Graphitic carbon nanostructures from cellulose

Graphitic carbon nanostructures have been synthesized from cellulose via a simple methodology that essentially consists of the steps: (i) hydrothermal treatment of cellulose at 250 °C and (ii) impregnation of the carbonaceous product with a nickel salt followed by thermal treatment at 900 °C. The formation of graphitic carbon nanostructures seems to occur by a dissolution–precipitation mechanism in which amorphous carbon is dissolved in the catalyst nanoparticles and then precipitated as graphitic carbon around the catalyst particles. The subsequent removal of the nickel nanoparticles and amorphous carbon by oxidative treatment leads to graphitic nanostructures with a coil morphology. This material exhibits a high degree of crystallinity and large and accessible surface area.The financial support for this research work provided by the Spanish MCyT (MAT2008-00407) is gratefully acknowledged. M. S. acknowledges the assistance of the Spanish MCyT for the award of a Postdoctoral Mobility contract.Peer reviewe

Superior Capacitive Performance of Hydrochar-Based Porous Carbons in Aqueous Electrolytes

This is the accepted version of the following article: Fuertes, A. B. and Sevilla, M. (2015), Superior Capacitive Performance of Hydrochar-Based Porous Carbons in Aqueous Electrolytes. ChemSusChem, 8: 1049–1057. doi: 10.1002/cssc.201403267, which has been published in final form at http://dx.doi.org/10.1002/cssc.201403267. This article may be used for non-commercial purposes in accordance with the Wiley Self-Archiving PolicyBiomass-based highly porous carbons with excellent performances in aqueous electrolyte-based supercapacitors have been developed. The synthesis of these materials is based on the chemical activation of biomass-based hydrochar. The addition of melamine to the activation mixture leads to porous carbons with a porosity consisting of micropores/small mesopores. Furthermore, melamine promotes the introduction of nitrogen heteroatoms in the carbon framework, along with abundant oxygen functionalities, to improve the wettability. The materials produced in the presence or absence of melamine exhibit high specific capacitances in aqueous electrolytes (>270 F g−1 in H2SO4 and >190 F g−1 in Li2SO4). Additionally, the mesopores present in the melamine-based micro-/mesoporous carbons notably improve the ion-transport kinetics, especially in Li2SO4. Furthermore, in Li2SO4, they remain stable up to a cell voltage of 1.6 V; thus exhibiting superior energy and power characteristics than those in H2SO4.This research work was supported by the Spanish MINECO (MAT2012-31651). M. S. thanks the Spanish MINECO for her Ramón y Cajal contract.Peer reviewe

Direct Synthesis of Highly Porous Interconnected Carbon Nanosheets and Their Application as High-Performance Supercapacitors

An easy, one-step procedure is proposed for the synthesis of highly porous carbon nanosheets with an excellent performance as supercapacitor electrodes. The procedure is based on the carbonization of an organic salt, i.e., potassium citrate, at a temperature in the 750–900 °C range. In this way, carbon particles made up of interconnected carbon nanosheets with a thickness of <80 nm are obtained. The porosity of the carbon nanosheets consists essentially of micropores distributed in two pore systems of 0.7–0.85 nm and 0.95–1.6 nm. Importantly, the micropore sizes of both systems can be enlarged by simply increasing the carbonization temperature. Furthermore, the carbon nanosheets possess BET surface areas in the ∼1400–2200 m2 g–1 range and electronic conductivities in the range of 1.7–7.4 S cm–1 (measured at 7.1 MPa). These materials behave as high-performance supercapacitor electrodes in organic electrolyte and exhibit an excellent power handling ability and a superb robustness over long-term cycling. Excellent results were obtained with the supercapacitor fabricated from the material synthesized at 850 °C in terms of both gravimetric and volumetric energy and power densities. This device was able to deliver ∼13 Wh kg–1 (5.2 Wh L–1) at an extremely high power density of 78 kW kg–1 (31 kW L–1) and ∼30 Wh kg–1 (12 Wh L–1) at a power density of 13 kW kg–1 (5.2 kW L–1) (voltage range of 2.7 V).This research work was supported by the Spanish MINECO (MAT2012-31651). M.S. acknowledges the award of a Ramón y Cajal contract.Peer reviewe

Fabrication of porous carbon monoliths with a graphitic framework

[EN] Macro/mesoporous carbon monoliths with a graphitic framework were synthesized by carbonizing polymeric monoliths of poly(benzoxazine-co-resol). The overall synthesis process consists of the following steps: (a) the preparation of polymeric monoliths by co-polymerization of resorcinol and formaldehyde with a polyamine (tetraethylenepentamine), (b) doping the polymer with a metallic salt of Fe, Ni or Co, (c) carbonization and (d) the removal of inorganic nanoparticles. The metal nanoparticles (Fe, Ni or Co) formed during the carbonization step catalyse the conversion of a fraction of amorphous carbon into graphitic domains. The resulting carbon monoliths contain >50 wt.% of graphitic carbon, which considerably improves their electrical conductivity. The use of tetraethylenepentamine in the synthesis results in a nitrogen-containing framework. Textural characterization of these materials shows that they have a dual porosity made up of macropores and mesopores (∼2–10 nm), with a BET surface area in the 280–400 m2 g−1 range. We tested these materials as electrodes in organic electrolyte supercapacitors and found that no conductive additive is needed due to their high electrical conductivity. In addition, they show a specific capacitance of up to 35 F g−1, excellent rate and cycling performance, delivering up to 10 kW kg−1 at high current densities.The financial support for this research work provided by the Spanish MCyT (CQT2011-24776 and MAT2012-31651) is gratefully acknowledged. M. S. thanks the Spanish MCyT for the award of a Ramón y Cajal contract.Peer reviewe

Procedimiento para la preparación de membranas de carbono para la separación de gases permanentes

Referencia OEPM: P9801024.-- Fecha de solicitud: 18/05/1998.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Procedimiento para la preparación de membranas de carbono para la separación de gases permanentes. El procedimiento incluye las siguientes etapas principales: disolución de un polímero precursor en un líquido para la obtención de una disolución polimérica transparente, deposición de la disolución sobre un soporte de carbono, introducción del substrato recubierto homogéneamente en un líquido en el cual precipita, formándose la membrana polimérica. Su aplicación principal es para la separación de gases permanentes.Peer reviewe

Carboxyl-functionalized mesoporous silica–carbon composites as highly efficient adsorbents in liquid phase

[EN] Mesoporous silica–carbon composites functionalized with acidic oxygen groups were prepared by oxidation of a layer of carbon deposited inside the silica pores. The synthesis procedure involved the following steps: (a) removal of the silica surfactant, (b) impregnation of the silica pores with a carbon precursor, (c) carbonization and (d) oxidation with ammonium persulfate. The resulting silica–carbon composites contained around 25–30 wt.% of carbonaceous matter with a high density of acid oxygen groups attached to the deposited carbon layer (i.e. –COOH, –Cdouble bond; length as m-dashO and –OH). The structural characteristics of the parent silica were retained by the oxidized composite materials, which exhibit a high surface area, a large pore volume and a well-ordered porosity made up of uniform mesopores. The oxygen-functionalized silica–carbon composites were found to be excellent adsorbents of basic dyes (e.g. methylene blue) and heavy metals (i.e. Cu2+, Zn2+ and Pb2+) in aqueous media.This work was supported by the Spanish MICINN (Project CQT2011-24776). M.S. and P.V-V. acknowledge Ramon y Cajal and JAE-Predoc contracts, respectively.Peer reviewe

Free-standing hybrid films based on graphene and porous carbon particles for flexible supercapacitors

Free-standing flexible solid-state supercapacitors are attracting attention as a power supply for electronic equipment. Here we report a novel strategy to fabricate free-standing flexible hybrid papers made up of porous carbon particles combined with graphene sheets. The synergetic effect between the carbon particles and the graphene sheets entails two important advantages: (a) binder-free electrodes formed by carbon particles can be built with the assistance of the graphene sheets and (b) the restacking of the graphene sheets is avoided to a great extent due to the fact that the carbon particles act as spacers. These hybrid papers combine important properties for their use in solid-state supercapacitors: (a) large specific surface area, (b) good electrical conductivity, (c) high packing density and (d) excellent flexibility. They exhibit a volumetric electrochemical performance which is clearly superior to electrodes fabricated with carbon particles agglomerated with a binder. In addition, they achieve an excellent areal capacitance (103 mF cm−2) at current densities as high as 1400 mA cm−2 and are able to deliver a large amount of energy (∼12 μW h cm−2) at high power densities (316 mW cm−2). In this work, a robust, flexible and high-performance solid-state supercapacitor has been assembled using such hybrid papers.This research work was supported by the FICYT Regional Project (GRUPIN14- 102), and the Spanish MINECO-FEDER (CTQ2015-63552-R).Peer reviewe

Assessment of the Role of Micropore Size and N-Doping in CO2 Capture by Porous Carbons

The role of micropore size and N-doping in CO2 capture by microporous carbons has been investigated by analyzing the CO2 adsorption properties of two types of activated carbons with analogous textural properties: (a) N-free carbon microspheres and (b) N-doped carbon microspheres. Both materials exhibit a porosity made up exclusively of micropores ranging in size between <0.6 nm in the case of the pristine materials and up to 1.6 nm for the highly activated carbons (47% burnoff). The N-doped carbons possess ∼3 wt % of N heteroatoms that are incorporated into several types of functional groups (i.e., pyrrole/pyridone, pyridine, quaternary, and pyridine-N-oxide). Under conventional operation conditions (i.e., T ∼ 0–25 °C and PCO2 ∼ 0–1 bar), CO2 adsorption proceeds via a volume-filling mechanism, the size limit for volume-filling being ∼0.7–0.8 nm. Under these circumstances, the adsorption of CO2 by nonfunctionalized porous carbons is mainly determined by the volume of the micropores with a size below 0.8 nm. It was also observed that the CO2 capture capacities of undoped and N-doped carbons are analogous which shows that the nitrogen functionalities present in these N-doped samples do not influence CO2 adsorption. Taking into account the temperature invariance of the characteristic curve postulated by the Dubinin theory, we show that CO2 uptakes can be accurately predicted by using the adsorption data measured at just one temperature.The financial support for this research work provided by the Spanish MINECO (MAT2012-31651) is gratefully acknowledgedPeer reviewe

High-performance CO2 sorbents from algae

[EN] Highly porous N-doped carbon materials with apparent surface areas in the 1300–2400 m2 g−1 range and pore volumes up to 1.2 cm3 g−1 have been synthesized from hydrothermal carbons obtained from mixtures of algae and glucose. The porosity of these materials is made up of uniform micropores, most of them having sizes <1 nm. Moreover, they have N contents in the 1.1–4.7 wt% range, and the heteroatom is mainly a pyridone-type structure. These microporous carbons present unprecedented large CO2 capture capacities, up to 7.4 mmol g−1 (1 bar, 0 °C). The importance of the pore size on the CO2 capture capacity of microporous carbon materials is clearly demonstrated. Indeed, a good correlation between the CO2 capture capacity at sub-atmospheric pressure and the volume of narrow micropores is observed. The results suggest that pyridinic-N, pyridonic/pyrrolic-N and quaternary-N do not contribute significantly to the CO2 adsorption capacity, owing probably to their low basicity in comparison with amines. These findings will help the design of high-performance CO2 capture sorbents.The financial support for this research work provided by the Spanish MCyT (CQT2011-24776) is gratefully acknowledged. M.S. acknowledges the assistance of the Spanish MCINN for its award of a Ramón y Cajal contract.Peer reviewe

Highly Porous Renewable Carbons for Enhanced Storage of Energy-Related Gases (H2 and CO2) at High Pressures

Hydrochar, i.e., hydrothermally carbonized biomass, is generating great interest as a precursor for the synthesis of advanced carbon materials owing to economical, sustainability, and availability issues. Hereby, its versatility to produce adsorbents with a porosity adjusted to the targeted application, i.e., low or high pressure gas adsorption applications, is shown. Such tailoring of the porosity is achieved through the addition of melamine to the mixture hydrochar/KOH used in the activation process. Thereby, high surface area carbons (>3200 m2 g–1) with a bimodal porosity in the micromesopore range are obtained, whereas conventional KOH chemical activation leads to microporous materials (surface area <3100 m2 g–1). The micromesoporous materials thus synthesized show enhanced ability to store both H2 and CO2 at high pressure (≥20 bar). Indeed, the uptake capacities recorded at 20 bar, ca. 7 wt % H2 (−196 °C) and 19–21 mmol CO2 g–1 (25 °C) are among the highest ever reported for porous materials. Furthermore, the micromesoporous sorbents are far from saturation at 20 bar and achieve much higher CO2 uptake at 40 bar (up to 31 mmol of CO2 g–1; 25 °C) compared to 23 mmol of CO2 g–1 for the microporous materials. In addition, the micromesoporous materials show enhanced working capacities since the abundant mesoporosity ensures higher capture at high uptake pressure and the retention of lower amounts of adsorbed gas at the regeneration pressure used in PSA systems.This research work was supported by Spanish Ministerio de Economía y Competitividad, MINECO (MAT2012-31651), and by Fondo Europeo de Desarrollo Regional (FEDER). M. S. thanks the Ministerio de Ciencia e Innovación for her Ramón y Cajal contract. We thank the Rajamangala University of Technology Srivijaya (RMUTSV), Thailand for funding and a studentship for WS, and the Kingdom of Saudi Arabia for funding a PhD studentship for NB.Peer reviewe