A mechanistic study of the electrochemical oxygen reduction on the model semiconductor n-Ge(100) by ATR-IR and DFT

The electrochemical oxygen reduction reaction (ORR) on a n-Ge(100) surface in 0.1 M HClO4 was investigated in situ and operando using a combination of attenuated total reflection infrared (ATR-IR) spectroscopy and density functional (DFT) calculations. The vibrational modes of the detected intermediates were assigned based on DFT calculations of solvated model clusters such as Ge-bound superoxides and peroxides. ATR-IR shows the Ge-bound superoxide with a transition dipole moment oriented at (28 ± 10)° with respect to the surface normal. At slightly negative potentials, the surface-bound peroxide is identified by an OOH bending mode as a further intermediate, oriented at a similar angle. At strongly negative potentials, a surface-bound perchlorate is found. The findings indicate a multistep mechanism of the ORR. The reaction is furthermore coupled with the hydrogen evolution reaction (HER).