The Ligand Effect: CO Desorption from Pt/Ru Catalysts

Abstract

Density Functional Theory (DFT) calculations of the adsorption energy of CO, for a platinum overlayer on Ru(0001), have been performed. For all coverages a significant reduction in the binding energy of up to 0.5 eV has been observed compared to that obtained on Pt(111). In addition, a Steady‐State Isotopic Transient Kinetic Analysis (SSITKA) study has been performed to determine the desorption rate dependence on the partial pressure of CO over commercial Pt/Ru electrocatalysts. As expected, no significant difference in the rate of exchange of CO at any given pressure is observed on going from Pt to Pt/Ru electrocatalysts when the diluted gas used was argon since the CO states will be filled to the same desorption energy for the two catalysts. However on changing the diluent gas to hydrogen, a reduction in the exchange rate for CO is observed clearly reflecting the lower CO binding energy and the increased competition for sites at the surface of the catalyst. The reduction efficiency of the Pt/Ru electrocatalyst was also studied and found to be highly dependent on whether CO or hydrogen was used. These results will be discussed with reference to the anode catalysis of the Polymer Electrolyte Membrane Fuel Cell (PEMFC).

Dynamics of Surface Exchange Reactions Between Au and Pt for HER and HOR

“…The amount of Au clusters deposited onto the carbon paper was held constant at 20 L of 5 ϫ 10 −4 M solution ͑10 nmol Au͒. Assuming the packing arrangement leading to stable magic-sized clusters 27 of 55 atoms in a 1.6 nm cluster, this volume ͑20 L͒ corresponded to 1.1 ϫ 10 14 clusters and a surface area of 8.8 cm 2 . If a spherical geometry is assumed, then 127 atoms/1.6 nm Au cluster led to 4.7 ϫ 10 13 clusters.…”

“…The E-TEK Au particles ͑20 mg͒ were mixed into a 2.5:1 ethanol ͑96%͒: Nafion ͑5% in ethanol͒ slurry and drop-cast onto a Toray carbon paper gas diffusion layer ͑GDL͒. Depending on the size, the total number of E-TEK Au particles was ϳ1.4 ϫ 10 12 ͑for 30 nm particles͒ and ϳ4.9 ϫ 10 12 ͑for 20 nm particles͒, yielding theoretical Au surface areas of ϳ40 and 61 cm 2 , respectively. The gold reduction peak for these particles gave an area of 150 cm 2 ͑see the area determination approach under the section "Cyclic voltammetry"͒, suggesting that there may be smaller particles also present in the size distribution.…”

“…A combined Pt-M ͑where M is another metal͒ system could serve two purposes: to minimize the amount of expensive Pt present in the system while maintaining high activity and to stabilize Pt against dissolution 1 or detrimental reactions such as CO poisoning. [2][3][4] Recently, computational methods have been utilized to aid efforts in screening candidate materials for specific catalytic reactions such as the HER. 5 Using density functional theory ͑DFT͒ and combining many criteria including catalytic activity and stability, Greeley et al 5,6 demonstrated the ability to predict potential surface alloy candidates such as Pt-Bi with a high activity for HER.…”

Effect of O2Plasma Treatments of Carbon Supports on Pt-Ru Electrocatalysts

“…Pt-Ru bimetallic catalysts thus have been regarded as the best materials for methanol electrode-oxidation, and correspondingly have seen widespread use. [10][11][12][13] Nonetheless, it remains fundamentally important to improve the properties of Pt impregnated support materials.…”

Study of CO Oxidation on Well-Characterized Pt-Ru/C Electrocatalysts Having Different Composition

“…The other one is the ligand mechanism, which is based on modification of electronic property of the Pt by a second metal in the catalyst. [32][33][34][35] The modified electronic property results in the different chemisorption property (or lower desorption energy) of the catalyst for CO so that the CO coverage on the Pt sites used for H2 oxidation is reduced. However, the mechanisms responsible for enhanced activity for CO oxidation still remain controversial.…”