The mechanism of the hydrogen evolution reaction on niobium is evaluated in alkaline media at 24 °C. The reaction order of zero, along with the observed Tafel slopes of 120 mV/decade (standard deviation 8 mV/dec.), indicate the Heyrovsky reaction mechanism to be applicable for the hydrogen evolution reaction. The presence of anions such as sulfate and chloride does not influence the mechanism.

Le comportement electrochimique du magnesium en milieux legerement alcalins ROBERT-Lours BROSSARDCentre de Recherchrs pour la Defense, Otta,t,a, Otzt., Cette etude a condult a I'elaboration d'un modele qui permet d'expliquer le comportement anodique du magnesium sans faire appel a la formation d'intermediaires. Ce modele lie etroitement les caracteristiques du comportement anodique aux proprietes du produit de corrosion qui se voit traverse par un reseau d e pores dans toute son epaisseur. L e courant et I'hydrogene gazeux circulent par les pores tandis que la nature poreuse de ce film explique qu'il soit faiblement protecteur. Par ailleurs. la surconsommation de magnesium qu'entraine le degagement d'hydrogene s'explique a partir de la dissolution de fines particules de magnesium prisonnieres dans le produit de corrosion. De plus, I'activation de I'electrode des le retour a I'abandon est attribue a la mise a nu du metal a I'extremite des pores durant la dissolution anodique.Enfin. la substitution des chlorures par les sulfates comme electrolyte n'affecte nullement la valeur de la tension corrigee de I'anode pour la chute ohmique qui demeurc constantc a -1.65 V (1E.C.S.) approximativement. ROBERT-LOUIS BROSSARD and D O M I~I Q U E -L O U I SP I R O~. Can. J . Chem. 58,30(1980). This study of the anodic behavior of magnesium in simulated seawater has shown that the corrosion product formed at the surface of the electrode depends mainly on the nature of ions dissolved in the electrolyte. Analyses of the corrosion product, formed in the presence of a high concentration of chloride ions. are compatible with the formation of a compound having approximately the formula 5Mg(OH),.MgCI,. However, this complex is gradually transformed over a period of several hours into Mg(OH),.A model of the oxidation mechanism is presented in which the characteristics of the anodic behavior of magnesium are related to the structure of the oxidation layer. For example, the activation of the surface of the anode, the kinetics of the hydrogen evolution reaction. and the large difference between values of corrected and uncorrected electrode potential can all be explained by this model. It is the resistance of the film to the flow of current which controls the kinetics of anodic dissolution of magnesium.

The model proposed by Vijh of an emf produced by a metal-oxide reaction in metal(1) -polymer-metal(2) cannot explain many experimental observations including the presence of a voltage under a vacuum, the influence of different polymers upon this voltage and its temperature dependence. These observations can be understood if protons are released from residual acid groups in the polymer and not by the electrochemical reaction itself.

The cathodic and photocathodic behavior of electrodes of phthalocyanines without metal or complexed to copper or iron (H2Pc, CuPc, and FePc) has been studied in acidic, neutral, and alkaline media. In the dark, the polarization curve of the electrode of FePc shows two peaks of reduction which are not observed with the other phthalocyanines; these are associated with the reduction of the central cation. Lighting the semiconducting electrodes does not produce any effect on the reaction of production of hydrogen. An analysis of the curves of capacity vs. potential indicates the presence of intermediate levels localized within the forbidden band of the semiconductors and covering about 1% of their sites on the surface. The results can be explained if the phthalocyanines are considered to be semiconducting electrodes of type p. The energy of the bands and of the surface states can be depicted with a semiconductor–electrolyte interphase model and the nature of the charge transfers inhibited by the presence of these interfacial states is discussed. [Journal translation]