Methanol electro-oxidation and induced sintering on Pt nanoclusters supported on thin-film Al2O3/NiAl(1 0 0)

The electrocatalytic oxidation of methanol was investigated on Pt nanoclusters on thin-film Al2O3/NiAl(1 0 0). The Pt clusters, grown from vapour deposition, have a fcc phase, a specific orientation (0 0 1) parallel to the oxide surface, and a mean diameter 2.25 nm and height 0.4 nm. During the CV scans, significant sintering occurs: the clusters aggregate and their size increases to a mean diameter 9-11 nm and height 0.8-1.0 nm. At a greater Pt coverage, even larger but fractal, irregular-sized clusters are formed. The structure of the aggregate clusters remains the fcc phase but with plane (1 1 1) randomly oriented with respect to the oxide surface. The sintering involves not only lateral agglomeration of clusters but also three-dimensional mass transport and structural re-organization in the clusters. These clusters formed at greater coverages exhibit reactivity toward oxidation of methanol comparable to that of Pt nanoparticles on Ru electrodes, whereas the reactivity for lower Pt coverages decreases quickly with the CV scan.