Taurine Electrografting onto Porous Electrodes Improves Redox Flow Battery Performance.

The surface properties of porous carbonaceous electrodes govern the performance, durability, and ultimately the cost of redox flow batteries (RFBs). State-of-the-art carbon fiber-based electrode interfaces suffer from limited kinetic activity and incomplete wettability, fundamentally limiting the performance. Surface treatments for electrodes such as thermal and acid activation are a common practice to make them more suitable for aqueous RFBs; however, these treatments offer limited control over the desired functional properties. Here, we propose, for the first time, electrografting as a facile, rapid, and versatile technique to enable task-specific functionalization of porous carbonaceous electrodes for use in RFBs. Electrografting allows covalent attachment of organic molecules on conductive substrates upon application of an electrochemical driving force, and the vast library of available organic molecules can unlock a broad range of desired functional properties. To showcase the potential of electrografting for RFBs, we elect to investigate taurine, an amine with a highly hydrophilic sulfonic acid tail. Oxidative electrografting with cyclic voltammetry allows covalent attachment of taurine through the amine group to the fiber surface, resulting in taurine-functionalized carbon cloth electrodes. In situ polarization and impedance spectroscopy in single-electrolyte flow cells reveal that taurine-treated cloth electrodes result in 40% lower charge transfer and 25% lower mass transfer resistances than off-the-shelf cloth electrodes. We find that taurine-treated electrode interfaces promote faster Fe