Measurement of Surface Diffusion at the Electrochemical Interface by In Situ Linear Optical Diffraction

A new in situ method for measuring the surface diffusion rates of adsorbates on electrode surfaces in electrolyte solution is presented. The method is based on the generation of a periodic spatial modulation of the adsorbate coverage via interfering laser pulses and subsequent monitoring of the diffusion-induced decay of this pattern using the optical diffraction signal of a second laser. Proof-of-principle measurements of the surface diffusion of adsorbed sulfur on Pt(111) electrodes in 0.1 M H₂SO₄ indicate potential- and coverage-dependent diffusion constants that are significantly higher than those of sulfur on Pt(111) under vacuum conditions.