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[Science] Highly Crystalline Multimetallic Nanoframes with Three-Dimensional Electrocatalytic Surfaces

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发表于 2014-2-28 08:16:06 |显示全部楼层
Published Online February 27 2014
< Science Express Index
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Science DOI: 10.1126/science.1249061
REPORT
Highly Crystalline Multimetallic Nanoframes with Three-Dimensional Electrocatalytic Surfaces
Chen Chen1,2,3,*, Yijin Kang4,*, Ziyang Huo1,2, Zhongwei Zhu1,2, Wenyu Huang1,2, Huolin L. Xin2, Joshua D. Snyder4, Dongguo Li4, Jeffrey A. Herron5, Manos Mavrikakis5, Miaofang Chi6, Karren L. More6, Yadong Li3, Nenad M. Markovic4, Gabor A. Somorjai1,2, Peidong Yang1,2,7,8,†, Vojislav R. Stamenkovic4,†
+ Author Affiliations

1Department of Chemistry, University of California, Berkeley, CA 94720, USA.
2Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
3Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China.
4Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA.
5Department of Chemical and Biological Engineering, University of Wisconsin, Madison, WI 53706, USA.
6Division of Material Science and Technology, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
7Department of Chemistry, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia.
8Kavli Energy NanoSciences Institute at the University of California, Berkeley, and Lawrence Berkeley National Laboratory.
↵†Corresponding author. E-mail: p_yang@berkeley.edu (P.Y.); vrstamenkovic@anl.gov (V.R.S.)
↵* These authors contributed equally to this work.

ABSTRACT

Control of structure at the atomic level can precisely and effectively tune catalytic properties of materials, enabling enhancement in both activity and durability. We report synthesis of a highly active and durable class of electrocatalysts by exploiting the structural evolution of Pt-Ni bimetallic nanocrystals. The starting material, crystalline PtNi3 polyhedra, transformed in solution by interior erosion into Pt3Ni nanoframes with surfaces that have three-dimensional molecular accessibility. The edges of these PtNi3 polyhedra, which were Pt rich, are maintained in the final Pt3Ni nanoframes. Both the interior and exterior catalytic surfaces of this open framework structure are composed of the nano-segregated Pt-Skin structure that exhibits enhanced oxygen reduction reaction (ORR) activity. The Pt3Ni nanoframe catalysts achieved over 36 and 22-fold enhancement in mass and specific activities, respectively, for this reaction versus ORR in comparison to state-of-the-art Pt/C catalysts during prolonged exposure to reaction conditions.

Received for publication 27 November 2013.
Accepted for publication 14 February 2014.

http://www.sciencemag.org/conten ... ce.1249061.abstract

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发表于 2014-2-28 20:31:39 |显示全部楼层
Fuel cells put in the frame with catalysts that need far less platinum       
                               

The platinum nanoframes have 22 times the catalytic activity of standard electrodes  © Science/AAAS

US scientists have created an exceptional fuel cell catalyst that contains far less platinum – conventional catalysts need 36 times more platinum to hit the same levels of activity. The manufacturing process, which was discovered by accident, uses simple techniques that the researchers believe can be easily scaled-up. The work could help to make fuel cells economically viable for applications such as cars as the precious metal makes up much of the cost of the cell.Fuel cells react hydrogen with oxygen to produce water, using the electricity generated by the redox reaction to power a motor. The most effective catalyst is platinum, which is, unfortunately, extremely expensive and scarce. Chemists are searching for alternatives, such as doped carbon nanotubes, but at present commercial fuel cells usually use platinum.
Current designs usually use platinum nanoparticles in an inert porous carbon matrix, maximising the availability of the platinum to the reactants. In 2007, Vojislav Stamenkovic of Argonne National Laboratory, US, and colleagues demonstrated that alloying platinum with nickel to make Pt3Ni makes the surface much more active by modifying the electronic structure of the platinum. They did not know, however, how to produce Pt3Ni nanoparticles suitable for use in fuel cells.
The latest work came about when Peidong Yang's group at the University of California, Berkeley, was studying solid polyhedral PtNi3 nanoparticles. ‘My postdoc, Chen Chen, after he'd made all these nanoparticles, stored them in an open environment where air could dissolve in the solvent,’ says Yang. Two weeks later, he checked his sample using a transmission electron microscope and was surprised to find that they had turned into hollow nanoframes. Running the reaction at a higher temperature shortened this to 12 hours.
Subsequent analysis showed that the oxygen dissolving in the solvent had selectively etched the nickel, producing Pt3Ni. When thermally annealed the nanoframes' internal and external edges developed a highly active platinum skin. The hollow shape of the nanoparticles allowed reactants to access all edges, increasing activity 22-fold over current platinum–carbon catalysts.
They were also surprisingly robust. In the laboratory, they subjected the nanoframes to the electrical stresses and strains that they would receive if formulated in a fuel cell that was discharged 10,000 times and only saw a negligable loss of activity. In contrast, platinum–carbon catalysts lose around 40% of their activity during such a test as the platinum dissolves in the electrolyte. The simplicity of the manufacturing process should mean that the process could be readily scaled up to produce much more efficient fuel cells requiring far less platinum in the near future.
Radoslav Adzic, a fuel cell expert at Brookhaven National Laboratory in the US, wants to see the nanoframes in a real fuel cell to prove their industrial readiness as, if nickel were to leak out, it could ‘damage the fuel cell irreversibly’. He also believes that the time to produce the nanoframes still needs to be shortened to produce the catalyst industrially. Nevertheless, he says, ‘the catalyst's activity is excellent – probably the highest that has been achieved so far’.
                             
References
C Chen et al, Science, 2014, DOI: 10.1126/science.1249061

http://www.rsc.org/chemistryworl ... -platinum-nanoframe
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发表于 2014-3-21 08:09:40 |显示全部楼层
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