New, inexpensive production materials boost promise of hydrogen fuel

Generating electricity is not the only way to turn sunlight into energy we can use on demand. The sun can also drive reactions to create chemical fuels, such as hydrogen, that can in turn power cars, trucks and trains. Scientists have now combined cheap, oxide-based materials to split water into hydrogen and oxygen gases using solar energy with a solar-to-hydrogen conversion efficiency of 1.7 percent, the highest reported for any oxide-based photoelectrode system.

The trouble with solar fuel production is the cost of producing the sun-capturing semiconductors and the catalysts to generate fuel. The most efficient materials are far too expensive to produce fuel at a price that can compete with gasoline.

"In order to make commercially viable devices for solar fuel production, the material and the processing costs should be reduced significantly while achieving a high solar-to-fuel conversion efficiency," says Kyoung-Shin Choi, a chemistry professor at the University of Wisconsin-Madison.

In a study published last week in the journal Science, Choi and postdoctoral researcher Tae Woo Kim combined cheap, oxide-based materials to split water into hydrogen and oxygen gases using solar energy with a solar-to-hydrogen conversion efficiency of 1.7 percent, the highest reported for any oxide-based photoelectrode system.

Choi created solar cells from bismuth vanadate using electrodeposition -- the same process employed to make gold-plated jewelry or surface-coat car bodies -- to boost the compound's surface area to a remarkable 32 square meters for each gram.

"Without fancy equipment, high temperature or high pressure, we made a nanoporous semiconductor of very tiny particles that have a high surface area," says Choi, whose work is supported by the National Science Foundation. "More surface area means more contact area with water, and, therefore, more efficient water splitting."

Bismuth vanadate needs a hand in speeding the reaction that produces fuel, and that's where the paired catalysts come in.

While there are many research groups working on the development of photoelectric semiconductors, and many working on the development of water-splitting catalysts, according to Choi, the semiconductor-catalyst junction gets relatively little attention.

"The problem is, in the end you have to put them together," she says. "Even if you have the best semiconductor in the world and the best catalyst in the world, their overall efficiency can be limited by the semiconductor-catalyst interface."

Choi and Kim exploited a pair of cheap and somewhat flawed catalysts -- iron oxide and nickel oxide -- by stacking them on the bismuth vanadate to take advantage of their relative strengths.

"Since no one catalyst can make a good interface with both the semiconductor and the water that is our reactant, we choose to split that work into two parts," Choi says. "The iron oxide makes a good junction with bismuth vanadate, and the nickel oxide makes a good catalytic interface with water. So we use them together."

The dual-layer catalyst design enabled simultaneous optimization of semiconductor-catalyst junction and catalyst-water junction.

"Combining this cheap catalyst duo with our nanoporous high surface area semiconductor electrode resulted in the construction of an inexpensive all oxide-based photoelectrode system with a record high efficiency," Choi says.

She expects the basic work done to prove the efficiency enhancement by nanoporous bismuth vanadate electrode and dual catalyst layers will provide labs around the world with fodder for leaps forward.

"Other researchers studying different types of semiconductors or different types of catalysts can start to use this approach to identify which combinations of materials can be even more efficient," says Choi, whose lab is already tweaking their design. "Which some engineering, the efficiency we achieved could be further improved very fast." 

Today, as inspired by the huge energy demands that we are expected to suffer in the following decades, I think that this post is really worth it!

Carbon nanotube fibers outperform copper in carrying electrical current

Carbon nanotube-based fibers have greater capacity to carry electrical current than copper cables of the same mass, scientists show.

Nanotube fibers.

 On a pound-per-pound basis, carbon nanotube-based fibers invented at Rice University have greater capacity to carry electrical current than copper cables of the same mass, according to new research.

While individual nanotubes are capable of transmitting nearly 1,000 times more current than copper, the same tubes coalesced into a fiber using other technologies fail long before reaching that capacity.

But a series of tests at Rice showed the wet-spun carbon nanotube fiber still handily beat copper, carrying up to four times as much current as a copper wire of the same mass.

Scanning electron microscope images show typical carbon nanotube fibers created at Rice University and broken into two by high-current-induced Joule heating. Rice researchers broke the fibers in different conditions -- air, argon, nitrogen and a vacuum -- to see how well they handled high current. The fibers proved overall to be better at carrying electrical current than copper cables of the same mass. (Credit: Kono Lab/Rice University)

That, said the researchers, makes nanotube-based cables an ideal platform for lightweight power transmission in systems where weight is a significant factor, like aerospace applications.

The analysis led by Rice professors Junichiro Kono and Matteo Pasquali appeared online this week in the journal Advanced Functional Materials. Just a year ago the journal Science reported that Pasquali's lab, in collaboration with scientists at the Dutch firm Teijin Aramid, created a very strong conductive fiber out of carbon nanotubes.

Present-day transmission cables made of copper or aluminum are heavy because their low tensile strength requires steel-core reinforcement.

Scientists working with nanoscale materials have long thought there's a better way to move electricity from here to there. Certain types of carbon nanotubes can carry far more electricity than copper. The ideal cable would be made of long metallic "armchair" nanotubes that would transmit current over great distances with negligible loss, but such a cable is not feasible because it's not yet possible to manufacture pure armchairs in bulk, Pasquali said.

In the meantime, the Pasquali lab has created a method to spin fiber from a mix of nanotube types that still outperforms copper. The cable developed by Pasquali and Teijin Aramid is strong and flexible even though at 20 microns wide, it's thinner than a human hair.

Pasquali turned to Kono and his colleagues, including lead author Xuan Wang, a postdoctoral researcher at Rice, to quantify the fiber's capabilities.

Pasquali said there has been a disconnect between electrical engineers who study the current carrying capacity of conductors and materials scientists working on carbon nanotubes. "That has generated some confusion in the literature over the right comparisons to make," he said. "Jun and Xuan really got to the bottom of how to do these measurements well and compare apples to apples."

The researchers analyzed the fiber's "current carrying capacity" (CCC), or ampacity, with a custom rig that allowed them to test it alongside metal cables of the same diameter. The cables were tested while they were suspended in the open air, in a vacuum and in nitrogen or argon environments.

Electric cables heat up because of resistance. When the current load exceeds the cable's safe capacity, they get too hot and break. The researchers found nanotube fibers exposed to nitrogen performed best, followed by argon and open air, all of which were able to cool through convection. The same nanotube fibers in a vacuum could only cool by radiation and had the lowest CCC.

"The outcome is that these fibers have the highest CCC ever reported for any carbon-based fibers," Kono said. "Copper still has better resistivity by an order of magnitude, but we have the advantage that carbon fiber is light. So if you divide the CCC by the mass, we win."

Kono plans to further investigate and explore the fiber's multifunctional aspects, including flexible optoelectronic device applications.

A test rig designed by the Kono Lab at Rice allowed nanofiber and copper cables of equivalent mass to be compared. Image courtesy of the Kono Lab

Pasquali suggested the thread-like fibers are light enough to deliver power to aerial vehicles. "Suppose you want to power an unmanned aerial vehicle from the ground," he mused. "You could make it like a kite, with power supplied by our fibers. I wish Ben Franklin were here to see that!"

The paper's co-authors are Rice alumnus Natnael Behabtu and graduate students Colin Young and Dmitri Tsentalovich. Kono is a professor of electrical and computer engineering, of physics and astronomy, and of materials science and nanoenginyeering. Pasquali is a professor of chemical and biomolecular engineering, chemistry, and materials science and nanoengineering. Tsentalovich, Kono and Pasquali are members of the Richard E. Smalley Institute for Nanoscale Science and Technology.

The key for success is just working hard and try to do your best. But it also has to be with being at the right place at the right time.

Making frozen smoke: Commercializing aerogel fabrication process

One day, "frozen smoke" could improve some of our favorite machines, including cars. 

Aerogel samples.

"When you hold aerogel it feels like nothing -- like frozen smoke. It's about 95 to 97 percent air," said Ann Anderson, professor of mechanical engineering. "Nano-porous, solid and very low density, aerogel is made by removing solvents from a wet-gel. It's used for many purposes, like thermal insulation (on the Mars Rover), in windows or in extreme-weather clothing and sensors."

Together with Brad Bruno, associate professor of mechanical engineering, Mary Carroll, professor of chemistry and others, Anderson is studying the feasibility of commercializing their aerogel fabrication process. A time and money-saver, it could appeal to industries already using aerogel made in other ways.

During rapid supercritical extraction (RSCE), chemicals gel together (like Jell-O) in a hot press; the resulting wet-gel is dried by removing solvents (the wet part). The remaining aerogel (dried gel), is created in hours, rather than the days or weeks alternative methods take.

RSCE, Anderson said, is also approximately seven times cheaper, requiring one hour of labor for every 8 hours the other methods need.

A good place for such a process, and Union aerogel, is the automotive industry.

"Our 3-way catalytic aerogels promote chemical reactions that convert the three major pollutants in automotive exhaust -- unburned hydrocarbons, nitrogen oxides and carbon monoxide -- into less harmful water, nitrogen and carbon dioxide," Anderson said. "Because aerogels have very high surface areas and good thermal properties, we think they could replace precious metals, like platinum, used in current catalytic converters."

Indeed, the surface area of one 0.5-gram bit of aerogel equals 250 square meters.

"That's a lot of surface area for gases to come in contact with, facilitating very efficient pollution mitigation," Anderson said.

The team's work has received support from the National Science Foundation, the ACS Petroleum Research Fund and the Union College Faculty Research Fund.

Such amazing materials are also possible thaks to people that are researching continuously to solve out social demands. I think that we scientists should be more taken into account by the whole community because those developments are of great importance. 

Have a nice and extremely scientific week!

Researcher turns sights on prostate cancer, tissue engineering, blood vessel repair

When biology and materials science converge, the results can be new materials that can be used to deliver targeted drugs, repair damaged arteries or rebuild failing tissues, such as the anterior cruciate ligament, the ACL injury that can end sports careers. One bioengineer is developing polymers designed to target all three.

In this image, polymers are cross linked by both click reactions and condensation reactions and present key-lock clickable surfaces for easy biomolecule conjugation.

Tissue engineering with click chemistry

Finding the right balance between mechanical strength and elasticity in artificial tissue scaffolding has been problematic, as has been the need to add in the desirable traits of biocompatibility and controlled biodegradability. In a recent article in Advanced Materials, Yang and his colleagues in Penn State's Department of Biomedical Engineering and the Academy of Orthopedics of Guangdong Province in China report on the use of thermal click chemistry to make crosslinked citrate-based biodegradable elastomers with high mechanical strength (up to 40 MPa of tensile stress) with easy surface biofunctionalization. In comparison, the ACL has a tensile strength of 38 MPa and most biodegradable elastomers have a dry tensile strength below 10MPa. Click chemistry is a relatively new technique used primarily in drug discovery that uses a few reliable reactions to lock or "click" together small units of biomaterials in simple processes. Yang believes that this is the first reported use of click chemistry to design versatile biodegradable elastomers for tissue engineering.

Beyond superior mechanical strength, Yang's click polymers provide user-friendly and site-specific functionalization with bioactive molecules to, for instance, promote cell growth. In addition the click polymers show a desirable type of biodegradability he calls "first slow then fast." In many tissue engineering applications the preservation of mechanical strength of the artificial scaffolding during the early period of tissue regeneration is important. Yet many elastomeric polymers begin to degrade at a steady rate after implantation. The click polymer in this study, called POC-click-3, had low degradation for a sustained period compared to other polymers, but then rapidly degraded.

Yang and colleagues believe that their clickable biodegradable elastomer design will greatly expand the application of biodegradable polymers in areas such as drug delivery, orthopedic fixation devices, tissue engineering and other types of medical implants. The paper, "Click Chemistry Plays a Dual Role in Biodegradable Polymer Design," was coauthored by Jinshan Guo, Zhiwei Xie, Richard T. Tran and Jian Yang of Penn State, and Denghui Xie, Dadi Jin, and Xiaochun Bai of the Academy of Orthopedics of Guangdong Province.

Blood Vessel Repair

Yang has recently received funding from the National Institutes of Health on a project to develop nanoparticles that promote healing in damaged endothelium, the lining of blood vessels, which can be injured in surgical procedures that unblock clogged arteries.

"Angioplasty and stenting often damage arterial walls," Yang explains, "with a significant risk of subsequent complications, such as re-narrowing of the artery or blood clot." Platelets accumulate on the damaged vessel, initiating clot formation. Other cells can deposit on the cell wall, building up a blockage. The result is multiple surgeries and multiple stent replacements.

Yang and his co-PI Kytai Truong Nguyen at University of Texas Arlington will develop and test a polymer nanoparticle that mimics the platelet in the blood that forms the clot and create a cover over the damage. Their nanoparticle is decorated with a ligand called GP1b peptide that links to endothelial progenitor cells circulating in the blood that can grow into mature endothelial cells. Over time, the nanoparticles will degrade harmlessly as the new blood vessel lining repairs the damage, avoiding the need for a stent. "The surgeon will still do angioplasty first, but not put in a stent. Instead they will inject the nanoparticle solution, if necessary more than once," Yang explains.

"Our nanoparticles have two functions: They will serve as a temporary template to cover injured vascular wall to prevent the underlying smooth muscle cells' over growth inward to block the artery. Once the nanoparticles attach to the vessel wall the platelets cannot attach. Then the nanoparticles will catch the circulating endothelial progenitor cells to form a healthy endothelium on the injured vascular wall. Once the missions are done, the nanoparticles will simply disappear without causing any long-term toxicity. These injectable nanoparticles have worked well in animal models in studies with our collaborators at UT Arlington," Yang says. The team received $1.4 million over four years from the National Institutes of Health to develop this technology.

Attacking prostate cancer

In a second recent award from NIH, Yang and co-principal investigator Jer-Tsong Hsieh, the Dr. John McConnell Distinguished Chair in Prostate Cancer Research at the University of Texas Southwestern Medical Center, received $1.6 million over five years to develop biodegradable nanoparticles to image and treat prostate cancer.

Prostate cancer is the second leading cause of cancer death in American men. If the cancer develops treatment resistance the tumors will keep growing and spread to other parts of the body. To prevent that, Yang and Hsieh will try to identify a prostate cancer specific drug called a genotoxin that will attack the cancer cells, and develop a fluorescent nanoparticle to target the cancer cells. Yang's group plans to add magnetic resonance imaging particles to the fluorescent nanoparticles in order to find the exact location of the tumor. If surgical removal of the cancer is required, fluorescent nanoparticles will attach to cancer cells and help the surgeon identify those small clusters of cancer cells that are usually invisible to the eye.

"We will need to optimize the genotoxin, and make sure we can put it into the nanoparticle. Then we will have to tune the nanoparticle to emit strong fluorescence, and also control the release of the drug into the tumor and not the bloodstream. But we are confident we can do all that," Yang says.

There is a huge need of investing money in this kind of research, otherwise we would not be able to increase the live expectancy. Science is the key, do not forget never this!