In situ dual-beam coincidence second harmonic generation as a probe of spatially resolved dynamics at electrochemical interfaces

In situ dual-beam coincidence second harmonic generation was used to monitor spatially resolved dynamics at the Pt(111)/CO-saturated 0.1 M HClO₄ interface. The results obtained showed that, for potential steps from 30 to about 870 mV vs RHE, the full electrooxidation of CO as evidenced from SHG occurred at different times for the two areas of the Pt(111) surface probed by the beams. On this basis, the diffusional rates of adsorbed CO cannot be assumed to be generally large enough as to render the entire surface in a homogeneous state, as invoked by the mean field approximation model.