LAUSR

Abstract Structural changes in water layers on a CO-covered Pt electrode triggered by rapid pulsed laser heating of the interface are studied using potential transient measurements. When the laser energy density is below 20 mJ cm − 2 , the water layers undergo a change in orientation, which causes a negative shift in the rest potential that recovers within 20 μs with the cooling of the interface. In contrast, when the laser intensity exceeds 20 mJ cm − 2 , the CO is desorbed and the rest potential first experiences a positive shift, which is followed by a negative shift. This positive shift is caused by replacement of the CO by water and subsequent restructuring of the water layer. The restructuring rate depends strongly on the electrolyte cation: the rest potential reaches a maximum value within ~ 100 μs for hydrophilic cations such as H + and Li + , whereas it takes > 10 ms for hydrophobic cations such as Et 4 N + and Bu 4 N + . Surface-enhanced IR absorption measurements suggest that the water molecules around the hydrophobic cations are more strongly hydrogen-bonded than those around the hydrophilic cations. Because the restructuring involves a reforming of the hydrogen-bonding network at the electric double layer, Et 4 N + and Bu 4 N + , which have more strongly hydrogen-bonded hydration shells, require more time than H + and Li + .