Double layer capacity and methanol coverage on platinum in perchloric acid solution

Abstract

Measurements of the capacity of the a.c. impedance of a smooth platinum electrode were carried out with 300 c/s at 30°C in 1 N HClO4 with different amounts of methanol as a function of potential in the potential range between hydrogen and oxygen evolution. Polarography with superimposed a.c. voltage was used. The technique is described. The capacity/potential curves allow qualitative conclusions on the methanol adsorption in the hydrogen region, the double layer region, and the region of oxygen adsorption. The conclusions are confirmed by comparison with the results of direct measurements of the methanol coverage. The methanol coverage was computed with the aid of two approximate equations from the double layer capacity and compared with the respective values of the direct determination in the double layer region. The agreement appears satisfactory at higher coverage while the deviations become greater at medium and low coverage.