Formation mechanism of Pt single-crystal nanoparticles in proton exchange membrane fuel cells

In proton exchange membrane fuel cells, hydrogen permeated from the anode to the cathode was found to reduce soluble Pt species and produce faceted and dendritic Pt nanoparticles in the cathode ionomer. Moving away from the carbon support particles, the morphology of Pt nanoparticles changed from dendritic shapes to truncated tetrahedrons, truncated octahedrons, and truncated square cuboids. Transmission electron microscopy results suggest that the homogeneity of the driving force (supersaturation) for reduction of soluble Pt at the growing surface could dictate the transition from dendritic to faceted growth, and the competition between surface energy and interfacial kinetics of Pt reduction could govern the shape of faceted Pt nanoparticles. (c) 2007 The Electrochemical Society.