Organic Trimer Molecule Electrode as a High-Performance Next-Generation Supercapacitor Material
Authors: Rego Arjun , Evans Elliot , Noor Navid , Gourley Storm William D , Foroozan Amirhossein , Higgins Drew 
Published: August 2024

As greenhouse gas emissions such as CO2 continue to increase on a global scale, countries around the world are making changes to reduce their net emissions. One of the primary actions being taken is attempting to decarbonize the transportation sector by moving away from fossil fuel-powered vehicles and adopting electric vehicles (EVs). Supercapacitors are electrical energy storage devices similar in concept to batteries, however they achieve a higher power output, faster charge and discharge rates, and greater longevity. These properties make them excellent devices to work in tandem with batteries that advance their collective performance capabilities in EVs. Supercapacitors using inorganic materials such as transition metal oxides have been explored extensively and although there have been advancements in the field, they continue to struggle with limitations such as mechanical degradation during cycling, low conductivity which slows the charging-discharging processes, and the utilization of environmentally toxic metals. On the other hand, quinones are a class of organic materials considered as the most promising candidates for organic electrodes due to their ≥ 2 reversible redox-active carbonyl groups, inexpensiveness, ease of structural modifications, and environmental sustainability. However, like many organic materials, they suffer from low electrical conductivity and dissolution in electrolyte. To minimize dissolution while retaining and improving its advantages, polymerizing quinones has become a popular modification alternative, especially via polyimide and polythioether bonds. However, because polymer chains are so large and inherently have low electronic conductivity, polymerizing quinones inhibits charge transfer throughout a matrix with a carbon substrate (i.e., rGO, CNT, carbon black) due to interference with the conductive network.

In this research, a smaller molecule was made from covalently bonding two different quinones via imide bonds to make an organic trimer. This helped reduce dissolution in electrolyte compared to its monomeric components via increasing the molecular weight while also improving the energy storage capabilities as a supercapacitor electrode. This is attributed to this molecule retaining the original redox active sites of its monomers and its conjugated network which allows it to achieve a 6-electron transfer mechanism per molecule. Its smaller size compared to a polymer is also hypothesized to reduce the degree of conductivity interruptions it causes when part of a carbon substrate network. While polymer chains can agglomerate easily, decreasing its available specific surface area, this trimer may be more available to participate in Faradaic processes. This research hereby reports an electrode material with very high capacitance (318 Fg-1 at 5 mVs-1) and good cycling stability utilizing a low-cost carbon black substrate for supercapacitor applications to improve the performance of next-generation EVs.