Carbon catalysts, ionomer contents and operating conditions of an aqueous organic flow battery fabricated by a catalyst-coated membrane

Abstract

Abstract An aqueous organic flow battery is studied using quinone as the electroactive material. Anthraquinone-2-sulfonic acid (AQS) and 4,5-dihydroxybenzene-1,3-disulfonic acid (BQDS) exhibit a fast kinetically reversible reaction, where the reduction potentials are ~0.17 and ~0.93 V (vs. a standard hydrogen electrode). A full-cell AQS/BQDS flow battery is assembled, where a membrane electrode assembly is fabricated by a catalyst-coated membrane using carbon as the catalyst. The Coulombic and energy efficiencies of the full cell are ~97.1% and ~37.5%, respectively. Carbon catalysts are tested with graphene showing entirely superior performance than carbon black (Vulcan XC-72R) for both the charging and discharging processes. Moreover, the ionomer content in the catalyst ink is examined and the optimal content is ~17.7% by weight of dry mass of Nafion. Furthermore, operating conditions, such as flow rate and concentration, are evaluated. The polarization curves depend accordingly on the flow rate and concentration for both charging and discharging. In addition, the open-circuit voltage of the full cell is mainly controlled by the concentration and at a very low flow rate, the polarization curve decreases dramatically, particularly for high current density due to the lack of reactive material.