PEDRO VITOR DUARTE DA CRUZ
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Artigo IPEN-doc 27415 The effect of vacuum annealing and HDDR processing on the electrochemical characteristics of activated carbon and graphene oxide for the production of supercapacitors electrodes2020 - 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.Artigo IPEN-doc 27410 Low-temperature reduction of graphene oxide using the HDDR process for electrochemical supercapacitor applications2020 - 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.Dissertação IPEN-doc 26727 Efeito do tratamento térmico a vácuo e do processo HDDR nas propriedades eletroquímicas de supercapacitores à base de carbono ativado e óxido de grafeno reduzido2019 - CRUZ, PEDRO V.D. daO 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).