Reactivity and extent of poisoning during methanol electro-oxidation on platinum (100) and (111): A comparative study

Abstract

The reactivity and self-poisoning of platinum in the electrocatalytic oxidation of methanol depends on surface structure and potential. To study these effects, we determined the charge passed, extent of poisoning, and yield of complete oxidation product (CO 2) from electrocatalysis of methanol on Pt(100) and Pt(111) electrodes through chronoamperometry and linear sweep voltammetry. Measurements were performed in a dual cell apparatus with perchloric acid supporting electrolyte at room temperature. Methanol was reacted at constant potential within the range 0.35–0.7 V RHE for 60 s. Linear sweep voltammetry in methanol-free electrolyte allowed for measurement of adsorbed partial oxidation products. The most significant differences in behavior between Pt(100) and (111) occurred below 0.5 V. In this potential range reaction on Pt(100) saturates, producing exclusively CO, while on Pt(111) reaction is slow, but sustained, and produces small quantities of CO 2. The extent of poisoning showed a pronounced maximum at 0.6 V for reaction on Pt(111), but remained relatively constant on Pt(100) below 0.65 V. Between 0.5 and 0.7 V the charge passed and CO 2 yields compared favorably on both surfaces. In this intermediate potential range, the different CO coverages which form from methanol reaction represents the most significant structural effect. Although the Pt(100) surface exhibits a greater tendency to dehydrogenate methanol, the Pt(111) surface oxidizes CO more efficiently. This balance between the rate of CO formation and oxidation results in greater poisoning of the (100) surface. We discuss both kinetic and mechanistic aspects of the methanol reaction, and pay particular attention to the applicability of a parallel reaction mechanism for methanol.