Electrochemical study on the poisoning intermediate formed from methanol dissociation at low index and stepped platinum surfaces

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Abstract

Self-poisoning in the electrocatalytic oxidation of small organic molecules is a fundamental subject in electrocatalysis. This phenomenon is due to an intermediate, denoted the poisoning intermediate or poison, which may be formed according to a spontaneous dissociation process. The poison formed from methanol dissociation at platinum is studied electrochemically in this paper using as electrocatalysts eleven platinum single-crystal planes (Pt (100), Pt (111), Pt (110), Pt (310), Pt (511), Pt (610), Pt (211), Pt (331), Pt (332), Pt (320), Pt (210)) and one platinum polyonented surface. The results show that the poison formation as well as its oxidation depend strongly on the platinum surface structure. For a given orientation, quantitative analysis shows that the poison formed from methanol dissociation behaves in a similar way to the poison formed from formic acid dissociation. The number (n) of electrons transferred per hydrogen site to oxidize and to desorb the poison never exceeds 2. Values of n close to 2 are obtained with Pt (111), Pt (100) and surfaces having (100) terraces in the absence of specific adsorption of anions. In a general way, for a given orientation the value of n decreases when specific adsorption of anions occurs, i.e. when perchloric anions are replaced by sulphuric anions. This has been interpreted as a change in the mode of bonding of the poison to the surface. The maximum value of 2 for n suggests, in agreement with EMIRS results, that the poison in this case may be a CO-like species linearly bound to the surface. Other modes of bonding are assumed to be present simultaneously at the surface for lower n values, principally linear and bridged CO.

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