Zero charge potentials and work function of rhodium

The data on the behavior of rhodium and platinum electroplates in sulfate solutions acquired by the method of potentiometric titration under isoelectric conditions are presented. These results are compared with the data obtained earlier by the same method for rhodium and platinum in chloride media. The potentials of zero free charge (pzfc) and zero total charge (pztc) and their dependence on the solution pH are determined. The reasons for the pH-induced changes in the dependences of the free surface charge on the potential are analyzed. It is demonstrated that the measurements on electrodes of disperse materials make it possible to assess the reliability of certain procedures used in processing the data found by the CO-displacement method and also in the determination of pztc and pzfc of single-crystal faces and other well characterized surfaces of platinum-group metals. The data on pztc and potentials of zero displaced charges (pzdc) for disperse and polycrystalline rhodium electrodes, rhodium single crystal faces and Rh adlayers on platinum crystal faces are summarized. The correlation between the potentials of zero charge (pzc) and the electron work function is considered. Actually, both pzfc and pztc can be used in building such correlations; however, preference should be given to the former. It is concluded that together with platinum and palladium, rhodium pertains to materials with the high interfacial term, which is probably due to the strong chemisorption of water on its surface.

► The pH-induced changes in EDL structure of Pt metals are analysed on basis of thermodynamics of perfectly polarizable electrode.
► The data for disperse materials, single-crystal faces and other well characterized surfaces are compared.
► The correlation between the potentials of zero charge and electron work functions is considered.
► Together with Pt and Pd, Rh pertains to materials with the high interfacial term.