Reactivity and stability of platinum and platinum alloy catalysts toward the oxygen reduction reaction

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Title: Reactivity and stability of platinum and platinum alloy catalysts toward the oxygen reduction reaction
Author: Calvo, Sergio Rafael
Abstract: Density functional theory (DFT ) is used to study the reactivity of Pt and Pt -M (M : Pd , Co , Ni , V , and Rh ) alloy catalysts towards the oxygen reduction reaction (ORR ) as a function of the alloy overall composition and surface atomic distribution and compared to that on pure Pt surfaces . Reactivity is evaluated on the basis of the adsorption strength of oxygenated compounds which are intermediate species of the four -electron oxygen reduction reaction , separating the effect of the first electron -proton transfer from that of the three last electron -proton transfer steps . It is found that most homogeneous distribution PtxM catalysts thermodynamically favor the dissociation of adsorbed OOH in comparison with pure Platinum and adsorb strongly O and OH due to the strong oxyphilicity of the M elements . On the other hand , in all cases skin Platinum surfaces catalysts do not favor the dissociation of adsorbed OOH and do favor the reduction of M -O and M -OH with respect to Platinum . Considering the overall pathway of the reactions to catalyze the ORR most of the skin Platinum monolayer catalysts provide more negative free energy changes and should behave at least in a similar way than Platinum in following order : Pt3V (skin Pt ) > Pt3Co (skin Pt ) > Pt3Ni (skin Pt ) > Pt > PtPd (skin ) > Pt4Rh (skin Pt ) > PtPd3 (skin ) . In all cases , the reactivity is shown to be not only sensitive to the overall composition of the catalyst , but most importantly to the surface atomic distribution . Proposed electrochemical dissolution reactions of the catalyst atoms are also analyzed for the ORR catalysts , by computing the free energy changes of Platinum and bimetallic Pt -X (X : Co , Pd , Ni , and Rh ) catalysts . It is found that Platinum is thermodynamically more stable than Pt -alloys in Pt3Co , Pt3Pd , Pt3Ni and Pt4Rh .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2457
Date: 2009-05-15

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Reactivity and stability of platinum and platinum alloy catalysts toward the oxygen reduction reaction. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2457 .

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