Oxygen Reduction Reaction on Au Revisited at Different pH Values using in situ Surface-Enhanced Raman Spectroscopy.

The mechanisms of the oxygen reduction reaction (ORR) on Au surfaces are revisited in electrolytes with different pH values by using a combination of electrochemical and in situ surface-enhanced Raman scattering spectroscopy. Surprisingly, the in situ Raman signal of the O-O stretching vibration was detected during the ORR on a Au surface by using a λ=785 nm laser. Both the intermediate products O and H O could be detected, which indicates the difficulty of the further reduction H O and results in a lower electron transfer number, especially in neutral and acid electrolytes. The weak absorption ability of HO on the Au surface may explain the poor ORR in neutral and acid electrolytes. This work not only provides a deep insight to understand the reduction mechanisms of O on Au in electrolytes with different pH values but also supplies a new idea for the selection and optimization of electrolytes and efficient electrocatalysts for oxygen reduction.