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 (H2SO4) was a supporting electrolyte. However, in this study, ammonium chloride (NH4Cl) is suggested as the electrolyte for the first time. By changing the supporting electrolyte from H2SO4 to NH4Cl, the cell voltage of RFB is improved from 0.76 V to 1.01 V. To investigate the effect of NH4Cl supporting electrolyte of the performance of RFB, the full-cell tests of RFB using 2,7-AQDS and Tiron that are dissolved in NH4Cl 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/cm2 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.