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, 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. 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 carbon sheets form a 3-D network that has good pore connectivity and high electronic conductivity," said graduate student John To, a co-lead author of the study. "We also added potassium hydroxide to chemically activate the carbon sheets and increase their surface area." The result: designer carbon that can be fine-tuned for a variety of applications.