Heat treatment and potential cycling effects on surface morphology, particle size, and catalytic activity of Pt/C catalysts studied by 13C NMR, TEM, XRD and CV

Pt particles of 20% Pt/C samples grew both by repetitive potential cycling and heat treatment. Average particle size variation is linearly proportional to the number of potential cycles while it is proportional to an exponential function of heating temperature. HR-TEM results show rough and irregular Pt surfaces in repetitively potential cycled samples and well-defined cubo-octahedrons without many defects in heat treated samples. This difference of surface morphology plays a main role to produce opposite electrocatalytic activity variation versus particle size of the samples prepared by potential cycling and heat treatment. Our results demonstrate that in terms of noble metal usage Pt particles with an average size of similar to 5 nm is the most efficient catalyst if the particle shapes are well defined cubo-octahedrons. In that aspect, heat treatment is better than potential cycling to prepare catalysts. (c) 2006 Elsevier B.V. All rights reserved.