Portugaliae
Electrochimica Acta

The electrocatalytic property of electrode materials is the key for getting high cell current and low overvoltage of a fuel cell from fuels electro-oxidation. The bridge between laboratory scale fuel cell development and its fully commercialization is the development of inexpensive but energetic electrode materials. The catalytic actions of an electrode substrate are strongly influenced by the morphology and the grain fineness of the deposited materials. The present investigation aims at finding the effect of electrode deposition mode viz. direct current and pulse current coating, to produce an electrodeposited substrate that can deliver the highest current in a direct ethanol fuel cell. Nickel (Ni) is one of such non precious materials which has been produced through electro synthesis by both pulse current (PC) and direct current (DC) coating. It has been found that the morphology of the deposited is highly influenced by the current density, duty cycle, electrolyte chemistry and right selection of deposition potential on the cathodic polarization curve around the Tafel lines. Electrochemical characterization has been done by cyclic voltammetry (CV), chronoamperometry (CA) and potentiodynamic polarization (PD) studies. The substrate of the electrodeposited material has also been characterized by X-Ray Diffraction analysis (XRD), Energy Dispersive X-Ray Analysis (EDXA) and Scanning Electron Microscope (SEM). It has also been found that the electro synthesis by pulse current coating at pre-selected deposition potential, right at the end of Tafel region, at 40 ºC temperature and 150 second deposition time, gives the highest delivering current of ethanol fuel oxidation.

The inhibiting effect of Ailanthus altissima aqueous extract, as a corrosion inhibitor for Zn in a 0.5 M HCl solution, has been evaluated by weight loss (WL), hydrogen evolution (HE), potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. Obtained results showed that this extract offered good protection against Zn corrosion, and exhibited high inhibition efficiencies. The IE was found to increase with an increasing extract dose. Results revealed that this extract acted as a mixed-type inhibitor, and adsorbed onto the Zn surface following Temkin isotherm. Obtained results were justified from the study of surface morphology.

This paper deals with the theory and kinetics of oxalic acid electrochemical oxidation, in an acidic solution containing sodium chloride, using a manganese dioxide rotating cylinder anode. Voltammetric and galvanostatic electrolysis techniques were used. The voltametric study shows a higher anodic wave corresponding to chlorine oxidation on the MnO2 electrode, prevailing oxalic acid indirect oxidation. Galvanostatic electrolysis studies confirmed that the rate constant is affected by chloride concentration, current density, agitation and temperature. Electrochemical oxidation rate was found to be a pseudo-first order kinetic process. A strongly linear relationship between the rate constant and chloride concentration was observed, while polynomial relations, with respect to current density and temperature, were found. The activation energy was found to be 14.541 kJ/mol, which suggests a diffusion control kinetic step in oxalic acid degradation. The findings of the present research validate that oxalic acid incineration can be successfully carried out on a MnO2 anode, in NaCl presence.

Thymus Sahraouian essential oil (TSEO), as a new corrosion eco-friendly inhibitor, has been used to protect mild steel in 1 M HCl. Weight loss, three potentiodynamic polarization methods (Tafel, Stern and Stern-Geary), and electrochemical impedance spectroscopy measurements were undertaken to evaluate corrosion inhibition by TSEO. TSEO acted as an efficient corrosion inhibitor for mild steel in 1 M HCl, and its inhibition efficiency increased with a concentration of 77.82 % at 2 g L-1. The polarization curves revealed that TSEO acted as a mixed type inhibitor, with predominant anodic action. The EIS studies were fitted to a suitable equivalent circuit model, at 293 K, only reflecting a one-time constant characteristic of a charge transfer process. Besides, the higher is the temperature the lowest is the inhibiting efficiency. The kinetic parameters were in favour of an electrostatic character of TSEO components adsorption onto the mild steel surface, and adsorption followed the Langmuir isotherm model. Micrographic scanning electron microscopy and energy dispersive X-ray spectroscopy analyses confirmed the formation of a protective adsorbed film upon the mild steel surface.

Conducting polypyrrole was synthesized, and applied with a paint coating on a low carbon steel sample. By using linear polarization technique, the corrosion rates of uncoated and painted low carbon steel samples, in 3.5 wt% NaCl, were determined, and found to be 5 mpy and 0.1 mpy, respectively. The uncoated and conducting polypyrrole coated steel samples were immersed in a simulated carbonated concrete pore solution, and electrochemical studies were carried out. The shift of corrosion potential in the positive direction implies that the polypyrrole coating gives corrosion protection to low carbon steel, in the anodic direction. As compared to uncoated low carbon samples, polypyrrole coated low carbon steel samples exhibited higher impedance values, but their corrosion resistance decreased with increasing chloride ions in a carbonated pore solution.