Surface segregation and stability of core-shell alloy catalysts for oxygen reduction in acid medium. Phys Chem Chem Phys

Department of Chemical Engineering, Texas A & M University, College Station, TX 77843, USA.
Physical Chemistry Chemical Physics (Impact Factor: 4.49). 03/2010; 12(9):2209-18. DOI: 10.1039/b917899f
Source: PubMed


Density functional theory is used for the evaluation of surface segregation, trends for dissolution of Pt surface atoms in acid medium, and oxygen reduction reaction activity of core-shell materials, containing a monolayer of platinum over a monometallic or bimetallic core. Two groups of cores are investigated: Pt/X with X = Ir, Au; Pd, Rh, Ag; Co, Ni, Cu; and Pt/Pd(3)X, with X = Co, Fe, Cr, V, Ti, Ir, Re. It is found that all the 4d and 5d pure cores may serve as stable cores, and their beneficial effect on the Pt monolayer may be further tuned by alloying the core to another element, here chosen from 3d or 5d groups. The Pd(3)X cores enhance the stability of the surface Pt atoms both in vacuum and under adsorbed oxygen; however the high oxygen philicity of some of the X elements induces their surface segregation that may cause surface poisoning with oxygenated species and their dissolution in acid medium.

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    • "However, some of the Pt-TM alloys are electrochemically unstable due to the dissolution of the surface TM atoms [5] [10] in acidic media. Thus, many Pt-alloys formed from Platinum Group Metals (PGMs) are proposed for MOR [11] [12] [13] and ORR [14] [15], demonstrating higher catalytic activities and improved electrochemical stability compared to bimetallic Pt-TM alloys [16]. Among Pt-PGM alloys, Pt-Ir displayed improved activities toward "
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    • "Moreover, we note that the effect of the reduced lattice constant of the Ir-Co cores by the Pd interlayer clearly is reflected in the adsorption energies of the adsorbates. Ramírez-Caballero et al. [37] recently reported adsorption energies of O and OH, respectively, on Pt/Pd (bulk) as −4.21 and −2.33 eV; the values of O and OH, correspondingly, for Pt/PdIr 3 Co are −3.62 and −2.47 eV, and for Pt/Pd/IrCo are −3.48 and −2.10 eV. To summarize, this section describes a simple method of improving Pt monolayer core-shell catalysts that have an inadequate Pt-core interaction causing their relatively low ORR activity. "
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