In the current research, sulfonated poly (phenylene oxide) (SPPO)/MXene nanosheets cation exchange membranes (CEM) were prepared by solution casting technique. SPPO with different sulfonation degrees (DS) were synthesized, and MXene nanosheets were etched from the MAX phase. The effect of sulfonation degrees (31, 36,and 43 %), polymer concentration (19, 22, and 25 wt%), and MXene loading (0.5, 1, and 2 wt%) on mechanical properties, electrochemical characteristics, and permselectivity of the CEMs were studied. The results showed that an increase in DS, the presence of hydrophilic MXene nanosheets, and a decrease in polymer concentration had synergistic effects on enhancing the hydrophilicity and conductivity of the fabricated CEMs. The ion exchange capacity (IEC) increased with enhancement of DS and MXene loading due to more attaching the functional groups to the polymer structure. On the other hand, an increase in polymer concentration resulted in the reduction of IEC. The tensile strength of CEMs had a reduction trend when the sulfonation degree increased, and polymer concentration decreased. Presence of MXene nanosheets significantly improved the values of permselectivity and tensile strength; For example, permselectivity increased from 80.92 % to 92.30 % by adding 2 % of MXene to the casting solution containing 25 wt% of SPPO with a sulfonation degree of 36 %.

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