Kiev, Ukraine, June 21, 2007

Surface Dynamic Effects in Electrocatalysis of Methanol Oxidation
on TiO₂-Nanotube-Supported Bifunctional Nanocluster Catalysts

Abstract.  Surface dynamic aspects in catalysis of methanol oxidation reaction have been studied in conjunction with developments in nanoscience and the evolving fuel cell technologies. Extensive studies of nanostructured catalysts revealed strong dependencies of catalytic activity on nanoparticle size and interatomic interactions, resulting in scale-dependent modifications of electronic properties. For very small catalyst-support clusters, we have found strong enhancement of the ligand effect for bimetallic catalysts of the type Pt_nM_m attributed to the changes in local density of states of Pt atoms neighboring the additive metal atom M. This enhancement results in a decreased barrier for surface diffusion of adsorbed CO_ad intermediates through the cooperative diffusion mechanism, based on structural relaxation of the catalyst-support cluster, proposed in this work. The strong ligand effect counteracts the Schwoebel potential well effect, the latter being responsible for accumulation of poisoning intermediates at kink/edge sites on the catalyst surface and gradual decrease of catalytic activity with decreasing size of catalyst nanoparticles. The experimental investigations include submonolayer films of bi-functional catalysts (PtRu, PtFe) deposited on nanotube TiO₂ supporting films, offering high activity and low poisoning rate. The 2D lattice expansion and contraction associated with interactions with adsorbates, as well as other ligand effects will be discussed in detail.

Students contributing to this research: Kenneth Moot, Matthew Fayette, Indeewari Dela