Tag Archives: UNIST

Eco-friendly nitrogen-doped graphene nanoplatelets from South Korea

South Korean researchers from Ulsan National Institute of Science and Technology (UNIST) have devised a new technique to fix nitrogen to graphene, from the July 24, 2013 news item on Azonano,

A simple, low-cost and eco-friendly method of creating nitrogen-doped graphene nanoplatelets (NGnPs), which could be used in dye-sensitized solar cells and fuel cells, is published in Scientific Reports today.

The work, carried out at Ulsan National Institute of Science and Technology (UNIST) in South Korea, could be a step towards replacing conventional platinum (Pt)-based catalysts for energy conversion.

The UNIST July 23, 2013 news release by Eunhee Song, which originated the news item, provides some context for why the technique is exciting interest,

The search for economically viable alternatives to fossil fuels has attracted attention among energy communities because of increasing energy prices and climate change. Solar cells and fuel cells are to be promising alternatives, but Pt-based (platinum-based) electrodes are expensive and susceptible to environmental damage.

Nitrogen fixation is where nitrogen (N2) in the atmosphere is converted into ammonia (NH3). Fixation processes free up nitrogen atoms from their diatomic form to be used in other ways, but nitrogen does not easily react with other chemicals to form new compounds.

The most common method of industrial nitrogen fixation is the Harber-Bosch process, which requires extremely harsh conditions, 200 atm of pressure and 400 °C of temperature.

The UNIST team previously reported that dry ball-milling can efficiently produce chemically modified graphene particles in large quantities*. This research, in Scientific Reports, presents another innovation to improve the materials. Along the way, the research team discovered a novel nitrogen fixation process.

They focus on modifications with nitrogen, developing a technique with direct nitrogen fixation, carbon-nitrogen bond formation, at the broken edges of graphite frameworks using ball-milling graphite in the presence of nitrogen gas.

In my search for this latest paper I found an earlier piece of work based on a wet-chemical reaction and published in the Journal of the American Chemical Society,

Nitrogen-Doped Graphene Nanoplatelets from Simple Solution Edge-Functionalization for n-Type Field-Effect Transistors by Dong Wook Chang, Eun Kwang Lee, Eun Yeob Park, Hojeong Yu, Hyun-Jung Choi, In-Yup Jeon, Gyung-Joo Sohn, Dongbin Shin, Noejung Park, Joon Hak Oh, Liming Dai, and Jong-Beom Baek. J. Am. Chem. Soc., 2013, 135 (24), pp 8981–8988 DOI: 10.1021/ja402555n Publication Date (Web): May 27, 2013
Copyright © 2013 American Chemical Society

That paper is behind a paywall while this latest work featuring a ‘dry’ technique is open access,

Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion by In-Yup Jeon, Hyun-Jung Choi, Myung Jong Ju, In Taek Choi, Kimin Lim, Jaejung Ko, Hwan Kyu Kim, Jae Cheon Kim, Jae-Joon Lee, Dongbin Shin, Sun-Min Jung, Jeong-Min Seo, Min-Jung Kim, Noejung Park, Liming Dai, & Jong-Beom Baek. Scientific Reports 3, Article number: 2260 doi:10.1038/srep02260 Published 23 July 2013

This team has been quite prolific recently. I last mentioned them in a June 7, 2013 posting highlighting another iteration of this ‘dry’ technique.

Fuel cells break free of metal catalysts (graphene instead of platinum) with research from joint Korea-US research team

Fuel cells—I used to hear a lot about them as there is a company in the region, Ballard Power Systems which specializes in that field. There was a lot of excitement in the late 1990s and into the 2000s and then nothing. Given the hype of the early days, I was expecting fuel-cell-powered-cars by now.  A June 5, 2013 Case Western Reserve University news release on EurekAlert may provide an answer as to why fuel cells have not been adopted more widely,

Researchers from South Korea, Case Western Reserve University and University of North Texas have discovered an inexpensive and easily produced catalyst that performs better than platinum in oxygen-reduction reactions.

The finding, detailed in Nature’s Scientific Reports online today, is a step toward eliminating what industry regards as the largest obstacle to large-scale commercialization of fuel cell technology.

Fuel cells can be more efficient than internal combustion engines, silent, and at least one type produces zero greenhouse emissions at the tail pipe. Car and bus manufacturers as well as makers of residential and small-business-sized generators have been testing and developing different forms of fuel cells for more than a decade but the high cost and insufficiencies of platinum catalysts have been the Achilles heel.

The news release goes on to provide context for the work and details about the new graphene catalyst,

Like a battery, a fuel cell converts chemical energy into electrical energy. It works by removing an electron from a fuel, usually hydrogen or methanol mixed with water, at the cell’s anode, or positive electrode, creating a current.Hydrogen ions produced then pass through a membrane to the cathode, or negative electrode. Here, oxygen molecules from the air are split and reduced by the addition of electrons and combined with the hydrogen ions to form water and heat—the only byproducts.

A better, cheaper catalyst than scarce and costly platinum is required if hydrogen fuel cells and direct methanol fuel cells are to become realistic alternatives to fossil fuels, the authors say.

The technology to make alternative catalysts builds on a simple and cheap industrial process several of the researchers developed to make graphene sheets from graphite.

Inside a ball miller, which is a canister filled with steel balls, the researchers broke graphite down into single-layer graphene nanoparticles. While the canister turned, they injected chlorine, bromine or iodine gas to produce different catalysts.

In each case, gas molecules replaced carbon atoms along the zigzag edges of nanoplatelets created by milling. Not only were the edges then favorable to binding with oxygen molecules, but the bond strength between the two oxygen atoms weakened. The weaker the oxygen bonds became, the more efficiently the oxygen was reduced and converted to water at the cathode.

In testing, a cathode coated with iodine-edged nanoplatelets performed best. A cathode coated with bromine-edged nanoparticles generated 7 percent less current than the commercial cathode coated with platinum, the chlorine-edged nanoplatelets 40 percent less.

In a test of durability, electrodes coated with the nanoplatelets maintained 85.6 percent to 87.4 percent of their initial current after 10,000 cycles while the platinum electrodes maintained only 62.5 percent.

Carbon monoxide was added to replicate the poisoning that many scientists blame for the poor performance of platinum at the cathode. The performance of the graphene-based catalysts was unaffected.

When methanol was added to replicate methanol crossover from the anode to cathode in direct methanol fuel cells, the current density of the platinum catalyst dropped sharply. Again, the graphene-based catalysts were unaffected.

One of the researchers sums up the research (from the news release),

“We made metal-free catalysts using an affordable and scalable process,” said Liming Dai, the Kent Hale Smith Professor of macromolecular science and engineering at Case Western Reserve and one of the report’s authors. “The catalysts are more stable than platinum catalysts and tolerate carbon monoxide poisoning and methanol crossover.”

And, in their initial tests, a cathode coated with one form of catalyst—graphene nanoparticles edged with iodine—proved more efficient in the oxygen reduction reaction, generating 33 percent more current than a commercial cathode coated with platinum generated.

For those who want more,

Facile, scalable synthesis of edge-halogenated graphene nanoplatelets as efficient metal-free eletrocatalysts for oxygen reduction reaction by In-Yup Jeon, Hyun-Jung Choi, Min Choi, Jeong-Min Seo, Sun-Min Jung, Min-Jung Kim, Sheng Zhang, Lipeng Zhang, Zhenhai Xia, Liming Dai, Noejung Park, & Jong-Beom Baek. Scientific Reports 3, Article number: 1810 doi:10.1038/srep01810 Published 05 June 2013

The paper is open access.

LEDs for your contact lenses from Korea’s Ulsan National Institute of Science and Technology

Probably the most exciting application for this work from Korea is where stretchable graphene-metal nanowire electrodes can be fitted to soft contact lenses paving the way for picture-taking and scanning lenses. A May 30, 2013 news item on Nanowerk describes the research in broad terms (Note: A link has been removed),

A hybrid transparent and stretchable electrode could open the new way for flexible displays, solar cells, and even electronic devices fitted on a curvature substrate such as soft eye contact lenses, by the UNIST (Ulsan National Institute of Science and Technology) research team (“High-Performance, Transparent, and Stretchable Electrodes Using Graphene–Metal Nanowire Hybrid Structures”).

The UNIST May 31, 2013 news release by Eunhee Song about the research provides context and detail,

Transparent electrodes are in and of themselves nothing all that new – they have been widely used in things like touch screens, flat-screen TVs, solar cells and light-emitting devices. Currently transparent electrodes are commonly made from a material known as indium tin oxide (ITO). Although it suffices for its job, it’s brittle, cracking and losing functionality if flexed. It also degrades over time, and is somewhat expensive due to the limited quantities of indium metal.

As an alternative, the networks of randomly distributed mNWs [metal nanowires] have been considered as promising candidates for next-generation transparent electrodes, due to their low-cost, high-speed fabrication of transparent electrodes.

However, the number of disadvantage of the mNW networks has limited their integration into commercial devices. They have low breakdown voltage, typically high NW-NW junction resistance, high contact resistance between network and active materials, material instability and poor adhesion to plastic substrates.

UNIST scientists here, combined graphene with silver nanowires to form a thin, transparent and stretchable electrode. Combining graphene and silver nanowires in a hybrid material overcomes weakness of individual material.

Graphene is also well known as good a candidate for transparent electrode because of their unique electrical properties and high mechanical flexibility. However, scalable graphene synthesis methods for commercialization produces lower quality graphene with individual segments called grains which increases the electrical resistance at boundaries between these grains.

Silver nanowires, on the other hand, have high resistance because they are randomly oriented like a jumble of toothpicks facing in different directions. In this random orientation, there are many contact between nanowires, resulting in high resistance due to large junction resistance of nanowires. Due to these drawbacks, neither is good for conducting electricity, but a hybrid structure, combined from two materials, is.

As a result, it presents a high electrical and optical performance with mechanical flexibility and stretchability for flexible electronics. The hybrid Transparent electrode reportedly has a low “sheet resistance” while preserving high transmittance. There’s almost no change in its resistance when bent and folded where ITO is bent, its resistance increases significantly. Additionally the hybrid material reportedly has a low “sheet resistance” while preserving electrical and optical properties reliable against thermal oxidation condition

The graphene-mNW hybrid structure developed by the research team, as a new class of such electrodes, may soon find use in a variety of other applications. The research team demonstrated Inorganic light-emitting diode (ILDED) devices fitted on a soft eye contact lens using the transparent, stretchable interconnects of the hybrid electrodes as an application example.

Here are some images from the research team,

Hybrid transparent and stretchable electrode as part of norganic light-emitting diode (ILDED) devices fitted on a soft eye contact lens. Image courtesy of  Korea's UNIST(Ulsan National Institute of Science and Technology)

Hybrid transparent and stretchable electrode as part of norganic light-emitting diode (ILDED) devices fitted on a soft eye contact lens. Image courtesy of Korea’s UNIST (Ulsan National Institute of Science and Technology)

There has already been an in vivo study of the ‘electrified’ soft contact lens (from the news release),

As an in vivo study, this contact lens was worn by a live rabbit eye for five hours and none of abnormal behavior, such as bloodshot eye or the rubbing of eye areas, of the live rabbit had been observed.

Wearing eye contact lenses, picture-taking and scanning, is not a scene on Sci-Fi movie anymore.

Jang-Ung Park, professor of the School of Nano-Bioscience and Chemical Engineering, UNIST, led the effort.

“We believe the hybridization between two-dimensional and one-dimensional nanomaterials presents a promising strategy toward flexible, wearable electronics and implantable biosensor devices, and indicate the substantial promise of future electronics,” said Prof. Park.

Here’s a close-up of a test bunny’s eye,

Rabbit's (bunny's) eye with Inorganic light-emitting diode (ILDED) devices fitted on a soft eye contact lens (using the transparent, stretchable interconnects of the hybrid electrodes).  Courtesy of UNIST (Ulsan National Institute of Science and Technology)

Rabbit’s (bunny’s) eye with Inorganic light-emitting diode (ILDED) devices fitted on a soft eye contact lens (using the transparent, stretchable interconnects of the hybrid electrodes).
Courtesy of UNIST (Ulsan National Institute of Science and Technology)

I wonder how one would control the picture-taking, scanning capabilities. In any event, here’s a link to and a citation for the research paper,

High-Performance, Transparent, and Stretchable Electrodes Using Graphene–Metal Nanowire Hybrid Structures by Mi-Sun Lee, Kyongsoo Lee, So-Yun Kim, Heejoo Lee, Jihun Park, Kwang-Hyuk Choi, Han-Ki Kim, Dae-Gon Kim, Dae-Young Lee, SungWoo Nam, and Jang-Ung Park. Nano Lett. [Nano Letters], Article ASAP DOI: 10.1021/nl401070p Publication Date (Web): May 23, 2013

Copyright © 2013 American Chemical Society

This paper is behind a paywall.