercapacitors and batteries.
TL;DR: The structure of this, only second MXene with formula M4X3, was investigated with pair distribution function analysis, and the resistivity of a cold-pressed disc was 0.0046 Ω m, rendering this MXene one of the most conductive to date.
TL;DR: In this paper, the electrochemical behavior of Ti3C2, a two-dimensional titanium carbide from the MXene family, in H2SO4 electrolyte is reported.
TL;DR: In situ TEM analysis coupled with Raman spectroscopy revealed the formation of either anatase nanoparticles or planar rutile nanocrystals, which were controlled by the time, temperature and heating rate as mentioned in this paper.
Abstract: Two-dimensional Ti3C2, also known as “MXene”, was oxidized in air under two different oxidizing regimes in order to produce carbon-supported TiO2. In situ TEM analysis coupled with Raman spectroscopy revealed the formation of either anatase nanoparticles or planar rutile nanocrystals, which were controlled by the time, temperature and heating rate.
TL;DR: In this paper, a fast microwave irradiation-mediated approach has been proposed for manufacturing multiwall carbon nanotube (MWCNT)-graphene hybrid aerogels, in which MWCNTs are vertically anchored on the surface of cell walls of GAs.
Abstract: Spilled oil represents a menace to the aquatic ecosystem and the whole environment in general and requires timely cleanup. Among all the avaliable technologies, oil sorption has attracted the most attention because of its simplicity and high level of effectiveness. The key for the development of this technology is convenient fabrication of high-performance oil sorbents that can be used repeatedly. In this work, a fast microwave irradiation-mediated approach has been proposed for manufacturing multiwall carbon nanotube (MWCNT)–graphene hybrid aerogels, in which MWCNTs are vertically anchored on the surface of cell walls of graphene aerogels. The hybrid monoliths show superhydrophobicity and superoleophilicity, a large pore volume, a large pore size, and excellent compressibility, demonstrating outstanding performance for recyclable oil sorption.
TL;DR: Understanding nanoscale processes in energy storagematerials is essential to uncover the underlying mechanisms and with this knowledge, new concepts can be formulated that will be developed into revolutionary new electrical energy storage devices and technologies.
Abstract: A CSNano has been attracting a large number of submissions onmaterials for electrical energy storage and publishing several in each recent issues (read two examples from the May 2014 issue). The need for more efficient storage of electrical energy at all scales, from solar and wind farms to wearable electronics like Google Glass, requires development of devices offering the high energy densities of batteries along with the long cycle lives, high powers, and short charging times of supercapacitors. This has led to a dramatic expansion of research activities at the energy frontier, but why do we need “nano” in energy storage? Indeed, there are many reasons: (1) Short diffusion distances make it possible to charge batteries faster or to draw high current in a short time (increase the power). (2) Large expansion that leads to failure and short cycle lives of microparticles can be accommodated;silicon use in Li-ion battery anodes is a good example, as nanoparticles can survive cycling. Thus, we can use materials capable of larger energy storage or increase the lifetime of currently used materials. (3) Transport of multivalent ions in bulk materials is slow, and use of nanomaterials can enable practical Mgor Al-ion batteries, capable of storing much more energy than the currently used Li-ion batteries. This list is hardly exhaustive, but it is already clear that nanostructuring of existing materials (e.g., metal oxides or silicon) and development of new nanomaterials (e.g., twodimensional, 2D, carbides, and carbonitrides;MXenes ) and hybrid nanomaterials/ nanostructures (e.g., nanoparticles on graphene) are seen as pathways to new solutions for electrical energy storage. Nanoscale design of the structure and chemistry of electrode materials may enable us to develop a new generation of devices that approach the theoretical limit for electrochemical storage and deliver electrical energy rapidly and efficiently. On the fundamental side, understanding nanoscale processes in energy storagematerials is essential to uncover the underlying mechanisms. With this knowledge, new concepts can be formulated that will be developed into revolutionary new electrical energy storage devices and technologies. A large variety of processes that occur during charge storage may be confusing for chemists and material scientists that are new to the field. In battery materials, conversion from one state to another occurs at a constant potential until the phase transformation is completed. Charge storage in supercapacitors typically includes ion adsorption in the electric double-layer capacitor (EDLC) or fastelectrochemical reactionat thesurface of the activematerial (pseudocapacitors). Rapidly available surface charge without diffusion limitation is the origin of their high power density, and the absence of bulk phase transformation leads to high reversibility and long life (up to 1,000,000 cycles). However, since the charge is confined to the surface, the energy densities of EDLCs are less than those of batteries (three-dimensional, 3D, chemical storage). Classical (2D) double-layer charge storage is possible on theplanar surfaces of graphene aerogels or convex outer surfaces of carbon nanotubes or onions. In commercially used microporous activated carbons, ions are confined (electrosorbed) in pores. This process is significantly different than the conventional double layer and is rather similar to gas adsorption or adsorption of organicmolecules fromwater by activated carbons, but driven by an electrical rather than a chemical potential. Nanomaterials and hybrid nanomaterials may enable us to build energy storage devices with the energy densities of the best batteries but with the high power, fast charging, and Nanoscale design of the structure and chemistry of electrode materials may enable us to develop a new generation of devices that approach the theoretical limit for electrochemical storage and deliver electrical energy rapidly and efficiently.
TL;DR: In this article, the authors reported the electrochemical enhancement methods followed by annealing at different temperatures in air to add and adjust the redox active functional groups on freestanding CNT films.
TL;DR: The structures of nanocrystalline pristine, potassium hydroxide and sodium acetate intercalated new two-dimensional materials Ti3C2 MXenes were studied using the x-ray atomic pair distribution function technique.
Abstract: The structures of nanocrystalline pristine, potassium hydroxide and sodium acetate intercalated new two-dimensional materials ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}$ MXenes were studied using the x-ray atomic pair distribution function technique. Pristine MXene has a hexagonal structure with $a=b=3.0505(5)\text{ }\text{ }\AA{}$, $c=19.86(2)\text{ }\text{ }\AA{}$ (S.G. $P{6}_{3}/mmc$ No. 194). Both hydroxyl and fluoride terminating species are present. The intercalation of ${\mathrm{K}}^{+}$ or ${\mathrm{Na}}^{+}$ ions expands the ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}$ layers perpendicular to the planes but shrinks the in-plane $a$ and $b$ lattice parameters.
TL;DR: Cables and wires are used to conduct electricity, but can they also store energy if they are encased by a supercapacitor device?
Abstract: Cables and wires are used to conduct electricity, but can they also store energy? The answer is a resounding 'yes', if they are encased by a supercapacitor device — a finding that might open up many applications.
TL;DR: In this paper, the authors synthesized highly porous carbon spheres (CSs) of submicrometer size to investigate their performance in film and suspension electrodes, and studied the effects of carbonization and activation temperatures on the electrochemical performance of the CSs.
TL;DR: This approach forgoes energy-intensive thermal treatments and presents a novel method for developing carbons with finely tuned pores for a variety of applications, such as supercapacitor, battery electrodes or CO2 capture.
Abstract: Porous carbons are widely used in energy storage and gas separation applications, but their synthesis always involves high temperatures. Herein we electrochemically selectively extract, at ambient ...
TL;DR: In this paper, the authors showed that hydrogenated MoO3 (MoO3−x) shows enhanced conductivity based on, both first principle calculations and single nanobelt measurements.
TL;DR: These outstanding properties qualify the PDMS/CGA composites developed here as promising candidates for a wide range of applications such as in sensors, actuators, and materials used for biochemical separation and tissue engineering.
Abstract: The idea of extending functions of graphene aerogels and achieving specific applications has aroused wide attention recently. A solution to this challenge is the formation of a hybrid structure where the graphene aerogels are decorated with other functional nanostructures. An infiltration–evaporation–curing strategy has been proposed by the formation of hybrid structure containing poly(dimethylsiloxane) (PDMS) and compressible graphene aerogel (CGA), where the cellular walls of the CGA are coated uniformly with an integrated polymer layer. The resulting composite shows enhanced compressive strength and a stable Young’s modulus that are superior to those of pure CGAs. This unique structure combines the advantages of both components, giving rise to an excellent electromechanical performance, where the bulk resistance repeatedly shows a synchronous and linear response to variation of the volume during compression at a wide range of compressed rates. Furthermore, the foamlike structure delivers a water drople...
TL;DR: In this paper, a new type of capacitive deionization (CDI) system, based on capacitive suspension electrodes (CSEs), was developed for the purpose of desalting brackish and seawater through the use of flowable carbon suspensions.
TL;DR: In this article, the potential and time-dependent changes in the electric double layer (EDL) structure of an imidazolium-based room temperature ionic liquid (RTIL) electrolyte at an epitaxial graphene (EG) surface were studied.
Abstract: We studied the potential and time-dependent changes in the electric double layer (EDL) structure of an imidazolium-based room temperature ionic liquid (RTIL) electrolyte at an epitaxial graphene (EG) surface. We used in situ X-ray reflectivity (XR) to determine the EDL structure at static potentials, during cyclic voltammetry (CV) and potential step measurements. The static potential structures were also investigated with fully atomistic molecular dynamics (MD) simulations. Combined XR and MD results show that the EDL structure has alternating anion/cation layers within the first nanometer of the interface and that these structures are distinct at the most positive and negative static potentials (1.0 and −0.4 V, respectively) applied in this study. The dynamical response of the EDL to potential steps has a slow component (>10 s) and the RTIL structure shows hysteresis during CV scans (e.g., at 100 mV/s scan rate). Our results reveal that both the slow kinetics and hysteresis are due to the reorganization ...
TL;DR: In this article, density functional theory (DFT) calculations of the nucleus-independent chemical shift (NICS) near various sp2-hybridized carbon fragments are presented to explore the structural factors that may affect the resonance frequencies observed for adsorbed species.
Abstract: Nuclear magnetic resonance (NMR) spectroscopy is increasingly being used to study the adsorption of molecules in porous carbons, a process which underpins applications ranging from electrochemical energy storage to water purification. Here we present density functional theory (DFT) calculations of the nucleus-independent chemical shift (NICS) near various sp2-hybridized carbon fragments to explore the structural factors that may affect the resonance frequencies observed for adsorbed species. The domain size of the delocalized electron system affects the calculated NICSs, with larger domains giving rise to larger chemical shieldings. In slit pores, overlap of the ring current effects from the pore walls is shown to increase the chemical shielding. Finally, curvature in the carbon sheets is shown to have a significant effect on the NICS. The trends observed are consistent with existing NMR results as well as new spectra presented for an electrolyte adsorbed on carbide-derived carbons prepared at different t...
TL;DR: It was shown that an expanded voltage window of 1.6 V could be achieved when combining a composite MnO2-carbon black (cathode) and an activated carbon suspension (anode) in a charge balanced asymmetric device.
Abstract: In this study, we examine the use of a percolating network of metal oxide (MnO2) as the active material in a suspension electrode as a way to increase the capacitance and energy density of an electrochemical flow capacitor. Amorphous manganese oxide was synthesized via a low-temperature hydrothermal approach and combined with carbon black to form composite flowable electrodes of different compositions. All suspension electrodes were tested in static configurations and consisted of an active solid material (MnO2 or activated carbon) immersed in aqueous neutral electrolyte (1 M Na2SO4). Increasing concentrations of carbon black led to better rate performance but at the cost of capacitance and viscosity. Furthermore, it was shown that an expanded voltage window of 1.6 V could be achieved when combining a composite MnO2-carbon black (cathode) and an activated carbon suspension (anode) in a charge balanced asymmetric device. The expansion of the voltage window led to a significant increase in the energy densit...