SCANNING ELECTROCHEMICAL MICROSCOPY .14. SCANNING ELECTROCHEMICAL MICROSCOPE INDUCED DESORPTION - A NEW TECHNIQUE FOR THE MEASUREMENT OF ADSORPTION DESORPTION-KINETICS AND SURFACE-DIFFUSION RATES AT THE SOLID LIQUID INTERFACE

Scanning electrochemical microscope induced desorption (SECMID) is introduced as a new technique for the measurement of adsorption/desorption kinetics and surface diffusion rates at the solid/liquid interface, which is generally applicable to the study of reversible processes involving electroactive adsorbates. The method utilizes the ultramicroelectrode (UME) probe of a scanning electrochemical microscope, located close to the sample surface, to perturb the equilibrium of the solid/liquid interfacial adsorption/desorption process under investigation and to measure the resulting flux of adsorbate desorbing from the surface. This is achieved through the application of a potential step to the UME such that the solution component of the adsorbate is electrolyzed at a diffusion-limited rate. The resulting UME current is a measure of the rate of diffusion through solution, the adsorption/desorption kinetics, and the rate of surface diffusion. A theoretical treatment of the chronoamperometric (current-time) response of SECMID is developed, and experimental strategies for obtaining both adsorption/desorption kinetics and surface diffusion rates are delineated. Particular emphasis is given to the adsorption/desorption of H+ on hydrous metal oxides. The applicability of the technique is illustrated with experiments on the adsorption/desorption of H+ on rutile (001) and aluminosilicate, albite (NaAlSi3O8), (010) surfaces.