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[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.]

Stanford, SLAC team cages silicon microparticles in graphene for stable, high-energy anode for Li-ion batteries

January 28, 2016

A team from Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory has developed a new practical, high-energy-capacity lithium-ion battery anode out of silicon by encapsulating Si microparticles (∼1–3 µm) using conformally synthesized cages of multilayered graphene.

The graphene cage acts as a mechanically strong and flexible buffer during deep cycling, allowing the silicon microparticles to expand and fracture within the cage while retaining electrical connectivity on both the particle and electrode level.

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Graphene ultracapacitor company Skeleton Technologies secures €4M from KIC InnoEnergy; targeting 20 Wh/kg by 2020

European ultracapacitor manufacturer Skeleton Technologies received a €4-million (US$4.4-million) investment from KIC InnoEnergy, an investment company dedicated to promoting sustainable innovation and entrepreneurship in Europe’s energy industry.

The €4m investment from KIC InnoEnergy—the shareholders of which include ABB, EDF, Iberdrola and Total—will be used to further develop the competitive advantage of Skeleton Technologies’ ultracapacitors. The company aims to reach the ambitious target of 20 Wh/kg energy density for its technology by 2020.

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Northwestern researchers discover crumpled graphene balls are a promising lubricant additive

January 26, 2016

Researchers at Northwestern University’s McCormick School of Engineering have found that crumpled graphene balls are an extremely promising lubricant additive. In a series of tests, a polyalphaolefin base oil with only 0.01–0.1 wt % of crumpled graphene balls outperformed a fully formulated commercial lubricant in terms of friction and wear reduction. A paper on their work is published in the Proceedings of the National Academy of Sciences.

For the average car, 15% of the fuel consumption is spent overcoming friction in the engine and transmission. While oil helps reduce this friction, researchers have long sought additives that enhance oil’s performance. Ultrafine particles are often used as lubricant additives because they are capable of reducing friction and protecting surfaces from wear. They also tend to be more stable than molecular additives under high thermal and mechanical stresses during rubbing. However, they also can aggregate, reducing the effective concentration.

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LLNL team finds hydrogen treatment improves performance of graphene nanofoam anodes in Li-ion batteries

November 05, 2015

Lawrence Livermore National Laboratory researchers have found, through experiments and calculations, that hydrogen-treated graphene nanofoam (GNF) anodes in lithium-ion batteries (LIBs) show higher capacity and faster transport. The research suggests that controlled hydrogen treatment may be used as a strategy for optimizing lithium transport and reversible storage in other graphene-based anode materials. An open-access paper on their work is published in Nature Scientific Reports.

Commercial applications of graphene materials for energy storage devices, including lithium ion batteries and supercapacitors, hinge critically on the ability to produce these materials in large quantities and at low cost. However, the chemical synthesis methods frequently used leave behind significant amounts of atomic hydrogen, whose effect on the electrochemical performance of graphene derivatives is difficult to determine.

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Atomic cobalt on nitrogen-doped graphene catalyst shows promise to replace platinum for hydrogen production

October 21, 2015

The Rice lab of chemist James Tour and colleagues at the Chinese Academy of Sciences, the University of Texas at San Antonio and the University of Houston have developed a robust, solid-state catalyst that shows promise to replace expensive platinum for hydrogen generation.

The new electrocatalyst, based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene (Co-NG), is robust and highly active in aqueous media with very low overpotentials (30 mV). In an open-access paper published in Nature Communications, the researchers suggested that the unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.

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Very high-performance silicon anodes with engineered graphene assemblies

August 27, 2015

Researchers in China have developed a self-supporting high-performance silicon anode for Li-ion batteries (LIBs) consisting of silicon-nanoparticle-impregnated assemblies of templated carbon-bridged oriented graphene.

The binder-free anodes demonstrate exceptional lithium storage performances, simultaneously attaining high gravimetric capacity (1390 mAh g–1 at 2 A g–1 with respect to the total electrode weight); high volumetric capacity (1807 mAh cm–3—more than three times that of graphite anodes); remarkable rate capability (900 mAh g–1 at 8 A g–1); excellent cyclic stability (0.025% decay per cycle over 200 cycles); and competing areal capacity (as high as 4 and 6 mAh cm–2 at 15 and 3 mA cm–2, respectively) that approaches the level of commercial lithium-ion batteries. A paper on their work is published in the ACS journal Nano Letters.

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Laser-burned graphene could replace platinum as fuel cell catalyst

August 21, 2015

Researchers at the Tour Lab at Rice University developed an improved cost-effective approach using direct laser scribing to prepare graphene embedded with various types of metallic nanoparticles. The resulting metal oxide-laser induced graphene (MO-LIG) is highly active in electrochemical oxygen reduction reactions with a low metal loading of less than 1 at%. As such, it could be a candidate to replace expensive platinum in catalysts for fuel cells and other applications.

In addition, the researchers noted in their open access paper published in ACS Nano, the nanoparticles can vary from metal oxide to metal dichalcogenides through lateral doping, making the composite active in other electrocatalytic reactions such as hydrogen evolution.

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NSF funds new center for advanced 2-D coatings; energy conversion and storage

August 13, 2015

A new NSF-funded Industry/University Collaborative Research Center (I/UCRC) at Penn State and Rice University will study the design and development of advanced coatings based on two-dimensional (2D) layered materials to solve fundamental scientific and technological challenges that include: corrosion, oxidation and abrasion, friction and wear, energy storage and harvesting, and the large-scale synthesis and deposition of novel multifunctional coatings.

The Center for Atomically Thin Multifunctional Coatings, (ATOMIC), is one of more than 80 Industry/University Cooperative Research Program centers established by the National Science Foundation (NSF) to encourage scientific collaboration between academia and industry. It is the only NSF center dedicated to the development of advanced 2-D coatings.

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Manchester team greatly broadens thermal window of thermoelectric material using graphene; potential vehicle applications for waste heat recovery

July 22, 2015

Researchers at the University of Manchester (UK) have shown that the thermal operating window of the thermoelectric material lanthanum strontium titanium oxide (LSTO) can be expanded down to room temperature by addition of a small amount of graphene. Applications of LSTO-based thermoelectric materials are currently limited by their high operating temperatures of >700 °C.

Rather than working within the usual narrow “thermal window”, these bulk graphene/LSTO nanocomposites exhibit useful ZT values across a broad temperature range of several hundred degrees, the team reported in the journal ACS Applied Materials & Interfaces. This increase in operating performance can enable future applications such as thermoelectric generators in vehicles for waste heat recovery and other sectors, the researchers suggested.

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Argonne researchers develop macroscale superlubricity system with help of Mira supercomputer; potential for “lubricant genome”

Argonne scientists have used the Mira supercomputer to identify and to improve a new mechanism for eliminating friction, which fed into the development of a hybrid material that exhibited superlubricity—a state in which friction essentially disappears—at the macroscale—i.e., at engineering scale—for the first time. A paper on their work was published in the journal Science.

They showed that superlubricity can be realized when graphene is used in combination with nanodiamond particles and diamond-like carbon (DLC). Simulations showed that sliding of the graphene patches around the tiny nanodiamond particles led to nanoscrolls with reduced contact area that slide easily against the amorphous diamond-like carbon surface, achieving incommensurate contact and a substantially reduced coefficient of friction (~0.004).

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New rationally designed high-performance Li-S cathode; rate performance, capacity and long life

July 10, 2015

Researchers in China report the development of a rationally designed Li−S cathode consisting of a freestanding composite thin film assembled from sulfur nanoparticles, reduced graphene oxide (rGO), and a multifunctional additive poly(anthraquinonyl sulfide) (PAQS): nano-S:rGO:PAQS.

The resulting cathode exhibits an initial specific capacity of 1255 mAh g−1 with a decay rate as low as 0.046% per cycles over 1,200 cycles. Importantly, the nano-S:rGO:PAQS batteries exhibit significant rate performances. They maintain a reversible capacity of ∼615 mAh g−1 at a rate of 13.744 A g−1 (=8 C) after more than 60 cycles at various rates and can still have a reversible capacity of ∼1000 mAh g−1 when further cycled at 0.25 C. A paper explaining their work appears in the ACS journal Nano Letters.

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Lux: graphene severely underperforming commercially against “massive hype”

July 06, 2015

Market analyst firm Lux Research has maintained a skeptical stance about the commercial prospects of graphene even in the light of the material’s compelling properties. In a 2012 report “Is Graphene the Next Silicon...Or Just the Next Carbon Nanotube?”, Lux examined the interplay between graphene’s compelling performance properties as an advanced material, and the significant hurdles it would inevitably face transitioning from the lab to the marketplace. A research and patent boom along with impressive technical performance is far from a guarantee of commercial success.

Lux is now answering its own question with the assertion that graphene looks much closer to the next carbon nanotube than the next silicon. Reasons the firm gives for this assessment include:

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Skeleton Technologies launches new range of high-performance ultracapacitors; up to 111 kW/kg and 9.6 Wh/kg; hybrid truck application coming

June 30, 2015

Skeleton Technologies (earlier post) has launched a new range of cylindrical ultracapacitors that offers specific power performance of up to 111 kW/kg (SC450, 450F) and specific energy up to 9.6 Wh/kg (SC4500, 4500F) with ESR as low as 0.075 mΩ (SC3000, 3000F)—the highest performance cylindrical cell ultracapacitors in the market.

Through the use of its patented graphene material, the new series features a capacitance of up to 4500 farads (the SC4500 cell). By contrast, the closest competitor product has a capacitance of 3400 farads. Skeleton claims this is the single biggest increase in energy density for ultracapacitors in the past 15 years.

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New Samsung silicon anode with graphene boosts volumetric capacity of LiCoO2 Li-ion cell 1.5x after 200 cycles; gravimetric capacity the same

June 27, 2015

A team at Samsung Advanced Institue of Technology (SAIT, Samsung’s global R&D hub) reports in an open access paper published in the journal Nature Communications on a new approach to advance high-capacity silicon (Si) anodes for Li-ion batteries (LIBs) to commercial viability, with a particular focus on improving the volumetric capacity of LIBs.

The SAIT team fabricated the anode material by growing graphene directly on a silicon surfaces while avoiding Si carbide (SiC) formation by developing a chemical vapor deposition (CVD) process that includes CO2 as a mild oxidant. The graphene-coated silicon nanoparticles (Gr-Si NPs) reach a volumetric capacity of 2,500 mAh cm−3 (versus 550 mAh cm−3 of commercial graphite), the highest volumetric value among those reported to date for any LIB anodes while exhibiting excellent cycling and rate performance.

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Tsinghua team develops high-efficiency and high-stability Li metal anodes for Li-sulfur batteries

June 14, 2015

Researchers from Tsinghua University have developed what they call a “promising strategy” to tackle the intrinsic problems of lithium metal anodes for Lithium sulfur batteries—dendritic and mossy metal depositing on the anode during repeated cycles leading to serious safety concerns and low Coulombic efficiency.

As described in a paper published in the journal ACS Nano, the researchers devised a nanostructured graphene framework coated by an in situ formed solid electrolyte interphase (SEI) with Li depositing in the pores (SEI-coated graphene, SCG). The graphene-based metal anode demonstrated superior dendrite-inhibition behavior in 70 hours of lithiation, while a control cell with a copper foil-based metal anode short-circuited after only 4 hours of lithiation at 0.5 mA cm–2.

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MIT team finds chemical functionalization can lead to efficient graphene-based thermoelectric materials

April 14, 2015

Researchers at MIT are predicting that predict that suitable chemical functionalization of graphene can result in a large enhancement in the Seebeck coefficient for thermoelectric materials, leading to an increase in the room-temperature power factor of a factor of 2 compared to pristine graphene, despite degraded electrical conductivity.

Furthermore, the presence of patterns on graphene reduces the thermal conductivity, which when taken together leads to an increase in the figure of merit for functionalized graphene by up to 2 orders of magnitude over that of pristine graphene, reaching its maximum ZT ∼ 3 at room temperature according to their calculations, as reported in a paper in the ACS journal Nano Letters. These results suggest that appropriate chemical functionalization could lead to efficient graphene-based thermoelectric materials.

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Vertically aligned sulfur-graphene nanowall cathodes for Li-sulfur batteries deliver high capacity and rate performance

April 11, 2015

A team at Beihang University in China has synthesized cathode materials for Li-sulfur batteries consisting of vertically aligned sulfur–graphene (S-G) nanowalls on electrically conductive substrates. In each individual S-G nanowall, the sulfur nanoparticles are homogeneously anchored between graphene layers; ordered graphene arrays arrange perpendicularly to the substrates, enabling fast diffusion of both lithium ions and electrons.

As reported in their paper in the ACS journal Nano Letters, the cathodes achieve a high reversible capacity of 1261 mAh g–1 in the first cycle and more than 1210 mAh g–1 after 120 cycles with excellent cyclability and high-rate performance (more than 400 mAh g–1 at 8C, 13.36 A g–1). This is the best demonstrated rate performance for sulfur–graphene cathodes to date, according to the team.

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Northwestern-led team finds slightly imperfect graphene can serve as a highly selective proton separation membrane

March 18, 2015

Researchers from Northwestern University, together with collaborators from Oak Ridge National Laboratory, the University of Virginia, the University of Minnesota, Pennsylvania State University and the University of Puerto Rico, have discovered that protons can transfer easily through graphene—conventionally thought to be unfit for proton transfer absent nanoscale holes or dopants—through rare, naturally occurring atomic defects.

In an open access paper published in the journal Nature Communications, the researchers reported that a slightly imperfect graphene membrane’s speed and selectivity are much better than that of conventional proton separation membranes, offering engineers a new and simpler mechanism for fuel cell design.

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Researchers synthesize new 2D carbon-sulfur MAX-phase-derived material for Li-S battery electrode

Drexel researchers, along with colleagues at Aix-Marseille University in France, have synthesized two-dimensional carbon/sulfur (C/S) nanolaminate materials. Covalent bonding between C and S is observed in the nanolaminates, which along with and an extremely uniform distribution of sulfur between the atomically thin carbon layers make them promising electrode materials for Li-S batteries. A paper on their work is published in the journal Angewandte Chemie International Edition.

The international research collaboration led by Drexel’s Dr. Yury Gogotsi produced the nanolaminate by extracting the titanium from a three-dimensional material called a Ti2SC MAX phase. (Earlier post.) The resulting products are composed of multi-layers of C/S flakes, with predominantly amorphous and some graphene-like structures. The paper was selected as a VIP article and will be featured on the journal cover.

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SUTD team proposes low-temperature thermionic converter with graphene cathode; about 45% efficiency

March 09, 2015

Researchers at the Singapore University of Technology and Design (SUTD) are proposing that it is possible to design an efficient graphene-cathode-based thermionic energy converter (TIC)—a device for converting heat to electricity leveraging the phenomenon of thermionic emission, or the release of electrons from a hot body—operating at around 900 K (626 °C) or lower, as compared with a conventional metal-based cathode TIC operating at about 1500 K (1227 °C).

With a graphene-based cathode at 900 K and a metallic anode, the efficiency of the proposed TIC would be about 45%, they concluded in a paper on the work published in the journal Physical Review Applied. If realized, an efficient, low-temperature TIC could provide a supplementary or an alternative approach to thermoelectric devices for waste heat recovery using low grade waste heat—i.e, from engine exhaust or industrial processes.

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Silica-coated sulfur nanoparticles with mildly reduced graphene oxide as Li-S battery cathode

March 04, 2015

One of the main obstacles to the commercialization of high-energy density lithium-sulfur batteries is the tendency for lithium polysulfides—the lithium and sulfur reaction products—to dissolve in the battery’s electrolyte and travel to the opposite electrode permanently. This causes the battery’s capacity to decrease over its lifetime.

To prevent this polysulfide shuttle, researchers in the Bourns College of Engineering at the University of California, Riverside have fabricated SiO2-coated sulfur particles (SCSPs) for cathode material. With the addition of mildly reduced graphene oxide (mrGO) to the material, SCSPs maintain more than 700 mAh g−1 after the 50th cycle. A paper on their work is published in the RSC journal Nanoscale.

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Rice graphene aerogel catalyst doped with boron and nitrogen outperform platinum in fuel cell ORR

March 02, 2015

Graphene nanoribbons formed into a three-dimensional aerogel and doped with boron and nitrogen (3D BNC NRs) exhibit the highest onset and half-wave potentials among the reported metal-free catalysts for the oxygen reduction reaction (ORR) in alkaline fuel cells, and show superior performance compared to commercial Pt/C catalyst, according to a new study by Rice University researchers.

A team led by materials scientist Pulickel Ajayan and chemist James Tour made metal-free aerogels from graphene nanoribbons and various levels of boron and nitrogen to test their electrochemical properties. In research reported in the ACS journal Chemistry of Materials, they reported that versions with about 10 atom % boron and nitrogen were most efficient in catalyzing the ORR.

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