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Powering our future

Michael Stavola shows a block of multicrystalline silicon, used by engineers to make solar cells.

The Fusion Research Group includes Alexi Pankin, Tariq Rafiq, Arnold Kritz and Glenn Bateman.

Researchers are faced with many challenges in the new millennium, and undoubtedly one of the biggest is finding a cheap and efficient way to harness alternative energy. As natural resources become depleted, scientists and engineers are seeking new ways to fuel the world's power grid.

In the College of Arts and Sciences, basic and applied scientists are working to create new sources of energy while trying to understand the defects that cause existing methods to be ineffective. Designing a new application like fusion has the potential to revolutionize the way society obtains energy, while revamping sources like solar power and fuel cells will make existing models more efficient and economical.

Fusion fix 

When it was first conceived in the 1950s, it was easy for scientists to dismiss the concept of fusion-a self-sustaining stream of energy-as a pipe dream. Fusion, which uses magnetically confined plasma to generate unlimited amounts of energy, occurs when hydrogen atoms collide and fuse together under extreme heat and pressure. But in the last decade, a growing body of evidence is starting to show that the once fantastical idea may in fact contribute to the ultimate solution. 

"In terms of developing a long-term sustainable form of energy, fusion really is the bright hope on the horizon," says Arnold Kritz, professor of physics, who has been studying fusion for 40 years. "The debate surrounding the concept of fusion isn't a scientific one-we know that fusion works. The question is whether it can produce energy on a large scale at an economic cost that society can sustain." 

Unfortunately, it is also a question that may take several decades to answer with any certainty. The International Thermonuclear experimental Reactor (ITER), the $10 billion international project designed to build an experimental fusion reactor, known as a tokamak, in Southern France, won't be ready for initial tests until 2020. And even after the demo reactor is created and tested, it typically takes 15 to 25 years for any new technology to be adopted into the power grid. 

In an energy crisis, there is no time to waste on a concept that could fail. That is why Kritz has spent more than 20 years designing a predictive integrated modeling capability- that simulates the actual physical phenomena that occur inside a tokamak. 

"By gaining a deeper understanding of the fundamental phenomenon that governs the behavior of these plasmas, we can simulate exactly what is going on in the tokamak in terms of atomic physics, radiation, energy transport, particle transformation and the flow of heat," Kritz explains. 

Tokamaks use magnetic fields to control the location of electrically charged particles, causing the particles to undergo fusion rather than lose their energy to the wall. So far, scientists have proven that fusion is possible by generating 16 megawatts of fusion power in a tokamak in England, but in order for fusion to be self-sustaining, these tokamaks need to generate power without input power from the grid. Kritz and colleagues in the Lehigh Fusion Group have been able to show these conditions are possible using the predictive integrated modeling computer codes.

"Our simulations have shown that inputting 40 to 50 megawatts of power and outputting 400 to 500 megawatts is a reasonable expectation for the ITER tokamak," Kritz reports. 

Fusion modeling research carried out at Lehigh is essential to ITER's success. Once the fusion reactor is built, every 400-second experiment will have an amortized cost of $1 million. As a result, researchers need to know exactly what to expect and be ready to interpret the data. 

As a leading researcher in the field, Kritz has monitored fusion research grants for the U.S. Department of Energy. He collaborates with other major fusion centers, like General Atomics in San Diego, the Princeton Plasma Physics Laboratory, and MIT's Plasma Science and Fusion Center, to verify his results, but the predictive integrative model is unique to Lehigh. Recently, his team was also called upon by the U.S. Department of Energy to work on a hybrid application of fusion research that combines it with fission capabilities, which involve splitting atoms to produce a self-sustaining stream of energy. It is possible that a fusion-fission hybrid may result in fusion contributing to energy production in the next 10 or 15 years. 

Energy economics 

Fusion research, while bright, will take at least another 70 years to develop. Therefore, in addition to creating new sources of energy, researchers must also maximize the potential of existing forms of alternative energy. At Lehigh, scientists are studying ways to make renewable sources of energy, like solar, more efficient. Solar cells are relatively easy to make, but high price tags have kept them from receiving widespread adoption.

That is where Michael Stavola, professor of physics and associate dean for research and graduate programs, comes in. His laboratory seeks to understand one of the most basic material problems in engineering: making cheap materials function well. 

"Solar energy is a perfect source of energy," says Stavola. "There are no carbon emissions, pollution or radioactive wastes. The only issue is cost. We have to find a way to make solar cells cheap enough to compete with burning oil or coal, without sacrificing their ability to generate electricity."

Silicon, the second most plentiful element in the earth's crust, is used in more than 90 percent of solar cells for power modules. Its most perfect form, single-crystal silicon- which is used in microchips-can be used to manufacture solar cells with high efficiencies but is too expensive for widespread use. To keep costs down, manufacturers use a cheaper, less pure form of silicon called multicrystalline silicon. But as a result, these solar cells are less efficient and generate less electricity.

"It is a fairly common problem," he says. "Lower the quality and cost of the materials and the number of defects increases."

It's a simple problem, but with a not-so-simple solution. Stavola says it is impossible to make these defects go away entirely. Instead, engineers have learned to live with them. For nearly 25 years, he and his students have been working to understand the chemistry and physics of the defects that exist in semiconductors. In particular, his team has been studying the role hydrogen plays and its ability to neutralize undesirable defects and impurities.

Adding hydrogen makes solar cells produced from inexpensive, defective silicon materials more efficient. "Hydrogen acts as a Band-Aid of sorts," Stavola explains. "You get your energy at a reduced price."

"Engineers have learned to make solar cells from multicrystalline silicon, but scientists do not understand the basic chemistry of the impurities that exist in them. There is an entire layer of fundamental science associated with the effect of hydrogen on the production of industrial solar cells that we do not understand. 

"After 25 years of fundamental research on hydrogen in semiconductors, we can now apply what we have learned to problems that will help industry create better solar cells." 

Fundamental thinking 

Fundamental scientists test and troubleshoot the basic principles and ideas that are someday, hopefully, put into application by engineers. Another researcher going back to the basics is David Moore, assistant professor of chemistry. As a nanoscientist, he manipulates chemical structures on the atomic level. Though still in its adolescence, his research aims to provide the basic understanding that is needed to improve existing alternative energy applications. 

"Nanoparticle catalysts have shown great promise in alternative energy applications, but in many cases, that potential has not been realized due to practical difficulties," he explains. "The exploration of the fundamental science of nanoparticle catalysts provides vital information to scientists and engineers working to develop and improve alternative energy technologies such as hydrogen fuel cells." 

In the lab, Moore studies the interaction between molecules and nanoparticle catalysts, which are used to speed up chemical reactions in fuel cells and show great promise for future alternative energy applications. The problem, however, is that scientists do not always understand the fundamental chemical mechanisms underlying the practical applications. That is why Moore is taking a step back and trying to understand the basic science behind how these nanoparticle catalysts effect chemical changes in reactant molecules. Such low-level interactions between molecules and nanoparticles are studied routinely using computational chemistry, but Moore's research represents the first direct experimental observation of these processes. "The computational results can be extraordinarily useful, but we must be sure that they truly reflect the experimental reality of the system," says Moore. 

Moore's approach is to trap nanoparticles and reactant molecules in an ultracold environment, in order to study how the nanocatalysts speed up important chemical reactions. His initial experiments aim to elucidate catalytic oxidation of carbon monoxide on gold nanoparticles. Carbon monoxide is a potent poison for the platinum nanocatalysts used in electrochemical hydrogen fuel cells, and thus must be eliminated from hydrogen fuel streams. 

"Catalysis is all about improving the speed and efficiency of chemical reactions," says Moore. "Carbon monoxide oxidation is ordinarily a very slow process, but these gold nanocatalysts speed it up quite dramatically. The problem is that no one knows precisely how they do it. 

"Not knowing the mechanism might not be such a big deal if the gold nanocatalysts worked perfectly," he explains, "but unfortunately that's not the case. While their initial activity may be very high, it falls off too quickly for practical use." 

Moore hopes that gaining a deeper understanding of the catalytic mechanisms involved will help speed development of improved catalysts. "Once we have a handle on the basic science, we can use our technique to compare and contrast different nanocatalyst materials, to identify those that exhibit similar catalytic properties." A particular focus is to find alternatives to the use of precious metals, to lower costs and enhance sustainability of these technologies. 

Moore's long-term goal is to use his experimental techniques to bring to light details of the chemistry underlying many different alternative energy applications. 

"Hydrogen fuel cells, efficient batteries, solar cells, artificial photosynthesis-all of these technologies are based on catalysis, and there are nanoparticle-based approaches to all of them, yet in no case is the fundamental chemistry completely understood," says Moore. "If we can help gain this understanding, it should speed development of these vital new technologies."

Story by Carolyn Sayre

Posted on Monday, June 07, 2010

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