Infrared Reflection Absorption Spectroscopy of the Sulfuric Acid Anion on Low and High Index Planes of Palladium

The sulfuric acid anion (HSO 4 - or SO 4 2- ) adsorbed on Pd single-crystal electrodes was studied using infrared reflection absorption spectroscopy (IRAS) in 0.05 M H 2 SO 4 solution. Surfaces examined are flat ones (Pd(111) and Pd(100)) and stepped ones (Pd(110) (= 2(111)−(111)) and Pd(311) (= 2(111)−(100))). All of the surfaces give a single IRAS band around 1200 cm -1 that is assigned to S−O stretching vibration. The integrated band intensity depends on the crystal orientation significantly, i.e., Pd(311) ∼ Pd(110) ≪ Pd(100) < Pd(111), showing that the flat surfaces adsorb more sulfuric acid anion than the stepped ones. Magnitude of the band shift (d ν /d E ) on the flat surfaces is nearly twice as high as that on the stepped ones.