Big step for next-generation fuel cells and electrolyzers
Date:
February 27, 2014
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
Researchers have discovered a highly promising new class of nanocatalysts
for fuel cells and water-alkali electrolyzers that are an order of
magnitude higher in activity than the target set by the US Department Of
Energy for 2017.
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These schematic illustrations and corresponding transmission electron
microscope images show the evolution of platinum/nickel from polyhedra to
dodecahedron nanoframes with platinum-enriched skin.
*Credit: Image courtesy of DOE/Lawrence Berkeley National Laboratory*
[Click to enlarge image]
A big step in the development of next-generation fuel cells and
water-alkali electrolyzers has been achieved with the discovery of a new
class of bimetallic nanocatalysts that are an order of magnitude higher in
activity than the target set by the U.S. Department of Energy (DOE) for
2017. The new catalysts, hollow polyhedral nanoframes of platinum and
nickel, feature a three-dimensional catalytic surface activity that makes
them significantly more efficient and far less expensive than the best
platinum catalysts used in today's fuel cells and alkaline electrolyzers.
This research was a collaborative effort between DOE's Lawrence Berkeley
National Laboratory (Berkeley Lab) and Argonne National Laboratory (ANL).
"We report the synthesis of a highly active and durable class of
electrocatalysts by exploiting the structural evolution of platinum/nickel
bimetallic nanocrystals," says Peidong Yang, a chemist with Berkeley Lab's
Materials Sciences Division, who led the discovery of these new catalysts.
"Our catalysts feature a unique hollow nanoframe structure with
three-dimensional platinum-rich surfaces accessible for catalytic
reactions. By greatly reducing the amount of platinum needed for oxygen
reduction and hydrogen evolution reactions, our new class of nanocatalysts
should lead to the design of next-generation catalysts with greatly reduced
cost but significantly enhanced activities."
Yang, who also holds appointments with the University of California (UC)
Berkeley and the Kavli Energy NanoSciences Institute at Berkeley, is one of
the corresponding authors of a paper in *Science *that describes this
research. The paper is titled "Highly Crystalline Multimetallic Nanoframes
with Three-Dimensional Electrocatalytic Surfaces." The other corresponding
author is Vojislav Stamenkovic, a chemist with ANL's Materials Science
Division, who led the testing of this new class of electrocatalysts.
Fuel cells and electrolyzers can help meet the ever-increasing demands for
electrical power while substantially reducing the emission of carbon and
other atmospheric pollutants. These technologies are based on either the
oxygen reduction reaction (fuel cells), or the hydrogen evolution reaction
(electrolyzers). Currently, the best electrocatalyst for both reactions
consists of platinum nanoparticles dispersed on carbon. Though quite
effective, the high cost and limited availability of platinum makes
large-scale use of this approach a major challenge for both stationary and
portable electrochemical applications.
"Intense research efforts have been focused on developing high-performance
electrocatalysts with minimal precious metal content and cost," Yang says.
"In an earlier study, the ANL scientists showed that forming a
nano-segregated platinum skin over a bulk single-crystal platinum/nickel
alloy enhances catalytic activity but the materials cannot be easily
integrated into electrochemical devices. We needed to be able to reproduce
the outstanding catalytic performance of these materials in
nanoparticulates that offered high surface areas."
Yang and his colleagues at Berkeley accomplished this by transforming solid
polyhedral bimetallic nanoparticles of platinum and nickel into hollow
nanoframes. The solid polyhedral nanoparticles are synthesized in the
reagent oleylamine, then soaked in a solvent, such as hexane or chloroform,
for either two weeks at room temperature, or for 12 hours at 120 degrees
Celsius. The solvent, with its dissolved oxygen, causes a natural interior
erosion to take place that results in a hollow dodecahedron nanoframe.
Annealing these dodecahedron nanoframes in argon gas creates a platinum
skin on the nanoframe surfaces.
"In contrast to other synthesis procedures for hollow nanostructures that
involve corrosion induced by harsh oxidizing agents or applied potential,
our method proceeds spontaneously in air," Yang says. "The open structure
of our platinum/nickel nanoframes addresses some of the major design
criteria for advanced nanoscale electrocatalysts, including, high
surface-to-volume ratio, 3-D surface molecular accessibility, and
significantly reduced precious metal utilization."
In electrocatalytic performance tests at ANL, the platinum/nickel
nanoframes when encapsulated in an ionic liquid exhibited a 36-fold
enhancement in mass activity and 22-fold enhancement in specific activity
compared with platinum nanoparticles dispersed on carbon for the oxygen
reduction reaction. These nanoframe electrocatalysts, modified by
electrochemically deposited nickel hydroxide, were also tested for the
hydrogen evolution reaction and showed that catalytic activity was enhanced
by an order-of-magnitude over platinum/carbon catalysts.
"Our results demonstrate the beneficial effects of the hollow nanoframe's
open architecture and surface compositional profile," Yang says. "Our
technique for making these hollow nanoframes can be readily applied to
other multimetallic electrocatalysts or gas phase catalysts. I am quite
optimistic about its commercial viability."
Other co-authors of the *Science *paper in addition to Yang and Stamenkovic
are Chen Chen, Yijin Kang, Ziyang Huo, Zhongwei Zhu, Wenyu Huang, Huolin
Xin, Joshua Snyder, Dongguo Li, Jeffrey Herron, Manos Mavrikakis, Miaofang
Chi, Karren More, Yadong Li, Nenad Markovic and Gabor Somorjai.
------------------------------
*Story Source:*
The above story is based on
materials<http://newscenter.lbl.gov/news-releases/2014/02/27/next-generation-fuel-cells-and-electrolyzers-researchers-at-berkeley-and-argonne-national-labs-develop-highly-promising-new-class-of-nanocatalyst/>provided
by *DOE/Lawrence
Berkeley National Laboratory* <http://www.lbl.gov>. *Note: Materials may be
edited for content and length.*
------------------------------
*Journal Reference*:
1. Chen Chen, Yijin Kang, Ziyang Huo, Zhongwei Zhu, Wenyu Huang, Huolin
L. Xin, Joshua D. Snyder, Dongguo Li, Jeffrey A. Herron, Manos Mavrikakis,
Miaofang Chi, Karren L. More, Yadong Li, Nenad M. Markovic, Gabor A.
Somorjai, Peidong Yang, Vojislav R. Stamenkovic. *Highly Crystalline
Multimetallic Nanoframes with Three-Dimensional Electrocatalytic Surfaces*.
*Science*, 2014 DOI:
10.1126/science.1249061<http://dx.doi.org/10.1126/science.1249061>
