Highly dispersed nanostructured platinum catalyst for oxygen reduction reaction. The roles of the platinum precursor and the synthesis conditions

Abstract

Nowadays, platinum based electro-catalysts are made mostly from hexachloroplatinic acid and its salts. The possibility of using other platinum sources such as platinum (IV) nitrate, has been largely overlooked. In this study, we employed this precursor and prepared platinum based catalysts on an annealed graphene oxide support by two different synthetic protocols. The structure and morphology of the obtained composites have then been investigated by a set of advanced instrumental methods, which, in particular, let us visualize individual Pt atoms. The use of platinum (IV) nitrate and the synthesis in non-aqueous medium leads to the size of platinum species, not attainable with alternative methods/precursors. In the material, prepared at 25°C in isopropanol, platinum is present in the form of nanoparticles with an average size of 1.4 nm, as well as in the form of single atoms. In the material, synthesized at 180°C in ethylene glycol, platinum exists in the form of nanoparticles with an average size of 2.8 nm. Both materials exhibit excellent catalytic activities towards the oxygen reduction reaction. The catalyst with smaller platinum species demonstrates higher efficiency and promotes the 4e¯ mechanism by reducing oxygen to water.