Redox flow battery features

Like aforementioned organic cathode materials in solid-electrode lithium batteries, tunable molecular structure is their important feature through which their electrochemical properties such as redox potential and solubility can be changed. The active organic materials in flow batteries espouse the same dogma. For example, quinone based molecules are common active species employed in flow batteries and their stmcture can be readily tuned to achieve favorable electrochemical properties [170, 174, 178]. With tuned small organic molecules called 9,10-anthraquinone-2,7-disulphonic acid (AQDS), a team of Harvard scientists demonstrated that AQDS underwent extremely rapid and reversible two-electron two-proton reduction in sulphuric acid [170]. An aqueous flow battery with the quinone/hydroquinone couple as anode and the Br2/Br redox couple as cathode yielded a peak power density exceeding 0.6 W cm at 1.3 A com (Fig. 14). 

The Daniell cell illustrates the basic features of an electrochemical cell. Electrochemical cells always involve a redox reaction. Oxidation occurs at the cathode of the cell and reduction takes place at the anode. Electrons always flow from the anode to the cathode. Electrochemical cells come in many arrangements. To gain an appreciation for the variety of electrochemical cells, consider all the types of batteries available. 

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