Image courtesy of Richard Robinson
2D nanosheets of sodium cobalt oxide made from a novel new process (top: scanning electron microscope image of stacked and folded nanosheets, and bottom: transmission electron microscope image combined with optical microscope image of 350 micron-long exfoliated nanosheet).
Researchers developing a novel synthesis technique using electric fields to move sodium (Na) atoms in solution-processed mixed metal oxides have created millimeter-length nanosheets of sodium cobalt oxide (NaxCoO2). Nanosheets are expected to have different properties than the bulk materials from which they originate. The creation of new nanosheet materials is leading researchers to explore whether valuable properties—such as high thermoelectric power factor, high electrical conductivity, superconductivity, and strong correlation of charge carriers—are enhanced in nanosheet form.
This novel, scalable and low-cost synthesis method enables fabrication of millimeter lengths of nanometer-thick sheets of a complex metal oxide, and is capable of producing tens of thousands of nanosheets with dimensions large enough to use in devices. For example, NaxCoO2 has potential as a cathode material in sodium ion batteries and as an electrocatalyst support in fuel cells.
Scientists at the Energy Materials Center at Cornell (emc2), a DOE Energy Frontier Research Center, have developed a novel synthesis for millimeter-length nanosheets of the complex metal oxide, sodium cobalt oxide (NaxCoO2). The scalable method is capable of producing tens of thousands of nanosheets with dimensions large enough to use in devices. Similar to the unusual 2-D form of carbon known as graphene, nanosheets of metal oxide crystals present exciting opportunities to study and exploit their novel electronic, ferromagnetic, magneto-optical, electrochemical, catalytic, and photoresponsive properties, while being stable at high temperatures and in severe chemical environments. Researchers used an electric field to move, or demix, the sodium (Na) cations in a pellet of mixed metal oxides. The nanosheets formed in the resulting Na-enriched regions of the pellet have thicknesses in the tens of nanometers while their lateral lengths are millimeters, resulting in a very dramatic, anisotropic aspect ratio (10–5: 1 : 1). The stacks of nanosheets are readily peeled-off to make free-standing, individual sheets, reaching up to 350 microns in length with thicknesses of only 20–100 nm. Although they are ceramics, these nanosheet materials display ductility during bending and the individual nanosheets are transparent to visible light.
Richard D. Robinson
Director of the Energy Materials Center at Cornell EFRC
DOE Office of Science, Office of Basic Energy Sciences, Energy Frontier Research Center (EFRC) Program; National Science Foundation MRSEC program for the Cornell Center for Materials Research (preliminary sol-gel synthesis procedure and early nanosheet characterization)
Aksit, Mahmut; Toledo, DavidP.; and Robinson, RichardD. “Scalable nanomanufacturing of millimetre-length 2D NaxCoO2 nanosheets”J. Mater. Chem., 22, 5936-5944 (2012). [DOI: 10.1039/C2JM15550H]
Energy Materials Center at Cornell (emc2) EFRC
Cornell Center for Materials Research
Collaborations, Non-DOE Interagency Collaboration