Abstract
Surface structures of Pd(111) and Pd(100) electrodes have been determined at 0.50 V (RHE) in 0.1 M HClO4 saturated with Ar or O2 using surface X-ray scattering (SXS). Both surfaces have unreconstructed (1×1) in-plane structure. The surface layers on Pd(111) do not relax in Ar saturated solution: the interlayer spacing between the first and the second layers d12 agrees with that of the bulk. In O2 saturated solution, the value of d12 is expanded by 1.8% on Pd(111), whereas the value of d23 (interlayer spacing between the second and third layers) is the same as that of the bulk. No relaxation is also observed on Pd(100) in Ar saturated solution. In O2 saturated solution, however, d23 as well as d12 is expanded by 5.7% on Pd(100).
