IRREVERSIBLY ADSORBED AS AT FULL BLOCKAGE ON PT(111) ELECTRODES - SURFACE STOICHIOMETRY

Irreversibly adsorbed arsenic adlayers on Pt(111) electrodes have been studied at full blockage. The voltammetric profiles for 0.1M HClO4, 0 .05 M H2SO4, and 0.1M HClO4 + 0.01M sodium acetate solutions, present only small differences, indicating minimal anion effects on the arseni c surface redox process. Significant contributions to the voltammetric charge due to anion adsorption are highly unlikely, as suggested by t he almost negligible amounts of adsorbed acetate anions on the arsenic -covered surface found by in situ FTIRS. A Pt(111)-(root 3x root 3)R30 degrees-As adlayer structure has been imaged by STM on emersed sample s. This structure, with an ideal coverage of 0.33 As/Pt, together with the voltammetric charge density arising from the surface redox proces s of arsenic adsorbate, around 240 mu C cm(-2), supports a stoichiomet ry involving three electrons per As adatom, which blocks three platinu m adsorption sites. (C) 1997 Elsevier Science S.A.