Browsing by Author "Yu, Ted H."

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Dealloyed Pt2Os nanoparticles for enhanced oxygen reduction reaction in acidic electrolytes
(2014-05-05)
Lee, Yi-Juei
;
Hsieh, Yu-Chi
;
Tsai, Ho-Cheng
;
Lu, I-Te
;
Wu, Yue-Han
Carbon-supported Pt2Os (Pt2Os/C) nanoparticles in 3.55 nm sizes are synthesized from a wet chemical reflux process. Subsequently, the Pt2Os/C undergoes a dealloying treatment in which multiple cyclic voltammetric scans are imposed to dissolve the Os atoms selectively from the surface of the Pt2Os nanoparticles. X-ray diffraction signals from the dealloyed sample (DA-Pt2Os/C) indicate a fcc phase and composition analysis suggests Pt4Os. Line scans from the scanning transmission electron microscope confirm that the surface of Pt4Os is depleted with the Os atoms. This agrees with our quantum mechanics (Density Funtional theory) calculations, which predict for the Pt3Os composition that the surface skin layer is pure Pt. The DA-Pt2Os/C shows impressive electrocatalytic behaviors (0.29 mA mu g(Pt)(-1) in mass activity and 1.03 mA cm(Pt)(-2) in specific activity) for the oxygen reduction reaction (ORR) in oxygen-saturated 0.1 M aqueous HClO4 solution, as compared to those of commercially available Pt/C and as-synthesized Pt2Os/C. In stability test, the DA-Pt2Os/C demonstrates a better retention of ORR activities and a smaller loss of electrochemical active surface area. We verify experimentally that a four-electron step is responsible for the ORR process occurring on the DA-Pt2Os/C. (C) 2014 Elsevier B.V. All rights reserved.
Density Functional Theory Study of Pt3M Alloy Surface Segregation with Adsorbed O/OH and Pt3Os as Catalysts for Oxygen Reduction Reaction
(2014-11-20)
Tsai, Ho-Cheng
;
Yu, Ted H.
;
Sha, Yao
;
Merinov, Boris V.
;
Wu, Pu-Wei
Using quantum mechanics calculations, we have studied the segregation energy with adsorbed O and OH for 28 Pt3M alloys, where M is a transition metal. The calculations found surface segregation to become energetically unfavorable for Pt3Co and Pt3Ni, as well as for the most other Pt binary alloys, in the presence of adsorbed O and OH. However, Pt3Os and Pt3Ir remain surface segregated and show the best energy preference among the alloys studied for both adsorbed species on the surface. Binding energies of various oxygen reduction reaction (ORR) intermediates on the Pt(111) and Pt3Os(111) surfaces were calculated and analyzed. Energy barriers for different ORR steps were computed for Pt and Pt3Os catalysts, and the rate-determining steps (RDS) were identified. It turns out that the RDS barrier for the Pt3Os alloy catalyst is lower than the corresponding barrier for pure Pt. This result allows us to predict a better ORR performance of Pt3Os compared to that of pure Pt.