Tuning Nitrogen-Doped Carbon Electrodes via Synthesis Temperature Adjustment to Improve Sodium- and Lithium-Ion Storage

Structural imperfections, heteroatom dopants, and the interconnected pore structure of carbon materials have a huge impact on their electrochemical performance in lithium-ion and sodium-ion batteries due to the specific ion transport and the dominant storage mechanism at surface defect sites. In this work, mesopore-enriched nitrogen-doped carbon (NC) materials were produced with template-assisted chemical vapor deposition using calcium tartrate as the template precursor and acetonitrile as the carbon and nitrogen source. The chemical states of nitrogen, the volume of mesopores, and the specific surface areas of the materials were regulated by adjusting the synthesis temperature. The electrochemical testing of NC materials synthesized at 650, 750, and 850 °C revealed the best performance of the NC-650 sample, which was able to deliver 182 mA·h·g−1 in sodium-ion batteries and 1158 mA·h·g−1 in lithium-ion batteries at a current density of 0.05 A·g−1. Our study shows the role of defect sites, including carbon monovacancies and nitrogen-terminated vacancies, in the binding and accumulation of sodium. The results provide a strategy for managing the carbon structure and nitrogen states to achieve a high alkali-metal-ion storage capacity and long cycling stability, thereby facilitating the electrochemical application of NC materials

Chlorinated holey double-walled carbon nanotubes for relative humidity sensor

International audienceA chemical procedure for modification of double-walled carbon nanotubes (DWCNTs) to enhance their response to humidity was developed. The DWCNTs walls were etched by hot concentrated sulfuric acid, after what the edge carbon sites were saturated by chlorine via reaction with CCl4 vapor. This treatment increases the dispersibility of DWCNTs in solvents, removes oxygen groups, and produces chlorine-decorated holes in the outer walls. Networks of chlorinated holey DWCNTs showed a high repeatable response to humid environment and a good reversible behavior after the sensor purging by dry air. The density functional theory calculations predict enhanced polarization of the DWCNTs when they contain chlorine-decorated holes in the outer walls and physisorption of H2O molecules near chlorine atoms. These two effects are the cause of an intense low-noise signal to gaseous H2O and easy sensor recovery

Chemiresistive Properties of Imprinted Fluorinated Graphene Films

The electrical conductivity of graphene materials is strongly sensitive to the surface adsorbates, which makes them an excellent platform for the development of gas sensor devices. Functionalization of the surface of graphene opens up the possibility of adjusting the sensor to a target molecule. Here, we investigated the sensor properties of fluorinated graphene films towards exposure to low concentrations of nitrogen dioxide NO2. The films were produced by liquid-phase exfoliation of fluorinated graphite samples with a composition of CF0.08, CF0.23, and CF0.33. Fluorination of graphite using a BrF3/Br2 mixture at room temperature resulted in the covalent attachment of fluorine to basal carbon atoms, which was confirmed by X-ray photoelectron and Raman spectroscopies. Depending on the fluorination degree, the graphite powders had a different dispersion ability in toluene, which affected an average lateral size and thickness of the flakes. The films obtained from fluorinated graphite CF0.33 showed the highest relative response ca. 43% towards 100 ppm NO2 and the best recovery ca. 37% at room temperature

Enhancement of Volumetric Capacitance of Binder-Free Single-Walled Carbon Nanotube Film via Fluorination

Robust electrode materials without the addition of binders allow increasing efficiency of electrical storage devices. We demonstrate the fabrication of binder-free electrodes from modified single-walled carbon nanotubes (SWCNTs) for electrochemical double-layer capacitors (EDLCs). Modification of SWCNTs included a sonication in 1,2-dichlorobenzene and/or fluorination with gaseous BrF3 at room temperature. The sonication caused the shortening of SWCNTs and the splitting of their bundles. As a result, the film prepared from such SWCNTs had a higher density and attached a larger amount of fluorine as compared to the film from non-sonicated SWCNTs. In EDLCs with 1M H2SO4 electrolyte, the fluorinated films were gradually defluorinated, which lead to an increase of the specific capacitance by 2.5–4 times in comparison with the initial values. Although the highest gravimetric capacitance (29 F g−1 at 100 mV s−1) was observed for the binder-free film from non-modified SWCNT, the fluorinated film from the sonicated SWCNTs had an enhanced volumetric capacitance (44 F cm−3 at 100 mV s−1). Initial SWCNT films and defluorinated films showed stable work in EDLCs during several thousand cycles

Role of interface interactions in the sensitivity of sulfur-modified single-walled carbon nanotubes for nitrogen dioxide gas sensing

Single-walled carbon nanotubes (SWCNTs) possess the unique ability to tune their functional properties by modifying the outer surface or interior space. Using the same modifier – sulfur, we demonstrate a difference in sensing properties of coated and filled single-walled carbon nanotubes to gaseous nitrogen dioxide. A comprehensive investigation of materials by transmission electron microscopy, X-ray photoelectron spectroscopy, density functional theory, and kinetics simulation led to an in-depth understanding of the factors influencing the sensor response of sulfur-modified SWCNTs, such as the role of surface and volumetric processes and interface effects. The sulfur-filled nanotubes with sulfur coating showed an outstanding sensitivity to detect nitrogen dioxide over a range from 1 ppb to 10 ppm due to the involvement of sulfur species in charge transfer between nanotubes and adsorbed molecules. Our data create a platform for the development of sensitive and reversible gas sensors using nanotube-based networks.The research was supported by the Ministry of Science and Higher Education of the Russian Federation (No. 121031700314-5). The authors thank the Helmholtz-Zentrum Berlin für Materialien und Energie for allocation of a beamtime and support within bilateral program “Russian-German Laboratory at BESSY II”. O.V. Sedelnikova acknowledges the Scholarship of the President of the Russian Federation (SP-1593.2021.1). The work on the fabrication of SWCNT films was supported by the Russian Science Foundation (grant 21-73-00229). V.O. Koroteev acknowledges financial support by the Spanish Ministry of Economy and Competitiveness (MINECO) within the Maria de Maeztu Units of Excellence Programme – MDM-2016-0618. A.A. Makarova acknowledges BMBF (grant no. 05K19KER). The EEL-SPIM inalysis was conducted at the Laboratorio de Microscopias Avanzadas (LMA) at the Instituto de Nanociencia de Aragon (INA) - Universidad de Zaragoza (Spain). R. Arenal acknowledges the support from the Spanish MICINN (PID2019-104739GB-100/AEI/10.13039/501100011033), from the European Union's Horizon 2020 programme under the project “ESTEEM3” (823717) and from the Government of Aragon (grant number E13_20R).Peer reviewe

Tuning Nitrogen-Doped Carbon Electrodes via Synthesis Temperature Adjustment to Improve Sodium- and Lithium-Ion Storage

Structural imperfections, heteroatom dopants, and the interconnected pore structure of carbon materials have a huge impact on their electrochemical performance in lithium-ion and sodium-ion batteries due to the specific ion transport and the dominant storage mechanism at surface defect sites. In this work, mesopore-enriched nitrogen-doped carbon (NC) materials were produced with template-assisted chemical vapor deposition using calcium tartrate as the template precursor and acetonitrile as the carbon and nitrogen source. The chemical states of nitrogen, the volume of mesopores, and the specific surface areas of the materials were regulated by adjusting the synthesis temperature. The electrochemical testing of NC materials synthesized at 650, 750, and 850 °C revealed the best performance of the NC-650 sample, which was able to deliver 182 mA·h·g−1 in sodium-ion batteries and 1158 mA·h·g−1 in lithium-ion batteries at a current density of 0.05 A·g−1. Our study shows the role of defect sites, including carbon monovacancies and nitrogen-terminated vacancies, in the binding and accumulation of sodium. The results provide a strategy for managing the carbon structure and nitrogen states to achieve a high alkali-metal-ion storage capacity and long cycling stability, thereby facilitating the electrochemical application of NC materials