While carbon dioxide (CO2) can be released into the environment through a number of natural processes, such as through animal respiration and the cycling of carbon within the atmosphere, oceans and soil, its role as a primary greenhouse gas has been attributed to a number of serious health consequences. Produced as a result of the combustion of fossil fuels, CO2 emissions have been associated with raising the average global temperature, which thereby seriously affects normal weather patterns, the populations’ water supplies and induces changes to the growing season for important food products1.
Despite efforts that are taken to limit the amount of CO2 emissions that are released into the environment, such as choosing to take public transportation instead of a personal vehicle to work each day, the production and persistence of CO2 remains a significant environmental concern.
To further combat this issue, Researchers have looked towards CO2 recycling, a process that aims towards taking CO2 gases that would normally remain in the environment and negatively interact with biological creatures, and instead convert CO2 into a reusable and sustainable technology.
When combined with an ideal catalyst, CO2 can be broken up into its individual carbon and oxygen molecules, and subsequently used as building blocks for any number of different materials. Various different research initiatives have looked towards how this CO2 conversion can be used to create new materials, such as concrete and clean fuel, however, while practical in theory, this conversion process typically requires a high amount of energy to be utilized as a result of the ultrahigh stability of CO2.
Researchers at Michigan Technology University’s Department of Material Sciences and Engineering in collaboration with Brookhaven National Laboratory’s Center for Functional Nanomaterials have recently developed a three-dimensional (3D) microporous graphene material by using carbon dioxide (CO2). The 3D cabbage-coral-like graphene developed by Liang Chang’s team has excellent superconductor properties and can potentially be used in several applications that require efficient energy storage and discharge.
The conversion of CO2 to graphene requires a lot of energy to break a stable CO2 structure and form graphene, however, Chang’s team has designed an exothermic reaction involving a reaction between sodium (Na) and CO2 at a high temperature of 520°C to facilitate this reaction2. A novel 3D microporous graphene with a large surface area consisting of micropores on the surface of graphene, which fold into larger macropores, also known as mesopores; both of which facilitate the adsorption of electrolyte ions.
The larger mesopores act as an electrolyte reservoir, while the smaller micropores enable the rapid adsorption of the electrolytes without requiring the withdrawal of ions from deep inside2.
Supercapacitors are energy storage devices that are widely used in systems that require efficient charge/discharge cycles, such as elevators and other hybrid devices including buses, trains, etc. Commercial supercapacitors utilize activated carbon consisting of swaths of deep micropores2. During energy storage, the electrolyte ions must seep and diffuse through the pores of the supercapacitor, thereby increasing charging time.
The 3D microporous graphene produced here exhibits a larger surface area and an arrangement of micropores and mesopores that facilitate rapid charging, allowing this novel material to be a great super capacitor option2.
Using aqueous electrolyte, the 3D graphene material developed by Liang Chang’s team showed a great gravimetric capacitance of 200 F/g, which is three times higher than the gravimetric capacitance of 70.8 F/g achieved with the commercially used activated carbon2. This unique graphene material was also found to have ultrahigh aerial capacitance of 1.28 F/cm2, extraordinary rate capability that measures to be 83.5 % from 0.5 to 10 A/g as well as great cycling stability with 86.2 % retention even after 5000 cycles2.
Taken together, the 3D graphene developed from CO2 showed unique structure and excellent supercapacitor properties and suggests that it could be used as a great substitute for current supercapacitor materials made of activated carbon2.
- “Overview of Greenhouse Gases” – United States Environmental Protection Agency
- “An ideal Electrode Material, 3D Surface-Microporous Graphene for Supercapacitors with Ultrahigh Areal Capacitance” L. Chang, D. Stacchiola, et al. ACS Applied Materials & Interfaces. (2017). DOI: 10.1021/acsami.7b07381.