Grape seed carbons for studying the influence of texture on supercapacitor behaviour in aqueous electrolytes

Microporous carbon materials having a negligible contribution of mesopores have been synthesised by cyclic oxidation/desorption of grape seeds char using air, ozone and HNO3 as oxidant agents. By adequate selection of the operating conditions (oxidation procedure and number of cycles), it is possible to tune the volume and pore size distribution (PSD) of carbon materials and therefore determine the influence of carbon textural properties on the electrochemical behaviour of carbon-carbon symmetric supercapacitors operating in different aqueous electrolytes. The results confirm that although energy density can be improved using neutral electrolytes because of their higher stability potential window compared to acidic or basic electrolytes, it is important to adapt the textural properties of the carbon materials to improve the ions' diffusion inside the porosity for assuring the charging of the double layer at high current densities to reach high power densitiesThe authors greatly appreciate the financial support from the Spanish Ministerio de Ciencia e Innovación (CTQ2009-09983

Solvent-free ionic liquids as in situ probes for assessing the effect of ion size on the performance of electrical double layer capacitors

The authors thank Norit for kindly supplying the activated carbon adsorbent. COA thanks MEC, Spain, for the financial support (EX2004-0612). Poznań University of Technology is also acknowledged (Project DS 32/007/2005). The help of Dr. Parra with the Modelling Software and of Dr. Khomenko in the conductivity measurements is acknowledged.Peer reviewe

Factores que controlan la eliminación de SO2 por fibras de carbón y carbones activados: estudio del mecanismo de oxidación de SO2

DGCYT y CICYT (Proyectos AMB96-0799 y QUI97-2051-CE

The Large Electrochemical Capacitance of Microporous Doped Carbon Obtained by Using a Zeolite Template

9 pages, 7 figures.A novel microporous templated carbon material doped with nitrogen is synthesized by using a two-step nanocasting process using acrylonitrile (AN) and propylene as precursors, and Na-Y zeolite as a scaffold. Liquid-phase impregnation and in situ polymerization of the nitrogenated precursor inside the nanochannels of the inorganic scaffold, followed by gas-phase impregnation with propylene, enables pore-size control and functionality tuning of the resulting carbon material. The material thereby obtained has a narrow pore-size distribution (PSD), within the micropore range, and a large amount of heteroatoms (i.e., oxygen and nitrogen). In addition, the carbon material inherits the ordered structure of the inorganic host. Such features simultaneously present in the carbon result in it being ideal for use as an electrode in a supercapacitor. Although presenting a moderately developed specific surface area (S_BET = 1680 m2 g-1), the templated carbon material displays a large gravimetric capacitance (340 F g-1) in aqueous media because of the combined electrochemical activity of the heteroatoms and the accessible porosity. This material can operate at 1.2 V in an aqueous medium with good cycleability - beyond 10 000 cycles - and is extremely promising for use in the development of high-energy-density supercapacitors.The authors thank Norit for kindly supplying the activated carbon adsorbent. C.O.A. thanks MEC, Spain, for financial support (EX2004-0612). The kind help of R. Benoit for the XPS data is acknowledged.Peer reviewe

Synthesis of oxy-hydroxyfluorinated anatase nanoparticles grown on carbon nanotubes

International audienceThe synthesis of composite materials containing carbon nanotubes (CNTs) and inorganic nanocrystals is of interest to combine the specific properties of each components. While literature provides broad studies on the growth of anatase TiO2 onto CNTs, it has never been reported how the presence of aqueous HF could affect the chemical composition of CNTs. Here, we demonstrated that CNTs are inactive toward fluorination during the solvothermal synthesis of an oxy-hydroxyfluorinated compound featuring the anatase-type structure. We further showed that functionalized CNTs offer nucleation sites that favor nanocrystals growth. As a result, the prepared composite features CNTs that are decorated by anatase nanocrystals. The results also showed that, in this condition, titanium alkoxide readily react with HF via a fluorolysis reaction allowing stabilizing high content of fluorine within the anatase network

Polarization-induced distortion of ions in the pores of carbon electrodes for electrochemical capacitors

This paper reports the effect of confining ionic species of the electrolyte inside the porosity of carbon electrodes during the performance of electrochemical capacitors. Solvent-free ionic liquids and a conventional organic medium were used as electrolytes, while two series of carbons with controlled pore sizes – one of them obtained from nanocasting procedure – were used as electrode materials. Our results demonstrate that under the effect of the electric field applied during the polarization of the electrodes, desolvated ions enter distorted in pores smaller than their limiting size. In such conditions of confinement, it is demonstrated that the traditional concept of an electric double-layer formed by solvated ions adsorbed on both pore walls does not apply for sub-nanometer size pores.The authors thank Actitex (France) for kindly supplying the carbon cloth. COA thanks her Ramon y Cajal Research Contract and the Spanish–French Collaborative Grant (Accion Integrada HF2006-0115) for supporting her stay at CRMDPeer reviewe

NbSe2 Nanosheets/Nanorolls Obtained via Fast and Direct Aqueous Electrochemical Exfoliation for High-Capacity Lithium Storage

Layered transition-metal dichalcogenides (LTMDs) in two-dimensional (2D) form are attractive for electrochemical energy storage, but research efforts in this realm have so far largely focused on the best-known members of such a family of materials, mainly MoS2, MoSe2, and WS2. To exploit the potential of further, currently less-studied 2D LTMDs, targeted methods for their production, preferably by cost-effective and sustainable means, as well as control over their nanomorphology, are highly desirable. Here, we report a quick and straightforward route for the preparation of 2D NbSe2 and other metallic 2D LTMDs that relies on delaminating their bulk parent solid under aqueous cathodic conditions. Unlike typical electrochemical exfoliation methods for 2D materials, which generally require an additional processing step (e.g., sonication) to complete delamination, the present electrolytic strategy yielded directly exfoliated nano-objects in a very short time (1-2 min) and with significant yields (∼16 wt %). Moreover, the dominant morphology of the exfoliated 2D NbSe2 products could be tuned between rolled-up nanosheets (nanorolls) and unfolded nanosheets, depending on the solvent where the nano-objects were dispersed (water or isopropanol). This rather unusual delamination behavior of NbSe2 was explored and concluded to occur via a redox mechanism that involves some degree of hydrolytic oxidation of the material triggered by the cathodic treatment. The delamination strategy could be extended to other metallic LTMDs, such as NbS2 and VSe2. When tested toward electrochemical lithium storage, electrodes based on the exfoliated NbSe2 products delivered very high capacity values, up to 750-800 mA h g-1 at 0.5 A g-1, where the positive effect of the nanoroll morphology, associated to increased accessibility of the lithium storage sites, was made apparent. Overall, these results are expected to expand the availability of fit-for-purpose 2D LTMDs by resorting to simple and expeditious production strategies of low environmental impact.D.F.C., S.G.-D., S.V.R., J.M.M., and J.I.P. gratefully acknowledge funding by the Spanish Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) as well as the European Regional Development Fund (ERDF, A way of making Europe) through grant PID2021-125246OB-I00, and by Plan de Ciencia, Tecnología e Innovación (PCTI) 2018–2022 del Principado de Asturias and the ERDF through grant IDI/2021/000037. S.G.-D. is grateful to the Spanish MINECO for his predoctoral contract [BES/2016 077830]. E.R.-P. thanks the Région Centre val de Loire in France [Project APR-IR SCAP-3D, convention n°2017-00117284] for financial support.Peer reviewe

Two-Dimensional MoS2 Nanosheets Derived from Cathodic Exfoliation for Lithium Storage Applications

The preparation of 2H-phase MoS2 thin nanosheets by electrochemical delamination remains a challenge, despite numerous efforts in this direction. In this work, by choosing appropriate intercalating cations for cathodic delamination, the insertion process was facilitated, leading to a higher degree of exfoliation while maintaining the original 2H-phase of the starting bulk MoS2 material. Specifically, trimethylalkylammonium cations were tested as electrolytes, outperforming their bulkier tetraalkylammonium counterparts, which have been the focus of past studies. The performance of novel electrochemically derived 2H-phase MoS2 nanosheets as electrode material for electrochemical energy storage in lithium-ion batteries was investigated. The lower thickness and thus higher flexibility of cathodically exfoliated MoS2 promoted better electrochemical performance compared to liquid-phase and ultrasonically assisted exfoliated MoS2, both in terms of capacity (447 vs. 371 mA·h·g−1 at 0.2 A·g−1) and rate capability (30% vs. 8% capacity retained when the current density was increased from 0.2 A·g−1 to 5 A·g−1), as well as cycle life (44% vs. 17% capacity retention at 0.2 A·g−1 after 580 cycles). Overall, the present work provides a convenient route for obtaining MoS2 thin nanosheets for their advantageous use as anode material for lithium storage

Supplementary Material for Two-Dimensional MoS2 Nanosheets Derived from Cathodic Exfoliation for Lithium Storage Applications

Figure S1: microscopic and spectroscopic characterization of ultrasound-assisted liquid-phase exfoliated MoS2 colloidal dispersions. Figure S2: AFM characterization of cathodically exfoliated MoS2 materials obtained using ammonium salts other than HTMABr as electrolyte. Figure S3: X-ray diffraction patterns of bulk and exfoliated MoS2 materials. Figure S4: cyclic voltammograms and electrochemical impedance spectroscopy (EIS) of the exfoliated MoS2 materials after long-term cycling. Figure S5: microscopic characterization of the ee-MoS2 electrodes. Figure S6: post-mortem microscopic characterization of the ee-MoS2 electrodes cycled at 0.2 A g−1. Figure S7: post-mortem microscopic characterization of the ee-MoS2 electrodes cycled at 0.5 A g−1. Figure S8: post-mortem microscopic characterization of the lpe-MoS2 electrodes cycled at 0.2 A g−1. Supplementary Movies S1–S3: electrochemical expansion of MoS2 over 30 min using HTMABr, TEACl and THACl as electrolytes, respectively.Peer reviewe