New Fuel-Cell Design Powered by Graphene-Wrapped Nanocrystals

Thin sheets of graphene oxide (red sheets) have natural, atomic-scale defects that allow hydrogen gas molecules to pass through while blocking larger molecules such as oxygen (O2) and water (H2O). Berkeley Lab researchers encapsulated nanoscale magnesium crystals (yellow) with graphene oxide sheets to produce a new formula for metal hydride fuel cells. Source: (Jeong Yun Kim)

Hydrogen is the lightest and most plentiful element on Earth and in our universe. So it shouldn't be a big surprise that scientists are pursuing hydrogen as a clean, carbon-free, virtually limitless energy source for cars and for a range of other uses, from portable generators to telecommunications towers--with water as the only byproduct of combustion.

While there remain scientific challenges to making hydrogen-based energy sources more competitive with current automotive propulsion systems and other energy technologies, researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new materials recipe for a battery-like hydrogen fuel cell--which surrounds hydrogen-absorbing magnesium nanocrystals with atomically thin graphene sheets--to push its performance forward in key areas.

The graphene shields the nanocrystals from oxygen and moisture and contaminants, while tiny, natural holes allow the smaller hydrogen molecules to pass through. This filtering process overcomes common problems degrading the performance of metal hydrides for hydrogen storage.

These graphene-encapsulated magnesium crystals act as "sponges" for hydrogen, offering a very compact and safe way to take in and store hydrogen. The nanocrystals also permit faster fueling, and reduce the overall "tank" size.

"Among metal hydride-based materials for hydrogen storage for fuel-cell vehicle applications, our materials have good performance in terms of capacity, reversibility, kinetics and stability," said Eun Seon Cho, a postdoctoral researcher at Berkeley Lab and lead author of a study related to the new fuel cell formula, published recently in Nature Communications.

In a hydrogen fuel cell-powered vehicle using these materials, known as a "metal hydride" (hydrogen bound with a metal) fuel cell, hydrogen gas pumped into a vehicle would be chemically absorbed by the magnesium nanocrystaline powder and rendered safe at low pressures.

Low-Noise QCL Driver Available for Reverse Polarity Configurations

The low-noise QCL OEM driver has enabled countless applications with its patented circuitry. Now, the reverse polarity driver, a current source, is available in the OEM package. Often with epi-down configurations of the QCL the exit lead is attached to the case and it is desirable to ground it. While floating both connections would make it possible to use the standard QCL OEM, simply use the QCL OEM(+) and ground the connection. The Analog Input for remote setpoint input operates at 0 to +5V input, with bandwidth up to 1-2 MHz for the QCL500(+) and 500 kHz for the QCL2000(+).

These Low-Noise QCL OEM(+) Series Drivers have the lowest current noise density of any commercially available driver. Powering your QCL with this driver will enable better performance—at lower cost and in less time—than otherwise possible. This is the right driver for QCLs that require a high-precision and ultra-low noise current source. The 500 mA QCL OEM(+) driver exhibits noise performance of 0.5 μA RMS to 100 kHz, and an average current noise density of 1.5 nA / √Hz.

Nanocrystal Self-Assembly Sheds Its Secrets

A scanning electron micrograph of a nanocrystal superlattice shows long-range ordering over large domains. (Credit: Tisdale Lab)

The secret to a long-hidden magic trick behind the self-assembly of nanocrystal structures is starting to be revealed.

The transformation of simple colloidal particles—bits of matter suspended in solution—into tightly packed, beautiful lace-like meshes, or superlattices, has puzzled researchers for decades. Pretty pictures in themselves, these tiny superlattices, also called quantum dots, are being used to create more vivid display screens as well as arrays of optical sensory devices. The ultimate potential of quantum dots to make any surface into a smart screen or energy source hinges, in part, on understanding how they form.

Through a combination of techniques including controlled solvent evaporation and synchrotron X-ray scattering, the real time self-assembly of nanocrystal structures has now become observable in-situ. The findings were reported in the journal Nature Materials in a paper by Assistant Prof. William Tisdale and grad student Mark Weidman, both at MIT's Department of Chemical Engineering, and Detlef-M. Smilgies at the Cornell High Energy Synchrotron Source (CHESS).

The researchers anticipate their new findings will have implications for the direct manipulation of resulting superlattices, with the possibility of on-demand fabrication and the potential to generate principles for the formation of related soft materials such as proteins and polymers.

Quantum dot disco

New Method Prints Nanomaterials with Plasma

The nozzle firing a jet of carbon nanotubes with helium plasma off and on. When the plasma is off, the density of carbon nanotubes is small. The plasma focuses the nanotubes onto the substrate with high density and good adhesion. Courtesy of NASA Ames Research Center

Printing has come a long way since the days of Johannes Gutenberg. Now, researchers have developed a new method that uses plasma to print nanomaterials onto a 3D object or flexible surface, such as paper or cloth. The technique could make it easier and cheaper to build devices like wearable chemical and biological sensors, flexible memory devices and batteries, and integrated circuits.

One of the most common methods to deposit nanomaterials—such as a layer of nanoparticles or nanotubes—onto a surface is with an inkjet printer similar to an ordinary printer found in an office. Although they use well-established technology and are relatively cheap, inkjet printers have limitations. They can't print on textiles or other flexible materials, let alone 3D objects. They also must print liquid ink, and not all materials are easily made into a liquid.

Some nanomaterials can be printed using aerosol printing techniques. But the material must be heated several hundreds of degrees to consolidate into a thin and smooth film. The extra step is impossible for printing on cloth or other materials that can burn, and means higher cost for the materials that can take the heat.

The plasma method skips this heating step and works at temperatures not much warmer than 40 degrees Celsius. "You can use it to deposit things on paper, plastic, cotton or any kind of textile," said Meyya Meyyappan of NASA Ames Research Center. "It's ideal for soft substrates." It also doesn't require the printing material to be liquid.

Wrinkles and Crumples Make Graphene Better

Wrinkles and crumples, introduced by placing graphene on shrinky polymers, can enhance graphene's properties. Courtesy of Hurt and Wong Labs / Brown University

PROVIDENCE, RI — Crumple a piece of paper, and it’s probably destined for the trash can; but new research shows that repeatedly crumpling sheets of the nanomaterial graphene can actually enhance some of its properties. In some cases, the more crumpled the better.

The research by engineers fromBrown University shows that graphene, wrinkled and crumpled in a multi-step process, becomes significantly better at repelling water—a property that could be useful in making self-cleaning surfaces. Crumpled graphene also has enhanced electrochemical properties, which could make it more useful as electrodes in batteries and fuel cells.

The results are published in the journal Advanced Materials.

Generations of wrinkles

This new research builds on previous work done by Robert Hurt and Ian Wong, from Brown’s School of Engineering. The team had previously showed that by introducing wrinkles into graphene, they could make substrates for culturing cells that were more similar to the complex environments in which cells grow in the body. For this latest work, the researchers led by Po-Yen Chen, a Hibbit postdoctoral fellow, wanted to build more complex architectures incorporating both wrinkles and crumples. “I wanted to see if there was a way to create higher-generational structures,” Chen said.

To do that, the researchers deposited layers of graphene oxide onto shrink films—polymer membranes that shrink when heated (kids may know these as Shrinky Dinks). As the films shrink, the graphene on top is compressed, causing it to wrinkle and crumple. To see what kind of structures they could create, the researchers compressed the same graphene sheets multiple times. After the first shrink, the film was dissolved away, and the graphene was placed in a new film to be shrunk again.

Researchers Invent Tougher Plastic

ORNL's tough new plastic is made with 50 percent renewable content from biomass. (Credit: Oak Ridge National Laboratory, U.S. Dept. of Energy; conceptual art by Mark Robbins)

Your car's bumper is probably made of a moldable thermoplastic polymer called ABS, shorthand for its acrylonitrile, butadiene and styrene components. Light, strong and tough, it is also the stuff of ventilation pipes, protective headgear, kitchen appliances, Lego bricks and many other consumer products. Useful as it is, one of its drawbacks is that it is made using chemicals derived from petroleum.

Now, researchers at the Department of Energy'sOak Ridge National Laboratory have made a better thermoplastic by replacing styrene with lignin, a brittle, rigid polymer that, with cellulose, forms the woody cell walls of plants. In doing so, they have invented a solvent-free production process that interconnects equal parts of nanoscale lignin dispersed in a synthetic rubber matrix to produce a meltable, moldable, ductile material that's at least ten times tougher than ABS. The resulting thermoplastic—called ABL for acrylonitrile, butadiene, lignin—is recyclable, as it can be melted three times and still perform well. The results, published in the journal Advanced Functional Materials, may bring cleaner, cheaper raw materials to diverse manufacturers.

"The new ORNL thermoplastic has better performance than commodity plastics like ABS," said senior author Amit Naskar in ORNL's Materials Science and Technology Division, who along with co-inventor Chau Tran has filed a patent application for the process to make the new material. "We can call it a green product because 50 percent of its content is renewable, and technology to enable its commercial exploitation would reduce the need for petrochemicals."

The technology could make use of the lignin-rich biomass byproduct stream from biorefineries and pulp and paper mills. With the prices of natural gas and oil dropping, renewable fuels can't compete with fossil fuels, so biorefineries are exploring options for developing other economically viable products. Among cellulose, hemicellulose and lignin, the major structural constituents of plants, lignin is the most commercially underutilized. The ORNL study aimed to use it to produce, with an eye toward commercialization, a renewable thermoplastic with properties rivaling those of current petroleum-derived alternatives.

Innovative Device Studies Gold Nanoparticles In-Depth

​EPFL researchers have developed a way to explore and optimize gold nanoparticles, which are used in medicine, biology and solar cells.

Artists have used gold nanoparticles for centuries, because they produce vibrant colors when sunlight hits them. Their unique optical-electronics properties have put gold nanoparticles at the center of research, solar cells, sensors, chemotherapy, drug delivery, biological and medical applications, and electronic conductors. The properties of gold nanoparticles can be tuned by changing their size, shape, surface chemistry etc., but controlling these aspects is difficult.

Publishing in Nano Letters, researchers led by Fabrizio Carbone at EPFL have made an unprecedented study into the structure of gold nanoparticles. Working with Francesco Stellacci’s lab (EPFL), the researchers achieved this using a device called “small-angle time-resolved electron diffractometer”, which allowed them to study the structural arrangements of gold nanoparticles at ultrafast speeds – quadrillionths of a second.