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Nanomaterials Hold Promise for Producing Hydrogen from Water

March 21, 2018
Nanomaterials Hold Promise for Producing Hydrogen from Water

Hydrogen holds promise as an inexpensive form of clean energy, but finding an efficient and affordable way to produce the fuel from water – a technique known as water-splitting – remains a key scientific challenge.

A researcher from the University of Houston is working with a colleague in Taiwan to use hollow gold-silver nanoshells to boost the efficiency of photocatalysts, where the combined nanocomposite materials generate hydrogen from water, powered only by sunlight.

Randall Lee, Cullen Distinguished University Chair in chemistry and associate dean for research in the UH College of Natural Sciences and Mathematics, said the nanoshells allow the composite photocatalyst system to absorb a wider spectrum of available light, enhancing the ability of the photocatalyst to separate hydrogen from the water, leaving only oxygen as the byproduct.

Lee also is affiliated with the Texas Center for Superconductivity at UH. His work on the project is funded by a $150,000 grant from the U.S. Air Force Office of Scientific Research and follows several years of participation in the U.S. Air Force-Taiwan Nanoscience Initiative. His collaborator, Tai-Chou Lee of National Central University in Taoyuan City, Taiwan, was a former post-doctoral researcher in his lab at UH.

Hydrogen can be used in the form of fuel cells to power electric motors or burned in internal combustion engines. But finding a practical, inexpensive and environmentally friendly way to produce large amounts of hydrogen gas has been elusive.

Most hydrogen today is produced through steam methane reforming and coal gasification, methods that lack portability and raise the fuel’s carbon footprint despite the fact that it burns cleanly. Being able to produce hydrogen reliably and cheaply using only water and sunlight would be a major breakthrough.

Lee’s laboratory focuses on nanoparticles, nanoscale thin films and coatings and other nanomaterials for the energy and health care industries, while Tai-Chou Lee - the two are not related - works in photocatalysis, using light to trigger a chemical change.

UH's Lee said putting the two together - using surface-modified hollow gold-silver nanoshells to boost the efficiency of Tai-Chou Lee’s catalyst - is a marriage of fundamental research with an end application.

While traditional photocatalysts typically absorb light in the ultraviolet and short-wavelength visible ranges, adding the nanoshells allows the catalyst system to make additional use of long-wavelength visible and near infrared wavelengths, boosting its overall efficiency.

The researchers last year published early results from the work; Lee said the latest grant will allow him to enhance the efficiency of the nanoshells, which are made from a combination of gold and silver but coated with a dielectric material that is critical to achieving abundant hydrogen production.

“If you can use sunshine to generate fuel from water, that’s a really clean source of energy,” said Lee.

For more information, read the original news release.

New Approach Boosts Performance in Thermoelectric Materials

September 18, 2017
New Approach Boosts Performance in Thermoelectric Materials

Thermoelectric materials are considered a key resource for the future - able to produce electricity from sources of heat that would otherwise go to waste, from power plants, vehicle tailpipes and elsewhere, without generating additional greenhouse gases. Although a number of materials with thermoelectric properties have been discovered, most produce too little power for practical applications.

A team of researchers - from universities across the United States and China, as well as Oak Ridge National Laboratory - is reporting a new mechanism to boost performance through higher carrier mobility, increasing how quickly charge-carrying electrons can move across the material. The work, reported this week in the Proceedings of the National Academy of Science, focused on a recently discovered n-type magnesium-antimony material with a relatively high thermoelectric figure of merit, but lead author Zhifeng Ren said the concept could also apply to other materials.

“When you improve mobility, you improve electron transport and overall performance,” said Ren, M.D. Anderson Chair professor of physics at the University of Houston and principal investigator at the Texas Center for Superconductivity at UH.

Thermoelectric materials produce electricity by exploiting the flow of heat current from a warmer area to a cooler area, and their efficiency is calculated as the measure of how well the material converts heat into power. However, because waste heat is both an abundant and free source of fuel, the conversion rate is less important than the total amount of power that can be produced, Ren said. That has prompted researchers to look for ways to improve the power factor of thermoelectric materials.

Paul Ching-Wu Chu, TLL Temple Chair of Science, founding director and chief scientist of the Texas Center for Superconductivity, noted that Ren previously had demonstrated the importance of a material’s power factor in determining how well it will work in a thermoelectric device. Chu is a co-author for this most recent work, which he said “demonstrates in the n-type magnesium-antimony-based materials that the power factor can indeed be enhanced by properly tuning the carrier scattering in the material.”

“That provides a new avenue to more powerful thermoelectric devices,” he added.

Thermoelectric semiconductors come in two variations, n-type, created by replacing an element resulting in a “free” electron to carry the charge, and p-type, in which the replacing element has one fewer electron than the element which it replaced, leaving a “hole” that facilitates movement of energy as the electrons move across the material to fill the vacant spot.

The work reported in PNAS addresses the need for a more powerful n-type magnesium-antimony compound, expanding its potential as a thermoelectric material that can be paired with an effective p-type magnesium-antimony material, which had been previously reported.

The material’s power factor can be boosted by increasing carrier mobility, the researchers said. “Here we report a substantial enhancement in carrier mobility by tuning the carrier scattering mechanism in n-type Mg3Sb2-based materials,” they wrote. “… Our results clearly demonstrate that the strategy of tuning the carrier scattering mechanism is quite effective for improving the mobility and should also be applicable to other material systems.”

The researchers replaced a small fraction of magnesium in the compound with a variety of transition-metal elements, including iron, cobalt, hafnium and tantalum, to determine how best to boost carrier mobility and, through that, the material’s power factor.

“Our work,” the researchers conclude, “demonstrates that the carrier scattering mechanism could play a vital role in the thermoelectric properties of the material, and the concept of tuning the carrier scattering mechanism should be widely applicable to a variety of material systems.”

In addition to Chu and Ren, researchers involved with the project include Jun Mao, Jing Shuai, Shaowei Song and Zihang Liu, all of the University of Houston; Yixuan Wu and Yanzhong Pei of Tongji University; Rebecca Dally and Stephen Wilson of the University of California, Santa Barbara; Jiawei Zhou and Gang Chen of the Massachusetts Institute of Technology; Jifeng Sun and David Singh of the University of Missouri; Qinyong Zhang of Xihua University and Clarina dela Cruz of the Oak Ridge National Laboratory.

For more information, read the original news release.

Inexpensive Organic Material Gives Safe Batteries a Longer Life

June 19, 2017
Inexpensive Organic Material Gives Safe Batteries a Longer Life

Modern batteries power everything from cars to cell phones, but they are far from perfect - they catch fire, they perform poorly in cold weather and they have relatively short lifecycles, among other issues. Now researchers from the University of Houston have described a new class of material that addresses many of those concerns in Nature Materials.

The researchers, led by Yan Yao, associate professor of electrical and computer engineering, report their use of quinones - an inexpensive, earth-abundant and easily recyclable material - to create stable anode composites for any aqueous rechargeable battery.

"This new material is cheap and chemically stable in such a corrosive environment," said Yao, who is also a principal investigator with the Texas Center for Superconductivity at UH, with an appointment to the chemical and biomolecular engineering faculty. The material also can be used to create a "drop-in replacement" for current battery anodes, allowing the new material to be used without changing existing battery manufacturing lines, he said.

"This can get to market much faster," he said.

Yao and his lab, including research associate Yanliang Liang, who served as first author on the paper, began the work in 2013, after he was awarded $1 million from the Department of Energy's Advanced Research Project Agency - Energy (ARPA-E) RANGE program to develop new battery technology. Other researchers involved in the project include Yan Jing, Saman Gheytani and Kuan-Yi Lee, all of UH, Ping Liu of the University of California-San Diego, and Antonio Faccheti of Northwestern University.

Energy storage is the key to wider adoption of electric cars, wind and solar power, along with other clean energy technologies. But the development of battery storage systems, which would be able to store energy until it is needed and then be recharged with additional generation, has been hampered by the lack of batteries that meet a variety of requirements: environmentally friendly, safe, inexpensive and long-lasting.

"Aqueous rechargeable batteries featuring low-cost and nonflammable water-based electrolytes are intrinsically safe and ... (provide) robustness and cost advantages over competing lithium-ion batteries that use volatile organic electrolytes and are responsible for recent catastrophic explosions," the researchers wrote. But state-of-the-art aqueous rechargeable batteries have a short lifespan, making them unsuitable for applications where it isn't practical to replace them frequently.

The stumbling block, Yao said, has been the anode, the portion of the battery through which energy flows. Existing anode materials are intrinsically structurally and chemically unstable, meaning the battery is only efficient for a relatively short time.

They worked with quinones, an earth-abundant organic material which Yan said costs just $2 per kilogram, demonstrating the material's benefits in three formulations.

The differing formulations offer evidence that the material is an effective anode for both acid batteries and alkaline batteries, such as those used in a car, as well as emerging aqueous metal-ion batteries, Liang said. That means the quinones-based anode will work regardless of which technology dominates in the future, he said.

The new material also allows the batteries to work across temperature ranges, Liang said, unlike some conventional aqueous batteries, which are notoriously balky in cold weather.

Yao said consumers would quickly notice one key difference in this change to existing battery technology. "One of these batteries, as a car battery, could last 10 years," he said. In addition to slowing the deterioration of batteries for vehicles and stationary electricity storage batteries, it also would make battery disposal easier because the material does not contain heavy metals.

The researchers have filed for three patents for the technology and hope to find partners to commercialize the technology.

For more information, read the original news release.

Researchers Discover More Efficient Way to Split Water, Produce Hydrogen

September 19, 2016
Researchers Discover More Efficient Way to Split Water, Produce Hydrogen

Inexpensive, Nontoxic Catalyst Could Help Reduce Global Reliance on Fossil Fuels

Hydrogen is often considered a fuel for the future, in the form of fuel cells to power electric motors or burned in internal combustion engines. But finding a practical, inexpensive and nontoxic way to produce large amounts of hydrogen gas - especially by splitting water into its component parts, hydrogen and oxygen - has been a challenge.

A team of researchers from the University of Houston and the California Institute of Technology has reported a more efficient catalyst, using molybdenum sulfoselenide particles on three-dimensional porous nickel diselenide foam to increase catalytic activity.

The foam, made using commercially available nickel foam, significantly improved catalytic performance because it exposed more edge sites, where catalytic activity is higher than it is on flat surfaces, said Zhifeng Ren, MD Anderson Professor of physics at UH.

Ren is lead author of a paper in Nature Communications describing the discovery. Other researchers involved include Haiqing Zhou, Fang Yu, Jingying Sun, Ran He, Shuo Chen, Jiming Bao and Zhuan Zhu, all of UH, and Yufeng Huang, Robert J. Nielsen and William A. Goddard III of the California Institute of Technology.

For more information, read the original news release.

Houston scientist Dr. Paul Chu upends the physics world

July 24, 2016
Houston scientist Dr. Paul Chu upends the physics world

Thousands of scientists crammed the hallways of the Hilton Hotel in New York, jockeying for a seat inside the ballroom. Televisions were set up for the unlucky who couldn't squeeze inside for the event, which would later be dubbed the "Woodstock of Physics."

For more information, read the original news release.

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