The interfacial capacitance of Rh(111) in HCl solutions

The impedance spectra of Rh(111) in aqueous HCl solutions have been measured as function of potential. In the double layer region, just as for other platinum group metals, the equivalent circuit of the interface is a circuit of a R ad – W– C ad element combination parallely connected to a C dl capacitance; whereas at the H +/Cl − adsorbate exchange peak an additional parallel R ad,2 – C ad,2 branch appears in the equivalent circuit. The ( R ad – W– C ad ) and the R ad,2 – C ad,2 branches were demonstrated to be due to chloride and hydrogen adsorption, respectively. Due to the same anion appearing in the charging of C ad and C dl the two branches are coupled to each other.