| Summary: | The hydrogen-bromate flow battery represents one of the promising variants for hybrid power sources. Its membrane-electrode assembly (MEA) combines a hydrogen gas diffusion anode and a porous flow-through cathode where bromate reduction takes place from its acidized aqueous solution: BrO<sub>3</sub><sup>−</sup> + 6 H<sup>+</sup> + 6 e<sup>−</sup> = Br<sup>−</sup> + 3 H<sub>2</sub>O (*). The process of electric current generation occurs on the basis of the overall reaction: 3 H<sub>2</sub> + BrO<sub>3</sub><sup>−</sup> = Br<sup>−</sup> + 3 H<sub>2</sub>O (**), which has been studied in previous publications. Until this work, it has been unknown whether this device is able to function as a <i>rechargeable</i> power source. This means that the bromide anion, Br<sup>−</sup>, should be electrooxidized into the bromate anion, BrO<sub>3</sub><sup>−</sup>, in the course of the charging stage <i>inside the same cell under strongly acidic conditions,</i> while until now this process has only been carried out in neutral or alkaline solutions with specially designed anode materials. In this study, we have demonstrated that processes (*) and (**) can be performed in a <i>cyclic</i> manner, i.e., as a series of charge and discharge stages with the use of MEA: H<sub>2</sub>, Freidenberg H23C8 Pt-C/GP-IEM 103/Sigracet 39AA, HBr + H<sub>2</sub>SO<sub>4</sub>; square cross-section of 4 cm<sup>2</sup> surface area, under an alternating galvanostatic mode at a current density of 75 mA/cm<sup>2</sup>. The coulombic, voltaic and energy efficiencies of the flow battery under a cyclic regime, as well as the absorption spectra of the catholyte, were measured during its operation. The total amount of Br-containing compounds penetrating through the membrane into the anode space was also determined.
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