Grafting of Quinones on Carbons as Active Electrode Materials in Electrochemical Capacitors

Abstract

The electrochemical performance of electrochemical capacitors can be improved with electroactive quinone molecules. Systems based on redox active electrolyte as well as physisorbed and chemically grafted molecules have been investigated. In all these cases, carbon materials were used as substrate and electrode material. This short review will mainly describe work related to these systems and materials from the authors' laboratories. Nonetheless, some important studies from other research groups will be discussed.

Aqueous Energy Storage Device Based on LiMn2O4 (Spinel) Positive Electrode and Anthraquinone‐Modified Carbon‐Negative Electrode

“…As previously reported, the modification of the activated carbons by the AQ molecules decreases the specific surface area of the carbons from 1500 to 505 m 2 g −1 , and the pore volume decreases accordingly from 0.708 to 0.244 mL g −1 . The modified carbons contain mostly mesopores, since the grafted AQ molecules block most of the micropores of the activated carbons . Hence, this modification slightly reduces double‐layer capacitance by reducing microporosity, but in turn leads to a pronounced gain in specific capacity thanks to the added surface red‐ox activity.…”

“…This may be achieved by decorating the surface of activated carbons by moieties that are electrochemically active. To preserve the advantages of these systems in terms of high durability and power density, the extra red‐ox activity is maintained via surface moieties only (active nanoparticles or molecules attached to the carbon surface) . For instance, electrodes comprising nanoparticles of active transition metal oxides attached to or embedded in activated carbon matrices exhibited impressive performance in terms of specific capacity and cycle life, although the reported values can be sometimes questionable due to unrealistic mass loadings .…”

“…However, capacitive electrodes suffer from a disadvantage related to low specific capacity, which reaches a limit in neutral aqueous electrolytes to 100 F g −1 over a 1 V potential window, which translates into 28 mAh g −1 . The specific capacity of activated carbon‐based electrodes can be increased considerably by adding surface functional groups that possess red‐ox activity and thus can sustain reversible Faradaic reactions all over the carbon electrode surface . An interesting option is to chemically attach to the carbon surface organic molecules that exhibit pronounced red‐ox activity such as quinones .…”

“…An interesting option is to chemically attach to the carbon surface organic molecules that exhibit pronounced red‐ox activity such as quinones . Such modifications improve the capacity of the initially electrical double layer (EDL)‐type carbon electrode by adding a Faradaic component that leads to the gain in specific capacity . The use of red‐ox molecules such as 2‐aminoanthraquinone for this purpose is an example of a very good choice as it should be electroactive in acidic, neutral, and alkaline electrolyte solutions.…”

“…To preserve the advantages of these systems in terms of high durability and power density, the extra red-ox activity is maintained via surface moieties only (active nanoparticles or molecules attached to the carbon surface). [9][10][11][12][13][14][15] For instance, electrodes comprising nanoparticles of active transition metal oxides attached to or embedded in activated carbon matrices exhibited impressive performance in terms of specific capacity and cycle life, although the reported values can be sometimes questionable due to unrealistic mass loadings. [16,17] In a recent study, we have developed high specific capacity activated carbon electrodes for supercapacitors in which electrochemically active organic molecules were attached to the carbon surface by grafting processes to increase its capacity.…”