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 vario us electrolytes. They can all be interpreted by assuming one or two paralle l adsorption resistances in addition to the double layer capacity. Adsorpti on of Cl- and HSO4- at Pt(111) is very fast and at the limit of detectabili ty. Adsorption of H2PO4- has to be described by two parallel adsorption rea ctions, 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 ad sorption rate at Rh. (C) 1998 Elsevier Science Ltd. All rights reserved.