Berlin 2024 – scientific programme

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O: Fachverband Oberflächenphysik

O 32: Poster: Solid-Liquid Interfaces

O 32.4: Poster

Tuesday, March 19, 2024, 18:00–20:00, Poster C

Detection of surface intermediates for oxygen evolution on hematite using operando sum frequency spectroscopy — •Yuke Yang, Yujin Tong, and R. Kramer Campen — Faculty of Physics, University of Dusiburg-Essen, 47057 Duisburg, Germany

Hematite (α-Fe₂O₃) is a photoanode material that is widely studied for photoelectrochemical oxygen evolution (OER) due to its abundance, stability, non-toxicity, etc. However, the mechanism of OER on hematite that limits its performance is still undetermined. There is still controversy over single- and multi-hole mechanisms depending on the sample and electrolyte. Methods to probe the OER mechanism are indirect and thus possible control of the mechanism by the change in the sample is difficult to infer. Vibrational sum frequency spectroscopy (VSFS) is an interface-specific technique for systems containing bulk phases with inversion symmetry, which allows the direct observation of intermediates. Our VSFS results reveal the bias-dependent (dis)appearance of a succession of intermediates such as Fe-OH, Fe=O, and Fe-OOH. The results unambiguously show that the OER on our sample proceeds via a single-hole mechanism at pH 12.8. Additionally, we observe a bias-dependent surface phonon mode at around 650cm-1 due to lattice distortion, which may be related to the polaron formation and transport. Because of femtosecond pulses in the VSFS measurement, this work also suggests a path toward resolving chemical dynamics on ultrafast timescales.

Keywords: Photoelectrochemistry; OER mechanism; Surface intermediates; Vibrational sum frequency spectroscopy