Nav: Home

Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D

December 08, 2016

UPTON, NY- Catalysts are at the heart of fuel cells-devices that convert hydrogen and oxygen to water and enough electricity to power vehicles for hundreds of miles. But finding effective, inexpensive catalysts has been a key challenge to getting more of these hydrogen-powered, emission-free vehicles out on the road.

To help tackle this challenge, scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory used a high-resolution electron microscope to study nanoscale details of catalytic particles made of nickel and cobalt-inexpensive alternatives to the costly platinum used in most fuel cells today. A paper describing the research in the journal Nature Communications includes 3D, dynamic images that reveal how the particles' external and internal structure and chemical makeup change as they become catalytically active. Understanding these nanoscale structural and chemical features will help scientists learn what characteristics make the inexpensive particles most effective-and devise ways to optimize their performance.

Swiss-cheese surface area

One of the most important characteristics of a catalyst is having a high surface area compared to its volume. "Reactions happen on the surface," explained Huolin Xin, who led the work at Brookhaven's Center for Functional Nanomaterials (CFN). The more surface area there is, the higher the reactivity.

Tiny nanoparticles naturally have a large surface-to-volume ratio. However, the imaging techniques Xin and colleagues used to study the bimetallic nickel-and-cobalt particles revealed that these nanoparticles increase their surface area in an additional, unique way.

The transformation happens when the nanoparticles are oxidized. Instead of forming a metal oxide shell enclosing a single void in the center-as single-metal materials such as nickel and cobalt do-the bimetallic particles developed an extremely porous "Swiss cheese" like structure that was no longer hollow, Xin said.

"This is the first time anyone has shown how a bi-metallic material forms these Swiss cheese structures," Xin said.

Because the porous structure has a higher "packing density"-meaning more reactive material is packed into a smaller space than in hollow nanoparticles-it should result in higher catalytic activity, Xin said. The porous particles may also make stronger structures, which would be particularly useful in applications where mechanical specifications exclude weaker hollow structures, such as batteries.

Imaging the nanoscale details

Revealing the details of how these structures formed, including their chemical makeup, was no simple task. The scientists used chemical-sensitive electron tomography, which is a nanoscale version of a CAT scan, to track what was happening structurally and chemically on the surface and inside the particles in 3D as they were oxidizing. This process occurs as the sample is heated to 500 degrees Celsius.

"We custom-designed a sample holder that could withstand that change in temperature, while also letting us tilt the sample to scan it from every angle-all within a transmission electron microscope," Xin said.

These capabilities are unique to the CFN, a DOE Office of Science User Facility that offers both state-of-the-art instruments and the expertise of scientists like Xin to the entire scientific community through its user program.

Xin's team tracked precisely where metal ions were reacting with oxygen to become metal oxides-and discovered that the process takes place in two stages.

"In the first stage, oxidation occurs only on the surface, with metal ions moving out of the particles to react with the oxygen forming an oxide shell," Xin said. "In the second stage, however, oxidation starts to happen on the inside of the particles as well, suggesting that oxygen moves in."

The scientists suspected that tiny pinholes were created on the particles' surface as the oxide shell was forming, providing a pathway for the influx of oxygen. A closer look at one partially oxidized particle confirmed this suspicion, showing that as the oxide formed on the surface, it beaded up like droplets on a water-repellent surface, leaving tiny spaces in between.

The scientists also used "electron energy loss spectroscopy" and the distinct "chemical fingerprints" of nickel and cobalt to track where the individual elements were located within the particles as the oxidation process progressed. This gave them another way to see whether oxygen was finding a way into the particles.

"We found that cobalt moves preferentially to where the oxygen is," Xin explained. "This is because cobalt reacts more easily with oxygen than nickel does."

During early oxidation, cobalt preferentially moved to the exterior of the particles to engage in the formation of the oxide shell. But later-stage scans revealed that the internal surfaces of the Swiss cheese pores were rich in cobalt as well.

"This supports our previous idea that oxygen is getting inside and pulling the cobalt out to the surface of the internal pores to react," Xin said.

This ability to monitor the surface chemistry of nanoparticles, both externally and along the internal curved surfaces of pores, could result in a more rational approach to catalyst design, Xin said.

"People usually try to just mix particles and create a better catalyst by trial and error. But what really matters is the surface structure. This imaging technology gives us an accurate way to determine the composition of naturally curved surfaces and interfaces to understand why one catalyst will perform better than another."
-end-
This research was supported by the DOE Office of Science.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.

Visit Brookhaven Lab's electronic newsroom for links, news archives, graphics, and more at http://www.bnl.gov/newsroom, follow Brookhaven Lab on Twitter, http://twitter.com/BrookhavenLab, or find us on Facebook, http://www.facebook.com/BrookhavenLab/.

Related Links

Scientific paper: "Interrogation of bimetallic particle oxidation in three dimensions at the nanoscale"

Media contacts: Karen McNulty Walsh, (631) 344-8350, kmcnulty@bnl.gov, or Peter Genzer, (631) 344-3174, genzer@bnl.gov

DOE/Brookhaven National Laboratory

Related Nanoparticles Articles:

Chemists perform surgery on nanoparticles
A team of chemists led by Carnegie Mellon's Rongchao Jin has for the first time conducted site-specific surgery on a nanoparticle.
Nanoparticles remain unpredictable
The way that nanoparticles behave in the environment is extremely complex.
Gold standards for nanoparticles
KAUST researchers reveal how small organic 'citrate' ions can stabilize gold nanoparticles, assisting research on the structures' potential.
Lipid nanoparticles for gene therapy
Twenty-five years have passed since the publication of the first work on solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) as a system for delivering drugs.
Nanoparticles hitchhiking their way along strands of hair
In shampoo ads, hair always looks like a shiny, smooth surface.
Better contrast agents based on nanoparticles
Scientists at the University of Basel have developed nanoparticles which can serve as efficient contrast agents for magnetic resonance imaging.
Gentle cancer treatment using nanoparticles works
Cancer treatments based on laser irridation of tiny nanoparticles that are injected directly into the cancer tumor are working and can destroy the cancer from within.
Radiation-guided nanoparticles zero in on metastatic cancer
Zap a tumor with radiation to trigger expression of a molecule, then attack that molecule with a drug-loaded nanoparticle.
Nanoparticles can grow in cubic shape
Use of nanoparticles in many applications, e.g. for catalysis, relies on the surface area of the particles.
Nanoparticles deliver anticancer cluster bombs
Scientists have devised a triple-stage 'cluster bomb' system for delivering the chemotherapy drug cisplatin, via tiny nanoparticles designed to break up when they reach a tumor.

Related Nanoparticles Reading:

Nanoparticles: From Theory to Application
by Günter Schmid (Editor)

Nanoparticles - Nanocomposites – Nanomaterials: An Introduction for Beginners
by Dieter Vollath (Author)

Self-Assembly: From Surfactants to Nanoparticles (Wiley Series on Surface and Interfacial Chemistry)
by Ramanathan Nagarajan (Editor)

Gold Nanoparticles for Physics, Chemistry and Biology
by Catherine Louis (Author), Catherine Louis (Editor), Olivier Pluchery (Editor)

Gas-Phase Synthesis of Nanoparticles
by Yves Huttel (Editor)

Allergy and Immunotoxicology in Occupational Health (Current Topics in Environmental Health and Preventive Medicine)
by Takemi Otsuki (Editor), Claudia Petrarca (Editor), Mario Di Gioacchino (Editor)

Computational Modelling of Nanoparticles (Frontiers of Nanoscience Book 12)
by Elsevier

Nanoparticles: Building Blocks for Nanotechnology (Nanostructure Science and Technology)
by Springer

Protein-Nanoparticle Interactions: The Bio-Nano Interface (Springer Series in Biophysics)
by Masoud Rahman (Author), Sophie Laurent (Contributor), Nancy Tawil (Contributor), L'Hocine Yahia (Contributor), Morteza Mahmoudi (Contributor)

Iron Oxide Nanoparticles for Biomedical Applications: Synthesis, Functionalization and Application (Metal Oxides)
by Sophie Laurent (Editor), Morteza Mahmoudi (Editor), Ghenadii Korotcenkov Ph.D. in Physics and Technology of Semiconductor Materials and Devices Dr.Sci in Physics and Mathematics of Semiconductors and Dielectrics (Editor)

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Bias And Perception
How does bias distort our thinking, our listening, our beliefs... and even our search results? How can we fight it? This hour, TED speakers explore ideas about the unconscious biases that shape us. Guests include writer and broadcaster Yassmin Abdel-Magied, climatologist J. Marshall Shepherd, journalist Andreas Ekström, and experimental psychologist Tony Salvador.
Now Playing: Science for the People

#513 Dinosaur Tails
This week: dinosaurs! We're discussing dinosaur tails, bipedalism, paleontology public outreach, dinosaur MOOCs, and other neat dinosaur related things with Dr. Scott Persons from the University of Alberta, who is also the author of the book "Dinosaurs of the Alberta Badlands".