Stanford University scientists have created a new carbon material that significantly boosts the performance of energy-storage technologies.
"We have developed a 'designer carbon' that is both versatile and controllable," said Zhenan Bao, the senior author of the study and a professor of chemical engineering at Stanford. "Our study shows that this material has exceptional energy-storage capacity, enabling unprecedented performance in lithium-sulfur batteries and supercapacitors."
According to Bao, the new designer carbon represents a dramatic improvement over conventional activated carbon, an inexpensive material widely used in products ranging from water filters and air deodorizers to energy-storage devices.
"A lot of cheap activated carbon is made from coconut shells," Bao said. "To activate the carbon, manufacturers burn the coconut at high temperatures and then chemically treat it."
The activation process creates nanosized holes, or pores, that increase the surface area of the carbon, allowing it to catalyze more chemical reactions and store more electrical charges.
But activated carbon has serious drawbacks, Bao said. For example, there is little interconnectivity between the pores, which limits their ability to transport electricity.
"With activated carbon, there's no way to control pore connectivity," Bao said. "Also, lots of impurities from the coconut shells and other raw starting materials get carried into the carbon. As a refrigerator deodorant, conventional activated carbon is fine, but it doesn't provide high enough performance for electronic devices and energy-storage applications."
Instead of using coconut shells, Bao and her colleagues developed a new way to synthesize high-quality carbon using inexpensive – and uncontaminated – chemicals and polymers.
The process begins with conducting hydrogel, a water-based polymer with a spongy texture similar to soft contact lenses. For the study, the Stanford team used a mild carbonization and activation process to convert the polymer organic frameworks into nanometer-thick sheets of carbon. The result: designer carbon that can be fine-tuned for a variety of applications.
"We call it designer carbon because we can control its chemical composition, pore size and surface area simply by changing the type of polymers and organic linkers we use, or by adjusting the amount of heat we apply during the fabrication process," To said.
For example, raising the processing temperature from 750 degrees Fahrenheit (400 degrees Celsius) to 1,650 F (900 C) resulted in a 10-fold increase in pore volume.
Subsequent processing produced carbon material with a record-high surface area of 4,073 square meters per gram – the equivalent of three American football fields packed into an ounce of carbon. The maximum surface area achieved with conventional activated carbon is about 3,000 square meters per gram.
"High surface area is essential for many applications, including electrocatalysis, storing energy and capturing carbon dioxide emissions from factories and power plants," Bao said.
This story is reprinted from material from Stanford University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.