TDS STUDY OF THE ANODIC LAYER ON EMERSED POLYCRYSTALLINE PLATINUM

Polycrystalline platinum electrodes emersed from H2SO4 and HClO4 solut ions were transfered to ultrahigh vacuum for study by thermal desorpti on spectroscopy (TDS). The double layer was generated at potentials be tween 0.05 and 2.75 V. Our interest was focused on the surface coverag e with water, oxygen and sulphate as a function of the applied electro de potential. The desorption of O2 from polycrystalline Pt starts 500 mV earlier (at 700 mV/RHE) than the value obtained earlier on Pt(100). The chemical state of thin films generated for 30 s at positive poten tials seems to be a mixture of hydroxides and oxides. Whereas water de sorption signals increase in parallel with those of oxygen, the sulpha te coverage decreases with increasing potential. The growth of anodic layers induced by a square-wave cycling method was monitored by therma l desorption of water and oxygen as well as by cyclic voltammetry. In contrast with thin anodic layers, anions are incorporated into thick l ayers generated in H2SO4 and HClO4.