Purdue University School of Chemical Engineering GRADUATE SEMINAR SERIES Prof. Yue Wu School of Chemical Engineering "Advanced Nanostructures for Thermoelectric Applications" January 15, 2013 9:00-10:15 a.m. FRNY G140 Reception at 8:30 a.m. in Henson Atrium Abstract: According to a Lawrence Livermore National Lab survey in August 2010, nearly 57.8% of the total generated energy in US in 2009 was rejected into the environment, the majority being from power plants, transportation and manufacturing industries. Most of this waste heat is considered low-grade (40°C - 200°C), a level which is generally considered economically infeasible to recover at a high efficiency; consequently, it is typically dumped into the environment, mainly the aquatic ecosystem (especially for power plants and manufacture industries), through various cooling processes. Heat pollution can have a great negative influence on the surrounding aquatic ecosystems and these system inefficiencies also lead to higher energy costs overall. The rapid development of thermoelectric materials in the past decade has brought a new hope to the possibility of directly converting waste heat back to electricity based on the Seebeck effect. The performance of thermoelectric materials can be rated through a dimensionless quantity called figure of merit or ZT (ZT= σS2T/κ), where σ, κ, and S stand for electrical conductivity, thermal conductivity, and Seebeck coefficient, respectively. T is the average temperature between the hot and the cold sides. Recent efforts on the development of nanostructured thermoelectric materials from nanowires and nanocrystals show comparable or superior performance to bulk crystals with the same chemical compositions because of the dramatically reduced thermal conductivity due to phonon scattering at nanoscale surfaces and interfaces. However, critical gaps still remain that prevent scalable, practical manufacture and wide deployment of thermoelectric devices. First, most conventional thermoelectric materials, including both bulk crystals and nanostructured materials, are based on tellurides, antimonides, germanium, and rare earth element doped compounds. The bulk crystals or the composite disks fabricated by compressing/ sintering nanomaterials are micro-machined into millimeter-thick pillar structures; such processes impose a high demand on these expensive, scarce, and sometimes toxic materials. Further, during manufacture, much material is wasted, causing adverse environmental impact and high recycling costs. Second, the majority of nanostructure-based thermoelectric research is limited to lab-scale device fabrication and measurements performed on a single nanowire or a thin film of nanocrystals or heterostructures with maximum dimensions of hundreds micro-meters; this is mainly due to the lack of scalable and reproducible synthesis. In most cases, only milligrams of these nanomaterials can be obtained and there are large variations between different batches of samples. In the past three years, we have developed a transformative approach to address these challenges: (1) we have pioneered low cost and scalable solution-phase growth methods to mass produce thermoelectric nanowires and nanowire heterostructures to match the physical and economic magnitudes of energy use and economical sustainment in the manufacture/recycling; (2) we have enforced the compatibility and integratability of our material synthesis and process with existing manufacture infrastructure. Specifically, solution-phase production of nanomaterials with uniform morphology, size, and properties at industrial scale (at least kilogram level in relatively short period of time) using industrial standard reactors has been achieved so that the bulk thermoelectric properties can be measured on the bulk nanocomposite disks fabricated by spark plasma sintering or hot pressing the nanopowders. Notably, ball milling technique has been used to make bulk nanocomposite thermoelectric devices from the nanopowders with enhanced ZT, however, it is typically considered as an energy intensive process and lacks of good control in many key parameters. As a long-term goal, we have also explored the non-toxic and abundant complex metal oxide and sulfide based new thermoelectric materials for various temperature ranges. Traditional tellurides, antimonides, germanium, and rare earth doped compounds based thermoelectric materials exhibit a few obvious drawbacks, including the material instability (oxidation or decomposition) at high temperature, environmental concern of toxic heavy metals, and high recycling cost. Bio: Prof. Yue Wu graduated with best thesis award from Prof. Yitai Qian's group at University of Science and Technology of China (USTC), Hefei, Anhui, P. R. China, with a bachelor's degree in Chemistry in June, 2001. Then, he went to Harvard University and studied for his doctoral degree under the supervision of Prof. Charles M. Lieber. His Ph.D. research achievement on nanowire-based nanoelectronic devices has been featured by many public press releases, including Chemical and Engineering News, MRS Bulletin, Nature magazine, Materials Today magazine, Technology Review, and several awards, for example, Materials Research Society (MRS) Graduate Student Gold Award and Excellent Overseas Chinese Graduate Student Award from the Scholarship Council of the Ministry of Education in China. Prof. Wu received his doctoral degree in June, 2006 and was awarded the prestigious Miller Fellowship from University of California at Berkeley. At Berkeley, he worked with Prof. A. Paul Alivisatos for three years on nanostructure-based photovoltaic solar cells. In August 2009, Prof. Yue Wu joined the School of Chemical Engineering at Purdue University. His research is focusing on the improvement of energy efficiency through waste heat recovery into electricity using advanced nanostructured thermoelectric materials. In the past three years, Prof. Yue Wu's research has addressed many critical gaps in the field of thermoelectric and has led to many publications on high-profile journals, including five papers on Nano Letters (impact factor 13.198), two invited review articles, and one feature articles. His personal H-index is 20 with a total citation over 3800 times. Among his most highly cited publications, there are two on Nature (with citations of 630 and 527 times each) and two on Nano Letters (with citations of 495 and 472 times each). His innovative research has received many public media exposures, including Chemical & Engineering News, National Public Radio, etc. His research has also generated six pending patent applications filed by Purdue Research Foundation with two of them being pending for license and significant industrial collaborations with the world-leading companies like Intel, DuPont, Kaiteki Institute (by Mitsubishi Chemical), Electrical Power Research Institute (EPRI), DOW Chemical, and AZDEL. As a young faculty member, he is also the recipient of Air Force Summer Faculty Fellowship for three consecutive years (2010, 2011, and 2012), DuPont Young Professor Award, and he is one of the only two Purdue Nominees for the Packard Foundation Fellowship in 2010. His contribution to technology development has also been recognized by Nanotechnology Venture Competition Award (both individual award and team award as team leader) sponsored by the State of Indiana, Purdue University, and University of Notre Dame. His research has also received a lot of global attention/recognition and he has been invited as one of the only two invited speakers from United States (totally only ten worldwide) for Japan Nano 2013 sponsored by Japan National Institute of Materials Sciences and Japan Ministry of Education.