This grant provides funding for the development of a processing technique to manufacture nanocrystalline thermoelectric oxides for high efficiency energy harvesting; waste heat can be captured and converted to electricity. This process will provide a viable manufacturing technique that has the potential to be both economical and scalable. Thermo-electric oxide material will be electrospun into nanofibers which will then be consolidated via sintering into high-density high-efficiency bulk thermoelectric oxides with nanocrystalline structure. The resulting grain size is expected to be in the range of tens of nanometers which should substantially reduce the thermal conductivity of the material and at the same time improve the thermoelectric figure-of-merit (i.e conversion efficiency). Detailed and systematic characterization of the resulting structure and properties of thermoelectric nanofibers and bulk nanocrystalline oxides will also be carried out to investigate the processing-structure-property relationship of thermoelectric oxides. Thermoelectric materials that convert heat directly into electricity is promising in harvesting a vast amount of waste heat lost in energy cycle in an environment friendly manner.
If successful, the results of this research will lead to thermoelectric oxide materials with improved thermoelectric figure-of-merit and conversion efficiency, and will lay a foundation for high efficiency energy harvesting of waste heat. The manufacturing technique developed in this project can also be applied to process other nanocrystalline materials for a wide range of applications. The project will train graduate and undergraduate students. It will also offer outreach activities to K-12 schools though the Research Experience for Teachers program (RET), summer internship for high school students, and science demos at elementary schools.
Thermoelectric materials are capable of converting waste heat directly into electricity, as well as solid state heating and cooling. In this project, we developed a novel manufacturing technique to process nanocrysalline thermoelectric oxides in an effective, scalable, and economical manner. Specific outcomes include: (1) developing one-dimensional nanocrystalline thermoelectric oxide nanofibers using sol-gel based electrospinning process, with grain size in the range of 10~20nm and their thermoelectric effect confirmed by novel atomic force microscopy based techniques; (2) processing high-density bulk thermoelectric oxides from the electrospun nanofibers using spark plasma sintering and hot pressing, which show enhanced thermoelectric figure of merit compared to ceramics sintered from sol-gel processed powders; and (3) enhancing thermoelectric efficiency of nanostructured oxides by developing hybrid materials through doping and nanoscale second-phase fillers. Furthermore, we have also developed techniques and instrumentations to characterize the thermoelectric properties of oxides, as well as computational tools to predict thermoelectric properties of single-phase and composite materials. In particular, it has been demonstrated theoretically that the conversion efficiency of thermoelectrics can be improved by composite approach. On the broader impact, a number of undergraduate and graduate students were trained in the project, and a graduate/undergraduate course on thermoelectrics has been developed. Outreach activities including lab open house and demonstrations were carried out for K12 students as well as members of congress and their staffs. In particular, we have developed a demonstration unit that powers a fan by body heat from palm based on thermoelectric effect.
