(669e) Descriptors for Electrochemical Anion Adsorption and the Mechanism of Electrocatalytic Glycolic Acid Oxidation

The specific adsorption of anions is important in (electro)catalysis, as many anions are reactants (nitrate, formate) [1,2] or site-blocking spectators (sulfate, phosphate, acetate) [3,4] in many (electro)catalytic reactions. Their adsorption energy onto the electrode surface dictates their coverage, and therefore the activity and selectivity of these reactions. Using a combination of density functional theory computational modeling and detailed experiments on well-defined single-crystal electrodes, we have identified a molecular property of anions that is linearly correlated to their adsorption energies (at least across a set of structurally similar anions). We can therefore use this property as a descriptor to predict their adsorption energetics. We additionally used experiments on both single-crystal and polycrystalline platinum electrodes to understand the mechanism of glycolic acid oxidation, finding that the adsorbed glycolate anion is a reactive intermediate. By investigating the role of glycolate/glycolic-acid concentration and electrolyte pH, we find changing (and sometimes negative) reaction orders, which can be explained by a rate determining step which involves both adsorbed glycolate and adsorbed hydroxide, at least on Pt(111). While glycolic acid electrocatalytic oxidation could be industrially relevant, in (waste)water treatment or in glycolic acid fuel cells, the rate of this reaction on platinum is quite low. Therefore, we will instead discuss how a mechanistic understanding of glycolate oxidation can be used to help us understand that of other small molecules, such as methanol, ethylene glycol, and formic acid (which are kinetically faster but more complex).

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2. S.-E. Bae, K.L. Stewart, A.A. Gewirth; J. Am. Chem. Soc., 129, 10171-10180 (2007).
3. A.Cuesta, M. Escudero, B. Lanova, H. Baltruschat; Langmuir, 25, 6500-6507 (2009).
4. X. Chen, L.P. Granda-Marulanda, I.T. McCrum, M. Koper; Nature Communications, 13:38, 1-11 (2022).