Kinetics of hydrogen underpotential deposition at polycrystalline rhodium in acidic solutions

Kinetics of hydrogen underpotential deposition (H UPD) reaction at smooth polycrystalline rhodium wire has been studied in 0.1 M H₂SO₄ and HClO₄ using cyclic voltammetry and electrochemical impedance spectroscopy. Real surface area of the Rh electrodes was determined by hydrogen adsorption method.For all impedance spectra registered at potentials corresponding to the H UPD deviations from the ideal capacitive behavior was revealed and a constant phase element was used instead of capacitance for description of Rh impedance behavior. Double layer and adsorption capacitances and charge transfer resistances of the H UPD were determined as functions of the electrode potential. It has been found that the kinetics of the H UPD reaction at Rh is slower than that at polycrystalline Pt but similar to that found at polycrystalline Ru. Slightly higher values of R_ct were determined in perchloric acid.