Showing papers by "Sheng Dai published in 2014"
TL;DR: This work investigates the mechanism of oxygen-vacancy-mediated redox pseudocapacitance for a nanostructured lanthanum-based perovskite, LaMnO3, which is the first example of anion-based intercalation pseudocAPacitance as well as the first time oxygen interCalation has been exploited for fast energy storage.
Abstract: Perovskite oxides have attracted significant attention as energy conversion materials for metal-air battery and solid-oxide fuel-cell electrodes owing to their unique physical and electronic properties. Amongst these unique properties is the structural stability of the cation array in perovskites that can accommodate mobile oxygen ions under electrical polarization. Despite oxygen ion mobility and vacancies having been shown to play an important role in catalysis, their role in charge storage has yet to be explored. Herein we investigate the mechanism of oxygen-vacancy-mediated redox pseudocapacitance for a nanostructured lanthanum-based perovskite, LaMnO3. This is the first example of anion-based intercalation pseudocapacitance as well as the first time oxygen intercalation has been exploited for fast energy storage. Whereas previous pseudocapacitor and rechargeable battery charge storage studies have focused on cation intercalation, the anion-based mechanism presented here offers a new paradigm for electrochemical energy storage.
535 citations
TL;DR: The large pores and small dimensions of the N-heteroatom-doped carbon spheres contribute to the mass transportation by reducing and smoothing the diffusion pathways, leading to high electrocatalytic activity.
Abstract: The synthesis of highly nitrogen-doped mesoporous carbon spheres (NMCS) is reported. The large pores of the NMCS were obtained through self-polymerization of dopamine (DA) and spontaneous co-assembly of diblock copolymer micelles. The resultant narrowly dispersed NMCS possess large mesopores (ca. 16 nm) and small particle sizes (ca. 200 nm). The large pores and small dimensions of the N-heteroatom-doped carbon spheres contribute to the mass transportation by reducing and smoothing the diffusion pathways, leading to high electrocatalytic activity.
532 citations
TL;DR: This work synthesized mesoporous carbon from pre-cross-linked lignin gel impregnated with a surfactant as the pore-forming agent and activated the carbon through physical and chemical methods to obtain activated mesoporus carbon.
Abstract: We synthesized mesoporous carbon from pre-cross-linked lignin gel impregnated with a surfactant as the pore-forming agent and then activated the carbon through physical and chemical methods to obtain activated mesoporous carbon. The activated mesoporous carbons exhibited 1.5- to 6-fold increases in porosity with a maximum Brunauer–Emmett–Teller (BET) specific surface area of 1148 m2/g and a pore volume of 1.0 cm3/g. Both physical and chemical activation enhanced the mesoporosity along with significant microporosity. Plots of cyclic voltammetric data with the capacitor electrode made from these carbons showed an almost rectangular curve depicting the behavior of ideal double-layer capacitance. Although the pristine mesoporous carbon exhibited a range of surface-area-based capacitance similar to that of other known carbon-based supercapacitors, activation decreased the surface-area-based specific capacitance and enhanced the gravimetric specific capacitance of the mesoporous carbons. A vertical tail in the ...
332 citations
TL;DR: In this article, a high performance TiNb2O7 anode material with a nanoporous nature, which was prepared by a facile approach, exhibits an average storage voltage of 1.66 V, a reversible capacity of 281 mA h g−1, and an 84% capacity retention after 1000 cycles.
Abstract: A high performance TiNb2O7 anode material with a nanoporous nature, which was prepared by a facile approach, exhibits an average storage voltage of 1.66 V, a reversible capacity of 281 mA h g−1, and an 84% capacity retention after 1000 cycles, and may be suitable for long-life stationary lithium-ion batteries.
291 citations
TL;DR: The reported method stands as an environmentally friendly and low-cost alternative to hard or soft templating for the fabrication of mesoporous materials.
Abstract: The synthesis of mesoporous Prussian blue analogues through a template-free methodology and the application of these mesoporous materials as high-performance cathode materials in sodium-ion batteries is presented. Crystalline mesostructures were produced through a synergistically coupled nanocrystal formation and aggregation mechanism. As cathodes for sodium-ion batteries, the Prussian blue analogues all show a reversible capacity of 65 mA h g-1 at low current rate and show excellent cycle stability. The reported method stands as an environmentally friendly and low-cost alternative to hard or soft templating for the fabrication of mesoporous materials.
225 citations
TL;DR: A series of perovskite electrocatalysts that are highly active for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in an aqueous alkaline electrolyte was presented in this paper.
Abstract: We present a series of perovskite electrocatalysts that are highly active for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in an aqueous alkaline electrolyte. Lantha...
215 citations
TL;DR: The quantum mechanical (QM) diameters of several common gaseous molecules are obtained by determining the cross-sectional sizes of their iso-electronic density surfaces at a predetermined small value and it is shown that the QM diameters are in good agreement with the kinetic diameters.
Abstract: Kinetic diameters are often invoked in discussing gas adsorption and permeation in porous and polymeric materials. However, how these empirical kinetic diameters relate to the size and shape of the molecules as manifested by their “electron cloud” is unclear. In this paper, we obtain the quantum mechanical (QM) diameters of several common gaseous molecules by determining the cross-sectional sizes of their iso-electronic density surfaces at a predetermined small value. We show that the QM diameters are in good agreement with the kinetic diameters. For example, the trends for important gas pairs such as O2 versus N2 and CO2 versus N2 are consistent between the QM diameters and the most often quoted kinetic diameters. Hence, our work now provides a quantum mechanical basis for the empirical kinetic diameters and will be useful for designing separation media for small gaseous molecules according to their sizes.
201 citations
TL;DR: In this article, the anti-scuffing/anti-wear behavior and mechanism of an oil-miscible ionic liquid (IL), trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate, in a base oil at 1.0% concentration under both room and elevated temperatures were reported.
176 citations
TL;DR: A porous triazine and carbazole bifunctionalized task-specific polymer has been synthesized via a facile Friedel-Crafts reaction and exhibits excellent CO2 uptake and good adsorption selectivity for CO2 over N2.
176 citations
TL;DR: In this article, field column experiments have been performed at the Marine Sciences Laboratory of the Pacific Northwest National Laboratory using a laboratory-proven, amidoxime-based polymeric adsorbent developed at the Oak Ridge National Laboratory (ORNL).
Abstract: Uranium recovery from seawater has been investigated for several decades for the purpose of securing nuclear fuel for energy production. In this study, field column experiments have been performed at the Marine Sciences Laboratory of the Pacific Northwest National Laboratory (PNNL) using a laboratory-proven, amidoxime-based polymeric adsorbent developed at the Oak Ridge National Laboratory (ORNL). The adsorbent was packed either in in-line filters or in flow-through columns. The maximum amount of uranium uptake from seawater was 3.3 mg of U/g of adsorbent after 8 weeks of contact between the adsorbent and seawater. This uranium adsorption amount was about 3 times higher than the maximum amount achieved in this study by a leading adsorbent developed at the Japan Atomic Energy Agency (JAEA). Both adsorbents were tested under similar conditions. The results were used to update an assessment of the cost of large-scale recovery of uranium from seawater using the ORNL adsorbent. The updated uranium production c...
173 citations
TL;DR: High activity, outstanding thermal stability and good recyclability were observed over the core-shell nanocatalyst, and the solvent-free aerobic oxidation of diverse hydrocarbons and alcohols was further carried out to illustrate the benefits of such an architecture in catalysis.
Abstract: Here we describe a lab-in-a-shell strategy for the preparation of multifunctional core–shell nanospheres consisting of a core of metal clusters and an outer microporous silica shell. Various metal clusters (e.g., Pd and Pt) were encapsulated and confined in the void space mediated by the entrapped polymer dots inside hollow silica nanospheres acting first as complexing agent for metal ions and additionally as encapsulator for clusters, limiting growth and suppressing the sintering. The Pd clusters encapsulated in hybrid core–shell structures exhibit exceptional size-selective catalysis in allylic oxidations of substrates with the same reactive site but different molecular size (cyclohexene ∼0.5 nm, cholesteryl acetate ∼1.91 nm). The solvent-free aerobic oxidation of diverse hydrocarbons and alcohols was further carried out to illustrate the benefits of such an architecture in catalysis. High activity, outstanding thermal stability and good recyclability were observed over the core–shell nanocatalyst.
TL;DR: In situ cross-linking strategy for the preparation of polymeric molecular sieve membranes with hierarchical and tailorable porosity is reported, which could provide a possible alternative to 'classical' methods for the Preparation of porous membranes and, in some cases, the only viable synthetic route towards certain membranes.
Abstract: High-performance polymeric membranes for gas separation are attractive for molecular-level separations in industrial-scale chemical, energy and environmental processes. Molecular sieving materials are widely regarded as the next-generation membranes to simultaneously achieve high permeability and selectivity. However, most polymeric molecular sieve membranes are based on a few solution-processable polymers such as polymers of intrinsic microporosity. Here we report an in situ cross-linking strategy for the preparation of polymeric molecular sieve membranes with hierarchical and tailorable porosity. These membranes demonstrate exceptional performance as molecular sieves with high gas permeabilities and selectivities for smaller gas molecules, such as carbon dioxide and oxygen, over larger molecules such as nitrogen. Hence, these membranes have potential for large-scale gas separations of commercial and environmental relevance. Moreover, this strategy could provide a possible alternative to 'classical' methods for the preparation of porous membranes and, in some cases, the only viable synthetic route towards certain membranes.
TL;DR: In this paper, a novel adsorbent preparation method using atom-transfer radical polymerization (ATRP) combined with radiation-induced graft polymerization combined with RIGP was developed to synthesize an adaption for uranium recovery from seawater.
Abstract: A novel adsorbent preparation method using atom-transfer radical polymerization (ATRP) combined with radiation-induced graft polymerization (RIGP) was developed to synthesize an adsorbent for uranium recovery from seawater. The ATRP method allowed a much higher degree of grafting on the adsorbent fibers (595–2818%) than that allowed by RIGP alone. The adsorbents were prepared with varied compositions of amidoxime groups and hydrophilic acrylate groups. The successful preparation revealed that both ligand density and hydrophilicity were critical for optimal performance of the adsorbents. Adsorbents synthesized in this study showed a relatively high performance (141–179 mg g−1 at 49–62% adsorption) in laboratory screening tests using a uranium concentration of ∼6 ppm. This performance is much higher than that of known commercial adsorbents. However, actual seawater experiment showed impeded performance compared to the recently reported high-surface-area-fiber adsorbents, due to slow adsorption kinetics. The impeded performance motivated the investigation of the effect of hydrophilic block addition on the graft chain terminus. The addition of a hydrophilic block on the graft chain terminus nearly doubled the uranium adsorption capacity in seawater, from 1.56 mg g−1 to 3.02 mg g−1. The investigation revealed the importance of polymer chain conformation, in addition to the ligand and hydrophilic group ratio, for advanced adsorbent synthesis for uranium recovery from seawater.
TL;DR: In this paper, hybrid Li-air batteries fabricated with mesoporous NiCo2O4 nanoflakes directly grown onto nickel foam and N-doped mesoporic carbon loaded onto a hydrophobic carbon paper, respectively, were found to exhibit the best reported cycle life.
Abstract: Hybrid Li–air batteries fabricated with mesoporous NiCo2O4 nanoflakes directly grown onto nickel foam and N-doped mesoporous carbon loaded onto a hydrophobic carbon paper, respectively, as the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts are found to exhibit the best reported cycle life.
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, the authors examined the use of the amidoxime functional group grafted onto a hierarchical porous carbon framework for the selective capture and removal of carbon dioxide from combustion streams.
TL;DR: An ionothermal carbonization (ITC) method, via treating natural resources in nonmetal ionic liquids (ILs) at ∼200 °C, is established for the fabrication of porous heteroatom-doped carbon materials with high yield.
Abstract: The development of meaningful ways to transfer biomass into useful materials, more efficient energy carriers, and/or carbon storage deposits is a profound challenge of our days. Herein, an ionothermal carbonization (ITC) method, via treating natural resources (glucose, cellulose, and sugar cane bagesse) in nonmetal ionic liquids (ILs) at ∼200 °C, is established for the fabrication of porous heteroatom-doped carbon materials with high yield. Commercial ILs with bulky bis(trifluoromethylsulfonyl)imide anion or cross-linkable nitrile group were found to be efficient and recyclable templates for porosity control, leading to exciting nanoarchitectures with promising performance in oxygen reduction reaction. The optimized ILs (12 mL) can dissolve and directly convert up to 15 g of glucose into porous carbon materials (SBET: 272 m(2)/g) one time. This ITC method relies on the synergistic use of structure-directing effect, good biomass solubility, and excellent thermal stability of ILs, and provides a sustainable strategy for exploiting biomass.
TL;DR: This work uses a recently developed liquid cell for in situ electrochemical transmission electron microscopy to obtain insight into the electrolyte decomposition mechanisms and kinetics in lithium-ion (Li-ion) batteries by characterizing the dynamics of solid electrolyte interphase (SEI) formation and evolution.
Abstract: Complex, electrochemically driven transport processes form the basis of electrochemical energy storage devices. The direct imaging of electrochemical processes at high spatial resolution and within their native liquid electrolyte would significantly enhance our understanding of device functionality, but has remained elusive. In this work we use a recently developed liquid cell for in situ electrochemical transmission electron microscopy to obtain insight into the electrolyte decomposition mechanisms and kinetics in lithium-ion (Li-ion) batteries by characterizing the dynamics of solid electrolyte interphase (SEI) formation and evolution. Here we are able to visualize the detailed structure of the SEI that forms locally at the electrode/electrolyte interface during lithium intercalation into natural graphite from an organic Li-ion battery electrolyte. We quantify the SEI growth kinetics and observe the dynamic self-healing nature of the SEI with changes in cell potential.
TL;DR: In this paper, mesoporous graphene-like carbon sheets with high specific surface area and high pore volume were synthesized by using polyimide chemistry in the molten salt “solvent,” in which abundant pyromellitic dianhydride and aromatic diamine undergo polycondensation together with further carbonization in molten KCl-ZnCl2, in which in situ formed linear aromatic polyimides with a sp2 hybridized carbon skeleton could be directly coupled and rearranged into a two-dimensional graphenelike nanosheet around the “salt
Abstract: Nowadays, continuous scientific endeavors are being directed toward low-cost, mild, scalable and reliable synthesis of graphene-based materials, in order to advance various graphene-related applications. So far, specific surface areas of current bulk graphene powders or graphene-like nanosheets are much lower than the theoretical value (2630 m2 g−1) of individual graphene, remaining a challenge for carbon chemists. Herein, mesoporous graphene-like carbon sheets with high specific surface area (up to 2607 m2 g−1) and high pore volume (up to 3.12 cm3 g−1) were synthesized by using polyimide chemistry in the molten salt “solvent.” In this process, abundant pyromellitic dianhydride and aromatic diamine undergo polycondensation together with further carbonization in molten KCl–ZnCl2, in which in situ formed linear aromatic polyimide with a sp2 hybridized carbon skeleton could be directly coupled and rearranged into a two-dimensional graphene-like nanosheet around the “salt scaffold”. Carbon nanosheets with well-defined mesopores (∼3.5 nm) could be easily obtained by washing salt melts in water, while the salts could be recovered and reused for the subsequent reaction. The nitrogen atoms in amine also afforded the resulting carbon with uniform foreign atoms (nitrogen content = ∼6%). Moreover, holey carbon sheets with well-dispersed and through-plane nanoholes (diameter: 5–10 nm) could be constructed by using different monomers. Being a potential electrode material in supercapacitors, the as-made carbon nanosheet possessed a significant specific capacitance (131.4–275.5 F g−1) even at a scan rate of 2000 mV s−1. Additionally, powerful nanohybrids of carbon sheet–Co3O4 were also prepared with good performance in the aerobic oxidation of alcohols and amines to aldehydes and imines, respectively.
TL;DR: In this article, five functionalized ionic liquids (FILs), tetraethylammonium di(2-ethylhexyl)phosphate ([N 2222 ][DEHP]), tetrahexylphosphine (2,4,4-trimethylpentyl)dithiophosphinite (BTMPDTP), tetrasymmetric lithium bis(trifluoromethanesulfonyl)imide/bis(perfluoroethane sulfonyl), were synthesized and characterized.
TL;DR: A novel ambient Li-SO2 battery was developed through the introduction of ionic liquid electrolytes with tailored basicities to solvate SO2 by reversible chemical absorption by tuning the interactions of ILs with SO2.
Abstract: Li-SO2 batteries have a high energy density but bear serious safety problems that are associated with pressurized SO2 and flammable solvents in the system. Herein, a novel ambient Li-SO2 battery was developed through the introduction of ionic liquid (IL) electrolytes with tailored basicities to solvate SO2 by reversible chemical absorption. By tuning the interactions of ILs with SO2, a high energy density and good discharge performance with operating voltages above 2.8 V were obtained. This strategy based on reversible chemical absorption of SO2 in IL electrolytes enables the development of the next generation of ambient Li-SO2 batteries.
TL;DR: In this article, a unique class of air-stable and non-pyrophoric magnesium electrolytes based on alkoxide magnesium compounds was developed and the crystals obtained from this class of electrolytes exhibit a unique structure of tri-magnesium cluster, [Mg3Cl3(OR)2(THF)6]+ [(THFmCl3]−.
Abstract: A unique class of air-stable and non-pyrophoric magnesium electrolytes has been developed based on alkoxide magnesium compounds. The crystals obtained from this class of electrolytes exhibit a unique structure of tri-magnesium cluster, [Mg3Cl3(OR)2(THF)6]+ [(THF)MgCl3]−. High reversible capacities and good rate capabilities have been obtained in Mg–Mo6S8 batteries using these new electrolytes at both 20 and 50 °C.
TL;DR: The use of a perturbation-assisted nanofusion technique to construct hierarchically superstructured MOFs enabled the confinement of large dye species, resulting in fluorescent MOF materials, which can serve as a new type of ratiometric luminescent sensors for typical volatile organic compounds.
Abstract: Microporous metal–organic frameworks (MOFs) represent a new family of microporous materials, offering potential applications in gas separation and storage, catalysis, and membranes. The engineering of hierarchical superstructured MOFs, i.e., fabricating mesopores in microporous frameworks during the crystallization stage is expected to serve a myriad of applications for molecular adsorption, drug delivery, and catalysis. However, MOFs with mesopores are rarely studied because of the lack of a simple, effective way to construct mesoscale cavities in the structures. Here, we report the use of a perturbation-assisted nanofusion technique to construct hierarchically superstructured MOFs. In particular, the mesopores in the MOF structure enabled the confinement of large dye species, resulting in fluorescent MOF materials, which can serve as a new type of ratiometric luminescent sensors for typical volatile organic compounds.
TL;DR: Cr, N-codoped TiO2 mesoporous microspheres have been successfully synthesized by a facile hydrothermal reaction followed by annealing under an ammonia atmosphere as mentioned in this paper.
Abstract: Cr, N-codoped TiO2 mesoporous microspheres have been successfully synthesized by a facile hydrothermal reaction followed by annealing under an ammonia atmosphere Through introduction of Cr, the nitrogen doping level was increased from 281 at% for N-doped TiO2 to 568 at% for Cr, N-codoped TiO2, which improves the electrical conductivity of TiO2 When used as an anode for lithium-ion rechargeable batteries, the Cr, N-codoping TiO2 microspheres led to an enhanced performance of 1596 mA h g−1 at 5 C with a drop of less than 1% after 300 cycles
TL;DR: The temperature dependence of solubility for CO2 and N2 is examined and it is found that the CO2 solvation in IL is exothermic with a negative solvation enthalpy, while the N2solvation is endothermic, in agreement with the experiment.
Abstract: Solubility of eight common gases in the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [emim][Tf2N], ionic liquid was systematically investigated based on alchemical free energy calculations from molecular dynamics simulations. The simulated solubilities and trend in terms of Henry's law constants agree qualitatively with the experiment. Polar gases such as H2S and nonpolar gases with a large quadrupole moment such as CO2 show the highest solubility, while nonpolar gases of small quadrupole moments (such as N2 and H2) are least soluble. The solute-ionic liquid interaction correlates with the observed solubility order. We also examined the temperature dependence of solubility for CO2 and N2 and found that the CO2 solvation in IL is exothermic with a negative solvation enthalpy, while the N2 solvation is endothermic, in agreement with the experiment.
TL;DR: In this paper, the molecular-scale properties of the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, confined in nanometer-scale carbon pores have been investigated using small-angle X-ray and neutron scattering and fully atomistic molecular dynamics simulations.
Abstract: The molecular-scale properties of the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [C4mim+][Tf2N–], confined in nanometer-scale carbon pores have been investigated using small-angle X-ray and neutron scattering and fully atomistic molecular dynamics simulations. [C4mim+][Tf2N–] densities significantly higher than that of the bulk fluid at the same temperature and pressure result from the strong affinity of the RTIL cation with the carbon surface during the initial filling of slitlike, subnanometer micropores along the mesopore surfaces. Subsequent filling of cylindrical ∼8 nm mesopores in the mesoporous carbon matrix is accompanied by weak RTIL densification. The relative size of the micropores compared to the ion dimension, and the strong interaction between the RTIL and the slit-like micropore, disrupt the bulk RTIL structure. This results in a low-excluded volume, high-RTIL ion density configuration. The observed interfacial phenomena are simulate...
TL;DR: A novel solvent extraction process for trivalent lanthanides and yttrium from aqueous solutions into ILs, which was promoted by a hydrophilic 1-MIM or 2-M IM, and showed good selectivity for lanthanide compared to alkali metals and alkaline earth cations.
Abstract: 1-Methylimidazole (1-MIM) and 2-methylimidazole (2-MIM) are miscible in water and imidazolium based ionic liquids (ILs), and can coordinate with soft metal ions This paper reports a novel solvent extraction process for trivalent lanthanides and yttrium from aqueous solutions into ILs, which was promoted by a hydrophilic 1-MIM or 2-MIM Slope analysis confirmed that MIM in ILs formed a 1 : 1 complex with La3+ and Y3+ and a 1 : 4 complex with Eu3+ and Lu3+, depending on the atomic number of the metal and the metal–ligand interactions that have been characterized by FTIR spectroscopy and ESI-MS The effect of nitrate concentration on the extraction of lanthanides with 1-MIM in ILs was analysed It indicated that nitrate anions were involved in the extraction process Under the same conditions, the extraction of lanthanides with MIM into n-pentanol was carried out The extractability was by far lower than that obtained in ILs Both cationic exchange and neutral solvation mechanisms occurred in ILs and only the neutral solvation mechanism occurred in n-pentanol, which were demonstrated by the extraction tests and the structure of extracted species determined by ESI-MS The competitive extraction in ILs showed good selectivity for lanthanides compared to alkali metals and alkaline earth cations After extraction, lanthanides could be stripped very easily from the ionic liquid phase with dilute nitric acid From the temperature dependence data, the thermodynamic parameter values (ΔH, ΔS and ΔG) were calculated The results indicated that the extraction reactions were spontaneous and went through an endothermic process
TL;DR: Thiazolothiazole-linked porous organic polymers have been synthesized from a facile catalyst-free condensation reaction between aldehydes and dithiooxamide under solvothermal conditions and exhibit a highly selective uptake of CO2 over N2 under ambient conditions.
TL;DR: The IL electrolyte performance was correlated with increasing temperature, which limited the voltage stability window and led to the formation of a solid electrolyte interphase on the carbon electrode surface, evident in both the CV and EIS experiments.
Abstract: While most supercapacitors are limited in their performance by the stability of the electrolyte, using neat ionic liquids (ILs) as the electrolyte can expand the voltage window and temperature range of operation. In this study, ILs with bis(trifluoromethylsulfonyl)imide (Tf2N) as the anion were investigated as the electrolyte in onion-like carbon-based electrochemical capacitors. To probe the influence of cations on the electrochemical performance of supercapacitors, three different cations were used: 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium and 1,6-bis(3-methylimidazolium-1-yl). A series of electrochemical characterization tests was performed using cyclic voltammetry (CV), galvanostatic cycling and electrochemical impedance spectroscopy (EIS). Diffusion coefficients were measured using EIS and correlated with quasielastic neutron scattering and molecular dynamics simulation. These three techniques were used in parallel to confirm a consistent trend between the three ILs. It was found that the IL with the smaller sized cation had a larger diffusion coefficient, leading to a higher capacitance at faster charge-discharge rates. Furthermore, the IL electrolyte performance was correlated with increasing temperature, which limited the voltage stability window and led to the formation of a solid electrolyte interphase on the carbon electrode surface, evident in both the CV and EIS experiments.
TL;DR: Metal-free N-doped carbons with controllable pore texture served as catalysts for oxygen reduction reaction (ORR) with an activity comparable to that of Pt/C and shows that both the ORR activity and kinetics are strongly correlated with the pore size distribution.