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Conducting polymers (CPs) are undergoing a renewal in light of new challenges in energy storage posed by the environmental crisis through expanding their application to concepts of conducting redox polymers, nanostructured CPs and porous CPs. But if their conducting properties are widely documented, the same cannot be said for their structural properties, causing an increasing need of new solutions for the preparation of CPs with predetermined structures. In this study, we used a pentaerythritol core tertrafunctionalized with EDOT units as architectured monomer to prepare porous CPs with a controlled degree of openness and a hierarchical porous structure. Polymers were prepared by electrochemical and chemical oxidation of monomer solutions at different concentrations, and films were studied by cyclic voltammetry, quartz crystal microbalance, electrochemical impedance spectroscopy and gas sorption experiments. Results show that strong links exit between the porosity and the conductivity of films on the one hand, and the monomer concentration in the polymerization bath on the other, providing a simple way to control the textural and conducting properties of porous CPs. [ABSTRACT FROM AUTHOR]

The unique properties of 2D MXenes, such as metal‐like electrical conductivity and versatile surface chemistry, make them appealing for various applications, including energy storage. While surface terminations of 2D MXene are expected to have a key influence on their electrochemical properties, the conventional HF‐etching method limits the surface functional groups to F, OH, and O. In this study, O‐free, Cl‐terminated MXenes (noted as Ti3C2Clx) are first synthesized by a molten salt (FeCl2) etching route. Then, a substitution of surface termination from Cl to N is performed via post‐thermal treatment of Ti3C2Clx in Li3N containing molten salt electrolytes. While the Cl‐terminated pristine material does not show electrochemical activity, the surface‐modified, N‐containing Ti3C2Tx exhibits a unique capacitive‐like electrochemical signature in sulfuric acid aqueous electrolyte with rate performance—more than 300 F g−1 (84 mAh g−1) at 2 V s−1. These results show that control of the MXene surface chemistry enables the preparation of high‐performance electrodes in a previously not accessed limit of energy storage. [ABSTRACT FROM AUTHOR]

Kinetic data, for example, activation energy and reaction order, are crucial for the understanding of chemical reactions and processes. Here, we describe a novel method for obtaining kinetic data based on thermogravimetric measurements (TGA) that exploits in each measurement multiple successive isothermal steps (SIS). We applied this method to the notoriously challenging carbon combustion process for vastly different carbons for oxygen molar fractions between 1.4 % and 90 %. Our obtained apparent EA values are within the wide range of results in the literature and vary in a systematic way with the oxygen partial pressure. The improved accuracy and large amount of obtainable data allowed us to show that the majority of experimentally obtained apparent data for apparent EA are neither in a kinetic regime nor in a diffusion‐controlled one but rather in a transition regime. [ABSTRACT FROM AUTHOR]

Supercapacitors offer high power densities but require further improvements in energy densities for widespread commercial applications. In addition to the conventional strategy of using large surface area materials to enhance energy storage, recently, matching electrolyte ion sizes to material pore sizes has been shown to be particularly effective. However, synthesis and characterization of materials with precise pore sizes remain challenging. Herein, we propose to evaluate the layered structures in graphene derivatives as being analogous to pores and study the possibility of ion sieving. A class of pillared graphene based materials with suitable interlayer separation were synthesized, readily characterized by X-ray diffraction, and tested in various electrolytes. Electrochemical results show that the interlayer galleries could indeed sieve electrolyte ions based on size constrictions: ions with naked sizes that are smaller than the interlayer separation access the galleries, whereas the larger ions are restricted. These first observations of ion sieving in pillared graphene-based materials enable efficient charge storage through optimization of the d-spacing/ion size couple. [ABSTRACT FROM AUTHOR]

The areal energy density of on-chip micro-supercapacitors should be improved in order to obtain autonomous smart miniaturized sensors. To reach this goal, high surface capacitance electrode (>100 mF cm−2) has to be produced while keeping low the footprint area. For carbide-derived carbon (CDC) micro-supercapacitors, the properties of the metal carbide precursor have to be fine-tuned to fabricate thick electrodes. The ad-atoms diffusion process and atomic peening effect occurring during the titanium carbide sputtering process are shown to be the key parameters to produce low stress, highly conductive, and thick TiC films. The sputtered TiC at 10−3 mbar exhibits a high stress level, limiting the thickness of the TiC-CDC electrode to 1.5 µm with an areal capacitance that is less than 55 mF cm−2 in aqueous electrolyte. The pressure increase up to 10−2 mbar induces a clear reduction of the stress level while the layer thickness increases without any degradation of the TiC electronic conductivity. The volumetric capacitance of the TiC-CDC electrodes is equal to 350 F cm−3 regardless of the level of pressure. High values of areal capacitance (>100 mF cm−2) are achieved, whereas the TiC layer is relatively thick, which paves the way toward high-performance micro-supercapacitors. [ABSTRACT FROM AUTHOR]

Herein, we report an improved method for the physical grafting of 1-nitropyrene (Pyr-NO2) onto highly graphitized carbon onion. This is achieved through a lowering of the onset potential of the pyrene polymerization via in situ reduction of the NO2 group. The additional redox activity pertaining to the reduced NO2 enables exceeding the faradaic capacity, which is associated with the p-doping of the grafted pyrene backbone, as observed for pyrene, 1-aminopyrene, and unreduced Pyr-NO2. Theoretical calculations demonstrate the charge transfer and binding enthalpy capabilities of Pyr-NO2, which are significantly higher than those of the other two species, and which allow for improved p-stacking on the carbon surface. Upon 20 wt% grafting of Pyr-NO2, the capacity of the electrode jumps from 20 mA h gelectrode−1 to 38 mA h gelectrode−1, which corresponds to 110 mA h g−1 per mass of Pyr-NO2 and the average potential is increased by 200 mV. Very interestingly, this high performance is also coupled with outstanding retention with respect to both the initial capacity for more than 4000 cycles, as well as the power characteristics, demonstrating the considerable advantages of employing the present in situ grafting technique. [ABSTRACT FROM AUTHOR]

Thin films of (TTF)(TCNQ) (TTF=tetrathiafulvalene, TCNQ=tetracyanoquinodimethane) are deposited on Si (001), KBr, and stainless steel conversion coatings (SSCC) using chemical vapor deposition. These films are characterized by IR, XRD, conductivity measurements, and SEM. Conducting nanowires and nanorings of (TTF)(TCNQ) and nanowires of (TTF)[Ni(dmit) 2 ] 2 (typically, 20 nm×20 μm) are prepared by successively dipping SSCC in acetonitrile solutions of TTF and TCNQ, or (TTF) 3 (BF 4 ) and (Bu 4 N)[Ni(dmit) 2 ], respectively. These nanowires are observed by SEM. The (TTF)(TCNQ) nanowires are also observed by TEM and AFM and characterized by current-voltage measurements. Nanowires of (TTF)[Ni(dmit) 2 ] 2 are also obtained on silicon conversion coatings (SiCC) and characterized by Raman spectroscopy. [ABSTRACT FROM PUBLISHER]

Thin films of (TTF)(TCNQ) (TTF=tetrathiafulvalene, TCNQ=tetracyanoquinodimethane) are deposited on Si (001), KBr, and stainless steel conversion coatings (SSCC) using chemical vapor deposition. These films are characterized by IR, XRD, conductivity measurements, and SEM. Conducting nanowires and nanorings of (TTF)(TCNQ) and nanowires of (TTF)[Ni(dmit) 2 ] 2 (typically, 20 nm×20 μm) are prepared by successively dipping SSCC in acetonitrile solutions of TTF and TCNQ, or (TTF) 3 (BF 4 ) and (Bu 4 N)[Ni(dmit) 2 ], respectively. These nanowires are observed by SEM. The (TTF)(TCNQ) nanowires are also observed by TEM and AFM and characterized by current-voltage measurements. Nanowires of (TTF)[Ni(dmit) 2 ] 2 are also obtained on silicon conversion coatings (SiCC) and characterized by Raman spectroscopy. thin films nanowires nanorings chemical vapor deposition conversion coatings molecular conductors [ABSTRACT FROM AUTHOR]

Titelbild: Thermal Oxidation of Carbonaceous Nanomaterials Revisited: Evidence of Mechanism Changes (Angew. Die Ergebnisse deuten darauf hin, dass die chemische Reaktion bei der Kohlenstoffverbrennung noch lange nicht verstanden wurde, was auf spannende weitere Studien hindeutet. Die Ergebnisse deuten darauf hin, dass die chemische Reaktion bei der Kohlenstoffverbrennung noch lange nicht verstanden wurde, was auf spannende weitere Studien hindeutet. [Extracted from the article]

Kinetic data, for example, activation energy and reaction order, are crucial for the understanding of chemical reactions and processes. Here, we describe a novel method for obtaining kinetic data based on thermogravimetric measurements (TGA) that exploits in each measurement multiple successive isothermal steps (SIS). We applied this method to the notoriously challenging carbon combustion process for vastly different carbons for oxygen molar fractions between 1.4 % and 90 %. Our obtained apparent E A values are within the wide range of results in the literature and vary in a systematic way with the oxygen partial pressure. The improved accuracy and large amount of obtainable data allowed us to show that the majority of experimentally obtained apparent data for apparent E A are neither in a kinetic regime nor in a diffusion-controlled one but rather in a transition regime., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Nanoporous carbon-based supercapacitors store electricity through adsorption of ions from the electrolyte at the surface of the electrodes. Room temperature ionic liquids, which show the largest ion concentrations among organic liquid electrolytes, should in principle yield larger capacitances. Here, we show by using electrochemical measurements that the capacitance is not significantly affected when switching from a pure ionic liquid to a conventional organic electrolyte using the same ionic species. By performing additional molecular dynamics simulations, we interpret this result as an increasing difficulty of separating ions of opposite charges when they are more concentrated, that is, in the absence of a solvent that screens the Coulombic interactions. The charging mechanism consistently changes with ion concentration, switching from counterion adsorption in the diluted organic electrolyte to ion exchange in the pure ionic liquid. Contrarily to the capacitance, in-pore diffusion coefficients largely depend on the composition, with a noticeable slowing of the dynamics in the pure ionic liquid.

Supercapacitors are electrochemical devices which store energy by ion adsorption on the surface of a porous carbon. They are characterized by high power delivery. The use of nanoporous carbon to increase their energy density should not hinder their fast charging. However, the mechanisms for ion transport inside electrified nanopores remain largely unknown. Here we show that the diffusion is characterized by a hierarchy of time scales arising from ion confinement, solvation, and electrosorption effects. By combining electrochemistry experiments with molecular dynamics simulations, we determine the in-pore conductivities and diffusion coefficients and their variations with the applied potential. We show that the diffusion of the ions is slower by 1 order of magnitude compared to the bulk electrolyte. The desolvation of the ions occurs on much faster time scales than electrosorption.

Supercapacitors are electricity storage systems with high power performances. Their short charge/discharge times are due to fast adsorption/desorption rates for the ions of the electrolyte on the electrode surface. Nanoporous carbon electrodes, which give larger capacitances than simpler geometries, might be expected to show poorer power performances because of the longer times taken by the ions to access the electrode interior. Experiments do not show such trends, however, and this remains to be explained at the molecular scale. Here we show that carbide-derived carbons exhibit heterogeneous and fast charging dynamics. We perform molecular dynamics simulations, with realistically modeled nanoporous electrodes and an ionic liquid electrolyte, in which the system, originally at equilibrium in the uncharged state, is suddenly perturbed by the application of an electric potential difference between the electrodes. The electrodes respond by charging progressively from the interface to the bulk as ions are exchanged between the nanopores and the electrolyte region. The simulation results are then injected into an equivalent circuit model, which allows us to calculate charging times for macroscopic-scale devices.