In situ SEIRAS experiments. Au films were deposited onto Si ATR prisms by the chemical deposition method as described in our previous works A custom spectroelectrochemical cell with a three-electrode configuration was employed for all in-situ SEIRAS experiments 2 . Au film, a graphite rod and a 3.5 M KCl Ag/AgCl electrode were used as working, counter, and reference electrodes, respectively. The cell was placed into the sample compartment of the Bruker INVENIO ® FTIR Spectrometer equipped with a liquid nitrogen-cooled mercury cadmium telluride (MCT) detector. Cell potential was controlled by a Biologic SP150 potentiostat. All spectra were collected at a 4 cm -1 spectral resolution and corresponded to 64 coadded scans. (1) 3560 cm -1 with a peak width of 160 cm -1 (isolated water), ( ) 3410 cm -1 with a peak width of 260 cm -1 (asymmetrically H-bonded water) and ( ) 3200 cm -1 with a peak width of 280 cm -1 (symmetrically H-bonded water). based on the modified MHC formalism developed by Hammes-Schiffer and co-workers , the rate constant of PCET, 𝑘 &'! , could be expressed as: