Predicting the Double Layer Width on Pt(111) in Acid and Base with Theory and Extracting It from Experimental Voltammograms
2017
Zhao, Meng | Anderson, Alfred B.
Voltammograms measured for carefully prepared Pt(111) electrodes by the Alicante group show the presence of pH dependencies in the onset potentials for under potential deposited H deposition and for OH deposition from water oxidation. In this article we show that the second derivatives of voltammograms can be used to provide consistent and useful measures of the onset potentials for H and OH deposition. From analysis of the voltammograms, we find an increase in the width of the double layer potential region, beginning at 0.19 V and ending at 0.31 V, over the pH range of 1 to 14. We use density functional theory to calculate the onset potentials for 13 different water structures on Pt(111) and find the experimental trend is produced when the OH(ads) oxidation product surface is saturated with water molecules. The theory indicates that the onset potentials for OH₍ₐdₛ₎ coverages exceeding 1/3 ML are high, and in acidic electrolyte the potentials exceed those for OH₍ₐdₛ₎ oxidation to O₍ₐdₛ₎.
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