Nucleation/growth of the platinum nanoparticles under the liquid phase synthesis

Abstract

The need to reduce platinum content in PEMFC catalyst layers has sparked a new wave of interest in ways to control the microstructure of Pt/C catalysts, which must combine high platinum surface area and activity. A comparative study of platinum nanoparticle nucleation/growth under a liquid-phase synthesis of Pt/C materials, with formaldehyde and formic acid being used as reducing agents, has been carried out. Analysis of the color change in the reaction medium and the in situ spectral-kinetic studies performed with absorption spectroscopy, were used as methods to study the reactions kinetics. The effect of the synthesis temperature on the features of the Pt(IV) reduction stages, nucleation/growth of Pt(0) nanoparticles, as well as on the size of the resulting Pt nanoparticles were studied. The role of the ethylene glycol and its derivatives, formed in the reaction medium at high pH, in the processes of Pt(IV) reduction and in the Pt(0) nanoparticles formation, is shown. The positive effect of the dispersed carbon support on the morphological characteristics of the resulting Pt/C catalysts is demonstrated, with carbon being introduced into the reaction medium in the initial stage of the synthesis. The roles of homogeneous and heterogeneous phase formation in the synthesis of Pt nanoparticles and Pt/C materials in the liquid phase are estimated.