posted on 2020-09-18, 15:37authored byRuipeng Bai, Man Xue, Yuan Lin, Rui Wen, Yuan Guo, Zhen Zhang
Adsorption mechanisms
and electrochemical reaction mechanisms at
the molecular level are fundamental issues in electrochemistry. Here,
we used in situ second harmonic generation (SHG) combined with in
situ UV–vis spectra and potential step techniques to investigate
the dynamics of the adsorption and oxidation of 4-amino-4′-nitroazobenzene
(disperse orange 3, DO3) molecules on a polycrystalline Pt electrode.
Time-dependent SHG spectra with different polarization combinations
under certain potential steps confirmed that the SHG intensity change
in the DO3 molecules resulted from the number density change rather
than the orientation angle change. A double potential step experiment
and UV–vis spectra verified that the number density change
arose from the cooperative effects of adsorption and oxidation of
DO3 at the interfaces. Under an applied potential, the adsorption
rate of DO3 was greater than the electrooxidation rate in the first
hundred seconds until full coverage was achieved and the maximum SHG
intensity was reached. Subsequently, the oxidation of DO3 dominated
until equilibrium was established, while the SHG intensity stabilized.
In addition, the time-dependent SHG spectra showed that the rate constants
of the adsorption process and the oxidation reaction were strongly
dependent on the potential. This work provides in-depth insights into
the adsorption and electrochemical reaction at electrode/solution
interfaces.