Performance evaluation of aqueous redox flow battery using quinone redox couple dissolved in ammonium chloride electrolyte

− In this study, anthraquinone-2,7-disulfonic acid (2,7-AQDS) is used as negative active material and Tiron is used as positive active material for aqueous redox flow battery (RFB). In previous results that used the 2,7-AQDS and Tiron, sulfuric acid (H ₂ SO ₄ ) was a supporting electrolyte. However, in this study, ammonium chloride (NH ₄ Cl) is suggested as the electrolyte for the first time. By changing the supporting electrolyte from H ₂ SO ₄ to NH ₄ Cl, the cell voltage of RFB is improved from 0.76 V to 1.01 V. To investigate the effect of NH ₄ Cl supporting electrolyte of the performance of RFB, the full-cell tests of RFB using 2,7-AQDS and Tiron that are dissolved in NH ₄ Cl supporting electrolyte are carried out, while cut-off voltage range is a main parameter to determine their performance. When the cut-off voltage range is 0.2~1.6 V, the hydrogen evolution occurs during charging step. To address the side reaction effect, the cut-off voltage range is changed to 0.2~1.2 V. When the revised cut-off voltage range is used and the current density of 40 mA/cm ² is applied, hydrogen evolution is not observed and the optimal RFB shows the charge efficiency of 99% and discharge capacity of 3.3 Ah/L at 10cycle.