Nanotech

[Due to the increasing size of the archives, each topic page now contains only the prior 365 days of content. Access to older stories is now solely through the Monthly Archive pages or the site search function.]

Researchers demonstrate water splitting to generate hydrogen using ultra-small Si nanoparticles

January 18, 2013

Schematic showing CO2 laser pyrolysis synthesis of silicon nanoparticles transferred to a custom stainless steel prototype cartridge used to generate hydrogen for fuel cell applications. Credit: ACS, Erogbogbo et al. Click to enlarge.

A team of researchers from the University at Buffalo (SUNY) have demonstrated that hydrogen generation from ultra-small silicon nanoparticles (10 nm diameter) proceeds much more rapidly than expected based upon extrapolation of rates obtained using larger particles. The ultra-small particles react with water to generate hydrogen 1,000 times faster than bulk silicon, 100 times faster than previously reported Si structures, and 6 times faster than competing metal formulations.

In a paper published in the ACS journal Nano Letters, they report that the hydrogen production rate using 10 nm Si is 150 times that obtained using 100 nm particles—significantly exceeding the expected effect of increased surface to volume ratio. These results imply that nanosilicon could provide a practical approach for on-demand hydrogen production without the addition of heat, light, or electrical energy, they suggested.

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US/China research team proposes “solar energy funnel” to harness photons for electricity; using elastic strain to capture a wider spectrum

November 26, 2012

A visualization of the broad-spectrum solar energy funnel. Image: Yan Liang. Click to enlarge.

Researchers from Peking University in China and MIT are proposing using elastic strain as a viable agent to create an optoelectronic material with a spatially varying bandgap that is tunable for use in photovoltaics, photocatalysis and photodetection. In a paper published in Nature Photonics, they propose that a photovoltaic device made from a strain-engineered MoS₂ monolayer will capture a broad range of the solar spectrum and concentrate excitons or charge carriers.

The “funnel” is a metaphor: electrons and their counterparts, holes—which are split off from atoms by the energy of photons—are driven to the center of the structure by electronic forces. However, the material actually does assume the shape of a funnel—a stretched sheet of thin material, nano-indented at its center by a microscopic needle that produces a curved, funnel-like shape.

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IACT team using ALD to build nanobowls for tailored catalysts for biofuel production

October 27, 2012

A team of scientists from the Institute for Atom Efficient Chemical Transformations (IACT)—an Energy Frontier Research Center (earlier post) led by Argonne National Laboratory (ANL), and including Northwestern University, the University of Wisconsin and Purdue University—is using atomic layer deposition (ALD) to build nanoscale “bowls” that protect metal catalysts from the harsh conditions of biofuel refining.

In recent years, nanoparticles of metals such as platinum, iridium and palladium supported on metal oxide surfaces have been considered as catalysts to convert biomass into alternative fuels as efficiently as possible. Unfortunately, under typical biorefining conditions where liquid water may reach temperatures of 200 °C and pressures of 4,100 kilopascals (597 psi), the tiny metal nanoparticles can agglomerate into much larger particles which are not catalytically active. Additionally, these extreme conditions can dissolve the support.

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XG Sciences lands SBIR/STTR award to develop Si/graphene anodes for Li-ion batteries for EVs

October 15, 2012

Plot of current performance data in the lab for Si/graphene anodes. Source: XG Sciences. Click to enlarge.

As part of the FY 2012 Phase I Release 3 SBIR/STTR Award program, the US Department of Energy (DOE) has awarded Michigan-based XG Sciences, a manufacturer of graphene nanoplatelets (earlier post), a contract to develop low-cost, high-energy Si/graphene anodes for Li-ion batteries for use in extended range electric vehicle applications. XG Sciences will lead a team that includes battery maker LG Chem Power, Inc. and the Georgia Institute of Technology.

XG Sciences’ Silicon-graphene nanocomposite anode materials have demonstrated significant increases in energy storage capacity over traditional graphite and are manufactured with a commercially-proven, low-cost process using widely-available and economical starting materials. Current performance data from the company shows demonstrated specific capacity of 900 – 2000 mAh/g, with a 1^st cycle efficiency of 80+ %.

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New hierarchical nanosheet zeolite catalysts could improve efficiences in fuel, chemical and pharmaceutical production

June 29, 2012

The research team used a unique process to encourage growth of ultra-thin zeolite nanosheets at 90-degree angles, similar to building a house of cards. Credit: U of Minn. Click to enlarge.

An international team led by University of Minnesota chemical engineering and materials science professor Michael Tsapatsis reports in the journal Science on a prototype of a new catalyst made of orthogonally connected microporous zeolite nanosheets (earlier post). The new development could lead to major efficiencies and cost-savings in catalyst-dependent production of gasoline, plastics, biofuels, pharmaceuticals, and other chemicals.

The “house-of-cards” arrangement of the nanosheets creates a permanent network of 2- to 7-nanometer mesopores, which, along with the high external surface area and reduced micropore diffusion length, account for the higher reaction rates for bulky molecules relative to those of other mesoporous and conventional MFI zeolites. The structure improves efficiencies by giving molecules fast access to the catalysts where the chemical reactions occur.

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Carbon nanotube–graphene complexes show promise as low-cast, high-activity electrocatalysts for fuel cells or metal-air batteries

May 28, 2012

This drawing shows the damaged outer wall of a carbon nanotube with nanosized graphene pieces (white patches), which facilitate the formation of catalytic sites made of iron (yellow) and nitrogen (red) atoms. The catalyst reduces oxygen to water. Click to enlarge.

A team of researchers has demonstrated the ability of “partially unzipped” carbon nanotubes to act as an oxygen reduction electrocatalyst in both acidic and alkaline solution. The work, led by Stanford University’s Dr. Hongjie Dai, and reported in the journal Nature Nanotechnology, could lead to lower-cost alternatives to platinum for use in fuel cells and metal-aire batteries.

In the new process, the outer walls of the few-walled carbon nanotubes are partially unzipped, creating nanoscale sheets of graphene attached to the inner tubes (carbon nanotube–graphene complexes). The graphene sheets contain extremely small amounts of iron originated from nanotube growth seeds, and nitrogen impurities, which facilitate the formation of catalytic sites and boost the activity of the catalyst.

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MIT researchers engineer stable copper-gold nanoparticle catalysts for lower energy consumption CO2 reduction

April 13, 2012

Copper nanoparticles (NPs) are attractive catalysts for chemical reactions including the reduction of CO₂ to methane or methanol. However, copper is easily oxidized; as a result, the metal is unstable, which can significantly slow its reaction with carbon dioxide and produce unwanted byproducts such as carbon monoxide and formic acid. For NPs, this can be greatly accelerated because of the high surface-to-volume ratios, and thus can deteriorate catalyst lifetime.

Researchers at MIT engineered nanoparticles of copper (Cu) mixed with gold (Au), which is resistant to corrosion and oxidation, and measured the oxidation rate of the AuCu NPs as a function of composition. They found that increasing the percentage of gold improves the catalyst’s stability, and also found that the overpotential of AuCU NPs for reduction in the presence of CO₂ is lower than that for Au or Cu NPs alone. As a result of the findings, the researchers suggest that AuCu NPs could be a promising catalyst to lower the energy consumption of CO₂ reduction.

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