Infrared Reflection Absorption Spectroscopy of Sulfuric Acid Anion Adsorbed on Stepped Surfaces of Platinum Single-Crystal Electrodes

Abstract

Adsorption of sulfuric acid anion (HSO 4 - or SO 4 2- ) was studied using IRAS (infrared reflection absorption spectroscopy) on Pt(S)-[ n (111) × (111)] and Pt(S)-[ n (100) × (111)] electrodes in 0.05 M H 2 SO 4 . Pt(S)-[ n (111) × (111)] electrodes give two IRAS bands. One is from a sulfuric acid anion adsorbed on the terrace with 3-fold symmetry (∼1200 cm -1 ), and another is from that on the step with 2-fold symmetry (∼1200 cm -1 and ∼1100 cm -1 ). Relative band intensity from the 2-fold sulfuric acid anion (∼1100 cm -1 ) gets higher with the increase of step atom density. Pt(S)-[ n (100) × (111)] electrodes also show two IRAS bands around 1200 and 1100 cm -1 which originate from the sulfuric acid anion adsorbed on the terrace and the step with 2-fold symmetry. The relative intensity of the lower frequency band increased with the increase of the step atom density.