Adsorption and Oxidation of Formate at Au Electrodes

Date

2013-12-24

Authors

Strobl, Jonathan Richard

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Abstract

This work focuses on tracking formic acid adsorption as formate onto polycrystalline gold and its subsequent catalyzed oxidation to carbon dioxide. Formic acid oxidation is notoriously dependent on supporting electrolyte composition, a dependency that is little characterized. Additionally, the mechanism of oxidation is in disagreement in the literature. As such, the two preceding topics are the primary focus of this work, and are studied in HClO4 and H2SO4 solutions. Cyclic voltammetry experiments supplemented by mathematical modelling and fitting of data were used. Solution pH and adsorption of supporting electrolyte anions onto Au(poly) were very influential factors in determining formate coverages on Au(poly). This alone explains the effect of supporting electrolyte on this reaction. The coverage of adsorbed formate was found to be singularly responsible for determining the rate of formic acid oxidation. This implies a chemical rate limiting step for oxidation, leaving the oxidation rate constant independent of potential. Another segment of this work focuses on the statistical mechanics of lattice gases, namely the role of sites available for adsorption on the activity. This topic is central to the modelling of multiple adsorbing species in competition for the same adsorption sites. Activity for interaction-free lattice gases in the thermodynamic limit was found to be coverage of adsorbates over coverage of sites available for adsorption. This relationship was exploited to simulate coadsorption of two species, the first obeying the Langmuir isotherm and the second following the hard hexagon isotherm. This system was originally considered as a possible model for coadsorption of formate and sulfate in H2SO4 solutions, but did not match with data.

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Keywords

electrocatalysis, Formic Acid, Adsorption, kinetic mechanism

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