Graphene From CO2 May Be Made Into a Supercapacitor

Michigan Technological University researchers have developed a new way to make surface-microporous 3-D graphene, which has a unique structure of mesopores and micropores, that could be made into a supercapacitor.

The new process makes tiny dents in the surface of the graphene greatly enhancing its potential as a supercapacitor. Even better, it can be made from carbon dioxide. The process uses a heat-releasing reaction to dig micropores into 3-D graphene and could be a useful supercapacitor material.

The process is the focus of a new study published in the American Chemical Society’s Applied Materials & Interfaces.

The conversion of carbon dioxide to useful materials usually requires high energy input due to its ultrahigh stability. However, materials science professor Yun Hang Hu and his research team created a heat-releasing reaction between carbon dioxide and sodium to synthesize 3-D surface-microporous graphene.

Hu said, “3-D surface-microporous graphene is a brand-new material,” explaining the material’s surface is pockmarked with micropores and folds into larger mesopores, which both increase the surface area available for adsorption of electrolyte ions. “It would be an excellent electrode material for energy storage devices.”

Basically, a supercapacitor material needs to store and release an electrical charge. The limiting factor is how quickly ions can move through the material.

The supercapacitive properties of the unique structure of 3-D surface-microporous graphene make it suitable for elevators, buses, cranes and any application that requires a rapid charge/discharge cycle. Supercapacitors are an important type of energy storage device and have been widely used for regenerative braking systems in hybrid vehicles.

Current commercialized supercapacitors employ activated carbon using swaths of micropores to provide efficient charge accumulation. But, electrolyte ions have difficulty diffusing into or through activated carbon’s deep micropores, increasing the charging time.

“The new 3-D surface-microporous graphene solves this,” Hu said. “The interconnected mesopores are channels that can act as an electrolyte reservoir and the surface-micropores adsorb electrolyte ions without needing to pull the ions deep inside the micropore.”

The mesopore is like a harbor and the electrolyte ions are ships that can dock in the micropores. The ions don’t have to travel a great distance between sailing and docking, which greatly improves charge/discharge cycles they can steer through. As a result, the material exhibited an ultrahigh areal capacitance of 1.28 F/cm2, which is considered an excellent rate capability as well as superb cycling stability for supercapacitors.

To synthesize the material from carbon dioxide, Hu’s team added carbon dioxide to sodium, followed by increasing temperature to 520 degrees Celsius. The reaction can release heat instead of requiring energy input.

During the process, carbon dioxide not only forms 3-D graphene sheets, but also digs the micropores. The tiny dents are only 0.54 nanometers deep in the surface layers of graphene.

This is very much the best of innovation. One does wonder how the team had the imagination to set up the process. Its one of those “who would have thought” things, that strikes like lightning.

Should the process scale into products, they will be lightning fast capacitors as well.