CO ADSORPTION AND OXIDATION ON PT(111) ELECTRODES MODIFIED BY IRREVERSIBLY ADSORBED ARSENIC IN SULFURIC-ACID MEDIUM - COMPARISON WITH BISMUTH-MODIFIED ELECTRODES

CO adsorption and stripping on Pt(111) electrodes modified by irrevers ibly adsorbed bismuth and arsenic were studied in sulphuric acid mediu m. Coadsorbed bismuth and CO form a mixed adlayer, whereas arsenic ten ds to desorb in the presence of CO. Both adatoms modify the CO strippi ng process, resulting in the catalysis of CO oxidation, in which arsen ic is more effective than bismuth. Fourier transform IR (FTIR) studies demonstrate that bismuth stabilizes the adsorbed CO, while arsenic sh ows the opposite effect. In both cases, linear CO is the only species present on the electrode surface at high adatom coverage. The catalysi s mechanism is an adatom-mediated oxygen transfer for both cases, with an additional electronic effect when arsenic is on the surface. Using the CO stripping charge after adequate correction, the values of the CO coverage for the different adatom coverages were calculated. The re sults of the CO coverage agree well with the behaviour shown in the FT IR experiments.