Platinum on carbon-fibre paper catalysts for methanol electro-oxidation. Part 2.—Role of platinum surface area in determining catalytic activity for methanol and formic-acid electro-oxidation

Abstract

Intrinsic catalytic activity of platinum supported on pre-oxidised carbon-fibre paper has been shown to be dependent on platinum surface area for both methanol and formic-acid electro-oxidation. The activity for formic-acid oxidation decreases as the platinum surface area decreases whereas that of methanol initially increases, then decreases with decreasing platinum area, thus producing a maximum in the activity–surface-area relationship. The effects found are, with one exception, independent of the method used to prepare catalysts of differing platinum areas. The effects can be understood in terms of the mode of adsorption of the fuels on platinum and the known facts regarding the mechanism of their oxidation. The effects described above prevail to platinum surface area much lower than that normally observed where crystallite-size effects alone determine the phenomena and it is felt that the carbon support through a metal–support interaction plays a role in determining catalytic activity.The implications of this work are that there is little incentive to improve platinum dispersion in monometallic catalysts for methanol electro-oxidation beyond the dispersion at which maximum activity occurs. It is not yet established whether similar effects exist in the more attractive bimetallic catalysts used for methanol electro-oxidation.