The electro-oxidation of 4-amino-3-methyl-1,2,4-triazole-5-thione (MTSNH) on a bronze substrate in an alkaline methanol solution produces a homogeneous polymer film. The formation kinetics of the film was investigated using cyclic voltammetry, chronoamperommetry and electrochemical impedance spectroscopy. Cyclic voltammograms indicated that the polymer film (pMTSNH) was formed anodically between -350 and 350 mV/SCE. During the second cycle, the oxidation peak of the monomer disappeared, indicating the formation of the insulating film. We have also shown that the monomer oxidation reaction is essentially irreversible and controlled by a diffusion process. The inhibition efficiency of this polymer was determined by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution.

Um sensor amperométrico foi construído, usando-se ácidos húmicos para imobilização de íons Fe3+ em eletrodo de pasta de carbono (CPE-HA-Fe), e usado para determinação de ácido ascórbico (H2A). O voltamograma cíclico do eletrodo apresentou resposta eletroquímica devido ao par Fe3+/Fe2+ a E1/2=+0.78 V vs ECS, em eletrólito suporte KCl 0,5 mol L-1 e tampão acetato 0,2 mol L-1 /fosfato 0,020 mol L-1, a pH = 5,4. Quando H2A é adicionado à solução eletrolítica é observado processo de oxidação. A corrente obtida cronoamperometricamente a +0,87 V vs ECS, devido ao processo de oxidação, é proporcional à concentração, de acordo com a equação I(?A) = 7,6286 [H2A] (mmol L-1) + 1,9583, r = 0,9996, para concentrações entre 0,0 and 1,4 mmol L-1. O eletrodo apresentou alta estabilidade e foi usado para determinação de H2A em suco de laranja natural.

An amperometric sensor was constructed, by using humic acids to immobilize Fe3+ ions on a carbon paste electrode (CPE-HA-Fe), and used for ascorbic acid (H2A) determination. The cyclic voltammogram of the electrode showed electrochemical response due to the Fe3+/Fe2+ couple at E1/2=+0.78 V vs SCE, using 0.5 mol L-1 KCl and 0.2 mol L-1 acetate/0.020 mol L-1 phosphate buffer, at pH = 5.4, as supporting electrolyte. When H2A is added to the electrolyte solution it is observed an oxidation process. The oxidation current, obtained by chronoamperommetry at +0.87 V vs SCE, is proportional to the concentration, represented by the equation I(µA) = 7.6286 [H2A] (mmol L-1) + 1.9583, r = 0.9996, for concentrations between 0.0 and 1.4 mmol L-1. The electrode showed high stability and was used for H2A determination in a natural orange juice.

Abstract In this work the synthesis of Ni:Zn:S electrodes is described. The electrodes were prepared on a 316 SS substrate, for its use as electrodes in an alkaline electrolyzer. The synthesis of the electrodes consisted on firstly a nickel electrodeposit on 316 SS using a Watt bath and then by a chemical bath technique to deposit a film that turned out to be ZnS. After this, the electrodes were annealed at 3 different temperatures: 200, 250, and 300 ºC in an inert atmosphere. These electrodes were compared among themselves and against electrodes with only electrodeposit and electrodes without annealing. Studies of XRD show that all electrodes obtained are polycrystalline, and in the case of the nickel electrodes the grain size is of approximately 1 µm (from Scanning Electron Microscopy - SEM). Electrodes in which the chemical bath technique was used, did not show evidence of a ternary compound (i.e. NixZnySz) on the surface. Nevertheless, this compound could be present at the nickel-ZnS interface, for ZnS was observed as wurtzita phase on the suface, which indicates that chemical changes occurred after annealing those samples. By means of Electron Probe X- Ray analysis the presence of nickel oxides were observed on the electrode surface of electrodes with chemical bath, even before the thermal treatment; and when electrochemical tests were carried out with these electrodes, the content of sulfur (S) and zinc (Zn) diminished drastically on the surface of the electrode. Despite this, cyclic voltammetry studies do not show appreciable secondary reactions in the cathodic area, but there is evolution of hydrogen gas in all the electrodes. Also electrodes of Ni:Zn:S annealed at 300°C and 250oC used as cathodes showed acceptable behavior. This was shown by the smaller overpotential for hydrogen evolution compared with that shown by nickel. Chronoamperommetry studies showed that the electrodes have an appropriate stability after 22 hrs.

Resumen En este trabajo se describe la síntesis de electrodos de Ni:Zn:S preparados sobre un substrato de acero inoxidable 316 SS, para su empleo como electrodos en un electrolizador alcalino. La síntesis del electrodo consistió en el electrodepósito de níquel sobre acero inoxidable 316 SS utilizando para ello un baño de Watt y posteriormente la técnica de baño químico para el depósito, de lo que resulta ser una película de ZnS. Esta película se horneó a 3 diferentes temperaturas: 200, 250, y 300 ºC en una atmósfera inerte y las tres películas resultantes se comparan entre sí y contra un electrodo sin hornear y uno sin recubrimiento químico (sólo níquel electrodepositado). Los estudios de difracción de rayos X (DRX) muestran que los electrodos obtenidos son policristalinos, obteniéndose en el caso de los electrodos de níquel, tamaños de grano de aproximadamente 1 µm (vistos en microscopía de barrido electrónico). En los electrodos en los cuales se realizó el baño químico, no se encontró evidencia de algún compuesto ternario (por ejemplo NixZn ySz). Aunque este ultimo pudiera estar presente en la interfase níquel-ZnS, ya que por ejemplo se observó sulfuro de zinc presente como fase wurtzita en la superficie posterio al horneado. Mediante análisis en microsonda se observó la presencia de óxidos de níquel sobre la superficie de los electrodos con baño químico, incluso antes del tratamiento térmico; al hacer pruebas electroquímicas con dichos electrodos, se observa que el contenido de azufre (S) y zinc (Zn) disminuye drásticamente en la superficie del electrodo. No obstante lo anterior, los estudios de voltamperometría cíclica no muestran reacciones secundarias apreciables en la zona catódica, pero sí de evolución de hidrógeno gas en todos los electrodos. Además el comportamiento de los electrodos de Ni:Zn:S horneados a 300 y 250 oC como cátodos son aceptables, ya que su sobrepotencial para la evolución de hidrógeno con respecto al níquel es inferior. La cronoamperometría mostró que los electrodos muestran cierta estabilidad a partir de 22 horas de la prueba.