Design of Ternary Nanoalloy Catalysts: Effect of Nanoscale Alloying and Structural Perfection on Electrocatalytic Enhancement
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- 作者：Bridgid N. Wanjala ; Bin Fang ; Shiyao Shan ; Valeri Petkov ; Pengyu Zhu ; Rameshwori Loukrakpam ; Yongsheng Chen ; Jin Luo ; Jun Yin ; Lefu Yang ; Minhua Shao ; Chuan-Jian Zhong
- 刊名：Chemistry of Materials
- 出版年：2012
- 出版时间：November 27, 2012
- 年：2012
- 卷：24
- 期：22
- 页码：4283-4293
- 全文大小：625K
- 年卷期：v.24,no.22(November 27, 2012)
- ISSN：1520-5002
文摘
The ability to tune the atomic-scale structural and chemical ordering in nanoalloy catalysts is essential for achieving the ultimate goal of high activity and stability of catalyst by design. This article demonstrates this ability with a ternary nanoalloy of platinum with vanadium and cobalt for oxygen reduction reaction in fuel cells. The strategy is to enable nanoscale alloying and structural perfection through oxidative鈥搑eductive thermochemical treatments. The structural manipulation is shown to produce a significant enhancement in the electrocatalytic activity of the ternary nanoalloy catalysts for oxygen reduction reaction. Mass activities as high as 1 A/mg of Pt have been achieved by this strategy based on direct measurements of the kinetic currents from rotating disk electrode data. Using a synchrotron high-energy X-ray diffraction technique coupled with atomic pair function analysis and X-ray absorption fine structure spectroscopy as well as X-ray photoelectron spectroscopy, the atomic-scale structural and chemical ordering in nanoalloy catalysts prepared by the oxidative鈥搑eductive thermochemical treatments were examined. A phase transition has been observed, showing an fcc-type structure of the as-prepared and the lower-temperature-treated particles into an fct-type structure for the particles treated at the higher temperature. The results reveal a thermochemically driven evolution of the nanoalloys from a chemically disordered state into chemically ordered state with an enhanced degree of alloying. The increase in the chemical ordering and shrinking of interatomic distances as a result of thermochemical treatment at increased temperature is shown to increase the catalytic activity for oxygen reduction reaction, exhibiting an optimal activity at 600 掳C. It is the alloying and structural perfection that allows the optimization of the catalytic performance in a controllable way, highlighting the significant role of atomic-scale structural and chemical ordering in the design of nanoalloy catalysts.