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This research is supported by the award № DO1-286 / 07.10.2020 granted from by the Ministry of Education and Science of Bulgaria

In this work, carbon-based conducting electrodes based on two different types of carbon nanofibers (CNF) have been produced by the dip and dry coating method onto cotton substrates. Furthermore, activated carbon (Norit A Supra Eur) and manganese oxide (MnO2) have been subsequenlty added to the CNF-based dip-coated cotton fabrics electrodes and asymmetric supercapacitors have been constructed and tested with the focus of obtaining devices with increased capacitive performance. In particular, the carbon-based active layer was prepared by spreading on the CNF-based electrodes a slurry containing the activated carbon (AC) material, graphite fibres, polyvinylidene difluoride (PVDF) as binder and N,N dimethylacetamide (DMA) solvent, whereas the MnO2 based active layer was prepared by spreading on the CNF-based textile electrodes a slurry formed by MnO2, carbon black, graphite fibers, PVDF and DMA. A solution of 1M Na2SO4 impregnated in porous paper separator (Nippon Kodoshi Corportion, Japan) was employed as neutral aqueous electrolyte. The supercapacitors were electrochemical investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS). The results indicated that with this particular combination of carbon and manganese oxide active layers on CNF-based cotton fabrics it was possible to obtain specific capacitance of 100 F/g and a high specific energy density of 10 Wh/kg., This work was partly financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT – Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007136. A. J. Paleo acknowledges the support of COST Action CA15107- Multi-Functional Nano-Carbon Composite Materials Network (MultiComp) by means of a short term scientific mission (STSM)., info:eu-repo/semantics/publishedVersion

In this paper, we report the synthesis and characterization of mesoporous carbons, which were obtained using SBA-15 silica as the template material and sucrose as the carbon source. The prepared silica template and mesoporous carbons were characterized by nitrogen adsorption-desorption, low angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). Synthesized carbons were used to prepare composite electrodes for solid-state supercapacitors. The electrochemical characteristics of mesoporous carbons in supercapacitors were studied by cyclic voltammetry and electrochemical impedance spectroscopy. The study showed that a value of specific capacitance of 132 F g-1 (for a single electrode) was obtained with the CMK-3A mesoporous carbon, which was 68% higher than that of an activated carbon that was used as a reference material. The superior performance was 127% (12.05 ?F cm-2 vs. 5.3 ?F cm-2) when the double-layer capacitance of the mesoporous carbon was compared to that of the reference carbon. These findings for the mesoporous carbon-based supercapacitor were explained on the basis of a high pseudo-capacitance and other physico-chemical properties of this carbon, such as the pore structure, accessibility of pores to the electrolyte, and surface wettability by surface functional groups. All of these properties were improved compared to those of the activated carbon.

Rapporto tecnico relativo alle attività svolte per FIAMM dal 16/07/2009 al 15/07/2010

Manganese oxide in powder form was prepared by redox reaction of a Mn(II) salt with a permanganate (VII) salt and subsequent activation at 200 °C. Electrodes were prepared with manganese oxide and commercial activated carbon by a casting method. Supercapacitor tests were conducted on assemblies formed with manganese oxide based positive electrode and activated carbon based negative electrode. A porous material impregnated with 0.1 M Na2SO4 aqueous solution formed the electrolytic separator between electrodes. Electrochemical tests were carried out in a 4 cm2 test-cell with electrodes having different amounts of active materials. Ciclic voltammetry, galvanostatic charge-discharge and impedance measurements were carried out to study the electric behaviour of the electrodes and to correlate the supercapacitor performance with the characteristics of active materials. Cyclic voltammetry endurance tests evidenced a perfect stability of materials and electrolyte in the voltage window 0 - 1.6 V. A set of voltammetric curves obtained at different voltage scan rates is reported in Fig. 1. From a not optimised couple of electrodes a specific capacitance of 46 F/g of active materials in the supercapacitor was obtained and a energy density of about 16 Wh/kg was calculated. The charge-discharge curves (Fig. 2) as well as the voltammetric curves (Fig.1) evidenced a marked pseudocapacitive effect at supercapacitor voltage values upper 0.8 V determined by an increase of oxidation state of manganese at the positive electrode. To discriminate the effective capacitive contribution of the single electrode to the performance of supercapacitor the charge-discharge curves for each electrode were also collected. The so-obtained curves evidenced a marked pseudocapacitive effect occurring at positive electrode over 0.9 V (vs. SCE) while the negative electrode showed only double layer capacitance. Referring to the same couple of electrodes above mentioned and by using the individual charge-discharge curves specific capacitances of 290 F/g and 134 F/g were calculated for the positive and negative electrode, respectively. Electrochemical impedance spectroscopy measurements were utilised to determine internal resistance of studied supercapacitors at different voltages. The results of these measurements were correlated to the chemical species that form at the electrodes during supercapacitor operation.

Ordered mesoporous carbons (OMCc) are a new class of carbonaceous materials that have found remarkable interest in energy storage technologies as active materials for negative electrode of lithium battery [1] and as capacitive materials in supercapacitors [2]. In this regard, here we report a study on the synthesis and modification of OMCs, such as CMK-3, the preparation of electrodes and their characterization in solid state supercapacitors.

This study is a bibliometric analysis of worldwide scientific literature on research activity in the field of supercapacitors. To analyze the quality, quantity and influence of published scientific papers in this field, we have performed a search in the Scopus database and have analysed the relevant records. We then proceeded with rankings of authors and countries on the basis of different indicators: number of papers, citations, Hirsh index, and citations per paper. The analysis of aggregate records shows that the number of publications has increased remarkably since 2004. This is because in the last few years, there has been a rapid growth in publications coming from China and other Asian countries (Korea, Taiwan and India). China was found to be the leading country with 459 published papers and five authors on the list of the 30 most prolific scientists per number of publications. However, the Western countries also such as the United States, Canada and Europe, along with France, Poland, Italy and Germany have showed a high level of productivity on the basis of other metric indicators. The bibliometric analysis of data shows that the United States is the leading country after which Japan, France, Canada and Poland follow. Other countries such as Korea, Taiwan, India and Italy also have excellent results and appear often in the "top ten" countries or high ranking authors.

Sintesi

In this work the electrochemical behavior of anodes and cathodes of small size full solid-state supercapacitors which operated in continuous cycling tests has been investigated. The electrochemical measurements were carried out in a cell equipped with a reference electrode (r.e.). Two types of supercapacitors were studied, the first one, a symmetric supercapacitor, based on activated carbon materials in the electrodes and the other one, a hybrid supercapacitor, based on activated carbon materials and ruthenium oxide. The introduction in the cell of the r.e. allowed to follow the voltage changes at the anode and at the cathode during the cyclic voltammetry (CV) and the galvanostatic charge-discharge (CD) measurements. The evaluation of the influence of some parameters of the electrodes on the performance of the complete supercapacitor has been investigated in this work. We would demonstrate the utility of this method of investigation in the study of the behavior of both electrodes and of supercapacitors. As an example of study we report the influence of the amount of activated carbon or of the presence of ruthenium oxide in the electrodes on the electrochemical performances. In detail, it has been investigated the influence of amount of active carbon materials on behaviour of the anode and cathode and of the full supercapacitors during charge and discharge processes at different conditions of voltage sweep rates (CV tests) and currents (CD tests).

An ordered mesoporous carbon material has been synthesized and used together with solid polymer electrolyte (SPE) to realize a solid-state supercapacitor (SC). The synthesis of carbon consisted in the preliminary preparation of highly ordered mesoporous silica (SBA-15), used as a template material, that in a second step was impregnated with sucrose that after thermal treatment at 850 °C was transformed in carbon. The so prepared carbon is know as CMK-3 type carbon. The solid polymer electrolyte was synthesized using trimethyl silyl chlorosulfonate as sulfonating agent in homogeneous polymer solution of chloroform. The silyl sulfonate polysulfone is modified in the sulfonate form by reaction with sodium methoxide. The membranes were prepared by casting method. The prepared membranes were washed with water, dried and converted in protonic form for immersion in HCl solution before their characterization. Two samples of sulfonated polysulfone membrane (SPSf) were employed as electrolyte in the fabrication of solid-state supercapacitors. The former sample contained only the SPSf, whereas the second was in composite form being SPSf filled with 5% of SBA-15 silica. The electrodes for the supercapacitors was prepared with CMK-3 mesoporous carbon and Nafion ionomer. The latter had both the functions of binder and ion conductor. The structures of nanostructured silica template and carbon material was evaluated by transmission electron microscopy (TEM) small angle X-Ray diffraction (XRD) and BET analyses. The solid-state supercapacitors based on carbon electrodes and solid polymer electrolytes were characterized by cyclic voltammetry (CV), galvanostatic charge/discharge measurements and, electrochemical impedance spectroscopy (EIS) analyses. As a result, it was found that the supercapacitor with the composite SPSf membrane exhibited higher specific capacitance (105 F/g) compared to that with the membrane containing only SPSf (86 F/g). Further results on the structural features of synthesised nanostructured carbon, on the proton conductivity of the polymeric membranes and, on the effect of filler on supercapacitor performance will be shown during the presentation.

The influence of carbon properties on the capacitance performance of a supercapacitor based on carbon electrodes and solid polymer electrolyte is presented in this work. Three carbons of different surface area have been investigated. The carbons have been used in supercapacitors as received and after chemical treatment with nitric acid. The chemical treatment provides to modify the surface properties of carbons. The surface area of treated carbons modifies in different way in dependence of type of used carbon. However, independently by surface area of carbons, better capacitance performances have been obtained by supercapacitors using modified carbons. This is likely due at higher utilization of surface area of carbon caused by an increased hydrophilicity and consequently by a improved electrode/electrolyte interface. Decay in capacitance performance was evidenced during cycling test carried out in cyclic voltammetry mode on supercapacitor with treated carbon.

In the last years, Direct Methanol Fuel Cells (DMFCs) are gaining momentum as electrochemical power generators for application in electric cars. The choice of such low polluting technology is preferred with respect to similar energy systems, like batteries or hydrogen fed fuel cells, because of higher simplicity of design and suitable energy density. Nevertheless, a few problems inherent to the use of this technology are connected with the present electrolyte membranes. The electrolytes commonly utilized in DMFC systems are based on perfluorosulfonic polymers (Nafion and Dow); these dehydrate when the fuel cell is working at high temperatures and allow a large methanol cross-over. Dehydration and cross-over are detrimental effects for a proper fuel cell operation.

Membranes obtained from sulfonated polysulfone (SPSU) are possible substitute for the perfluorosulfonic ionomer membranes used in polymer electrolyte fuel cells (PEFC). In this work a milder sulfonation process was used to produce proton-conducting polymer from a commercial polysulfone. Sulfonation levels from 20 to 80% were achieved by varying the mole ratio between sulfonating agent and the unit of polymers. Intrinsic viscosity measurements do not evidence chain cleavage and polymer degradation of sulfonated samples respect to base polysulfone.

The performance of Pt-W electrocatalysts as CO tolerant anodes in polymer electrolyte fuel cells (PEFCs) was evaluated and compared with Pt-Ru, Pt-Sn and Pt anodes. Testing were carried out in pure hydrogen and in presence of 100 ppm CO. CO tolerance was measured as the loss in the cell voltage due to CO in the H-2 normalised to a pure H-2 fed standard anode. A voltage loss less than 25% at 0.6A/cm(2) was measured at 90 degrees C with Pt50Ru50/C and Pt50W50/C anodes. The promising results obtained with Pt-W binary anode catalyst, though non conclusive what concerns the stability vender this catalyst interesting for further investigation.

A simple analytical expression to determine cell potential (E) against current density (i) behaviour in polymer electrolyte fuel cells (PEFCs) was derived. The equation describes experimental data over the whole range of current density taking into account possible mass transport limitations. The empirical equation was used to fit experimental data obtained in a 50 cm(2) single cell in H-2/air operation using electrodes with low Pt loading (similar to 0.1 mg cm(-2)). A good agreement between theoretical and experimental data was found.

Dense membranes made of PEEKWC, a novel soluble poly(aryletheretherketone), and poly[bis(phenoxy)phosphazene] (PPOP) have been prepared and tested for gas transport properties. The polymers have been characterized by DSC, Wide Angle X-ray Diffraction, thermogravimetric analysis and show excellent thermal stability and permselectivity. Permeability to CO2, He, N2 and O2 have been measured at steady state from 25 to 85-degrees-C. CO2 solubility in PEEKWC has been determined at low pressures. PEEKWC is a glassy polymer with a dual mode sorption behavior for carbon dioxide. Differences in the gas transport properties in PPOP membranes with different origin and crystalline fractions cannot be interpreted only as a simple effect of the variation of average mobility of the amorphous polymeric chain segments.