Catalysis at nano level: Promoting Pt nanoparticle activity by Au decoration

Abstract

Formic acid is one of the most promising small organic molecules that can be used as fuel in polymer electrolyte fuel cells. These systems are recognized as high-efficiency energy conversion devices which could offer energy generated from electrochemical processes. At carbon supported platinum nanoparticles as state of the art anodic catalysts formic acid oxidation reaction (FAOR) proceeds through a dual path mechanism that includes the formation of CO in the indirect reaction pathway. Since CO is a catalytic poison, the best way to address this problem is to synthesize catalysts that would either provide prompt CO oxidation and removal, or favour the direct reaction pathway to completely avoid CO formation and electrode poisoning. PtAu systems are considered as efficient catalysts for FAOR due to the ensemble effect of Au on Pt, however the optimal ratio of these two elements is still quite vague. Given the experience with water in oil microemulsion synthesis for preparation of shape controlled Pt nanoparticles,1 bimetallic PtAu/C nanocatalysts were synthesized by the same procedure, following a simultaneous precursor reduction methodology.2 The amount of the capping agent used, was varied in order to cause formation of nanoparticles with different shape (cubic or tetrahedron like). Addition of a very low, but very finely dispersed amount of Au significantly increases the catalytic activity, and also affects kinetic of the particle growth, influencing the particle shape. Ordered structure of these particles contributes to their stability as well. These results were obtained by Electrochemical and High Resolution Transmission Electron Microscopy characterization (HRTEM) with Energy Dispersive X-ray Spectroscopy (EDXS), along with X-Ray Diffraction and (XRD) and X-Ray Photoelectron Spectroscopy (XPS).