Adsorption kinetics for carbon monoxide on platinum in hot phosphoric acid

Abstract

The availability and activity of platinum electrocatalyst sites for oxidation of the hydrogen in reformed natural gas has been one of the problems associated with efficient utilization of the platinum-anode catalyst. The major anode catalyst poison is carbon monoxide and the mechanism of poisoning of the hydrogen reaction by carbon monoxide has been reported. The equilibrium adsorptions and the rates of adsorption of CO on platinum surfaces were studied at a series of p co values between 0·01 and 0·10 atm in 96 per cent H 3PO 4 between 105 and 148°C. This range of partial pressures of CO is expected within an operating fuel cell. The adsorption isotherms are explicable in terms of single-site adsorption of the carbon monoxide molecule on the platinum surface atoms, causing a slow anion adsorption at the unpoisoned platinum sites. The equilibrium coverages for carbon monoxide on the platinum surfaces are independent of temperature in the range studied. Adsorption equations are used to describe the coverages of the platinum surface by carbon monoxide so that extrapolation of the data to both higher and lower carbon monoxide partial pressures gives reliable estimates of the resultant surface coverages.