Luís F. Marchesi

Effect of low and high methoxyl citrus pectin on the properties of polypyrrole based electroactive hydrogels

Electroactive hydrogels were prepared using commercial citric pectin, either raw (PC) or purified through dialysis (dPC), and chemically synthesized polypyrrole (PPy). 1H NMR analyses showed that PC is a low methoxyl pectin (degree of methoxylation, DM=46%) and dPC is a high methoxyl pectin (DM=77%). The pyrrole polymerization was monitored through UV-vis spectroscopy and both samples were observed to be good stabilizers for PPy in aqueous medium. The dispersions were used to prepare the hydrogels h-PC-PPy and h-dPC-PPy. The hydrogel h-dPC-PPy has a higher swelling index (SI≈25%) at pH 1.2 than the hydrogel h-PC-PPy (SI≈7%). Contrastingly, at pH 6.8 both hydrogels lost their mechanical integrity. Raman spectroscopy revealed that PPy is more oxidized in h-PC-PPy. Nevertheless, both hydrogels are electroactive and therefore can be considered for applications in which the control of the degree of swelling is desired.

Nickel-Copper Alloys Modified Electrodes: an Electrochemical Study on their Interfacial and Supercapacitive Properties

In this manuscript, we report the electrodeposition of nickel-copper alloys in a two steps methodology. Firstly, the copper electrode is oxidized to generate Cu ions followed by the reduction of both Ni and Cu. The electrodes were further cycled in KOH to convert the metallic alloy into the respective electroactive hydroxide. This methodology created an electrode with high roughness and distinct electrochemical behavior. The modified electrodes were also characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Finally, the modified electrodes were studied in their supercapacitive properties by galvanostatic charge and discharge curves; the electrodes showed a good specific capacitance of 58 mF cm. The results indicated a new strategy using a simple methodology to modified Cu-electrodes to develop supercapacitors at low cost.

Morphological and Electrochemical Analysis of a Self-Assembled Monolayer of 3-Mercaptopropionic Acid on Gold Electrode

This paper investigates the morphology of a polycrystalline gold electrode modified with a monolayer of 3-MPA (Au/MPA) constructed in different immersion times and thiol concentrations, using the techniques of electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). It was verified that both surface roughness as the capacitance of the Au/MPA are dependent on the concentration and the organization of the 3-MPA molecules adsorbed on the gold electrode surface. Voltammetric results demonstrated that the coverage is dependent on the immersion time and concentration of the 3-MPA solution. These results are in agreement with the EIS results which showed the increased in charge transfer resistance (Rct) as a function of the immersion time, due to increase of the electron transfer block caused by the monolayer. However, the Rct increased until 180 min. and higher immersion times did not show significant variations in resistance.

Análise Morfológica e Eletroquímica de uma Monocamada do Ácido 3-Mercaptopropiônico sobre Eletrodo de Ouro

Este artigo investiga a morfologia do eletrodo de ouro policristalino modificado com monocamada do 3-MPA (Au/MPA) construido em diferentes tempos de imersao e concentracoes do tiol, utilizando as tecnicas de espectroscopia de impedância eletroquimica (EIE) e microscopia de forca atomica. Verificou-se que tanto a rugosidade da superficie, como a capacitância do Au/MPA sao dependentes da concentracao e da organizacao das moleculas de 3-MPA adsorvidas na superficie do eletrodo de ouro. Resultados voltametricos demonstraram que o recobrimento e dependente do tempo de imersao e da concentracao da solucao de 3-MPA. Estes resultados estao de acordo com as medidas de EIE, pois estes mostraram um aumento na resistencia de transferencia de carga de ( Rct ) em funcao do tempo de imersao, devido ao aumento do bloqueio da transferencia de eletrons causado pela monocamada. No entanto, a Rct aumentou ate 180 min. e tempos de imersao superiores nao apresentaram variacoes significativas nos valores de resistencia. DOI: 10.5935/1984-6835.20150095