To boost the performance of the iron-chromium redox flow battery (ICRFB), opting an appropriate proton exchange membrane (PEM) as the core component of ICRFB is of great importance. For the purpose, in this paper, various widely adopted commercial Nafion membranes with a different thickness of 50 mu m (Nafion 212, N212), 126 mu m (N115), and 178 mu m (N117) are chosen for the sake of evaluating the influence of membrane thickness on the ICRFB single-cell performance. Physicochemical properties, electrolyte utilization, cell efficiency, long-term cycling stability, and the self-discharge process of ICRFBs based on a series of Nafion membranes are contrasted comprehensively. The cycling test of ICRFBs is carried out under the current density range of 40 to 120 mA/cm(2) for the charge-discharge process. As a result of the good equilibrium of membrane resistance and electro-active species permeability, Nafion 212 membrane exhibits the highest electrolyte utilization and energy efficiency during the operation, accompanied by the lowest overpotential. In the final part, the selection of Nafion membrane thickness was optimized on the basis of single-cell performance and the overall cost of the system.