Ethylene glycol partial oxidation on Co3O4 (001) surface: Interplay between solute’s surface coverage and aqueous solvation

Abstract

Using ab initio molecular dynamics simulations, we investigate the coverage dependent adsorption and decomposition of ethylene glycol (Egly), from the low coverage regime to surface saturation (0.13 ML to 0.44 ML) on the B-terminated Co₃O₄ (001) surface in dry and humid environments. We have analyzed the structure of Egly at the interface and identified the most probable binding mode and conformations. In dry conditions, Egly binds to the surface mostly via a bidendate mode and in a gauche conformation. Only single deprotonation events occur, leading to the formation of OHCH₂CH₂O species. A neutral aqueous solvent barely alters the situation. In the presence of a hydroxyl-rich aqueous solvent, OHCH₂CH₂O intermediates further decompose to form glycolaldehyde, which evolves to acetate and coexist together with OHCH₂CH₂O and OCH₂CH₂O species. This behavior holds from low coverage to half-saturation of the surface (up to 0.25 ML). Higher Egly population hinders oxidation and only hydrogen peroxide forms in favorable cases. Our work provides insight into the complex interplay between key factors governing the two-electron oxidation: the role of solvation, the relevant solute’s concentration range, the size of the active surface regions as well as the chemical state of interfacial water and its competition with Egly.