Thursday, October 20, 2011: 12:30 PM
L100 H (Minneapolis Convention Center)
A scalable nanomanufacturing technique is reported for batch fabrication of electrically-conducting 2D metal-oxide nanosheets of Na0.7CoO2. We report a sol-gel based, high temperature bottom-up synthesis which is a cost-effective route capable of producing tens of thousands of nanosheet layers packed into a macro-scale pellet. The synthetic procedure consists of sol-gel coordination of metal ions, auto-combustion, pressurized pellet formation, kinetic demixing, and calcination. The nanosheets are uniform in length and shape with highly anisotropic dimensions of nanometer sheet thickness and millimeter lateral lengths (10-5:1:1), and are readily delaminated into free-standing nanosheets. According to GIXRD, the nanosheet stacking has turbostratic arrangement with nanosheets misaligned rotationally with respect to stacking axis. Na0.7CoO2, in bulk form, is already a surprisingly good thermoelectric material with a thermoelectric (TE) power factor as high as the industry standard Bi2Te3 (50 vs. 40 µW/K2cm respectively). Also, it has been reported in the literature that 2D nanosheets are observed to reduce thermal conductivity of materials with a factor ~102 due to phonon confinement, which provides a significant increase in the thermoelectric efficiency. Therefore, in conjunction with low fabrication cost, the reported millimeter length Na0.7CoO2 nanosheets are expected to provide high thermoelectric efficiency with practical importance. Preliminary thermoelectric measurements have been obtained for turbostratically aranged millimeter-length nanosheet stackings.