Dynamics of double-layer restructuring on a platinum electrode covered by CO: Laser-induced potential transient measurement

The dynamic behavior of water molecules on CO-covered Pt electrode has been studied by laser induced temperature jump method. A 532-nm laser pulse quickly heats up the interface (δT ≈ 90 K) and perturbs the orientation of water, which results in a negative jump of the rest potential. The potential is relaxed with cooling the substrate (∼20 μs). This behavior is identical to that on the CO-free surface, but the amplitude of the negative jump is more than 30 times larger on the CO-covered surface. This large difference can be ascribed to the differences in the electric field at the interface and also in the interactions of water-Pt and water-CO; water is more flexible on CO. At high laser power densities exceed a threshold, the negative potential jump is followed by a slightly slower (∼70 μs) irreversible potential shift toward the positive direction. Infrared reflection absorption spectroscopy and picosecond two-pulse correlation experiments reveal that the subsequent positive shift arises from thermally activated desorption of CO. Adsorption of water and restructuring of the electric double layer after CO desorption is responsible to the positive shift. The rate of restructuring becomes slower as the initial potential becomes lower due to the increase in the electric field and the number of hydrated cations. The intense field and the hydrogen-bonding affect water structure in a long-range and enhance the collective motion of the water layers.