Resource World Magazine

90 www.resourceworld.com F E B R U A R Y / M A R C H 2 0 2 0 Green Technologies by Jane Foutz NEW DISCOVERY BOOSTS SILICON'S EFFI- CIENCY IN CONVERTING LIGHT TO ENERGY A team of researchers at The University of Texas, Austin and the University of California, Riverside have found a way to produce an energy transfer among sili- con and organic carbon-based molecules. This breakthrough has implications for information storage in quantum comput- ing, solar energy conversion, and medical imaging. The research is described in the journal, Nature Chemistry. According to the researchers, silicon is one of the planet's most abundant materi- als and a critical component in everything from the semiconductors that power our computers to the cells used in nearly all solar energy panels. Silicon has some problems, however, when it comes to con- verting light into electricity. Different light colors comprise photons, particles that carry light's energy. Silicon can efficiently convert red photons into electricity, but with blue photons, which carry twice the energy of red photons, silicon loses most of the energy as heat. The new discovery provides scientists with a way to boost silicon's efficiency by pairing it with a carbon-based material that converts blue photons into pairs of red photons that can be more efficiently used by silicon. This hybrid material can also be manipulated to operate in reverse, taking in red light and converting it into blue light, which has implications for medical treatments and quantum computing. "The organic molecule we've paired silicon with is a type of carbon ash called anthracene. It's basically soot," said Sean Roberts, a University of Texas, Austin assistant professor of chemistry. The paper describes a method for chemically con- necting silicon to anthracene, creating a molecular power line that allows energy to transfer between the silicon and the ash- like substance. "We now can finely tune this material to react to different wave- lengths of light. Imagine, for quantum computing, being able to tweak and opti- mize a material to turn one blue photon into two red photons or two red photons into one blue. It's perfect for information storage." "The challenge has been getting pairs of excited electrons out of these organic materials and into silicon. It can't be done just by depositing one on top of the other," Roberts said. "It takes building a new type of chemical interface between the silicon and this material to allow them to electron- ically communicate." Other efficient processes, called pho- ton up-conversion, previously relied on toxic materials. As the new approach uses exclusively non-toxic materials, it opens the door for applications in human medicine, bio-imaging and environmen- tally sustainable technologies, something that Roberts and fellow chemist Michael Rose are working toward. Funding for the research was provided by the National Science Foundation, the Robert A. Welch Foundation, the Research Corporation for Science Advancement, the US Air Force Office of Scientific Research and the US Department of Energy. LIQUID METAL CONVERTS WASTE HEAT TO ENERGY University of Texas at Dallas research- ers have developed a generator prototype that uses liquid metal to convert waste heat from sources, such as electric cars or data centers, into clean electricity. Said Dr. Babak Fahimi, Distinguished Chair in Engineering and professor of electrical engineering, "In data centers, for example, we spend a lot of time getting rid of the heat by using chillers and air condition- ing. Our work focuses on recycling that heat back to electricity." Data centers, electric car batteries and appliances, such as air conditioners gen- erate a largely untapped potential energy source, according to Fahimi. Most efforts to harvest energy from waste heat have focused on the heat byproducts from manufacturing, refineries and steel mills, which generate high temperatures. The project zeroes in on sources that generate lower-temperature heat, between 80 and 115 degrees Fahrenheit, which have been more challenging to convert to electricity. The researchers started with a magne- tohydrodynamic power (MHD) generator, a device that generates electricity by mov- ing fluid through a magnetic field. MHD generators were developed in the 1960s, but the technology has not been widely used. The technology has many potential applications. For example, data centers – the computers that store massive amounts of information that users access through cloud computing produce substantial waste heat while also consuming a lot of electricity. The technology also could improve the efficiency of electric vehicles by converting heat from the cars' batteries and exhaust (hybrid EVs) into electricity. "Renewable sources of energy such as electric cars all have fantastic merits. One thing we don't do anything about is how to recycle the heat they gener- ate," said Fahimi, founding director of the Renewable Energy and Vehicular Technology Laboratory at the university. He said, "If there is a way to recycle that heat back to electricity that would be fan- tastic." The research was funded by The University of Texas at Dallas. ELECTRIC CAR BATTERY CHARGING TIME REDUCED Researchers at Penn State University in

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