Department of Materials Science and Engineering, University of California-Los Angeles, Los Angeles, 90095, USA.
Nanoscale. 2012 Feb 7;4(3):845-51. doi: 10.1039/c1nr11374g. Epub 2011 Dec 13.
Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50 mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications.
双金属 Pt-Pd 核壳纳米晶体（NCs）通过两步法合成，其中 Pd 厚度从亚单层到多个原子层可控。基于不同的 Pd 厚度，系统研究和比较了核壳 NCs 在碱性溶液中用于燃料电池的氧还原反应（ORR）催化活性和甲醇氧化反应活性。结果发现，与商业 Pd 黑相比，Pd 壳有助于将 ORR 的过电位降低多达 50 mV，同时产生高达 3 倍的更高动力学电流密度。一氧化碳中毒测试表明，与 Pt NCs 和 Pt 黑相比，双金属 NCs 对 CO 中毒的抵抗力更强。还表明，双金属 Pt-Pd 核壳 NCs 可以增强甲醇氧化反应的电流密度，相对于 Pt 核 NCs 将过电位降低 35 mV。进一步的研究表明，Pd/Pt 比为 1/3，对应于 Pt 核 NCs 上几乎单层 Pd 的沉积，给出了最高的氧化电流密度和最低的过电位。本研究首次系统地研究了 Pd 原子壳层对 Pt-Pd 双金属纳米催化剂的影响，为设计用于燃料电池应用的高性能催化剂提供了有价值的指导。
