SFG study of platinum electrodes in perchloric acid solutions

Infrared–visible sum-frequency generation (SFG) spectroscopy has been used to study the structure of water molecules (and/or its derivatives OH−, H3O+ etc.) at aqueous electrolyte/electrode interfaces. For Pt(1 1 0) and Pt(1 0 0) electrodes in 0.1 M perchloric acid solution, we did not observe any significant O–H stretching resonance. In striking contrast to the resonant SFG signal, the nonresonant SFG (NRSFG) signal varies sensitively with the applied electrochemical potential, indicating that the interaction of water molecules with platinum electrodes is relatively weak as compared to that of H+ and ClO4− ions. From changes in the NRSFG signal and on the basis of an ionic adsorption model, we can also deduce that the potential of zero charge of Pt(1 1 0) in 0.1 M HClO4 should be located at about 0.22 V (vs. NHE). This value is in good agreement with that measured recently by electrochemical method.