The adsorption of hydrogen atoms oil a polycrystalline Pt electrode was examined in acid by surface-enhanced infrared (IR) spectroscopy, and the IR data was quantitatively compared with the kinetics of hydrogen evolution reaction (HER). The Pt-H stretching vibration was observed around 2100 cm(-1) in the H, evolution potential range (E < 0.1 V vs. RHE). The current of HER was proportional to the square of the band intensity at 0.02 < E < 0. 1 V. from which it was concluded that the adsorbed hydrogen atom is the reaction intermediate of HER and the combination of two adsorbed hydrogen atoms is rate-deter-mining. At E < 0.02 V. on the other hand, an inconsistency was found between the IR and electrochemical measurements due to the supersaturation of H-2 at the interface. (C) 2004 Elsevier B.V. All rights reserved.