[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.]
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.
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.
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.
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.
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.
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.
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.
Researchers suggest hybrid graphene oxide/cellulose microfibers could supersede carbon fibers
January 16, 2015
Researchers from Nanjing Forestry University and the University of Maryland have designed high-performance microfibers by hybridizing two-dimensional (2D) graphene oxide (GO) nanosheets and one-dimensional (1D) nanofibrillated cellulose (NFC) fibers. The resulting well-aligned, strong microfibers have the potential to supersede carbon fibers due to their low cost, the team suggests in an open access paper published in the journal NPG Asia Materials.
The hybrid microfibers are much stronger than microfibers composed of 1D NFC or 2D GO alone. In their paper, they reported that experimental results and molecular dynamics simulations reveal the synergistic effect between GO and NFC: the bonding between neighboring GO nanosheets is enhanced by NFC because the introduction of NFC provides the extra bonding options available between the nanosheets.
Review paper: Graphene and related materials (GRMs) may play major role in energy applications
January 02, 2015
The large specific surface area (SSA)—i.e., the surface-to-mass ratio—of graphene, combined with its high electrical conductivity, high mechanical strength, ease of functionalization, and potential for mass production, makes it an extremely attractive platform for energy applications, such as a transparent conductive electrode for solar cells or as flexible high-capacity electrode in lithium-ion batteries and supercapacitors, notes a team of researchers from Europe, the US and Korea, in a paper reviewing the role of graphene and related systems for energy conversion and storage published in the journal Science. The combination of chemical functionalization and curvature control also opens new opportunities for hydrogen storage.
In addition to graphene, they note, other two-dimensional crystals such as the transition metal dichalcogenides (TMDs) display insulating, semiconducting (with band gaps in the visible region of the spectrum), and metallic behavior and can enable novel device architectures also in combination with graphene. As with graphene, these materials can be integrated on flexible surfaces and can be mass-produced. Yet another class of 2D crystals is the MXenes (e.g., earlier post)—layered, hexagonal carbides and nitrides that can accommodate various ions and molecules between their layers by intercalation. MXene sheets are promising for energy applications, such as lithium-ion batteries, supercapacitors, and hydrogen storage.
ORNL teams embeds crown ethers in graphene for increased performance; potential for separations, sensors, batteries, biotech & more
December 28, 2014
|This sheet of graphene contains an array of crown ethers that can strongly bind select guest ions or molecules. Image credit: ORNL. Click to enlarge.|
A team led by the Department of Energy’s Oak Ridge National Laboratory has discovered a way to increase significantly the selectivity and binding strength of crown ethers by embedding them within a rigid framework of graphene. The results, published in Nature Communications, may enable broader use of crown ethers in diverse applications. Their strong, specific electrostatic binding may advance sensors, chemical separations, nuclear-waste cleanup, extraction of metals from ores, purification and recycling of rare-earth elements, water purification, biotechnology, energy production in durable lithium-ion batteries, catalysis, medicine and data storage.
Ethers are simple organic molecules in which an oxygen atom bridges two carbon atoms. When linked together in crown-shaped large molecular rings, they have the ability selectively to incorporate various atoms or molecules within the cavity formed by the ring. The size and shape of the cavity formed within a crown ether molecule confers selectivity for complementary ions and small molecules that fit it, like a lock and key. Crown ethers come in different sizes, so they can accommodate ions of different diameters.
Univ. of Manchester team finds monolayer graphene permeable to protons; implications for PEM fuel cell and other hydrogen technologies
November 28, 2014
Researchers at the University of Manchester in the UK have found that monolayers of graphene—which, as a perfect monolayer is impermeable to all gases and liquids—and its sister material boron nitride (BN) are highly permeable to protons, especially at elevated temperatures and if the films are covered with catalytic nanoparticles such as platinum. The finding could have a significant impact on proton exchange membrane fuel cell technologies and other hydrogen-based technologies.
The discovery is reported in the journal Nature by an international team led by Professor Sir Andre Geim, who, with Professor Sir Kostya Novoselov succeeded in producing, isolating, identifying and characterizing graphene in 2004 at the University of Manchester, an achievement for which the pair won the Nobel Prize in Physics in 2010. (Graphene had been studied theoretically as far back as 1947; professors Geim and Novoselov were the first to fabricate and to study the material.)
Graphene 3D Lab showing prototype 3D printed battery; potential for structural batteries
October 27, 2014
Graphene 3D Lab Inc., which develops, manufactures, and markets proprietary graphene-based nanocomposite materials for various types of 3D printing, including fused filament fabrication, has developed a 3D printable graphene battery. CEO Daniel Stolyarov, presented the prototype 3D printable graphene battery at the Inside 3D Printing Conference in Santa Clara, CA last week.
Graphene 3D Labs combines graphene nanoplatelets with thermoplastics used in FFF (fused filament fabrication) 3D printing, ultimately resulting in a functionalized 3D printing filament offering electrical conductivity. Currently, the process requires the separate printing of individual components—i.e., cathode, anode, electrolyte. However, a true multi-material 3D printer would enable the printing of the entire battery in one single print, the company notes.
Rice BN-doped graphene quantum dots/graphene platelet hybrid material can outperform platinum as fuel cell catalyst
October 13, 2014
|Preparation procedure for the BN-GQD/G nanocomposite. Credit: ACS, Fei et al. Click to enlarge.|
A team at Rice University has created a hybrid material combining graphene quantum dots (GQDs) and graphene platelets that can—depending upon its formulation—outperform platinum as a catalyst for fuel cells.
The material showed an oxygen reduction reaction (ORR) of about 15 millivolts more in positive onset potential—the start of the reaction—and 70% larger current density than platinum-based catalysts. The materials required to make the flake-like hybrids are much cheaper, too, said Dr. James Tour, whose lab created GQDs from coal last year. A paper on their new work is published in the journal ACS Nano.
European consortium investigating graphene-based materials for lightweight cars; energy-efficient and safe vehicles
June 30, 2014
The University of Sunderland (UK), working with a consortium of five other research partners from Italy, Spain and Germany, has been selected for funding by the €1-billion (US$1.4-billion) Graphene Flagship research initiative in Europe (earlier post) for their iGCAuto proposal. The researchers will explore the properties of graphene to determine how it behaves when used to enhance advanced composite materials used in the production of cars. The other partners are Centro Ricerche FIAT (Italy); Fraunhofer ICT (Germany); Interquimica (Spain); Nanesa S.r.l. (Italy); and Delta-Tech S.p.A. (Italy).
As part of the work, a novel graphene-based polymer material will be investigated, modeled, and designed to enhance both vehicle and occupant safety while remaining very light. This material will provide benefits such as improved strength, dimensional stability, and superior durability.