Display omitted
•Graphitic nanofibers (BCNFs) were produced from biogas by catalytic decomposition.•The electrochemical intercalation of PF6− anions into BCNF cathodes is investigated.•BCNF ...electrochemical performance as cathodes depends on their graphitic structure.•BCNF graphitic domain height determines the scope of PF6− anions intercalation.
The electrochemical intercalation of PF6− anions into graphitic nanomaterials of renewable origin with different degrees of structural order to be subsequently used as cathodes for sodium dual-ion batteries is herein investigated for the first time. Overall, the electrochemical performance of the biogas-derived carbon nanofibers depends on their graphitic structure, specifically on crystallite height which was found to be the determining parameter for the scope of electrochemical intercalation of PF6− anions into these nanomaterials.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Constant capacitance in nanopores of carbon monoliths García-Gómez, Alejandra; Moreno-Fernández, Gelines; Lobato, Belén ...
Physical chemistry chemical physics : PCCP,
01/2015, Volume:
17, Issue:
24
Journal Article
Peer reviewed
Open access
The results obtained for binder-free electrodes made of carbon monoliths with narrow micropore size distributions confirm that the specific capacitance in the electrolyte (C2H5)4NBF4/acetonitrile ...does not depend significantly on the micropore size and support the foregoing constant result of 0.094 ± 0.011 F m(-2).
The objective of this study is to optimize the performance of a graphitized carbon xerogel doped with graphene oxide (GXGO) as cathode for sodium dual‐ion batteries. Carbon xerogels are synthetic ...materials produced in large amounts, with well‐controlled chemistry, porosity and structure, by a simple and fast microwave process that has been scaled‐up. The intercalation of PF6− anions from various NaPF6 salt‐based electrolytes in a GXGO‐based cathode is investigated by considering the influence of the upper cut‐off voltage (UCOV) and of the electrolyte on the electrochemical parameters. The best results were attained in an electrolyte with a 2.0 M NaPF6 concentration in EC : EMC carbonate solvent mixture with added FEC, at a UCOV of 5.0 V. GXGO cathode provides a discharge capacity of 47 mAh g−1 after 2500 cycles with a coulombic efficiency of 97 %. Moreover, it shows great cycling stability and capacity retention of essentially 100 % after the initial cycles.
Xerogels for dual‐ion batteries: A graphitized carbon xerogel (GXGO) is studied as cathode for Na dual‐ion batteries. The intercalation of PF6− anions in GXGO from NaPF6 based electrolytes is optimized. FEC in the electrolyte improves GXGO coulombic efficiency and cycling stability. GXGO capacity increases substantially by using EC : EMC electrolyte solvent mixture. GXGO activation process is accelerated by increasing electrolyte salt concentration.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This research is focused in the missing link between the specific surface area of carbons surface and their electrochemical capacitance. Current protocols used for the characterization of carbons ...applied in supercapacitors electrodes induce inconsistencies in the values of the interfacial capacitance (in F m−2), which is hindering the optimization of supercapacitors. The constraints of both the physisorption of N2 at 77 K and the standard methods used for the isotherm analysis frequently lead to a misleading picture of the porosity. Moreover, the specific surface area of carbons loses their meaning when the supercapacitor operates with organic electrolytes and ionic liquids and the actual surface involved in charge storage has to be assessed by molecular probes suiting the critical dimensions of the ions. In the case of certain carbons such as graphene type-materials, the voltage-driven mechanism may facilitate the access of electrolyte ions to spaces between carbon layers, providing a larger area than that estimated by gas adsorption. Finally, the morphological and porous features of carbons can be extremely modified when they are processed in electrodes. Due to their impact, all these issues should not be neglected and the characterization protocols must be adapted for this specific application of carbons.
Display omitted
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In recent years, the research on lithium-ion batteries (LIBs) to improve their lifetime, efficiency and energy density has led to the use of silicon-based materials as a promising anode alternative ...to graphite. Specifically, crystalline silicon (
Si) and silicon carbide (SiC) obtained from deposition or reduction processes (e.g., magnesiothermal reduction) stand out for their electrochemical properties. However, the synthesis routes proposed until now have limitations that make them difficult to afford or operate on a large scale. For this reason, in this work, carbon-silicon (C-Si) hybrid materials synthesized through an efficient route are evaluated as the potential precursor for the obtention of both
Si and SiC species in a single material. The feasibility and influence of the magnesiothermal reduction process were evaluated, and materials with 10 wt.% of reduced Si and 10-26 wt.% of SiC were obtained. Both species play a role in the improvement of the performance of silicon-based materials as anodes in lithium-ion batteries. In comparison with materials obtained by the reduction of silica gels and composites, the reduced C-Si hybrid gels stand out thanks to the homogeneous distribution and stability of the species developed.
This study analyses and compares the behaviour of 5 commercial porous carbons in the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) and its mixture with ...propylene carbonate (PC) as electrolytes. The results of this investigation show that the existence of a distribution of pore sizes and/or constrictions at the entrance of the pores leads to significant changes in the specific capacitance of the investigated materials. The use of PYR14TFSI as an electrolyte has a positive effect on the EDLC energy storage, but its high viscosity limits the power density. The mixture 50 : 50 wt% propylene carbonate-PYR14TFSI provides high operative voltage as well as low viscosity and thus notably enhances EDLC operation.
► Granulated scrap tyres are distilled at low temperature. ► The as-obtained char fraction is gasified at 1000°C. ► The syngas that may be used in a gas turbine. ► The gasification of this char is ...similar to those for semi-anthracite coal.
This work reports the effect of pressure on the steam/oxygen gasification at 1000°C of the char derived from low temperature–pressure distillation of granulated scrap tyres (GST). The study was based on the analysis of gas production, carbon conversion, cold gas efficiency and the high heating value (HHV) of the product. For comparison, similar analyses were carried out for the gasification of coals with different rank.
In spite of the relatively high ash (≈12wt.%) and sulphur (≈3wt.%) contents, the char produced in GST distillation can be regarded as a reasonable solid fuel with a calorific value of 34MJkg−1. The combustion properties of the char (EA≈50kJmol−1), its temperature of self-heating (≈264°C), ignition temperature (≈459°C) and burn-out temperature (≈676°C) were found to be similar to those of a semi-anthracite.
It is observed that the yield, H2 and CO contents and HHV of the syngas produced from char gasification increase with pressure. At 0.1MPa, 4.6Nm3kgchar−1 of syngas was produced, containing 28%v/v of H2 and CO and with a HHV around 3.7MJNm−3. At 1.5MPa, the syngas yield achieved 4.9Nm3kgchar−1 with 30%v/v of H2–CO and HHV of 4.1MJNm−3. Carbon conversion significantly increased from 87% at 0.1MPa to 98% at 1.5MPa.
It is shown that the char derived from distillation of granulated scrap tyres can be further gasified to render a gas of considerable heating value, especially when gasification proceeds at high pressure.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Display omitted
The current energy needs have put the focus on highly efficient energy storage systems such as supercapacitors. At present, much attention focuses on graphene-like materials as ...promising supercapacitor electrodes.
Here we show that reduced graphite oxide offers a very interesting potential. Materials obtained by oxidation of natural graphite and subsequent sonication and reduction by hydrazine achieve specific capacitances as high as 170F/g in H2SO4 and 84F/g in (C2H5)4NBF4/acetonitrile. Although the particle size of the raw graphite has no significant effect on the physico-chemical characteristics of the reduced materials, that exfoliated from smaller particles (<75μm) result more advantageous for the release of the stored electrical energy. This effect is particularly evident in the aqueous electrolyte.
Graphene-like materials may suffer from a drop in their specific surface area upon fabrication of electrodes with features of the existing commercial devices. This should be taken into account for a reliable interpretation of their performance in supercapacitors.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A detailed study of the intercalation/de‐intercalation mechanisms of PF6− anions in a graphite cathode of sodium dual‐ion batteries is carried out by cyclic voltammetry. The influence of the ...continuous anion intercalation/de‐intercalation on the graphite structure is investigated by ex‐situ XRD after cycling. It was concluded that the intercalation/de‐intercalation occurs through a combination of diffusion‐controlled and pseudocapacitive mechanisms. Initially, the contribution of the diffusion‐controlled is significant, specifically at the highest voltage and at the lowest scan rates which agrees with the slow kinetic of this mechanism and its usual prevalence in carbon materials with a graphitic structure. However, the continuous anion intercalation/de‐intercalation causes some deterioration of the graphite structural order, even from the initial cycles, as it was demonstrated by the evolution of the crystalline parameters, interlayer spacing, d002, and crystallite size, Lc. This deterioration hinders the diffusion‐controlled anion intercalation/de‐intercalation and, as a consequence, the pseudocapacitive becomes the main mechanism along cycling. Therefore, since graphite is capable of intercalating PF6− anions at high voltages through a capacitive mechanism, with its consequent rapid kinetics, this carbon material is an excellent candidate for using as cathode in high power sodium dual‐ion batteries, in which, kinetically fast mechanisms are required.
The pseudo‐capacitive mechanism plays a predominant role in the electrochemical intercalation/de‐intercalation of PF6− anions in graphite and this predominance becomes more evident with cycling due to certain graphite structural deterioration which hinder the diffusion‐controlled intercalation/de‐intercalation of the anions.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Pyrolysis is a technology with a promising future in the recycling of scrap tyres. This paper determines the thermal decomposition behaviour and kinetics of granulated scrap tyres (GST) by examining ...the thermogravimetric/derivative thermogravimetric (TGA/DTG) data obtained during their pyrolysis in an inert atmosphere at different heating rates. The model-free methods of Friedman, Flynn-Wall-Ozawa and Coats-Redfem were used to determine the reaction kinetics from the DTG data. The apparent activation energy and pre-exponential factor for the degradation of GST were calculated. A comparison with the results obtained by other authors was made.Original Abstract: Pirolize yra perspektyvi padangu perdirbimo technologija. Siame darbe aprasomas granuliuotu padangu atlieku (GST) terminis skilimas ir jo kinetika, nagrinejant termogravimetrines/diferencines termogravimetrines (TGA/DTG) analizes duomenis, gautus pirolizes inertiniu duju atmosferoje metu, esant skirtingiems kaitinimo greiciams. Reakcijos kinetikai remiantis DTG duomenimis nustatyti darbe taikyti Friedmano, Flynno-Wallo-Ozawos ir Coatso-Redferno metodai. Nustatyta tikroji aktyvacijos energija, reikalinga GST degradacijai, ir prieseksponentinis daugiklis. Gauti rezultatai palyginti su kitu autoriu pateiktais rezultatais.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
PDF
