Study of the Pt (111) | electrolyte interface in the region close to neutral pH solutions by the laser induced temperature jump technique

Abstract

The laser-induced temperature jump method is used to determine the potential of maximum entropy (pme) of a Pt(111) single crystal electrode in contact with an aqueous solution, in a wide pH range and in the absence of specifically adsorbed anions. For this purpose, buffer solutions composed of a mixture of NaF and HClO4 are used. The results are compared with those from non-buffered perchlorate solutions. The use of the NaF/HF buffer allows extending the pH range from 3 to 6, approaching the situation of a neutral pH. Laser experiments show that the pme appears located at nearly the same potential position in the whole pH range between 3 and 6. This value is around 300mV vs SHE, in agreement with previous works. Moreover, the potential response to the fast thermal perturbation at high potentials, above the pme, indicates the presence of a slower contribution, resulting in a bipolar, non-monotonous, profile. Such behaviour is strongly affected by the presence of fluoride anion and/or hydrofluoric acid, thus evidencing a strong structural effect on interfacial water from these species. These results bring some light to the understanding of the interfacial properties in acid-neutral conditions, and also show the influence of different non-specifically adsorbed anions on the interfacial properties that cannot be evidenced only by cyclic voltammetry.