PEDRO VITOR DUARTE DA CRUZ

PEDRO VITOR DUARTE DA CRUZ

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Caracterização de materiais à base de grafeno sintetizados a partir de diferentes fontes de grafite
2023 - CASTRO, LAURA F.; CRUZ, PEDRO V.D. da; BONIFACIO, RAFAEL N.; LAZAR, DOLORES R.R.
Characteristics of electric double layer capacitors prepared with electrolytes based on deep eutectic solvents
2022 - GALDINO, G.S.; RODRIGUES, W.C.; CRUZ, P.D.; CASINI, J.S.; SAKATA, S.K.; FARIA, R.N.
The storage capacity of electric double layer capacitors or electrochemical supercapacitors with electrolytes based on deep eutectic solvents (DES) composed of L-lactic acid with several hydrogen bond acceptors (nicotinamide, L-alanine, ammonium acetate, sodium acetate, choline chloride, amino acetic acid) with a molar ratio of 7:1 have been investigated. A DES based on urea and choline chloride with at a molar ration of 2:1 has also been included for comparison. The electrochemical supercapacitors were prepared using commercial activated carbon electrodes after removing the volatile organic electrolyte with a vacuum pump. The characteristics of the electrochemical supercapacitors were determined by cyclic voltammetry at temperature room temperature and also after heating at 353 K using scan rates that varied from 2 to 25 mVs-1. Lowest scan rate led to higher specific capacitance of 150±8 Fg-1 with a maximum applied potential of 1.7 V for the urea and choline chloride DES with a molar ration of 2:1. The lactic acid with all the hydrogen bond acceptors with a molar ratio 7:1 it has been necessary to increase the temperature above room temperature to improve the specific capacitance.
Battery eletrolyte based on lithium perclorate for electrochemical supercapacitors
2022 - CRUZ, P.D.; FARIA, R.N.; LAZAR, D.R.
Propylene carbonate (PC) has been successfully employed in rechargeable batteries for quite a long time. Lithium perchlorate (LiClO4) was dissolved in propylene carbonate (C4H6O3) to form the liquid electrolyte for high energy battery systems. Due the high conductivity, common electrolytes for carbon-based electrochemical supercapacitors are the tetraethylammonium tetrafluoroborate salt (NEt4BF4) dissolved in propylene carbonate or acetonitrile (ACN). These organic solvents have a drawback of requiring a glove box for handling due to moisture susceptibility and also for their intrinsic toxicity. A glove box, which can be routinely operated at oxygen levels below 30 ppm, has a considerable capital, operational and maintenance cost. Organic electrolytes also evaporate easily and commercial supercapacitors are limited to operation close to room temperature (<70oC). In this study propylene carbonate has been replaced for propylene glycol (PG) which is practically non-toxic. Propylene glycol (C3H8O2) can be released into the environment via industrial releases or by disposal of consumer products. It is readily soluble in water and has a low sorption partition coefficient, having the ability to move through soil and to leach into ground water. Low vapor pressure (0.1 mmHg at 25°C) and high water solubility produces minimal volatilization to the atmosphere. Its low octanol/water partition coefficient indicates that bioconcentration should not happen. Propylene glycol is readily degraded in surface water and soil by chemical oxidation (or photochemical) and microbial digestion, with a short half-life (1–5 days) in aerobic or anaerobic conditions. Electrochemical supercapacitors have been produced with activated carbon commercial electrodes with electrolytes based on propylene glycol using lithium perchlorate in various molar ratios. These experimental devices have been tested by cyclic voltammetry under window potential from 1 V to 2.7 V and current from 10 mA to 150 mA at scanning rates of 1 mVs-1 and 10 mVs-1. Galvanostatic cycling was carried out using several current densities from 1.1 V to 2.7 V. Electrochemical impedance spectroscopy (EIS) was used with a 1 mHz to 100 KHz interval and an applied bias potential varying from 0 V to 10 V. Voltammetry curves at room temperature resulted in a specific capacitance 143 Fg-1 for the propylene glycol with lithium perchlorate electrolyte in a molar proportion of 2 to 1.
Characteristics of electric double layer capacitors produced with electrolytes based on deep eutectic solvents
2022 - GALDINO, G.S.; RODRIGUES, W.C.; CRUZ, P.D.; CASINI, J.S.; SAKATA, S.K.; FARIA, R.N.
The storage capacity of electric double layer capacitors or supercapacitors with electrolytes based on deep eutectic solvents (DES) has been investigated in this study. DES composed of L-lactic acid with nicotinamide, L-alanine, ammonium acetate, sodium acetate and choline chloride have all been prepared at a molar ratio of 7:1. Furthermore, urea with choline chloride at a molar ratio of 2:1 has also been used as electrolyte for the electrochemical supercapacitors. The DES supercapacitors were prepared using commercial activated carbon electrodes after removing the volatile organic electrolyte with back-pumping vacuum. The electric characteristics of these supercapacitors with DES electrolytes were determined by cyclic voltammetry at room temperature and above up to 80°C. The cyclic voltammetry scan rates were varied from 2 to 25 mVs-1. The lowest scan rate led to a high specific capacitance of 150±8 Fg-1 for urea with choline chloride at a molar ratio of 2:1 and using a maximum applied potential of 1.7 V. For higher molar ratio (7:1) of Llactic acid with the others hydrogen bond acceptors (HBA) it was necessary to increase the temperature above room temperature to improve the specific capacitance. The best results have been obtained with two solids (urea and choline chloride) as starting compounds for preparing the DES. Equivalent series resistances (ESR) have also been determined in this work employing galvanostatic cycling tests with current densities between 2 and 20 mAg-1.
The effect of vacuum annealing and HDDR processing on the electrochemical characteristics of activated carbon and graphene oxide for the production of supercapacitors electrodes
2020 - CRUZ, P.V.D.; COSENTINO, I.C.; GALEGO, E.; YOSHIKAWA, D.S.; FARIA, R.N.
Electric double-layer capacitors prepared using activated carbons have been subjected to vacuum heat treatments at low and high temperatures (200, 400, 600, 800 and 1000oC). The electrodes have been tested at a potential of 1.1 V employing a KOH electrolyte (1.0 and 6.0 mol.L-1). The effect of or HDDR upon the electrical properties has been investigated by cyclic voltammetry. It has been shown that the specific capacitance at 5 msV-1 increases from 50 Fg-1 to 130 Fg-1 after a heat treatment at 400oC for 1 hour under back pump vacuum. At 400°C the diminution in the specific capacitance with higher scanning rate (10 msV-1) was much less pronounced (from 130 Fg-1 to 100 Fg-1). Equivalent series resistance (ESR) and equivalent parallel resistance of supercapacitors electrodes have also been investigated. Internal resistances of the supercapacitors were calculated using the galvanostatic curves at current densities (100 mAg-1). A compositional and morphological evaluation of these electrodes showed no significant change on the activated carbon structure.
Low-temperature reduction of graphene oxide using the HDDR process for electrochemical supercapacitor applications
2020 - BENITEZ JARA, F.G.; CRUZ, P.D.V.; BARBOSA, L.P.; CASINI, J.C.S.; SAKATA, S.K.; PERUZZI, A.J.; FARIA, R.N.
In the present work, attempts of reducing a graphene oxide powder using a low temperature hydrogenation disproportionation desorption and the recombination process (L-HDDR) has been carried out. A lower processing temperature in large scale production is significant when costs are concerned. Graphite oxide was prepared using a modified Hummers’ method dispersed in ethanol and exfoliated using ultrasonication to produce Graphene Oxide (GO). Investigations have been carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results of L-HDDR processing graphene oxide powder, using unmixed hydrogen at 400°C and relatively low pressures (<2 bars) have been reported. X-ray diffraction patterns showed a reduction of graphene oxide with the L-HDDR process. The results showed that both processes, the L-HDDR as well as the standard HDDR, may be applied to the reduction of graphene oxide in order to produce supercapacitor materials. The advantage of employing the L-HDDR process is a relatively low temperature reducing the cost of treatment, what is a very important factor for producing a large amount of material. Thus, the L-HDDR process has been considered a promising alternative method of reducing graphene oxide with efficiency, with the possibility of large scale production.
Efeito do tratamento térmico a vácuo e do processo HDDR nas propriedades eletroquímicas de supercapacitores à base de carbono ativado e óxido de grafeno reduzido
2019 - CRUZ, PEDRO V.D. da
O aumento da necessidade de armazenamento de energia trouxe aos capacitores eletroquímicos de dupla camada elétrica (supercapacitores) maiores proporções nas pesquisas. Com isto, a principal necessidade se tornou o aumento de sua capacidade (capacitância). Visando isto, o presente trabalho busca investigar o efeito do carbono ativado, matéria prima de eletrodos para os supercapacitores, tratado termicamente vácuo em diferentes temperaturas (200, 400, 600, 800 e 1000 °C) e por meio do processo HDDR,nas alterações das características elétricas destes produtos. Foram escolhidos dois eletrólitos de baixa toxidade em duas concentrações para salientar suas diferenças, sendo sulfato de sódio (1,0 mol L-1) e hidróxido de potássio (1,0 e 6,0 mol L-1). As medidas utilizadas para esta caracterização se basearam nos ensaios de voltametria cíclica e ciclos galvanostáticos, efetuados em um analisador computadorizado, determinando a capacitância especifica e resistência interna. Foram realizados, também, ensaios utilizando as seguintes técnicas: impedância, termogravimetria, adsorção de nitrogênio, microscopia eletrônica de varredura (MEV) e difração de raios X (DRX).
Production and characterization of a hybrid composite of polypropylene reinforced with piassava (Attalea funifera Martius) fiber and light green clay
2019 - CORREIA, SABRINA A.; CRUZ, PEDRO V.; RODRIGUES, TASSON C.; MONTEIRO, ALEX; DIAZ, FRANCISCO R.V.; MOURA, ESPERIDIANA A.B.
Waste materials have been frequently used as reinforcing materials, to obtain a composite with better properties. Piassava palm is native to the state of Bahia (Brazil) and its fiber, piassava fiber (PF) is awaste material frequently used for industrial and domestic brooms, industrial brushes, carpets, and roofs. The light green clay (LGC) is a natural smectite Brazilian clay from the state of Paraiba. This work aims to produce and evaluate the advantages of this new product achieved by the inclusion of these two natural materials into polypropylene (PP) matrix. A melting extrusion process, using a twin-screw extruder and injection molding machine was used to obtain PP/LGC (97/3 wt%), PP/PF (90/10 wt%) and PP/LGC/PF (87/3/10 wt%) composites. The materials were characterized by mechanical tests, TG, DSC, SEM, and XRD analysis.
The effect of vacuum annealing and HDDR processing on the electrochemical characteristics of activated carbon and graphene oxide for the production of supercapacitors electrodes
2018 - CRUZ, P.D.; COSENTINO, I.C.; GALEGO, E.; YOSHIKAWA, D.; FARIA, R.N.
Electric double-layer capacitors or electrochemical supercapacitors prepared using activated carbons have been subjected to vacuum heat treatments at low and high temperatures (200, 400, 600, 800 and 1000°C). The activated carbon electrodes have been tested at a window potential of 1.1 V employing a KOH electrolyte (1.0 mol.L-1). The effect of thermal treatment (vacuum or HDDR) upon the electrical properties has been investigated by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). It has been shown that the specific capacitance at 5 msV-1 increases from 50 Fg-1 to 130 Fg-1 after a heat treatment at 400°C for 1 hour under back pump vacuum. At this temperature the diminution in the specific capacitance with higher scanning rate (10 msV-1) was much less pronounced (from 130 Fg-1 to 109 Fg-1). Equivalent series resistance (ESR) and equivalent parallel resistance of supercapacitors electrodes have also been investigated. Internal resistances of the supercapacitors were calculated using the galvanostatic curves at several current densities (10-100 mAg-1). BET analysis of the starting carbon and after thermal treatments have also been carried out in this investigation. The activated structures have been studied using scanning electron macroscopy (SEM) and X-ray diffraction. A compositional and morphological evaluation of these electrodes showed no significant change on the activated carbon structure. Reduced graphene oxide electrodes have also been prepared in this investigation for a comparison.
Microstructural and electrochemical studies of HDDR-graphene supercapacitors electrodes in KOH electrolyte
2018 - GALDINO, G.S.; SILVA, D.V.; CRUZ, P.D.; CASINI, J.S.; SAKATA, S.K.; FARIA, R.N.
In the past, the hydrogenation disproportionation desorption and recombination (HDDR) process has only been used to produced rare earth transition metal polymer bonded permanent magnets with outstanding performance. Recently, however, it has been shown that the HDDR process (850oC) can be successfully employed to produce reduced graphene oxide for electrochemical supercapacitors. In the present work, the electrochemical characteristics of HDDR-graphene supercapacitors have been compared to those obtained with chemically reduced commercial graphene oxide. Lower HDDR processing temperatures (200-600oC) have been used in this study for a comparison with previous investigations. The equivalent series and parallel resistances (EPR and ESR) and specific capacitance (Cs) of HDDR-graphene supercapacitors electrodes have been investigated using cyclic voltammetry. Room temperature specific capacitances calculated from cyclic voltammetry curves at scan rates of 2 mVs-1 reached ~160 Fg-1 in 1 molL-1 KOH electrolyte. Internal series resistances of the HDDR-graphene electrodes were measured using the galvanostatic curves also at room temperature. The microstructures of the electrode material have been investigated using scanning electron microscopy (SEM) and chemical microanalyses employing energy dispersive X-ray analysis (EDX).