Researchers at Berkeley and Argonne labs discover highly active new class of nanocatalysts for fuel cells; more efficient, lower cost
28 February 2014
A team led by researchers at Berkeley and Argonne National Labs have discovered a new class of bimetallic 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 (DOE) for 2017.
The new catalysts, hollow polyhedral nanoframes of platinum and nickel (Pt3Ni), 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, a collaborative effort between DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab) and Argonne National Laboratory (ANL), is reported in the journal Science.
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.
Platinum (Pt) is a highly efficient electrocatalyst for both the cathodic oxygen reduction reaction (ORR) in fuel cells (and metal-air batteries) and the hydrogen evolution reaction (HER) in alkaline electrolyzers. However, the high cost and scarcity of Pt are key obstacles for its broad deployment in fuel cells and metal-air batteries for both stationary and portable applications. Intense research efforts have been focused on developing high-performance electrocatalysts with minimal precious metal content and cost. Specifically, alloying Pt with non-noble metals can reduce the Pt content of electrocatalysts by increasing their intrinsic activity.
… However, these materials cannot be easily integrated into electro- chemical devices but their outstanding catalytic performance needs to be mimicked in nanoparticulate materials that offer high surface areas. Caged, hollow or porous nanoparticles offer a promising approach to meeting these performance goals.
… In this report, we present a novel class of electrocatalysts exploiting structural evolution of bimetallic nanoparticles during which PtNi3 solid polyhedra were transformed into hollow Pt3Ni nanoframes with surfaces that have three-dimensional (3D) molecular accessibility. Controlled thermal treatment of the resulting nanoframes formed the desired Pt-Skin surface structure. Synthesis of Pt3Ni nanoframes can be readily scaled up to produce high-performance electrocatalysts at gram-scale, and importantly our protocol can be generalized toward the design of other multimetallic nanoframe systems.—
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 °C. 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.
|These schematic illustrations and corresponding transmission electron microscope images show the evolution of platinum/nickel from polyhedra to dodecahedron nanoframes with platinum-enriched skin. Source: Berkeley Lab. Click to enlarge.|
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. 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.—Peidong Yang, with Berkeley Lab’s Materials Sciences Division, who led the discovery
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. 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.—Peidong Yang
This research was funded by the DOE Office of Science.
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, and Vojislav R. Stamenkovic (2014) “Highly Crystalline Multimetallic Nanoframes with Three-Dimensional Electrocatalytic Surfaces,” Science doi: 10.1126/science.1249061
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