Electrocatalyst anion adsorption

It is suggested that the anodic dissolution will be inhibited if the adsorbed anion and the reaction intermediate are stable and hardly dissolve in aqueous solution. On the contrary, if the reaction intermediate is relatively unstable and readily dissolves into aqueous solution, the anion will function as an electrocatalyst accelerating the metal dissolution rate. It is now common knowledge that hydroxide ions, OH, catalyze the anodic dissolution of metallic iron and nickel in acid solution [81,82]. It is also known that chloride ions inhibit the anodic dissolution of iron in acidic solution [83]. No clear-cut understanding is however seen in literature on why hydroxide ions catalyze but chloride ions inhibit the anodic dissolution of iron, even though the two kinds of anions are in the same group of hard base. We assume that the hardness level in the Lewis base of adsorbed anions will be one of the most effective factors that determine the catalytic activity of the adsorbates. Further clarification on the catalytic characteristics will require a quantum chemical approach to the adsorption of these anions on the metal surface. 

Finally, combined Ap XANES and EXAFS studies have recently been reported on other more complex electrocatalysts, including RuS," "" RhSe, Au/SnOx, Pt/NbOx, " and Pt/TPPTP/C (TPPTP = triphenyl phosphine triphosphate) " catalysts. The Ap XANES has also been used to study the effects of anion adsorption on Pt including bisulfate " and Cl,"" differentiate the various oxidation states of S dming the electrochemical oxidation of S on Pt ", and identify acetaldehyde-like intermediates during ethanol oxidation on Pt. In all of these studies, unprecedented new details on the coverage and binding sites of adsorbates in situ have been revealed. Further, similar XAS studies in gas phase cat-... 

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