Catalytic methanol electrooxidation by cathodized platinum electrodes in aqueous sulfate solutions

V. DIAZ; J. O. ZERBINO; M.G. SUSTERSIC; C.F. ZINOLA; M.E. MARTINS

Banff

Congreso; 58th Annual Meeting of the International Society of Electrochemistry; 2007

International Society of Electrochemistry

Platinum electrodes after prolonged cathodic polarization in sulphuric aqueous solutions show increase in the catalytic activity for methanol electrooxidation. Voltammograms resulting after potential holding between -1.0 V < E < 0.1 V during times longer than 30 min show catalytic oxidation currents at lower anodic potential, E= 0.65 V, than that for the untreated electrode that remains inactive. The polarization resistance obtained through impedance measurements, EIS, and using the Randles model, shows values three times lower than that of untreated surface. The analysis of the surfaces using voltammetry, modulated voltammetry, ellipsometry, microscopic analysis, SEM, and energy dispersive analysis of X-rays, EDAX, shows significant differences both in the electric double layer and in the hydrogen adsorption potential domains after the cathodic treatment. Localized sulfur deposits are detected preferentially near surface defects which promotes bubbles growth. One possible origin could be the effect of differential hydration in the reaction steps corresponding to the reduction pathway of adsorbed reactants