The rate of anion and hydrogen adsorption on Pt(111) and Rh(111)

Impedance spectra were measured for Pt(111) and Rh(111) electrodes in various electrolytes. They can all be interpreted by assuming one or two parallel adsorption resistances in addition to the double layer capacity. Adsorption of Cl − and HSO 4 − at Pt(111) is very fast and at the limit of detectability. Adsorption of H 2PO 4 − has to be described by two parallel adsorption reactions, one of which is possibly an adsorption connected with deprotonation. Adsorption of hydrogen at Rh(111) is much slower than at Pt(111); surface roughness has opposing effects on both metals and leads to an increased adsorption rate at Rh.