The vanadium redox flow battery (VRFB) store chemical energy and generate electricity by redox reactions between vanadium ions dissolved in electrolytes. The main components of VRFB are positive and negative porous electrodes, membrane, current collectors, electrolyte, and pumps. The electrolyte is composed of vanadium species and supporting electrolytes. The supporting electrolyte has two main functions: 1) to increase the electrolyte's ionic conductivity, and 2) to deliver hydrogen ions to the positive electrode reaction. The supporting electrolytes are many kinds of an acid such as sulfuric acid, hydrochloric acid, methane sulfonic acid, etc. Some study has been done to improve the performance of VRFB a mixed electrolyte supporting. Zhang et al. proved that the stabilities of vanadium ions in sulfuric acid solution could be improved marginally by adding some additives as stabilizing agents 1. Sha et al studied the effect of organic additives on positive electrolyte for vanadium redox battery They found that the energy efficiency for the electrolyte with D-sorbitol was higher than that electrolyte without additives 2. Chang et al investigated coulter dispersant IIIA additive into the positive electrolyte 3. The obtained result showed that the coulter dispersant IIIA increased the stability of the positive electrolyte in VRFB. According to the authors' knowledge, there is no a numeric study that comparing, the supporting electrolyte used in a VRFB. The aim of this study is to perform comparatively a numerical analyze of the supporting electrolyte of H2SO4 and HCl in the negative and positive electrodes. To achieve these objectives a two-dimensional model is developed with COMSOL Multiphysics under some assumptions and boundary conditions. The electrolyte potential is deeply investigated through the state of charge (SOC). The simulation result shows that the difference in the electrolyte potential between the supporting electrolyte of H2SO4 and HCl, the supporting electrolyte of H2SO4 possesses a higher potential compared to the HCl. This phenomenon is strongly related to the number of hydrogen protons delivered by the supporting electrolyte of H2SO4 which is more compared to that of HCl 4. Acknowledgement The authors would like to thank the Scientific Research Projects Unit of Erciyes University for funding under the contract no: FDK-2019-9340. Reference 1. J. Zhang et al., J. Appl. Electrochem., 41, 1215–1221 (2011). 2. S. Li et al., Electrochim. Acta, 56, 5483–5487 (2011). 3. F. Chang, C. Hu, X. Liu, L. Liu, and J. Zhang, Electrochim. Acta, 60, 334–338 (2012). 4. H. Yan et al., Membranes (Basel)., 10, 1–15 (2020). Figure 1