Search

The rapid spread of invasive Pampas grass (PG) is having not only ecosystems impact, but also significant economic and social effects. The tonnes of bulky waste from the plant disposal require proper treatment to avoid seed dispersal, greenhouse gas emissions and landscape damage. In the pursuit of zero-waste management, hydrothermal treatment (HT) appears as a challenging alternative. The possibility of mobile HT systems offers an alternative to accomplish on-site both the PG waste management and the application of the resulting by-products within a circular framework. As a first step, this research shows that, without a prior drying step, the hydrothermal treatment at 100-230 °C under autogenous water vapor pressure for only 30 min allows safe seeds inertization, while a stable carbon-enriched solid and an aqueous stream are generated. Prolonging the process for 2 h has no profitable effects. As the reaction temperature increases, the PG residue is converted into a material with 49–58 wt% of carbon, 41–32 wt% of oxygen and 3–4 wt% of ash. The pH (~6.3), low electrical conductivity (1.21–0.86 dS/m), high carbon content, open porosity (5–8 m2/g) and improved performance in seed germination and in the early growth test suggest the potential of HT-solids derived at 100–120 °C as amendment to sequester carbon in the soil and improve its physico-biological properties. The phytotoxicity detected in the peat/lignite-like solids obtained at 200–230 °C limits its application in soil, but calorific values of 22–24 MJ/kg indicate their suitability as CO2-neutral fuel. The agrochemical analysis of the liquid by-products indicates poor value on their own, but their use supplemented with compost may be an option., The authors gratefully acknowledge the funds provided by Consejería de Infraestructuras, Ordenación del Territorio y Medio Ambiente (Dirección General de Biodiversidad)-Principality of Asturias- Spain (grant 18.07-443F-703.011). The seeds germination tests were carried out with the support of the project LIFE Stop Cortaderia (LIFE17 NAT/ES/000495). The support provided by COGERSA SAU is highly acknowledged.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Sustainable Chemistry and Engineering, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acssuschemeng.9b04266, The implementation of sustainable strategies based on the integral valorization of residues is the most efficient way to achieve a profitable circular economy. This comprehensive study highlights the potential of apple waste from juice and cider production as a precursor of porous carbons and provides guidelines to achieve a wide spectrum of physicochemical properties. Hydrothermal carbonization (HTC) of apple bagasse is proposed as a feasible integrated process with zero waste that allows stabilizing this highly pollutant residue in the form of a carbon-enriched solid while extracting valuable compounds in the aqueous phase. The liquid fraction resulting from HTC at 200 °C contains a high total phenolic content and antioxidant activity, the major products being catechol (1,2-dihydroxybenzene) and 5-hydroxymethyl-2-furfural (HMF). The successful upgrading of the solid byproduct into porous carbons provides additional advantage for a more cost-effective waste management. It is reported that a simple one-step activation leads to apple-derived carbons with specific surface areas up to 2000 m2 g–1 and electrochemical capacitances as high as 260–290 F g–1. Their excellent performance as supercapacitor electrodes make them very promising for the storage of electrical energy from renewable sources., The funding from INTERREG V- SUDOE 2017 through project CEMOWAS2 (SOE2/P5/F0505) and from Plan de Ciencia, Tecnología e Innovación (PCTI) 2018-2020 del Principado de Asturias and the European Regional Development Fund (ERDF) through project IDI/2018/000233 is acknowledged. The SERIDA financial support for this work was managed by the National Institute of Research Agro-Food Technology (INIA) and co-financed with ERDF and ESF funds (RTA 2015-00060-CO4-03).

This study presents a challenging approach that addresses the efficient management of the organic fraction of municipal solid waste (OFMSW) by hydrothermal carbonization (HTC) for the development of novel sustainable low-CO2 building materials. Mild HTC treatment at 180 °C for 2 h transformed low-grade OFMSW into a renewable carbonaceous solid (hydrochar), which displays promising properties for application in particleboards. Taking advantage of the presence of extractives acting as natural binders, the hydrochar particles with sizes of, Funding from the European Regional Development Fund (ERDF) through project CEMOWAS2 (SOE2/P5/F0505)-INTERREG V SUDOE 2017 is acknowledged. Michael M. Santos thanks the University of Beira Interior and the Spanish National Research Council (CSIC) for the award of an Erasmus+ internship.

A comprehensive comparison of symmetrical supercapacitors assembling carbon electrodes with exclusively microporous, mesoporous or combined micro-mesoporous networks provides a critical outlook on the influence of pores size on the performance with ionic liquid-based electrolyte 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm-TFSI) dissolved in acetonitrile. Contrary to widespread claims, the results for an electrodes set involving carbons of different origin indicate that the presence of large pores does not ensure a better supercapacitor performance. At low current density, the capacitance is basically determined by the surface in pores above 0.8 nm, regardless of the pore size distribution. In addition, the beneficial effect of large pores on the response rate of the supercapacitor cannot be concluded in a straightforward manner. On the contrary, wide porosity in electrodes has detrimental effects that should not be underestimated as far as the competitiveness of the final device is concerned. The greater amount of electrolyte required by larger pores will increase both the weight and the cost of the cell. More importantly, the widening of carbon pores (even in the range of micropores) notably reduces the density of the corresponding electrodes and, consequently, the supercapacitor performance in volumetric terms may not be suitable for practical applications., This work was supported by Plan de Ciencia, Tecnología e Innovación (PCTI) 2018-2020 del Principado de Asturias and the European Regional Development Fund (ERDF) through project IDI/2018/000233.

Hydrothermal carbonization makes feasible the integral and profitable recovery of industrial apple waste within a zero-residue bio-economy. 82–96% of the energy and 80–93% of the C in the apple bagasse are retained in the solids generated by hydrothermal treatment at 180 and 230 °C for 2 and 4 h. Such processes stabilize the apple waste and lead to CO2 neutral solid fuels with calorific value close to 30 MJ/kg. The agrochemical properties of the solid by-products suggest their potential to improve soil quality. Aqueous streams containing valuable phenolic compounds and saturated fatty acids are generated simultaneously, which provide additional cost-effectiveness. The by-products characteristics can be suited to the final application by selecting the reaction temperature, whereas the process duration has less impact. Optical microscopy and reflectance measurements are presented, for the first time, as powerful tools for assessing the biomass transformation when subjected to hydrothermal treatment under different conditions., The funding from the European Regional Development Fund (ERDF) through project CEMOWAS2 (SOE2/P5/F0505)-INTERREG V SUDOE 2017 and Plan de Ciencia, Tecnología e Innovación (PCTI) 2018–2020 del Principado de Asturias and ERDF through project IDI/2018/000233 is acknowledged. The authors also acknowledge support from the Spanish State Plan for Scientific and Technical Research and Innovation (2013-2016), ref. AGL201675762-R. This study was partly supported by grant AGL2016-76832-R from the National Program for Research Aimed at the Challenges of Society (Spain).

An efficient alternative for the management and valorization of the huge amount of seasonal wastes generated by winery industries is shown. Sustainable porous carbons were successfully prepared by one-pot activation of grape bagasse, stalks and oil free-seeds. Benefiting from the high moisture of these residues, a prior hydrothermal carbonization increases the activation yield and generates carbons with less oxygen content and inorganic impurities. The mild physical or chemical activation of winery wastes resulted in highly microporous carbons with specific surface SBET up to 2053 m2/g and great potential for environmental protection and electrical energy storage. They are excellent sorbents for CO2 capture under post- and pre-combustion conditions (16 and 69 wt%, respectively) and achieve superior electrochemical capacitance of nearly 300 F/g in aqueous electrolyte and 180 F/g in ionic liquid based-medium., This study received financial support from CSIC in the frame of Project PIE-201680E035. N.Q. acknowledges a fellowship from Gobierno del Principado de Asturias (Programa Severo Ochoa). L.S. thanks the support from Programa Estatal de Promoción del Talento y su Empleabilidad en I + D + i and European Social Fund-Youth Employment Initiative.

This work shows relevant inconsistencies found in a paper recently published in Electrochim. Acta and how the conclusions are challenged by a more detailed textural characterization of a microporous carbon monolith.

This study is essentially based on innovative electrolytes such as the organic salt N-methyl-N-butylpyrrolidinium tetrafluoroborate (Pyr14BF4) dissolved in propylene carbonate (PC) and the pure ionic liquid (N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) and its solution in PC. Activated carbon cloths were used as self-standing binder-free electrodes. It is found that the presence of impurities in carbon electrodes may lead to electrolyte decomposition and electrode degradation which notably affect the electrochemical double-layer capacitor (EDLC) performance. Such processes greatly depend on the composition of both the electrode and the electrolyte, being much less significant with solvent-containing electrolytes. By raising the operation temperature to 60 °C, the EDLC performance in the ionic liquid Pyr14TFSI is notably improved due to a relevant decrease in the viscosity and increase in ionic conductivity. By contrast, the presence of impurities, e.g., Zn and Al, in the electrodes remarkably reduces the electrolyte stability and a thick layer of decomposition products completely covers the carbon fibers after cycling at high temperature. The ionic liquid in solution maintains the high maximum operative voltage of the net ionic liquid whereas its viscosity and ionic conductivity are close to those of the conventional Et4NBF4/PC. Furthermore, the presence of propylene carbonate as solvent prevents to some extent the ionic liquid degradation.

In this work, the incorporation of dicyanamide building blocks in organic–inorganic hybrid compounds is found to be a promising strategy for the synthesis of multiwalled carbon nanotubes embedded with magnetic nanoparticles (M@CNTs). Following a novel one-step, scalable and fast synthetic route, M@CNTs are obtained by simple calcination of the organic–inorganic hybrid perovskite [TPrA][M(dca)3] (TPrA = tetrapropylammonium, M = Ni2+ and Co2+, dca = dicyanamide). The resulting M@CNTs (M = Ni and Co) display a regular morphology and an essentially mesoporous network of ∼250 m2 g−1, whereas the Co@CNT composite displays a broad pore size distribution (PSD) up to 6 nm, Ni@CNTs show a strictly controlled unimodal PSD, centered at around 5 nm. Monitoring of their thermal decomposition by X-ray diffraction, electron microscopy, thermogravimetric and spectroscopic analyses allows proposing a calcination mechanism and establishing the conditions to obtain optimal materials. Moreover, magnetization studies reveal a ferromagnetic behaviour of the obtained M@CNTs, with small coercive fields due to the size of the magnetic nanoparticles. In addition, preliminary assays of oil adsorption–desorption capacity reveal a promising potential for spilled oil recovery using this easily-synthesized materials. All these physicochemical properties make these composites good candidates for other nitrogen-rich CNT common applications., The authors are grateful for the financial support from Ministerio de Economía y Competitividad MINECO and EU‐FEDER under project ENE2014‐56237‐C4‐4‐R and Xunta de Galicia under project GRC2014/042. J. M. B.‐G. wants to thanks Barrié Foundation for a predoctoral fellowship and S. Y.‐V. to the Xunta de Galicia for a postdoctoral fellowship

Graphene shows substantial promise in improving the technical performance of a range of applications. For its development and before its potential mass adoption, it is critical to understand the associated cradle-to-grave life cycle environmental impacts. Previous studies on graphene environmental performance do not include end of life and the potential environmental credits generated by graphene reuse. This study undertakes a cradle-to-grave approach to evaluating graphene applications, considering a case study of supercapacitors manufactured with graphene and activated carbon active materials. The analysis includes active materials commercial-size production, supercapacitors production, supercapacitors use phase in an automotive application, and their end of life in which both devices are recycled. With current material performance and energy mixes, the graphene-based supercapacitor would increase impacts in all environmental categories analysed, ranging from 27% higher human toxicity to 213% greater ozone depletion and showing a 48% increase in GHG emissions. This unfavourable result arises due to the tested graphene material exhibiting inferior specific capacitance to the activated carbon comparator, as well as a more energy-intensive production process. Prospective analysis considers hypothetical performance where both active materials reach their theoretical specific capacitance, and the decarbonisation of electricity generation. The environmental impacts of both the activated carbon and graphene supercapacitors are reduced in these prospective scenarios, with the graphene based supercapacitor becoming the least impacting solution due to its lower active material requirements. The graphene-based device shows 36% lower GHG emission and overall shows lower impacts ranging from 14% less mineral, fossil and renewable resource depletion to 43% less photochemical ozone formation. These results support graphene as a valid candidate material for substituting activated carbon in supercapacitors provided graphene technical performance is improved, production optimised, and recycling developed., This research has received funding from the European Commission's Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 266391.

With the awareness of the need for low-cost carbons for supercapacitors, the recycling of biomass wastes as precursors of activated carbons is focusing great interest. The comparison of a diversity of carbons derived from residues of industrial processing of grapes, apples and cherries reveals the utility of physical activation to achieve better volumetric performance in aqueous supercapacitors. Whereas the high porosity development of the materials obtained by KOH activation (mostly around 1500–2000 m2 g-1) provides a superior gravimetric capacitance up to nearly 300 F g-1 in 2 M H2SO4, the low density of the electrodes reduces the volumetric capacitance to 60–130 Fcm−3. Porous carbons produced by steam or CO2 reaches higher efficiency for compact devices. The physically activated materials display an ultramicroporous structure with standard surface areas of around 900 m2 g−1 and, therefore, their gravimetric capacitance is limited to 100–150 F g-1. However, harnessing the balance of porosity, density and good packaging, the corresponding electrodes reach 80–170 F cm−3, without sacrificing power delivery by the supercapacitor. Higher carbon yield and lower environmental impact represent additional advantages of the physical activation to produce biomass wastes derived-carbons., The funding from European Regional Development Fund (ERDF) through project CEMOWAS2 (SOE2/P5/F0505)-INTERREG V-SUDOE 2017 and Plan de Ciencia, Tecnología e Innovación (PCTI) 2018–2020 del Principado de Asturias (Spain) and the European Regional Development Fund (ERDF) through project IDI/2018/000233 is acknowledged.

In this work, we have successfully synthesized hollow microtubular crystals of the metal–organic framework (MOF) [Co2(NH2-bdc)2(dabco)]·[G] {G = H2O, N,N-dimethylformamide (DMF); NH2-bdc =2-amino-1,4-benzenedicarboxylate; dabco = 1,4-diazabicyclo[2.2.2]octane} by a very simple coordination-modulation method that avoids the use of an external modulator. Additionally, we have obtained the corresponding hollow microtubular crystals of Co3O4 through the solid-state thermolysis of the Co-MOF material at 400 °C. The as-prepared Co3O4 crystals exhibit the typical magnetic behavior for a nanostructured material with good crystallinity. Thus, this coordination-modulation method provides a simple route for the preparation of nanostructured porous frameworks and derived oxides and opens a way to prepare new materials with advanced properties.

We present a simple and effective alternative which optimizes electrodes based on low-cost carbons for high-performance supercapacitors. The combination with reduced graphene oxide (rGO) greatly improves the operation of microporous carbons easily produced by one-pot activation of grape seeds. The use of composite electrodes with rGO lowers the supercapacitor resistance and enables a much higher rate capability. The mixture of rGO flakes and particles of a highly porous carbon obtained by KOH activation allows retaining the high capacitance of 260 F g−1 of the standard electrodes at 1 mA cm−2 in aqueous H2SO4 whereas the value at 200 mA cm−2 is increased by around 2.4 times. Consequently, at high current density, the capacitor assembled with these composites stores eight times more energy and the power density is multiplied by four. The synergy between rGO and an ultramicroporous carbon produced by CO2-activation results extremely profitable, the cell assembled with composite electrodes reaching three times more energy and power at 200 mA cm−2 than the best performance of the standard counterpart. More importantly, the higher density of the composite electrodes leads to a capacitance of around 200 F cm−3 which translates into a remarkable improvement in the supercapacitor operation normalized to volume., T.A.C. gratefully acknowledges the funding from CSIC [Proyecto Intramural Especial 2016 8 0E035]. V.V. and V.S. thank the support by Slovak Research and Development Agency under the contract APVV-16-0319.

The successful tailoring of the ultramicroporosity remarkably increases the CO2 uptake capacity of low cost-carbons derived by a simple one-pot physical activation of olive stones, coffee grounds, almond shells and grape seeds. A porous network dominated by ∼40–46% of ultramicropores below 0.5 nm and no significant presence of pores above 0.7 nm boosts the CO2 uptake at 1 bar and 298 K around 40% compared to materials with similar micropore volume. A slight ultramicropore widening causes the drop to a standard pattern that depends mainly on the micropore volume. The detailed analysis of the CO2 isotherms within the Dubinin´s theory provides simple clues for the optimization of carbons for CO2 capture at ambient temperature and atmospheric pressure. Thus, a general pattern of around 7.2 mmol of CO2 captured per cm3 of ultramicropores is found for a variety of activated carbons and carbide derived-carbons with characteristic energy Eo of 29–22 kJ/mol. This feature is typical of materials with average micropore sizes from 0.65 to 1 nm. An enhancement of up to 10 mmol CO2/cm3 is achieved by carbons with Eo ranging between 30 and 32 kJ/mol which correlates with an extremely homogeneous porosity with average dimensions around 0.5 nm. The excellent fit of the present carbons into general patterns exclusively based on the textural features reveals no significant influence of their surface functionalities on the CO2 adsorption performance., N.Q. acknowledges a fellowship from the Gobierno del Principado de Asturias (Programa Severo Ochoa).

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., Financial support from EU 7FP (Project Electrograph-266391) is gratefully acknowledged. L.S. thanks the support from Programa Estatal de Promoción del Talento y su Empleabilidad en I+D+i and European Social Fund-Youth Employment Initiative. The authors wish to thank Danubia Nanotech sro. (Slovakia) and Abalonyx AS (Norway) for the gift of graphene materials of series GO-B and S77, respectively.

This work represents a systematic study of four conductive salts and their influence on the physicochemical properties of propylene-carbonate-based electrolytes for electrochemical double-layer capacitors (EDLCs). State-of-the-art tetraethylammonium tetrafluoroborate is compared with tetraethylammonium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium tetrafluoroborate, and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide. By applying these salts, operating voltages of up to 3.5 V can be achieved while retaining a high performance. Furthermore, the influence of the conductive salts on the carbon–electrolyte interface is studied by comparing the electrochemical performance of five commercial porous carbons in the respective electrolytes. The choice of conductive salt has a great influence on the electrochemical performance and maximum operating voltage of an EDLC system, as well as on the specific capacitance of the chosen carbon material; this makes the choice of both materials crucial for successful EDLC design.

Specific capacitance of carbons in aqueous KOH electrolyte seems to have two contributions, a double-layer capacitance and a pseudocapacitance. Moreover, the specific capacitance increases as the specific surface area does. Here, we report that the pseudocapacitance is associated with the K+ ion and the double-layer capacitance with both K+ and OH- ions. The former ion dominates the capacitance of a real two-electrode supercapacitor. Two microporous carbon monoliths with surface areas similar for micropores below 0.63 nm but different for larger micropores are chosen. There is a correlation between the double-layer capacitance due to those ions and the surface areas due to micropores with sizes above a certain value. It provides information on the size of those ions as they are electroadsorbed at the double layer. The dielectric permittivity associated with the K+ and OH - ion is discussed in relation to the confinement of these electroadsorbed ions in the micropores. © 2014 American Chemical Society., Financial support through the projects MAT2011-25198 and MP 1004 is gratefully acknowledged. V.B. thanks MINECO for R&C contract.

All rights reserved. Biocarbon monoliths were obtained from Eucalyptus grandis and the influence of wood anisotropy on the electrical and electrochemical performance as supercapacitor electrodes was studied. They were produced from wood pieces cut along the transversal and longitudinal direction of the tree trunk, followed by pyrolysis and, for some of them, also by activation with CO2. Monoliths with drilled channels were also obtained. All the monoliths were characterized by SEM, nitrogen adsorption/desorption isotherms, electrical conductivity measurements and electrochemical measurements, the latter in 2M aqueous H2SO4 electrolyte. Electrical conductivity and specific capacitance are higher for the transversal carbon monoliths than for the longitudinal ones. The electrical conductivity reaches values up to 27 S cm-1 for the transversal monolith. The specific capacitance reaches values up to 260 F g-1for the transversal monolith that was activated and drilled. However, the highest volumetric capacitance, of 90 F cm-3, is found for the longitudinal monolith that was activated and non-drilled. The energy density and power density, both referred to gravimetric and volumetric magnitudes, reach values as high as 36 Wh kg-1 and 12 Wh L-1, and 2181 W kg-1 and 783 W L-1, respectively. Comparison with a commercial powder activated carbon is provided.

This paper examines the recovery of carbon fibres from a composite used in the aeronautical industry, via a combined process of thermolysis and gasification in an air atmosphere. The waste was thermolysed at 500 C, 600 C or 700 C in a pilot plant to determine the optimum thermolysis temperature. The solid residues produced - char covered carbon fibres - were characterized by SEM and XPS. The optimum time for the gasification of the char covering the fibres was determined in a combined thermolysis/gasification assay. After thermolysis at the optimum temperature (500 C), 12 l/h of pure air were injected into the reactor and char gasification performed at 500 C for 30-180 min. The optimum gasification time was 30 min. Longer gasification times led to the production of fibres of smaller diameter with oxidized surfaces and reduced tensile strength. The optimally recovered fibres showed about 70% of the tensile strength of virgin fibres and some 90-96% of their elasticity. © 2013 Elsevier B.V. All rights reserved.

Low cost activated carbons have been produced via chemical activation, by using KOH at 700 °C, from the bamboo species Guadua Angustifolia and Bambusa Vulgaris Striata and the residues from shells of the fruits of Castanea Sativa and Juglans Regia as carbon precursors. The scanning electron microscopy micrographs show the conservation of the precursor shape in the case of the Guadua Angustifolia and Bambusa Vulgaris Striata activated carbons. Transmission electron microscopy analyses reveal that these materials consist of carbon platelet–like particles with variable length and thickness, formed by highly disordered graphene–like layers with sp2 content ≈ 95% and average mass density of 1.65 g/cm3 (25% below standard graphite). Textural parameters indicate a high porosity development with surface areas ranging from 850 to 1100 m2/g and average pore width centered in the supermicropores range (1.3–1.8 nm). The electrochemical performance of the activated carbons shows specific capacitance values at low current density (1 mA/cm2) as high as 161 F/g in the Juglans Regia activated carbon, as a result of its textural parameters and the presence of pseudocapacitance derived from surface oxygenated acidic groups (mainly quinones and ethers) identified in this activated carbon.

This paper reports the physico-chemical characteristics of the products derived from the thermolysis (thermolytic distillation) of waste silver fir (Abies alba Mill.) wood at different temperatures (400℃- 600℃) in a pilot scale plant. Depending on the thermolysis temperature, the procedure yielded 45 - 53 wt% pyroligneous acid with a high water content (80 - 86 wt%) and pH ≈ 3.6. The process also produced a carbonaceous solid or biochar (23 - 26 wt%), its properties strongly dependent on the thermolysis temperature. Gases (20 - 31 wt%) were also produced; these were transformed into electrical energy via a gas turbine. The pyroligneous acid was centrifuged to isolate a subfraction composed mostly of phenols (phenol, mequinol and furfural) with a total C content of 68 - 74 wt%. The remainder was subjected to fractionated distillation at laboratory scale, and the distillate subjected to liquid-liquid extraction using diethyl ether in two stages to obtain a bio-oil composed mainly of acetic acid (≈47%), aldehydes, ketones and alcohols (≈31%), phe- nols (≈18%) and aliphatic alcohols. The characteristics of the bio-oil depended on the thermolysis temperature.

Mn oxide and/or Co oxide are deposited on flexible carbon cloth by a cathodic potentiodynamic procedure from their respective sulfates. In KOH electrolyte, the charge stored from reversible redox reactions of the two oxides (battery response) overlaps with the charge stored from the double layer of the carbon cloth (supercapacitor response). These charges or capacities are compared. For the electrodes having one oxide only, either Mn or Co oxide, the highest capacity is obtained for 8 wt% oxide load. To overcome this limitation, both Mn and Co oxide are simultaneously or sequentially electrodeposited on carbon cloth over a broad compositional range. The electrode capacity can reach 71 mA · h · g¿1 or 0.9 mA · h · cm¿2, which are higher than the values found for the bare carbon cloth. The electrode capacity depends on the relative content of the carbon cloth and the two deposited oxides according to the rule of mixtures. The decrease of the specific surface area of the carbon cloth is discussed in relation to the deposited oxide. The high capacity retention vs current is due to the contribution of the carbon cloth substrate. The electrode cycle life is discussed on the basis of the supercapacitor response and battery one., Financial support from the project MAT2014-57687-R is gratefully acknowledged.

International audience; Hydrophobic activated carbons are considered as interesting materials for air or water remediation due to their enhanced affinity for slightly water-soluble organic species. In this context, a commercial activated carbon, in an extruded form, was fluorinated under mild conditions (pure fluorine gas at room temperature) in order to decrease its hydrophilic character and to preserve its microporosity. For comparison, a hydrogenated activated carbon was also prepared by H2 treatment. The resulting samples were characterised by various techniques in order to determine the evolution of the activated carbon materials in terms of composition (XPS, elemental analysis, TGA and NMR) and porosity (nitrogen physisorption (77 K), mercury intrusion and immersion calorimetry). For the fluorinated carbon, the nature of the CFx groups and the strength of the C-F bonds were also investigated using 13C and 19F solid state NMR and TGA techniques. A labile character of the C-F bond, so far exclusively observed for fluorine intercalation compounds, is also shown for the first time for a fluorinated activated carbon by water adsorption/desorption isotherms at room temperature. Care should then be taken for its use in presence of water.

Conglomerated and accreted porous carbon spheres have been obtained by the chlorination reaction of bis(cyclopentadienyl)titanium dichloride as carbon precursor. The spheres size distribution, derived from scanning electron microscopy observations, shows that the diameter intervals decreases from 70–525 nm at 400 °C to 40–370 nm at 900 °C. High-resolution transmission electron microscopy observations indicate that the spheres are formed by open and curved randomly stacked graphene-like layers. Electron energy loss spectroscopy studies show relative sp2/sp3 ratio higher than 95% and mass-density values (1.1–1.6 g cm−3) smaller than graphite. Nitrogen adsorption measurements reveal the presence of micro and mesopores whose contributions to the total porosity greatly depend on the preparation temperature. Galvanostatic charging–discharging measurements on the carbon material synthesized at 900 °C provide a specific capacitance of 106 F g−1 in the aqueous H2SO4 electrolyte and 80 F g−1 in the aprotic (C2H5)4NBF4/acetonitrile medium. These high values suggest the potentiality of this material for electrical energy storage in electrochemical double layer capacitors.

This paper examines the surface-related capacitance C/S of carbons with average micropore widths between 0.73 and 1.80 nm, using 1–2 M H2SO4, 6 M KOH and 1 M (C2H5)4NBF4 in acetonitrile as electrolytes. Following corrections for pseudocapacitance effects for the aqueous electrolytes and the use of an average surface area suggested by independent techniques, different from the BET area, it appears that C/S is practically independent of the micropore width. The analysis of the data with the help of recent models suggests that the dielectric constants ɛr of the different electrolytes may decrease with the pore size. It is surprising that the coexistence of two sets of values for the surface area of microporous carbons and its consequence on C/S have not received more attention in the past.

The interpretation of the performance of electrochemical capacitors based exclusively on the textural features and surface chemistry of carbons can be insufficient, or even misleading, in the case of materials prepared at low temperatures (typically below 800 °C). It is suggested that the gradual improvement of the electrochemical performances of carbon-based capacitors at high current densities, following heat treatments up to 900 °C, is mainly a consequence of the simultaneous increase in conductivity. This is illustrated by a study of carbons based on a mesoporous carbon prepared at 550 °C, which displays poor electrochemical performances and a low conductivity (4.6 × 10−6 S m−1). A first heat treatment at 700 °C leads to major structural, chemical and electrochemical changes, due to the collapse of the smaller mesopores and the formation of a microporous structure with average pore widths around 1.3 nm. One also observes a reduction in the surface oxygen density from 13 to approximately 5 μmol m−2. Further heat treatments at 800 and 900 °C do not modify significantly these characteristics, nor the surface-related capacitances at low current densities (1 mA cm−2) in the aqueous (2 M H2SO4) and organic (1 M (C2H5)4NBF4/CH3CN) electrolytes. On the other hand, one observes increasingly high rate capabilities which may be ascribed to the simultaneous increase in conductivity from 7.3 to 147.8 S m−1 between 700 and 900 °C., The authors wish to thank Dr. F. Rubiera and Dr. C. Pevida for the gift of carbons and Dr. J.A.Fernández for some electrochemical measurements.

Cylindrical carbon monoliths of 7 mm in diameter and certain heights (1, 2, 3, 4 and 5 mm) are studied as model electrodes for supercapacitors. The monoliths show a narrow microporous structure with average micropore size of 0.73 nm and specific surface area of 1086 m 2 g −1 . The monoliths show straight walls and channels, both arranged along the cylinder axis. The former account for a remarkable electrical conductivity (6.5 S cm −1 at room temperature). The latter allow a rapid ionic transport between the electrolyte bulk and the carbon walls and account for a high specific capacitance at high current density. The cell capacitance and resistance increase linearly with the monolith height according to C = (1.78 ± 0.06) h and ESR = (0.08 ± 0.01) h + (1.67 ± 0.04), respectively. The contribution of the electrolyte resistance, monolith resistance and monolith/collector resistance to ESR is discussed. The cell response time or constant time increases with the monolith height but according to a power dependence, τ = (4.5 ± 0.2) h (1.61 ± 0.03) . The carbon of the monoliths show in KOH electrolyte a specific capacitance of 150 F g −1 and a capacitance per surface area of 14 μF cm −2 .

This study shows that standard techniques used for carbons characterization, such as physical adsorption of CO2 at 273 K and N2 at 77 K, can be used to assess, with a good accuracy, the maximum capacity of carbons to capture CO2 under post- and pre-combustion conditions. The analysis of the corresponding adsorption isotherms, within the general theoretical framework of Dubinin's theory, leads to the values of the micropore volume, Wo, and the characteristic energy, Eo, of the carbons, which provide direct information on the equilibrium CO2 uptake of the carbons at different pressures and temperatures. Although in special cases slightly higher values can be obtained, an overall assessment of the textural parameters for a large variety of activated carbons, indicates that a CO2 uptake upper-bound around 10–11 wt% seems to be realistic for standard activated carbons under post-combustion conditions. In the case of pre-combustion conditions, this limit would not exceed 60–70 wt%., Thanks are due to Mast Carbon International Ltd. for supplying phenolic-resin-derived activated carbons. Work carried out with financial support from Spanish MICINN (Project ENE2008-05087). C.F.M. acknowledges a JAE-predoctoral grant from Spanish CSIC, co-financed by the European Social Fund.

A systematic study by complementary techniques shows that PET-waste from plastic vessels is a competitive precursor of carbon electrodes for supercapacitors. PET derived-activated carbons follow the general trends observed for highly porous carbons and display specific capacitances at low current density as high as 197 F g−1 in 2 M H2SO4 aqueous electrolyte and 98 F g−1 in the aprotic medium 1 M (C2H5)4NBF4/acetonitrile. Additionally, high performance has also been achieved at high current densities, which confirms the potential of this type of materials for electrical energy storage. A new method based on the basic solvolysis of PET-waste and the subsequent carbonization seems to be an interesting alternative to obtain porous carbons with enhanced properties for supercapacitors., The support of the autonomous regional government (J. de Andalucía, P. de Excelencia P06-FQM-01585) is acknowledged.

The study compares the structural and electrochemical properties of 12 porous carbons based on phenolic resins, using both aqueous (H2SO4) and aprotic ((C2H5)4NBF4 in acetonitrile) electrolytes. It appears that they fit into the general pattern observed for other carbons. The present carbons have micropore volumes varying between 0.29 and 0.66 cm3 g−1 and average pore widths Lo between 0.62 and 1.23 nm. Five samples are exclusively microporous, whereas seven also display a relatively important mesoporosity. This allows a direct comparison between pairs of carbons with similar micropore systems, with and without mesopores, in order to assess the role of mesoporosity in the electrochemical properties. It appears that mesopores have only a limited influence on the decrease in capacitance at high current density as opposed to earlier assumptions.

Composites are prepared by deposition of nanoparticles of RuO 2 · x H 2 O (1–4 nm) on two carbons: microporous carbon (1.3 nm of average micropore size) and mesoporous carbon (11 nm of average mesopore size). Two-preparation procedures are used: (i) procedure A consisting of repetitive impregnations of the carbons with RuCl 3 ·0.5H 2 O solutions, and (ii) procedure B based on impregnation of the carbons with Ru(acac) 3 vapour. The procedure B leads to supported RuO 2 · x H 2 O particles that appear more crystalline than those obtained by the procedure A. Specific capacitance and specific surface area of the composites are discussed as functions of the RuO 2 content, and different dependences for the composites derived from the two carbons are found. Mesoporous carbon is better support than microporous carbon. Procedure A leads to supported RuO 2 · x H 2 O particles with higher specific capacitance than the particles deposited by procedure B.

The present paper shows that the performance of an inexpensive activated carbon used in electrochemical capacitors can be significantly enhanced by a simple treatment with KOH at 850 °C. The changes in the specific surface area, as well as in the surface chemistry, lead to high capacitance values, which provide a noticeable energy density. The KOH-treatment of a commercial activated carbon leads to highly pure carbons with effective surface areas in the range of 1300–1500 m2 g−1 and gravimetric capacitances as high as three times that of the raw carbon. For re-activated carbons, one obtains at low current density (50 mA g−1) values of 200 F g−1 in aqueous electrolytes (1M H2SO4 and 6M KOH) and around 150 F g−1 in 1M (C2H5)4NBF4 in acetonitrile. Furthermore, the resulting carbons present an enhanced and stable performance for high charge/discharge load in organic and aqueous media. This work confirms the possibilities offered by immersion calorimetry on its own for the prediction of the specific capacitance of carbons in (C2H5)4NBF4/acetonitrile. On the other hand, it also shows the limitations of this technique to assess, with a good accuracy, the suitability of a carbon to be used as capacitor electrodes operating in aqueous electrolytes (H2SO4 and KOH)., The support from the Programme for Scientific and Technological Cooperation Spain-Poland is highly acknowledged

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., We thank Dr Jose M. Rojo (ICMM-CSIC) for his useful assistance. Financial support from Spanish MICINN (project MAT 2011-25198) is gratefully acknowledged. G. Moreno-Fernandez thanks Spanish MINECO for a FPI fellowship. We also acknowledge institutional support from the Unit of Information Resources for Research at the “Consejo Superior de Investigaciones Científicas” (CSIC) for the article-processing charges contribution.

RuO 2 · x H 2 O/NiO composites having RuO 2 contents in the range 0–100 wt.% have been prepared by a co-precipitation method. Structural, microstructural and textural transformations after heating the as-prepared composites at 200 and 600 °C have been followed by X-ray diffraction, scanning electron microscopy (SEM) and nitrogen adsorption/desorption isotherms. At 200 °C the composites are made of micrometric particles in which nanometric crystallites of the two oxides are aggregated. The composites show microporosity (0.02–0.10 cm 3 /g), mesoporosity (0.07–0.12 cm 3 /g) and relatively high specific surface area (62–309 m 2 /g). At 600 °C the composites are fully dehydrated and RuO 2 has crystallized and segregated. Microporosity and mesoporosity as well as specific surface area are strongly decreased. Specific capacitance and specific surface area of the composites heated at 200 and 600 °C have been measured and discussed on the basis of the RuO 2 content. For comparison the specific capacitance and specific surface area of mixtures of NiO and RuO 2 · x H 2 O (or RuO 2 ) have been taken as references. The higher specific capacitance of the 200 °C-heated composites compared to the 600 °C-heated ones is due to the higher specific surface area of the former and the higher pseudocapacitance of RuO 2 · x H 2 O compared to RuO 2 . The discussion reported in this work can be applied to other composites such as RuO 2 · x H 2 O/carbon and RuO 2 · x H 2 O/other oxides.

The characterization of the porous structure developed by the pillaring of a natural clay of the smectite class, a montmorillonite, with aluminum polycations using a relatively concentrated clay suspension (10 wt.%) is presented. Nitrogen adsorption data at 77 K and immersion calorimetry experiments with benzene, cyclohexane, tetraisopropyl o-titanate, and tri-2,4-xylylphosphate at 293 K have been considered for this purpose. Both slit-like and cylindrical pore models have been applied to the nitrogen adsorption results (p/p0 ≤ 0.2) to characterize the micropore region of the alumina-pillared clay. From the measured enthalpies of immersion into the various liquids, the presence of very narrow micropores or constrictions at the entry of the micropores in the alumina-pillared clay is suggested.

The paper examines the validity of two approaches frequently used to determine surface areas in activated carbons, namely the BET method and the use of immersion calorimetry. The study is based on 21 well characterized carbons, whose external and microporous surface areas, Se and Smi, have been determined by a variety of independent techniques. It appears clearly that SBET and the real surface area Smi + Se are in agreement only for carbons with average pore widths Lo around 0.8–1.1 nm. Beyond, SBET increases rapidly and SBET− Se is practically the monolayer equivalent of the micropore volume Wo. This confirms that a characterization of surface properties based on SBET is, a priori, not reliable. The study of the enthalpy of immersion of the carbons into benzene at 293 K, based on Dubinin’s theory, shows that ΔiH consists of three contributions, namely from the interactions with the micropore walls (−0.136 J m−2), the external surface (−0.114 J m−2), and from the volume W*o of liquid found between the surface layers in the micropores (−141 J cm−3). It appears that for carbons where Lo> 1 nm, the real surface area cannot be determined in a reliable way from the enthalpy of immersion and a specific heat of wetting alone.

By means of Monte Carlo simulations we show that a pore-width dependent dielectric permittivity, εp(L), may diminish the pore-size dependence of the surface-specific capacitance. This is different from the case of a fixed dielectric permittivity, εp = const, which leads to an increase of capacitance when the pore width becomes comparable to the ions size. Keywords: Supercapacitors, Nanoporous electrodes, Anomalous capacitance

This work shows that the gas separation performance of phenolic resin-based carbon membranes can be adjusted by controlling the pyrolysis processing variables (heat treatment temperature, heating rate, soaking time and atmosphere). A large variety of carbon membranes for gas separation have been developed by simple carbonization of a phenolic resin film deposited on a ceramic tubular support. Thus, molecular sieve carbon membranes (MSCMs) with good capabilities towards the separation of O 2 –N 2 , CO 2 –CH 4 , CO 2 –N 2 and olefin–paraffin mixtures as well as adsorption-selective carbon membranes (ASCMs) effective in the recovery of hydrocarbons from hydrocarbon–N 2 mixtures have been obtained.

The study of 26 microporous carbons with average pore widths Lo between 0.7 and 1.8 nm shows that the volume-related capacitance Cmi (F cm− 3) in the organic electrolyte (C2H5)4NBF4/acetonitrile is an inverse function of the average micropore width Lo. This means that for a given micropore volume Wo, the gravimetric capacitance C (F g− 1) is larger for carbons with smaller pores due to the higher surface to volume ratio. Furthermore, the increase of Cmi (F cm− 3) in smaller pores suggests that the surface-related capacitance C (F m− 2) should be relatively constant in slit-shaped micropores. This has important technological consequences for the design of carbon-based supercapacitors.

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 170 F/g in H2SO4 and 84 F/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 (, Financial support from EU 7FP [Project Electrograph-266391], the project VEGA 1254/12 (M.H.) and MICINN [MAT 2011-25198] (T.A.C.) is gratefully acknowledged. The authors are grateful to Prof. Viera Skákalová for the useful discussions and critical remarks.

A graphite oxide, obtained on a large scale at low cost as an intermediate in the graphene production, achieves specific capacitances (159 Fg−1 in H2SO4 and 82 Fg−1 in (C2H5)4NBF4 in acetonitrile) that compete with those of activated carbons and largely surpass the values obtained with graphene nanoplatelets. More promising, the high electrode density leads to volumetric capacitances of 177 and 59 F cm−3 in the aqueous and the organic electrolytes, respectively, which are above most data reported for carbons. In the aqueous electrolyte, the graphite oxide stands out on energy density when compared to graphene nanoplatelets and on power capability if compared to an activated carbon commercialized for supercapacitors, whereas in the organic electrolyte, the limited interlayer spacing restricts the mobility of the larger ions into the expanded graphitic structure. This study also illustrates that the specific surface of carbons measured by standard gas adsorption may not be a relevant parameter as it does not always match the electrochemically active area involved in the energy storage., Financial support to T.A.C. from EU 7FP (Project Electrograph- 266391) and MICINN (project MAT 2011-25198) is gratefully acknowledged. Financial support for graphene oxide development was obtained from the Research Council of Norway, through grant No 73146. The authors thank the Instituto Universitario de Investigación en Nanociencia de Aragón-Universidad de Zaragoza for the HRTEM images.

The preparation of a composite carbon membrane from a phenolic resin is described. The membrane is formed by a thin microporous carbon layer (thickness: 2 μm) obtained by pyrolysis (700°C, under vacuum) of a phenolic resin film supported on the inner face of a porous alumina tube. The separation characteristics of the resulting carbon membranes were analysed from permeation experiments with pure gases of different molecular size (He, CO2, O2, N2 and CH4) and separation of binary gas mixtures O2–N2 and CO2–CH4. An almost defect-free carbon membrane is obtained in only one casting step. The effective micropore size was estimated to be around 4.4 A. The prepared carbon membranes have demonstrated to be effective for separating gas mixtures such as O2–N2 (O2 permeance: 100 Barrer; O2–N2 separation factor: 12) and CO2–CH4 (CO2 permeance: 400 Barrer; CO2–CH4 separation factor: 150). The oxidation of the phenolic resin film with air at temperatures ranging from 150 to 300°C improves the gas permeance and originates a decrease in the permselectivity.

The preparation of a composite carbon membrane from Poly(vinylidene chloride-co-vinyl chloride) is described. The membrane is formed by a thin microporous carbon layer (Thickness, 0.8 μm) obtained by pyrolysis of a polymeric film supported over a macroporous carbon substrate (Pore size, 1 μm; Porosity, 30%). Single gas permeation experiments with pure gases of different molecular size (He, CO2, O2, N2 and CH4) were performed at different temperatures between 25°C and 150°C. It has been observed that the microporous carbon layer exhibits molecular sieving properties and it allows the separation of gases depending on their molecular size. The carbon membrane shows high selectivities for the separation of permanent gases like O2/N2 system (Selectivity≈14 at 25°C). Air preoxidation at 200°C for 6 h improves the permselectivity but a loss in gas permeance is observed.

The preparation of a composite carbon membrane for separation of gas mixtures is described. The membrane is formed by a thin microporous carbon layer (thickness, 2 μm) obtained by pyrolysis of a phenolic resin film supported over a macroporous carbon substrate (pore size, 1 μm; porosity, 30%). The microporous carbon layer exhibits molecular sieving properties and it allows the separation of gases depending on their molecular size. The micropore size was estimated to be around 4.2 A. Single and mixed gas permeation experiments were performed at different temperatures between 25°C and 150°C, and pressures between 1 and 3.5 bar. The carbon membrane shows high selectivities for the separation of permanent gases like O 2 /N 2 system (selectivity≈10 at 25°C). Gas mixtures like CO 2 /N 2 and CO 2 /CH 4 are successfully separated by means of prepared membranes. For example, the membrane prepared by carbonization at 700°C shows at 25°C the following separation factors: CO 2 /N 2 ≈45 and CO 2 /CH 4 ≈160.