Zundel-like and eigen-like hydrated protons on a platinum surface

Abstract

The nature of hydrated protons is an important topic in the fundamental study of electrode processes in acidic environment. For example, it is not yet clear whether hydrated protons are formed in the solution or on the electrode surface in the hydrogen evolution reaction on a Pt electrode. Using mass spectrometry and infrared spectroscopy, we show that hydrogen atoms are converted into hydrated protons directly on a Pt(111) surface coadsorbed with hydrogen and water in ultrahigh vacuum. The hydrated protons are preferentially stabilized as multiply hydrated species (H5O2+ and H7O3+) rather than as hydronium (H3O+) ions. These surface-bound hydrated protons may play an important role in the interconversion between adsorbed hydrogen atoms and solvated protons in solution. Hydrated protons on a Pt surface: Adsorbed atomic hydrogen on a Pt(111) surface is ionized to protons with the assistance of adsorbed water, resulting in the formation of protonated water clusters of certain preferential forms (H5O2+ and H7O3+). These surface-bound ions could play an important role in Pt electrode surface reactions.