Water-based fuel cell converts carbon emissions to electricity


This is a schematic illustration of Hybrid Na-CO2 System and its reaction mechanism. UNIST

Scientists from the Ulsan National Institute of Science and Technology (UNIST) developed a system which can continuously produce electrical energy and hydrogen by dissolving carbon dioxide in an aqueous solution.

The inspiration came from the fact that much of the carbon dioxide produced by humans is absorbed by the oceans, where it raises the level of acidity in the water.

Researchers used this concept to “melt” carbon dioxide in water in order to induce an electrochemical reaction. When acidity rises, the number of protons increases, and these protons attract electrons at a high rate. This can be used to create a battery system where electricity is produced by removing carbon dioxide.

The elements of the battery system are similar to a fuel cell, and include a cathode (sodium metal), a separator (NASICON), and an anode (catalyst). In this case, the catalysts are contained in the water and are connected to the cathode through a lead wire. The reaction begins when carbon dioxide is injected into the water and begins to break down into electricity and hydrogen. Not only is the electricity generated obviously useful, but the produced hydrogen could be used to fuel vehicles as well. The current efficiency of the system is up to 50 percent of the carbon dioxide being converted, which is impressive, although the system only operates on a small scale.

“Carbon capture, utilization, and sequestration (CCUS) technologies have recently received a great deal of attention for providing a pathway in dealing with global climate change,” Professor Guntae Kim of the School of Energy and Chemical Engineering at UNIST said in a statement. “The key to that technology is the easy conversion of chemically stable CO2 molecules to other materials. Our new system has solved this problem with [the] CO2 dissolution mechanism.”

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Transparent loudspeakers and MICs that let your skin play music – Ultra-Thin Nanomembranes may help the Hearing and Speech Impaired


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Their ultrathin, conductive, and transparent hybrid NMs can be applied to the fabrication of skin-attachable NM loudspeakers and voice-recognition microphones, which would be unobtrusive in appearance due to their excellent transparency and conformal contact capability.Credit: UNIST

An international team of researchers, affiliated with UNIST has presented an innovative wearable technology that will turn your skin into a loudspeaker.

This breakthrough has been led by Professor Hyunhyub Ko in the School of Energy and Chemical Engineering at UNIST. Created in part to help the hearing and speech impaired, the new technology can be further explored for various potential applications, such as wearable IoT sensors and conformal health care devices.

In the study, the research team has developed ultrathin, transparent, and conductive hybrid nanomembranes with nanoscale thickness, consisting of an orthogonal silver nanowire array embedded in a polymer matrix. They, then, demonstrated their nanomembrane by making it into a loudspeaker that can be attached to almost anything to produce sounds. The researchers also introduced a similar device, acting as a microphone, which can be connected to smartphones and computers to unlock voice-activated security systems.

Nanomembranes (NMs) are molcularly thin seperation layers with nanoscale thickness. Polymer NMs have attracted considerable attention owing to their outstanding advantages, such as extreme flexibility, ultralight weight, and excellent adhesibility in that they can be attached directly to almost any surface. However, they tear easily and exhibit no electrical conductivity.

The research team has solved such issues by embedding a silver nanowire network within a polymer-based nanomembrane. This has enabled the demonstration of skin-attachable and imperceptible loudspeaker and microphone.

“Our ultrathin, transparent, and conductive hybrid NMs facilitate conformal contact with curvilinear and dynamic surfaces without any cracking or rupture,” says Saewon Kang in the doctroral program of Energy and Chemical Engineering at UNIST, the first author of the study.

He adds, “These layers are capable of detecting sounds and vocal vibrations produced by the triboelectric voltage signals corresponding to sounds, which could be further explored for various potential applications, such as sound input/output devices.”

Using the hybrid NMs, the research team fabricated skin-attachable NM loudspeakers and microphones, which would be unobtrusive in appearance because of their excellent transparency and conformal contact capability. These wearable speakers and microphones are paper-thin, yet still capable of conducting sound signals.

“The biggest breakthrough of our research is the development of ultrathin, transparent, and conductive hybrid nanomembranes with nanoscale thickness, less than 100 nanometers,” says Professor Ko. “These outstanding optical, electrical, and mechanical properties of nanomembranes enable the demonstration of skin-attachable and imperceptible loudspeaker and microphone.”

The skin-attachable NM loudspeakers work by emitting thermoacoustic sound by the temperature-induced oscillation of the surrounding air. The periodic Joule heating that occurs when an electric current passes through a conductor and produces heat leads to these temperature oscillations. It has attracted considerable attention for being a stretchable, transparent, and skin-attachable loudspeaker.

Wearable microphones are sensors, attached to a speaker’s neck to even sense the vibration of the vocal folds. This sensor operates by converting the frictional force generated by the oscillation of the transparent conductive nanofiber into electric energy. For the operation of the microphone, the hybrid nanomembrane is inserted between elastic films with tiny patterns to precisely detect the sound and the vibration of the vocal cords based on a triboelectric voltage that results from the contact with the elastic films.

“For the commercial applications, the mechanical durability of nanomebranes and the performance of loudspeaker and microphone should be improved further,” says Professor Ko.

Story Source:

Materials provided by Ulsan National Institute of Science and Technology(UNIST)Note: Content may be edited for style and length.


Journal Reference:

  1. Saewon Kang, Seungse Cho, Ravi Shanker, Hochan Lee, Jonghwa Park, Doo-Seung Um, Youngoh Lee, Hyunhyub Ko. Transparent and conductive nanomembranes with orthogonal silver nanowire arrays for skin-attachable loudspeakers and microphonesScience Advances, 2018; 4 (8): eaas8772 DOI: 10.1126/sciadv.aas8772

UNIST researchers introduce novel catalyst for rechargeable metal-air batteries


UNIST Air Battery 154245_web

IMAGE: A MESOPOROUS NANOFIBER OF CATION ORDERED PEROVSKITE WAS PREPARED VIA ELECTROSPINNING PROCESS, WHICH EXHIBITED NOTABLE CELL PERFORMANCE AND EXCEPTIONALLY HIGH STABILITY FOR ZN-AIR BATTER: CREDIT UNIST

Research in lithium-ion batteries has opened up a plethora of possibilities in the development of next-generation batteries. In particular, the metal-air batteries with significantly greater energy density close to that of gasoline per kilogram, has recently been acknowledged and invested by world’s leading companies, like IBM.

A recent study, affiliated with UNIST has presented novel catalyst to accelerate the commercialization of metal-air batteries. This breakthrough has been jointly led by Professor Guntae Kim and Professor Jaephil Cho in the School of Energy and Chemical Engineering at UNIST in collaboration with Professor Yunfei Bu from Nanjing University of Science and Technology, Nanjing, China. Their new catalyst possesses the structure of nanofiber-based perovskite materials and exhibits excellent electrochemical performance, close that of today’s precious metal catalysts, yet still inexpensive.

A metal-air battery is a type of fuel cell or battery that uses the oxidation of a metal with oxygen from atmospheric air to produce electricity. It is equipped with an anode made up of pure metals–like lithium or zinc–and an air cathode that is connected to an inexhaustible source of air. The catalysts in the air cathode aids the electrochemical reaction of the cell with oxygen gas. Metal-air batteries have attracted significant research attention as the new generation of high-performance batteries as they the advantages of (1) simple structure, (2) extremely high energy density, and (3) a relatively inexpensive production.

The currently existing metal-air batteries use rare and expensive metal catalysts for their air electrodes, such as platinum (Pt) and iridium oxide (IrO?). This has hindered its further commercialization into the marketplace.

In the study, Professor Kim and his research team have developed a new catalyst, using the cation ordered double perovskite with high electrical conductivity and catalyic performance. They prepared a series of PrBa0.5Sr0.5Co2-xFexO5+δ (x = 0, 0.5, 1, 1.5, and 2, PBSCF) and determined the optimum cobalt (Co) and iron (Fe) contents through electrochemical evaluation.

“The structure of mesoporous PrBa0.5Sr0.5Co2-xFexO5+δ nanofiber (PBSCF-NF) has high surface areas, result from uniform pore diameters,” says Ohhun Gwon in the Combined M.S/Ph.D. of Energy and Chemical Engineering, the first author of the study. “This nanofiber has also brought significant improvements in the performance of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER).”

According to the research team, this nanofiber has improved the bi-functionality of ORR/OER. Particularly, the OER performance was about 9 times higher than that of state-of-the-art precious metal oxide IrO2 at overpotential of 0.3 V. Furthermore, it also demonstrated notable charge-discharge stability even at high current density in Zn-air batteries.

“We envision that the high electrochemical and catalytic performance of this material will play a major role in the commercialization of metal-air batteries,” says Professor Kim. “Metal-air battery technology is still in its infancy and extensive additional research efforts appear to be required before a viable commercial implementation is developed.”

He adds, “However, as many global corporates, such as IBM, Toyota, and Samsung Electronics are already working on the development of metal-air batteries, the technical challenges could soon be cleared out in a much faster pace than anticipated.”

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The findings of the research have been published online in the October issue of the prestigious journal ACS Nano. This study has been supported by the Mid-Career Researcher Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT and Future Planning and 2017 Research Fund of UNIST.

Journal Reference

Yunfei Bu, et. al., “A Highly Efficient and Robust Cation Ordered Perovskite Oxides as a Bi-Functional Catalyst for Rechargeable Zinc-Air Batteries”, ACS Nano, (2017).

Cost-effective Production of Hydrogen from Natural Resources


Silican Hydrogen Fuel 040516 id43049Silicon nanosheets (SiNSs) are one of most exciting recent discoveries. Owing to their unbeatable electro-optical properties and compatibility with existing silicon technology, SiNSs have been the most promising candidate for use in various applications, such as in the process of manufacturing semiconductors and producing hydrogen.
 

A joint research team, led by Prof. Jae Sung Lee and Prof. Soojin Park of Energy and Chemical Engineering at UNIST, has developed a a cost-effective and scalable technique for synthesizing SiNSs, using natural clay and salt. Through this research, UNIST has taken a major step towards mass production of this ground-breaking material with relatively low cost.

 

Schematic illustration showing the synthetic process for the preparation of silicon nanosheets
Schematic illustration showing the synthetic process for the preparation of SiNSs.
In their study, published in the current edition of NPG Asia Materials (“All-in-one Synthesis of Mesoporous Silicon Nanosheets from Natural Clay and Their Applicability to Hydrogen Evolution”), the research team reported an all-in-one strategy for the synthesis of high-purity SiNSs through the high-temperature molten salt (for example, NaCl)-induced exfoliation and simultaneous chemical reduction of natural clays.
According to the team, these newly synthesized Si nanosheets are key components in the production of ever smaller electronic devices due to their ultrathin (thickness of ~5 nm) body. Prof. Park states, “As the electrical and electronic devices are getting smaller and smaller, there is a great demand for manufacturing their individual componants to be nanoscale.” He continues, “Our new technique uses inexpensive natural clays and salt for preparing high-quality nanosheets, thereby cutting down production costs greatly.”
As shown in the figure above, in the synthetic process for the preparation of SiNSs, natural clay is exfolicated with molten NaCl. The exfoliated clay is, then, transformed into SiNSs by using Mg reductant. Here, Molten salts can be exchanged with intercalated alkylamines and metal cations inside clays. Then, Mg can reduce the interior of the clay minerals, generating additional heat to induce final exfoliation.
“Through the simultaneous molten-salt-induced exfoliation and chemical reduction of natural clay, both the salt and clay start to melt at a reaction temperature, ranging from 550°C to 700°C. The molten salt is, then, dissolved in the clay layers and disintegrated into individual nanosheets,” said Mr. Jaegeon Ryu, a doctoral researcher in Prof. Soojin Park’s lab and the first author of the study. He continues, “Using the metallothermic reduction, metallic oxides inside clays can be exchanged with silicon.”
The team reports that these nanosheets have a high surface area and contain mesoporous structures derived from the oxygen vacancies in the clay. They add, “These advantages make the nanosheets a highly suitable photocatalyst with an exceptionally high activity for the generation of hydrogen from a water–methanol mixture.”
Source: UNIST