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• Vanadium redox flow battery model was applied to a single cell geometry. • Different initial water and sulfuric concentrations in each electrolyte will mitigate the electrolyte imbalance. • The required difference in water concentration between the anolyte and catholyte decreases as current density increases. • Similar cell performances are observed between the cell performance simulated under same initial electrolyte concentrations and the optimum electrolyte concentrations. In all-vanadium redox flow battery (VRFB) systems, the electrolyte imbalance between the negative and positive electrodes inevitably occurs and subsequently necessitates costly electrolyte rebalancing procedures for long-term VRFB operation. We propose a new operating strategy for VRFBs that alleviates the electrolyte imbalance issue, which is to employ water and sulfuric acid at different concentrations as initial supporting electrolytes between the negative and positive electrodes. Using a three-dimensional VRFB model that was developed and validated in our previous study, we numerically demonstrate that the degree of electrolyte imbalance can be reduced by using appropriate compositions of the initial anolyte and catholyte. Detailed simulation results reveal that the diffusive water crossover flux between the negative and positive electrodes, which is a main contributor to electrolyte imbalance during charge-discharge cyclic operations, can be effectively suppressed by controlling the initial anolyte and catholyte compositions. [ABSTRACT FROM AUTHOR]