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The reduction of graphene oxide (GO) by means of thermal and/or chemical treatments leads to the production of reduced graphene oxide (rGO)—a material with improved electrical conductivity and considered a viable and low-cost alternative to pure graphene in several applications, including the production of supercapacitor electrodes. In the present work, GO was prepared by the oxidation of graphite recycled from spent Li-ion batteries using mixtures of sulfuric and phosphoric acids (with different H2SO4/H3PO4 ratios), leading to the production of materials with significant S and P contents. These materials were then thermally reduced, resulting in rGO papers that were investigated by solid-state 13C and 31P nuclear magnetic resonance, along with other methods. The electrochemical properties of the produced rGO papers were evaluated, including the recording of cyclic voltammetry and galvanostatic charge–discharge curves, besides electrochemical impedance spectroscopy analyses. The samples obtained by thermal reduction at 150 °C exhibited good rate capability at high current density and high capacitance retention after a large number of charge–discharge cycles. The results evidenced a strong relationship between the electrochemical properties of the produced materials and their chemical and structural features, especially for the samples containing both S and P elements. The methods described in this work represent, then, a facile and low-cost alternative for the production of rGO papers using graphite recycled from spent batteries, with promising applications as supercapacitor electrodes.

An in-house synthesized activated biocarbon (aBC) and commercial Vulcan carbon (V) were studied as PdSn catalyst supports for the ethanol oxidation reaction (EOR) in an alkaline medium. The results obtained showed that the PdSn/V electrocatalyst presented much higher catalytic performance than the PdSn/aBC. These results can be associated with the fact that the catalyst particles in the PdSn/V electrocatalyst presented a higher SnO2 concentration compared to PdSn/aBC. The presence of SnO2 has an electronic effect that accelerates the adsorption of ethanol on the surface of Pd, thus enhancing the ethanol oxidation kinetics and contributing to a significant improvement in the PdSn/V catalytic activity. However, no significant differences were observed in the EOR mechanism.

Supercapacitors have been studied due to their promising as powerful storage devices. The development of highly efficient electrodes is one way to manufacture supercapacitors with high energy and power efficiencies. Binary composites based on activated carbon fiber felt (ACFF) and polypyrrole (PPy) have been investigated to increase capacitance performance. ACF, when applied as a bulk electrode has limited electric characteristics while the PPy suffers from limited stability during cycling that reduces the initial performance. Based on the synergism effect, this work proposes the production of a binary composite based on ACFF produced from a low-cost precursor textile polyacrylonitrile (textile PAN) and the facile synthesis of PPy from the chemical route of polymerization. The binary composite formed by a 3D network with the interconnection of a more conductive form of PPy coated on ACFF was obtained. The resulting architecture was determinant to significantly increase the energy storage capacities when compared to the bulk ACFF electrode. From the galvanostatic charge and discharge curves, cyclic voltammetry and electrochemical impedance, the obtained composite had a specific capacitance about 302 F g−1 associated with low resistance and to a good density of energy and power.

Pseudocapacitive materials can enhance the energy storage performance of supercapacitors by making use of surface redox reactions. In recent years, different iron compounds have been investigated as pseudocapacitive materials, showing promising features for supercapacitor electrode applications. Carbon nanocomposites containing iron/phosphorus compounds have been prepared from porous carbon, followed by thermal treatment at different temperatures (700°C to 1000°C). The obtained supercapacitor electrodes were evaluated by electrochemical analyses using sulfuric acid electrolyte. The as-prepared nanocomposite contained nanostructured iron oxides or oxyhydroxides, whereas the nanocomposites prepared at 700°C to 900°C were composed of nanostructured iron phosphates. On the other hand, heat treatment at 1000°C caused the formation of nanocrystalline iron phosphides (mostly Fe2P nanoparticles). The Fe-containing samples showed enhanced specific capacitance (246 F g−1 to 447 F g−1 at 10 A g−1), which can be related to the pseudocapacitive contribution of the iron compounds. The sample heat treated at 1000°C exhibited favorable electrochemical performance, showing high electrical capacitance and good rate capability at 40 A g−1. These results reveal that porous carbon/iron phosphide nanocomposites are promising materials for use in supercapacitor electrode applications.

Direct ethanol fuel cells (DEFCs) are devices for clean and sustainable energy production, where the generation of electrical energy occurs as a result of the anodic ethanol oxidation reaction (EOR). One of the main challenges of these devices is the development of cost-effective and sustainable anodic catalysts, minimizing the use of noble metals such as Pd. In this sense, biomass-derived carbon-supported core–shell nanoparticles of PdNi-based electrocatalyst are of great interest for EOR and its application in DEFCs. The purpose of this work was to demonstrate the possibility of synthesizing a core–shell Ni@Pd electrocatalysts via hydrothermal method, in a fast, simple and environmental friendly way. A biomass hydrothermal liquefaction method using nickel and palladium salts was used to synthesize a biocarbon-supported nickel/palladium core–shell electrocatalyst (Ni@Pd/aHC). The electrocatalyst was morphological and chemical characterized in order to confirm the core–shell particle formation. The electrochemical characterization showed that the Ni@Pd/aHC sample has good electrocatalytic behaviour and good stability over time. The EOR mechanism on the sample and their influence in the faradaic efficiency of a cell were also studied by spectroelectrochemical analysis.

There are three basic steps to activated carbon fibers (ACF) manufacturing, from PAN fiber: oxidation/stabilization, carbonization and activation. Carbon material, specially ACF is a very attractive material to be used as supercapacitor electrode. The literature describes carbon material surface chemistry importance for supercapacitors application, mainly nitrogen groups by N-doping. Oxidation/stabilization is an important non-explored factor that influence the surface chemical functionality. This work describes the influence of oxidation/stabilization process on ACF production, from textile PAN fiber, and the non-doping nitrogen surface chemistry characteristic caused by the oxidation process design. Its textural, structural and surface was evaluated for supercapacitor electrode. The results show that the oxidation degree can be used as a mechanism of textural and surface chemistry control. The surface chemistry is the key of this work, different oxidation conditions can produce nitrogen compounds that help to increase specific capacitance. The tests showed an increase in capacitance higher than 100% in comparison to the standard oxidation.

This work presents kinetic and thermal data of three different biomass wastes with high availability in Uruguay. Samples were analysed by proximate, ultimate and thermogravimetric analyses, transient plane source, and a cone calorimeter. DTG results at different heating rates allowed us to identify different stages during the thermogravimetric analysis. Kinetic modelling per stages was realized for each stage observed during the heating of the biomass samples. The kinetic was modelled minimizing the square difference between the experimental data and theoretical values obtained with the model. Activation energy values were obtained for each stage, with values in the range 164-217 kJ mol for the decomposition of cellulose and hemicellulose, and between 190-507 kJ mol for the decomposition of lignin.

Oil shales from Mangrullo Formation (Uruguay) was assessed as a potential fuel for energy production. The assessment is based on a comprehensive characterization of the material from a thermal perspective. Co-combustion of this type of fuel with biomass waste can enhance the combustion performance and decrease hazardous gas emissions. The low heating value (3.2 MJ kg) of the Uruguayan oil shale indicates that it could be mixed with biomass to obtain better results. Stratified sampling of drill cores was used to obtain a representative sample. The morphological and structural characteristics of the oil shale were studied by X-ray diffraction and scanning electron microscopy. Chemical composition (hydrocarbons and minerals) of oil shales was investigated by X-ray diffraction, X-ray fluorescence, proximate and ultimate analysis and Fourier transform infrared spectroscopy. Rock Eval analysis was performed to measure richness and maturity of the Uruguayan oil shale, the results of the TOC content (8.93%) and the hydrogen index (525 mg HC/ g TOC) indicated that it constitutes an excellent source rock. The kinetic of the combustion and thermal properties of oil shale were studied. The activation energy of the different reaction stages was calculated using the Flynn-Wall-Ozawa model, then we obtained the pre-exponencial factor and the reaction order optimizing the theoretical model using the experimental data. Results indicated that the combustion of the oil shale exhibits multiple reaction stages with activations energies that varies between 152.2 and 316.4 kJ mol.

Carbon material is the largest material used as electrode on advanced energy storage devices. The modern lifestyle requires more energy, consequently, more smart energy use and efficient devices are needed. The constant evolution of materials technologies looking for green material and renewable raw material, that have minimal impact on the environment, is one of the most important subjects studied in recent years. The scientific and industry community are paying more attention to new forms of carbon such as nanotubes, graphene, and activated carbon fiber. The purpose of this work is to convert human hair into a hollow carbon filament to be used as a supercapacitor electrode. The human hair needs 3 stages to be converted into carbon filament: textile manufacture, oxidation, and carbonization. The electrochemical behavior was analyzed in a threeelectrode electrochemical cell system with 2 M of H2SO4 electrolyte medium. The behavior of the electrode was characterized electrochemically by galvanostatic charge/discharge curves, cyclic voltammetry, and electrochemical impedance spectroscopy, showing 163 F g-1 of a maximum value of specific capacitance. Keywords: Residue. Human hair. Felt. Carbon filament. Supercapacitor.

In the present work, an activated biocarbon (aBC) was studied as a support in Pd electrocatalyst for ethanol oxidation reaction (EOR) in alkaline medium. Pd/aBC sample was compared with a commercial Vulcan carbon supported Pd electrocatalyst. The Pd particles morphology were influenced by the high content of oxygenated surface functional groups of aBC support, which can be relevant for the synthesis of Pd based electrocatalysts, because the Pd particles formation mechanism involves the adsorption of Pd2+ on negative charged sites of aBC support. This adsorption occurs preferentially on electron donor sites such as oxygenated functional groups. Therefore, the higher concentration of these groups in aBC surface can determine a higher concentration of initial nuclei sites for Pd particles formation contributing to the particles agglomeration on aBC support, compromising the Pd/aBC electrocatalytic performance. For both prepared electrocatalysts, the spectroelectrochemical analysis demonstrates that the acetate ion is the main product of the EOR in the alkaline medium.

In this work, two different activated carbons were prepared from Uruguayan rice husk, using different carbonization times (1 and 4 h) and KOH as activating agent. The electrochemical characteristics as supercapacitor electrodes were evaluated in aqueous acidic media and correlated with their physicochemical properties, with special emphasis on the influence of the pore size. The activated carbon obtained with 4 h of carbonization time (CAct_4 h sample) presents the higher specific electrical capacitance value in three and two-electrode configuration, 248 F g−1@6.6 A g−1 and 186 F g−1@0.9 A g−1 respectively. This sample also showed the better rate capability and higher energy and power density (4.9 Wh kg−1 at 192 W kg−1). Its best performance can be associated with its higher specific surface area (2412 m2 g−1), more open microporosity (L0 = 2.4 nm) and lower content of impurities. According to the equivalent electrical circuit model obtained from the electrochemical impedance spectroscopy, this textural characteristics determine a higher charge storage and less electrochemical resistance related to the microporosity of the sample.

ICTAC recently published a series of recommendations for analyzing thermogravimetric experiments, one of which was the deconvolution of the DrTGA; however, it has received little use for processing fuel blends. In the present work, Lorentz distribution was used to deconvolve multi-stage processes in the co-combustion of oil shales and Eucalyptus grandis sawdust from Uruguay. The activation energies values were obtained using an isoconversional-iterative procedure and the maximum value were obtained for the oil shales (401 kJ mol − 1 ), which is correlated with its low combustibility. The activation energies values were used to calculate the pre-exponential Arrhenius factors and global orders. The thermogravimetric curves were rebuilt at different heating rates (5, 10, 20, 30, 40 and 50 K min − 1 ). Results indicated a good agreement between the theoretically calculated values and the experimental data, obtaining a maximum average error smaller than 3%.

This paper presents the study of a simple and fast method to prepare an activated hydrothermal carbon supported nickel electrocatalyst (Ni/aHC) for ethanol oxidation reaction (EOR) in alkaline medium. The cyclic voltammogram obtained for the Ni/aHC sample in a 1.0 mol L−1 NaOH solution shows an anodic and a cathodic peak. These redox couple reaction peaks can be related to the reversible formation of (NiO)OH. The catalytic activity of the Ni/aHC sample regarding the EOR is clearly evident from the cyclic voltammogram obtained in presence of ethanol, where a significant increase in the current density from 0.55 V vs. Hg/HgO is observed. This potential value, related with the onset potential (Eonset) of the EOR, is very close to the corresponding (NiO)OH formation potential, confirming that this species is directly involved in the EOR on the Ni/aHC electrocatalyst. The in-situ Attenuated Total Reflectance FTIR (in-situ ATR-FTIRS) spectra of this sample show two intense peaks related with acetate ion formation. Based on the ATR-FTIRS and electrochemical analyses, and in the literature information, a reaction pathway of the EOR on Ni/aHC in alkaline medium is proposed.

The main challenge for the development of a high efficiency supercapacitor is the electrode material. Developing electrode materials with high specific electrical capacitance and low electrical resistance enables an increase in the energy accumulated in the device. In addition, it is expected that the electrode material presents a simple procedure for preparation having low production cost and being environmentally friendly. This work is based on the deposition of silver nanoparticles on activated carbon felt (Ag@ACF) as a supercapacitor electrode. The samples were characterized by field emission gun scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and textural analysis. Supercapacitor behavior was evaluated by galvanostatic charge-discharge curves, cyclic voltammetry and electrochemical impedance spectroscopy using a symmetrical two-electrode Swagelok type cell, and three different aqueous solution electrolytes: 2 M H2SO4, 6 M KOH and 1 M Na2SO4. Ag@ACF presented a high specific capacitance in KOH, about 170 F g-1, which makes it an interesting material for supercapacitor electrodes and it showed good specific electrical capacitance, low resistance and high cyclability.

In this work the thermal behavior of wood impregnated with ZnCl2 is studied. Impregnation of wood with ZnCl2 is a treatment used in activated carbon production, and liquefaction and fast pyrolysis of biomass. Frequently, the impregnated wood is dried for several hours at temperatures above 370 K and then it is carbonized. Catalytic pyrolysis occurs, giving rise to a complex set of reactions. A TG/DTA study was done on the raw material, the activated carbon, the pure ZnCl2 and the intermediate products in order to study the mass and thermal changes occurring. Elemental analysis and SEM analysis were also carried out. An exothermic torrefaction develops during the drying step; the torrefied product is carbonized in an endothermic process that involves ZnCl2 volatilization. The washed impregnated wood carbonizes through an exothermic process that may involve the decomposition of cellulose, lignin and the solid product of hemicellulose torrefaction.

Different activated biocarbons (aBCs) were prepared from Eucalyptus grandis wood and activated Vulcan carbons (aVCs) were prepared from commercial Vulcan XC72 carbon. These carbon materials were used as a support in a PtSn/C electrocatalysts for ethanol electro-oxidation (EEO). Structural, morphological and chemical composition differences of the electrocatalysts were correlated to their electrocatalytic performance, and by in-situ Fourier Transform Infrared Spectroscopy in the Attenuated Total Reflectance mode (in-situ ATR-FTIRS), with the ethanol electro-oxidation mechanism (EEOM) pathways and product distributions at different potentials using sulfuric acid as a base electrolyte. The nature of the carbon support and it activation method affected the morphological and structural characteristics of the PtSn based electrocatalysts. The electrocatalytic performance of the electrocatalysts supported on the aBCs was better than that of the supported on the activated Vulcan carbons. The PtSn electrocatalysts using CO2 activated biocarbon support had a higher electrochemically active surface area (EASA), lower onset potential and greater current density for the EEO. It was determined that the EEO on all studied PtSn electrocatalysts in sulfuric acid media occurs mainly through the acetic acid and acetaldehyde production.

Activated carbon monoliths and oxidized carbon monoliths are prepared from Eucalyptus grandis wood by pyrolysis and subsequent activation under CO 2 (aCMs) and further functionalization using nitric acid (ox-aCMs). Their textural and chemical properties are compared and the electrochemical characteristics as supercapacitor electrodes are tested. The nitric acid treatment does not produce substantial changes in the textural properties of the monolith obtained. Elemental analysis and X-ray photoelectron spectroscopy (XPS) reveal that the oxidized monolith presents a high content of oxygenated functional groups that can participate in pseudocapacitive reactions. This determines that the oxidized monoliths have higher electrical capacitance (80 F cm −3 ) at low current densities and higher energy density (up to W v = 2.7 W h L −1 ) than the non-oxidized ones. The supercapacitor cell containing the oxidized monoliths presents higher total resistance values and response time compared to the non-oxidized monolith. The non-oxidized monolith showed the highest power density (up to P V = 94.5 W L −1 ).

Supercapacitors have received great attention in science and technology, due to its important qualities as the high cycle life, high power density, and variety of applications. The main challenge for the development of better devices is the electrode material. Developing electrode materials with high specific electrical capacitance and low electrical resistance enables an increase of energy accumulated in the supercapacitor. In addition, it is expected that the electrode material presents a simple procedure for preparation with low production cost and be friendly to the environment. In this work, a cheap and simple electroless process was involved to deposit chemical species of iron on a no expensive textile activated carbon fiber felt with interesting properties for application as supercapacitor electrode. The resulting binary composite (Fe@ACF) supercapacitor electrode possesses a high specific capacitance of 237 F g−1 at a current density of 0.2 A g−1 and only 3% of loss of its initial specific capacitance after 3000 charge-discharge cycles. These results reveal that the activated carbon fiber felt/iron composites are promising materials for supercapacitor electrode applications.

An electrical double-layer capacitor (EDLC) is based on the physical adsorption/desorption of electrolyte ions onto the surface of electrodes. Due to its high surface area and other properties, such as electrochemical stability and high electrical conductivity, carbon materials are the most widely used materials for EDLC electrodes. In this work, we study an activated carbon felt obtained from sheep wool felt (ACF’f) as a supercapacitor electrode. The ACF’f was characterized by elemental analysis, scanning electron microscopy (SEM), textural analysis, and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the ACF’f was tested in a two-electrode Swagelok®-type, using acidic and basic aqueous electrolytes. At low current densities, the maximum specific capacitance determined from the charge-discharge curves were 163 F·g−1 and 152 F·g−1, in acidic and basic electrolytes, respectively. The capacitance retention at higher current densities was better in acidic electrolyte while, for both electrolytes, the voltammogram of the sample presents a typical capacitive behaviour, being in accordance with the electrochemical results.

Direct ethanol fuel cells are based in ethanol electro-oxidation at low temperature and they constitute an alternative energy conversion system. However, they need catalysts in order to improve their efficiency, given that ethanol electro-oxidation is a slow-kinetic reaction. Among those catalysts platinum and platinum alloys play an important role in the increase of the ethanol cleavage kinetics for fuel cell application. However, to maximize the catalyst performance, support materials are needed in order to reduce the catalyst load considering its high cost. One of the more versatile catalyst supports is activated carbon. Recently, attention has focused on wood as carbon material precursor, because of its sustainability and also because the obtained carbons have excellent final properties. In the present work, activated carbon obtained by physical activation of Eucalyptus grandis wood (biocarbon) was tested as Pt and PtSn catalyst support, for ethanol electro-oxidation reaction. For comparison purposes, commercial activated carbon Vulcan XC72 was also tested. The catalyst supports were characterized by textural analysis, elemental analysis and infrared spectroscopy. The obtained catalysts were characterized regarding structure by XRD and their electrochemical behavior was evaluated by cyclic voltammetry. Biocarbon-supported PtSn electrocatalysts showed better electrochemical performance related to the commercial activated carbon (Vulcan XC72)-supported ones, since its developed current density and potential were the highest and its onset potential was the lowest. However, pure platinum showed better values for current density, potential and onset potential in Vulcan XC72-based activated carbons, being the untreated one the best support in this case.

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.

DSC and TG/DTA were used to study charcoals obtained from eucalyptus wood at different pyrolysis temperatures, as well as the exchanged energy, and the transformations involved during the pyrolysis process. Charcoals DSC curves showed two exothermic peaks, at ~610 and ~750 K. The first peak was squashed for those charcoals obtained at higher final pyrolysis temperatures, and it disappeared in the charcoals obtained at 873 and 923 K. The second peak intensity increased and its location changed at the higher temperatures. Charcoal characterization showed a rise of heat values with the pyrolysis temperature.

Wood residues are ordinary wastes in the forestry industry and their valorization is an important issue. Eucalyptus grandis wood dust was chosen as a model wood residue and biocarbons (BCs) and activated BCs were prepared from it and studied as active materials for supercapacitor electrodes. Several ordinary activation methods were used and microporous activated BCs with specific surface areas up to 900 m2 g-1, and different content of oxygenated surface groups were obtained. The preparation or activation temperature is the parameter that mainly affects the electrical conductivity. For temperatures above 700 °C, the samples reach an electrical conductivity as high as 1 S cm-1. The specific capacitance of the activated BCs reaches values up to 203 F g-1 in acidic electrolyte. The highest specific capacitance is obtained when chemical activation with ZnCl2 at 900 °C followed by chemical oxidation with nitric acid is used. BCs activated with ZnCl2 at 900 °C and CO2 at 800 °C displayed good rate capability and the maximum power density. Activation with ZnCl2 at 900 °C also leads to BCs with the maximum energy density. These results show that E. grandis wood dust is a promising low cost and environmental friendly precursor for biocarbon electrodes. © Springer Science+Business Media Dordrecht 2013., Financial support from the projects (MAT 2011-25198 and ANII PR_FSE_2009_1_09) is gratefully acknowledged. V. Barranco thanks the Spanish MINECO for R&C contract.

Activated carbon fibers (ACF) are known as excellent adsorbent materials due to their fast adsorption rate and easy handling characteristic. The ACF can be manufactured from the polyacrylonitrile fiber, based on an usual carbon fibers (CF) production process accomplished by an additional activation process. The aim of the present work is to describe the production, chemical/morphological characterization and application potentiality of activated carbon fiber felt (ACFF) produced from textile PAN fiber, using a set of homemade equipment. The 5.0 dtex PAN fiber tow with 200 thousand filaments was oxidized and used as raw material for felt production. The oxidized PAN fiber felt (OPFF) was displaced in a special sample holder, carbonized (900 °C) and then activated in CO2 atmosphere at 1000 °C in an electric tubular furnace. All steps of the process were performed as fast as possible, and characterization was done by 77 K N2 isotherms, adsorption isotherms in liquid phase, scanning electronic microscope, X-ray diffraction and surface chemistry by Bhoem methodology. The results confirmed the production of essentially microporous (pore < 3.2 nm, centered on 1.2 nm) and 1,300 m2/g surface area. The ACFF produced have demonstrated a strong potential application as electrode supercapacitor.

At present, there is great interest in using biomass as an alternative energetic source, as it is renewable and environmentally friendly. In the case of solid fuels, biomass has low energetic density, although it can be increased by charring and pelletizing. These methods also allow the improvement of physical properties, such as hydrophobicity and resistance to microbiological attack. In this work, the agglomeration of charcoal dust produced from sawmill waste with three different binders (wood tar, molasses and starch) was studied. The procedure included agglomeration and curing by heating in air atmosphere. The prepared charcoal pellets showed appropriate mechanical resistance, higher heating value than the original wood residues and higher energetic density than charcoal. Molasses and tar used as binders in the preparation of fuel pellets allow energy densification and an adequate durability of the products.