"The big challenge for this approach is assembling the materials," said Pint. "Constructing high-performance, functional devices out of nanoscale building blocks with any level of control has proven to be quite challenging, and when it is achieved it is difficult to repeat."
So Pint and his research team graduate students Landon Oakes, Andrew Westover and post-doctoral fellow Shahana Chatterjee decided to take a radically different approach: using porous silicon, a material with a controllable and well-defined nanostructure made by electrochemically etching the surface of a silicon wafer.
This allowed them to create surfaces with optimal nanostructures for supercapacitor electrodes, but it left them with a major problem. Silicon is generally considered unsuitable for use in supercapacitors because it reacts readily with some of chemicals in the electrolytes that provide the ions that store the electrical charge.
With experience in growing carbon nanostructures, Pint's group decided to try to coat the porous silicon surface with carbon. "We had no idea what would happen," said Pint. "Typically, researchers grow graphene from silicon-carbide materials at temperatures in excess of 1400 degrees Celsius. But at lower temperatures 600 to 700 degrees Celsius we certainly didn't expect graphene-like material growth."
When the researchers pulled the porous silicon out of the furnace, they found that it had turned from orange to purple or black. When they inspected it under a powerful scanning electron microscope they found that it looked nearly identical to the original material but
|Contact: David F. Salisbury|