Using principles from rocket science, researchers have created carbon with a record-breaking surface area. The material can soak up about twice the amount of CO2 as current activated carbon materials and has impressive energy-storage capabilities.
As you might remember from combining baking soda and vinegar to make a volcano in high school, when certain chemicals come in contact with each other, the results can be explosive.
Taking this principle to much more serious degrees, rocket scientists have been using something known as hypergolic reactions as fuel for a range of space craft for years. These are reactions between two chemicals (typically a fuel and an oxidizer) that are so violent that they can provide propulsion if channeled correctly. One of the more common combinations in the world of hypergolic propulsion, for instance, is mixing the fuel hydrazine with the oxidizer nitrogen tetroxide.
At Cornell University, postdoctoral researcher Nikolaos Chalmpes was using hypergolic reactions in a different way. He was creating materials from the powerful forces unleashed when various chemicals combined.
Thinking that such a technique might help increase the porosity of carbon, which would boost its surface area and make it better at storing energy and capturing carbon dioxide, Cornell professor Emmanuel Giannelis began working with Chalmpes on a new study.
“I was trying to understand how to harness and control these unexplored reactions for synthesizing various carbon nanostructures, and after adjusting various parameters, I discovered that we might be able to achieve ultrahigh porosity,” said Chalmpes, lead author of the study. “Until then, these reactions had only been used in rocket and aircraft systems, and deep space probes for propulsion and hydraulic power.”
The duo, with the help of a team of other scientists, was successful. They created carbon that has an astonishing surface area of 4,800 square meters per gram which, they say, is roughly equivalent to the size of a football field packed down neatly onto a teaspoon. "To the best of our knowledge, this area value is the highest reported in the literature," write the researchers in their study, which has been published in the journal ACS Nano.
Five carbon rings
The key to the material's success has to do with the fact that the hypergolic reaction creates carbon tubes that have high concentrations of molecular rings made from five carbon atoms instead of the usual six. This changes the angles of the bonds at the molecular level and adds to the stability of the tubes.
In the reaction, the tubes assembled themselves along a template created by the researchers to give the structure form. Finally, the resultant structure was coated in potassium hydroxide, which washes away less stable structures and leaves behind thousands of microscopic pores.
“When you do this very fast reaction, it creates a perfect situation where the system cannot relax and go to its lowest energy state, which it would normally do,” Giannelis said. “Because of the speed of hypergolic reactions, you can catch the material in a metastable configuration that you cannot get from the slow heating of a normal reaction.”
Carbon capture in T minus two minutes
After the material was created, the researchers tested it to see how much carbon dioxide it could sequester from the atmosphere. The result was that in just two minutes it was able to capture 99% of its total capacity, a yield that nearly doubles current activated carbon products. It was also shown to have four-times the energy storage ability of commercially available activated carbons, with a volumetric energy density of 60 watt-hours per liter.
“This approach offers an alternative strategy for designing and synthesizing carbon-based materials suitable for sorbents, catalyst supports and active materials for supercapacitors, particularly in applications requiring space efficiency,” said Chalmpes. “Furthermore, the unique experimental conditions of hypergolic reactions provide another pathway for the design and synthesis of electrocatalysts with enhanced properties.”
Source: Cornell Chronicle
