chapter  8
20 Pages

Simulation of Corrosive Dissolution of PtBinary Nano-Cluster in Acid Environment of Polymer Electrolyte Membrane (PEM) Fuel Cells

Summary ............................................................................................... 198 8.1 Introduction .................................................................................. 198 8.2. Methodology of Computation ...................................................... 201 8.3 Calculation Results ...................................................................... 206 8.4 Conclusions .................................................................................. 212 Keywords .............................................................................................. 213 References ............................................................................................. 213

SUMMARY

A corrosive dissolution model has been proposed for corrosive dissolution binary nanocluster surface of the formula PtnXm (where X – transition metals Cr, Fe, Co, Ni, Ru) of the core-shell structure in acid environment of low temperature fuel cells, which content molecules and ions of H2O, Cl

–, OH-, H3O +. This

model is based on calculations of adsorption behaviors of the environment component interaction with surfaces and activation barriers of platinum atom dissolution by means of quantum-chemical methods PM6 and DFT. Physicalchemical behaviors were established for structural and energy degradation of surfaces of platinum binary nanoclusters with core-shell structure Pt42X13 of different composition under the influence of H2O, Cl

–, OH-, H3O+. It was shown that transition metals Cr, Fe, Co, Ni, Ru, which form the core of our binary nanoclusters influence sufficiently on their adsorption behaviors and stability to corrosive dissolution, For example, Pt42Co13 is resistant to chlorine hydrated ions influence Cl-(H2O) because of much lower adsorption heat (27.5 kJ/mole) as compared with pure platinum nanocluster (195.8 kJ/mole), which should be explained by enhanced electron density in four-fold positions of the surface. It was discovered, that formation of a complex [Pt(OH) (H2O)4]

+ is possible on the surface of binary nanocluster surface in the environment of water molecules, oxygen atoms and hydroxonium ions, the activation energy of its departure from the surface being the highest for nanoclusters with cobalt and ruthenium in the row Pt55 < Pt42Co13 < Pt42Ru13. It was also shown, that local adsorption of chlorine ions on the hydrated surface of platinum nanoclusters may induce blocking of catalytic centers of their surface due to high adsorption ability of such ions or due to dissolution of platinum atoms with the formation of complexes [H2O(PtCl)]

n+, with lower activation energies of their departure from surface in comparison with pure Pt55 (more than in twice) with the exclusion of Pt42Co13, where an opposite effect was fixed (increase of activation energy in 60%).