Kinetics of hydrogen underpotential deposition at ruthenium in acidic solutions

Kinetics of the hydrogen underpotential deposition (H UPD) reaction at polycrystalline ruthenium in 0.1 M H2SO4 and HClO4 solutions was studied using cyclic voltammetry and electrochemical impedance spectroscopy. Surface of Ru electrode was prepared by: (i) simple mechanical polishing and (ii) polishing followed by cleaning in concentrated HNO3 and reduction at −0.05 V.The electrode real surface area was determined from the copper UPD charge and the specific double layer capacitance was estimated from impedance. The charge transfer resistance and double layer and adsorption capacitances were determined as functions of the electrode preparation method and anodic limit of the potential sweep in cyclic voltammetry.The kinetics is faster in sulfuric than in perchloric acid but cycling to positive potentials has smaller effect on the charge transfer resistance. It has been found that the kinetics of the H UPD at Ru is much slower than that at Pt and even slower than at Pd. The obtained results could give a new insight into electrosorption properties of the ruthenium catalyst.