ELECTROCHEMISTRY OF METHANOL AT LOW-INDEX CRYSTAL PLANES OF PLATINUM - AN INTEGRATED VOLTAMMETRIC AND CHRONOAMPEROMETRIC STUDY

We have studied a catalytic decomposition of methanol on low Miller in dex platinum surfaces, Pt(111), Pt(110), and Pt(100) in perchloric, su lfuric, and phosphoric acids at room temperature. The instantaneous me thanol oxidation current is unaffected by the methanolic CO formation (surface poisoning) and depends on platinum surface structure and comp osition of supporting electrolyte with respect to the anions. The high est oxidation current, 156 mA.cm(-2), is observed with the Pt(110) ele ctrode in perchloric acid solution at 0.200 V vs Ag/AgCl reference. In terms of turnover, this current translates to 163 molecules (Pt site) (-1).s(-1), a high rate exceeding previous expectations in methanol el ectrode kinetics. Overall, the oxidation current changes by 3 orders o f magnitude between the extreme cases examined in this study. Breaking up the total effect into individual components shows that the surface geometry and anionic effects are roughly comparable. Therefore, we ha ve an evidence that anion-platinum interactions are as important in de termining the methanol oxidation rate as is the surface geometry of th e Pt catalyst. Being encouraged by the magnitude of the oxidation curr ent, especially with the Pt(110) electrode, and by the control of the oxidation process through the structural and electrochemical variables of this research, we also report that the rate of methanolic CO forma tion follows the same pattern as does the oxidation current. Namely, t he CO poisoning is the highest for the Pt(110) electrode in perchloric acid and the slowest with the Pt(111) electrode in phosphoric acid. W e conclude that optimizing the structure of clean platinum, and soluti on composition, is not a sufficient remedy for platinum deactivation a nd that the CO poisoning process must be addressed with new force in b asic research on platinum fuel cell catalysis.