Effect of Adsorbed Sulfate on the Product Selectivity of Ethanol Oxidation on Pt Nanoparticles in Acidic Solution

Abstract

Herein, the effect of adsorbed sulfate on product selectivity in the electrooxidation of ethanol on a Pt electrode in acidic media was studied by comparing it with nonspecifically adsorbed perchlorate using cyclic voltammetry and chronoamperometry combined with high-performance liquid chromatography. The current density and product concentration show the first and second oxidation peaks at about 0.85 V (vs RHE) and about 1.25 V (vs RHE), respectively. Specifically adsorbed sulfate inhibits ethanol electrooxidation by the competitive adsorption with ethanol, and it especially has a stronger inhibition on the second peak primarily due to the H-bond interaction in Pt–OHads···SO42– that increases the difficulty of Pt–Ox formation. However, compared with the product concentration in perchlorate solution, the specifically adsorbed sulfate reverses the product distribution at the first peak; i.e., it considerably strengthens the formation of acetic acid. Additionally, the selectivity of acetic acid increases with the increasing pH of sulfate solutions at the upper potential, while the product selectivity is almost insensitive to the pH of the perchlorate solution. Combined with density functional theory calculations, these results reveal that adsorbed sulfate strengthens the adsorption of the key intermediate, geminal diol, on the Pt surface and then coadsorption of sulfate and active O-containing species increases the selectivity of acetic acid. Similar considerations may be applied to other specifically adsorbed ions, emphasizing that the electrolyte may affect not only the activity but also the reaction selectivity of electrocatalysis.