One-step synthesis of highly reduced graphene hydrogels for high power supercapacitor applications

Graphene hydrogels with high electrical conductivity were prepared by a one-step process using hydrazine hydrate as gel assembly agent (GH-HD). Conventional two-step process of gel formation and further reduction to prepare highly conducting gels was replaced by a single step involving equivalent amount of hydrazine. Optimized graphene oxide concentration was established to facilitate such monolith formation. Extensive characterization and control studies enabled understanding of the material properties and gel formation mechanism. The synthesized gel shows a high electrical conductivity of 1141 S/m. The supercapacitor based on GH-HD delivers a high specific capacitance of 190 F/g at a current density of 0.5 A/g and 123 F/g at very high current density of 100 A/g. Furthermore, excellent power capability and cyclic stability were also observed. 3D macroporous morphology of GH-HD makes it ideal for high rate supercapacitor applications

Ion Sieving Effects in Chemically Tuned Pillared Graphene Materials for Electrochemical Capacitors

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

Thiazonaphthalimide derivatives: Synthesis and interaction with DNA

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Porphyrin anchoring on Si(100) using a β-pyrrolic position

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A Simple Fluorescence Affinity Assay to Decipher Uranyl‐Binding to Native Proteins

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Matrix-Free DNP-Enhanced NMR Spectroscopy of Liposomes Using a Lipid-Anchored Biradical

International audienceMagic-angle spinning dynamic nuclear polarization (MAS-DNP) has been proven to be a powerful technique to enhance the sensitivity of solid-state NMR (SSNMR) in a wide range of systems. Here, we show that DNP can be used to polarize lipids using a lipid-anchored polarizing agent. More specifically, we introduce a C16-functionalized biradical, which allows localization of the polarizing agents in the lipid bilayer and DNP experiments to be performed in the absence of excess cryo-protectant molecules (glycerol, dimethyl sulfoxide, etc.). This constitutes another original example of the matrix-free DNP approach that we recently introduced

Frontispiece: Matrix-Free DNP-Enhanced NMR Spectroscopy of Liposomes Using a Lipid-Anchored Biradical

Matrix‐Free DNP on Lipid Membranes Dynamic nuclear polarization (DNP) has been proven to be a powerful technique to enhance the sensitivity of solid‐state NMR. However, until now, there has been limited success in its application to synthetic membrane‐type systems. In their Communication on page 4512 ff., G. De Paëpe et al. present an innovative approach based on system‐driven radical design in order to insert the polarizing agent inside a lipid bilayer. Combined with matrix‐free DNP, this strategy solves additive‐induced problems by releasing the need for a DNP‐compatible solvent

Revealing Electrolytic Ion Sorption in Layered Graphene Galleries through Low-Temperature Solid-State NMR

International audienceThere is an ever-growing desire to use and store energy from sustainable resources. Pillared graphene materials offer high capacitive performances in supercapacitors, presumably through enhanced electrolytic ion sorption in their chemically engineered inter-layer graphene galleries. Herein, a judicious combination of the removal of excess electrolytes, isotopic enrichment of the pillar molecules, and the use of low temperatures (100 K) enables solid-state nuclear magnetic resonance spectroscopy to efficiently probe nuclear spin polarization exchange between the electrolyte and the electrode. This provides the direct detection of electrolyte ions in proximity to the gallery pillars, evidencing the adsorption of ions in such two-dimensional galleries. However, when the ions are larger than the gallery d-spacing, they are not observed to enter the galleries, and the total storage capacity is accordingly reduced. This methodology provides a means to locate electrolyte ions upon charging or discharging devices and thus will be invaluable in the quest for the design of materials with vastly improved power densities

Toward the Improvement of Silicon-Based Composite Electrodes via an In-Situ Si@C-Graphene Composite Synthesis for Li-Ion Battery Applications

International audienceUsing Si as anode materials for Li-ion batteries remain challenging due to its morphological evolution and SEI modification upon cycling. The present work aims at developing a composite consisting of carbon-coated Si nanoparticles (Si@C NPs) intimately embedded in a three-dimensional (3D) graphene hydrogel (GHG) architecture to stabilize Si inside LiB electrodes. Instead of simply mixing both components, the novelty of the synthesis procedure lies in the in situ hydrothermal process, which was shown to successfully yield graphene oxide reduction, 3D graphene assembly production, and homogeneous distribution of Si@C NPs in the GHG matrix. Electrochemical characterizations in half-cells, on electrodes not containing additional conductive additive, revealed the importance of the protective C shell to achieve high specific capacity (up to 2200 mAh.g−1), along with good stability (200 cycles with an average Ceff > 99%). These performances are far superior to that of electrodes made with non-C-coated Si NPs or prepared by mixing both components. These observations highlight the synergetic effects of C shell on Si NPs, and of the single-step in situ preparation that enables the yield of a Si@C-GHG hybrid composite with physicochemical, structural, and morphological properties promoting sample conductivity and Li-ion diffusion pathways