Hydrogen Adsorption on Platinum Single Crystal Electrodes: I . Isotherms and Heats of Adsorption

Abstract

The adsorption of hydrogen on the three main faces (100), (111), and (110) of platinum single crystal electrodes has been studied in at different temperatures with the voltage sweep method. As on polycrystalline platinum electrodes, hydrogen adsorbs on each of the faces in two distinctly different binding states which present themselves as two pronounced maxima in the current‐voltage sweep curves. There are indications for a third binding state giving rise to a third, less pronounced maximum. The potentials at which the maxima occur are essentially the same for polycrystalline and for each of the three single crystal electrodes. However, the relative heights of the maxima are different in each case. The adsorption isotherms and the heats of adsorption are also notably different on the three faces. Under the usual assumption of one hydrogen atom adsorbed per platinum surface atom, initial roughness factors of 1.0–1.9 result which increase to 1.9–2.4 during the experiments. The results suggest that, in fact, each of the crystal faces exposes more than one crystal plane. The left pronounced maximum is assigned to a (110) plane, the right pronounced maximum to a (100) plane, and the third small maximum to a (111) plane. Different proportions of these planes determine the different shape of the curves obtained on the different nominal faces and on polycrystalline electrodes.