Regensburg 2019 – scientific programme

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O: Fachverband Oberflächenphysik

O 23: Solid-Liquid Interfaces II: Electrode Surfaces

O 23.2: Talk

Tuesday, April 2, 2019, 11:00–11:15, H5

Resolving the chemical identity of H₂SO₄ derived anions adsorbed on a Pt(111) electrode: they are sulfate. — R. Kramer Campen, Gregor Zwaschka, Igor Ying Zhang, Martin Wolf, and •Yujin Tong — Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany

One of the model systems in electrochemistry that has been extensively studied is the adsorption of sulfuric acid anions on Pt(111) electrode in acidic solution. While many properties of the adsorbed anion have been well resolved, its chemical nature, whether it is sulfate (SO₄²⁻) or bisulfate (HSO₄⁻) is still under debate. The controversy mainly originates from the difficulty in assigning the vibrational mode around 1250 cm⁻¹ which has been observed in previous infrared spectroscopic measurements. Here we apply interface-specific, vibrational sum frequency generation (VSF) spectroscopy and theoretical simulation to this problem. By taking advantage of the background-free nature of VSF spectroscopy, we are able to perform more reliable isotope exchange measurements than those done with conventional infrared spectroscopy. The chemical identity of the adsorbate is unambiguously revealed: it is SO₄²⁻ rather than HSO₄⁻ that adsorbed at the surface even in acidic solution (pH=0), where the dominate solute is essentially HSO₄⁻. The distinct different chemical nature of the anion at the surface and in the bulk suggests intriguing interaction between the electrode and the anions.