Renaud Denoyel

Single-ion BAB triblock copolymers as highly efficient electrolytes for lithium-metal batteries

Electrochemical energy storage is one of the main societal challenges of this century. The performances of classical lithium-ion technology based on liquid electrolytes have made great advances in the past two decades, but the intrinsic instability of liquid electrolytes results in safety issues. Solid polymer electrolytes would be a perfect solution to those safety issues, miniaturization and enhancement of energy density. However, as in liquids, the fraction of charge carried by lithium ions is small (<20%), limiting the power performances. Solid polymer electrolytes operate at 80 °C, resulting in poor mechanical properties and a limited electrochemical stability window. Here we describe a multifunctional single-ion polymer electrolyte based on polyanionic block copolymers comprising polystyrene segments. It overcomes most of the above limitations, with a lithium-ion transport number close to unity, excellent mechanical properties and an electrochemical stability window spanning 5 V versus Li(+)/Li. A prototype battery using this polyelectrolyte outperforms a conventional battery based on a polymer electrolyte.

Selective Removal of N‐Heterocyclic Aromatic Contaminants from Fuels by Lewis Acidic Metal–Organic Frameworks

Fossil fuels, such as diesel or gasoline, are blends of aromatic and aliphatic compounds that contain significant levels of heterocyclic aromatic contaminants. These contaminants have to be removed for environmental reasons. One of the most important issues is the presence of sulfur compounds, such as thiophene (TPH), benzothiophene (BT), and dibenzothiophene (DBT) in fuel feeds, which lead to the formation of SOx exhaust gases and eventually to acid rain. As environmental legislation becomes more stringent on SOx exhaust levels, it is imperative to keep lowering the sulfur concentrations to currently 10 ppmw S (parts per million by weight of sulfur) or less. The main industrial process is hydrodesulfurization (HDS) in which sulfur compounds are hydrogenated to hydrocarbons and H2S over typically a CoMo catalyst. However, nitrogen compounds, such as (substituted) indoles and carbazoles, which are also present in fossil fuels, compete for the active sites on these HDS catalysts, preventing a deep HDS. In the absence of nitrogen compounds, deep HDS can easily produce fuels with sulfur levels well below 10 ppmw, for instance by using the newest generations of materials based on Mo-W-Ni, which can lower sulfur levels to 5 ppmw. As the eventual aim is to have sulfur-free fuel, even these low concentrations will have to be removed. A promising way to selectively remove nitrogen contaminants would be adsorption on a microporous material. Efficient purification can be performed by adsorption as long as the interaction between the adsorbate and the adsorbent is relatively strong. A CuY zeolite has been described as a potential adsorbent for the removal of nitrogen compounds by p complexation, but the maximal capacity at saturation only amounted to 3 mg N per gram of adsorbent, and moreover sulfur compounds are adsorbed as well. An ideal adsorbent for such application should be easy to synthesize, stable in the given feed compositions, possess pores that are large enough to accommodate bulky organic molecules, such as carbazoles, have a sufficient capacity, and be highly selective for nitrogen over sulfur compounds. Metal–organic frameworks (MOFs) are an emerging class of highly porous materials, formed of inorganic subunits and organic linkers that bear multiple complexing functions (for example, carboxylates, phosphonates, and others), which enables a unique variety of potential interactions inside the pores. To date, they have been successfully used as adsorbents for the capture of greenhouse gases, such as CO2 and CH4, and in liquid-phase separations such as those of alkylaromatics and styrene, olefins and paraffins, and for fuel and water purification by adsorption of organic pollutants. Herein, we propose the use of mesoporous metal carboxylates with different topologies and compositions for the selective adsorption of nitrogen contaminants. These heterocyclic contaminants are found in fuel feeds that are typically aliphatic with a minor aromatic fraction. This system is simulated herein by using a solvent composed of heptane/toluene in a volumetric ratio of 80:20 (labeled hereafter as H/T). Specifically, the adsorptive removal of indole (IND), 2-methylindole (2MI), 1,2-dimethylindole (1,2DMI), carbazole (CBZ), and N-methylcarbazole (NMC) as well as of TPH, BT, and DBT has been studied. These molecules are the most important heterocyclic contaminants in fuel feeds. To study the influence of the toluenecontaining solvent on the adsorption and on the interaction strength between the host and the adsorbate, the adsorption of the contaminants has also been studied using a toluene/ [*] M. Maes, S. Schouteden, F. Vermoortele, Dr. L. Alaerts, Prof. Dr. D. E. De Vos Centre for Surface Chemistry and Catalysis Katholieke Universiteit Leuven Kasteelpark Arenberg 23, 3001 Leuven (Belgium) Fax: (+ 32)16-321-998 E-mail: dirk.devos@biw.kuleuven.be

Explanation of the Adsorption of Polar Vapors in the Highly Flexible Metal Organic Framework MIL-53(Cr)

A comparison of the adsorption of water, methanol, and ethanol polar vapors by the flexible porous chromium(III) terephthalate MIL-53(Cr) was investigated by complementary techniques including adsorption gravimetry, ex situ X-ray powder diffraction, microcalorimetry, thermal analysis, IR spectroscopy, and molecular modeling. The breathing steps observed during adsorption strongly depend on the nature of the vapor. With water, a significant contraction of the framework is observed. For the alcohols, the initial contraction is followed by an expansion of the framework. A combination of IR analysis, X-ray diffraction, and computer modeling leads to the molecular localization of the guest molecules and to the identification of the specific guest-guest and host-guest interactions. The enthalpies of adsorption, measured by microcalorimetry, show that the strength of the interactions decreases from ethanol to water. Differential scanning calorimetry experiments on an EtOH/H(2)O mixture suggest a selective adsorption of ethanol over water.

Influence of additives on Cu electrodeposition mechanisms in acid solution: direct current study supported by non-electrochemical measurements

Abstract The effect of polyethylene glycol (PEG) and chloride ions on copper electrodeposits is investigated by electrochemical measurements (cyclic voltammetry, current and potential pulses) coupled with an ellipsometric study at open circuit. When PEG is added to the Cu2+ solution, the modifications of the copper electrodeposition mechanism can be explained by a polymer-electrode interaction instead of a complex formation in solution. Since ellipsometry has shown no PEG adsorption at least at open circuit, that adsorption is assumed to be potential dependent. Moreover, the efficiency of PEG alone in solution, seems to be decreased when the deposit grows. With Cl− alone, an activation of copper deposition is performed. The simultaneous addition of the two additives induces a blocking effect of the copper reduction that continues on with time. X-ray diffraction, optical microscopy and atomic force microscopy (AFM) carried out complementary results, on bulk deposits obtained from solution with and without these additives. It has been found that a bright, compact and homogeneous coating is only obtained in presence of both additives. In that case, the texture of the deposit is modified and the roughness is significantly decreased to 0.5 μm.

Structural transitions in MIL-53 (Cr): view from outside and inside.

We present a unified thermodynamic description of the breathing transitions between large pore (lp) and narrow pore (np) phases of MIL-53 (Cr) observed during the adsorption of guest molecules and the mechanical compression in the process of mercury porosimetry. By revisiting recent experimental data on mercury intrusion and in situ XRD during CO(2) adsorption, we demonstrate that the magnitude of the adsorption stress exerted inside the pores by guest molecules, which is required for inducing the breathing transition, corresponds to the magnitude of the external pressure applied from the outside that causes the respective transformation between lp and np phases. We show that, when a stimulus is applied to breathing MOFs of MIL-53 type, these materials exhibit small reversible elastic deformations of lp and np phases of the order of 2-4%, while the breathing transition is associated with irreversible plastic deformation that leads to up to ∼40% change of the sample volume and a pronounced hysteresis. These results shed light on the specifics of the structural transformations in MIL-53 (Cr) and other soft porous crystals (SPC).

Properties of activated carbon controlling 2-Methylisoborneol adsorption

2-Methylisoborneol (MIB) is one of the most common taste and odour molecules found in water supplies. The use of activated carbons is known to be effective in removing MIB from water. In this work, it was found that the selection of an appropriate carbon for removing MIB from water depends on the carbon surface hydrophilicity, which can be determined via water adsorption analysis or elemental analysis. Provided the carbons used are microporous, the less hydrophilic carbons adsorb more MIB.

p-Xylene-Selective Metal-Organic Frameworks: A Case of Topology-Directed Selectivity

Para-disubstituted alkylaromatics such as p-xylene are preferentially adsorbed from an isomer mixture on three isostructural metal-organic frameworks: MIL-125(Ti) ([Ti(8)O(8)(OH)(4)(BDC)(6)]), MIL-125(Ti)-NH(2) ([Ti(8)O(8)(OH)(4)(BDC-NH(2))(6)]), and CAU-1(Al)-NH(2) ([Al(8)(OH)(4)(OCH(3))(8)(BDC-NH(2))(6)]) (BDC = 1,4-benzenedicarboxylate). Their unique structure contains octahedral cages, which can separate molecules on the basis of differences in packing and interaction with the pore walls, as well as smaller tetrahedral cages, which are capable of separating molecules by molecular sieving. These experimental data are in line with predictions by molecular simulations. Additional adsorption and microcalorimetric experiments provide insight in the complementary role of the two cage types in providing the para selectivity.

Single Crystal X-ray Diffraction Studies of Carbon Dioxide and Fuel-Related Gases Adsorbed on the Small Pore Scandium Terephthalate Metal Organic Framework, Sc2(O2CC6H4CO2)3

The adsorption behavior of the microporous scandium terephthalate Sc2(O2CC6H4CO2)3 for small fuel-related molecules has been measured. The structure shows an adsorption capacity for N2 and CO2 of 6.5 mmol g(-1) and is able to take up straight chain hydrocarbons. The mechanism of adsorption of CO2, CH4, and C2H6 has been determined by single crystal synchrotron X-ray diffraction at approximately 230 K. Adsorption of CO2 at 235 K and 1 bar pressure and H2 at 80 K and 0.25 bar results in each case in a symmetry change from orthorhombic Fddd to monoclinic C2/c through tilts in the terephthalate linkers. CO2 molecules take up different sites in the two symmetrically different channels that result from this symmetry change. The structure remains orthorhombic in 9 bar of CH4 and 5 bar of C2H6, and the adsorption sites are located. CH4 and C2H6 are observed to adopt sites within the channels, and C2H6 is also observed to adopt adsorption sites between phenyl groups in the channel walls, suggesting that the structure is sufficiently flexible to allow diffusion of small molecules between adjacent channels.

Liquid intrusion and alternative methods for the characterization of macroporous materials (IUPAC Technical Report)

This document deals with the characterization of porous materials having pore widths in the macropore range of 50 nm to 500 μm. In recent years, the development of advanced adsorbents and catalysts (e.g., monoliths having hierarchical pore networks) has brought about a renewed interest in macropore structures. Mercury intrusion–extrusion porosimetry is a well-established method, which is at present the most widely used for determining the macropore size distribution. However, because of the reservations raised by the use of mercury, it is now evident that the principles involved in the application of mercury porosimetry require reappraisal and that alternative methods are worth being listed and evaluated. The reliability of mercury porosimetry is discussed in the first part of the report along with the conditions required for its safe use. Other procedures for macropore size analysis, which are critically examined, include the intrusion of other non-wetting liquids and certain wetting liquids, capillary condensation, liquid permeation, imaging, and image analysis. The statistical reconstruction of porous materials and the use of macroporous reference materials (RMs) are also examined. Finally, the future of macropore analysis is discussed.

Hydration sequence of swelling clays: Evolutions of specific surface area and hydration energy

In order to identify the key steps and the driving force for the hydration process of swelling clays, the water adsorption isotherms and enthalpies were measured on monoionic montmorillonite samples saturated with alkali or calcium ions, and on bi-ionic samples saturated with a sodium-calcium mixture. The specific surface area evolution along the hydration process was determined using a recent interpretation of the experimental adsorption isotherms of swelling solids. Results are interpreted in structural terms. Compared with additional data from sample-controlled thermal analysis (SCTA), the results confirm experimentally that the hydration of Li- and Na-montmorillonite is mainly a cation-controlled process, in contrast with the hydration of Cs samples in which the cation contribution to hydration is negligible, as we have already demonstrated using electrostatic calculations or conductivity measurements.