The current study focuses on synthesizing a cost-effective high proton conductive and low oxygen crossover proton exchange membrane. The membrane is prepared using modified biochar from chili stalk waste in a sulfonated polyether sulfone polymer for microbial fuel cell applications for tamarind wastewater treatment. The membrane shows desired modification confirmed through instrumental characterization using FTIR, XRD, TGA, and SEM. The ultimate analysis confirmed the high carbon and nitrogen content in modified biochar that induces elevated proton conductivity (0.098 Scm � 1) and less oxygen diffusivity (3.33 x 10-8 m2 s-1) in a 5% modified biochar doped sulfonated polyether sulfone membrane with a desired mechanical strength, IEC, and moisture content. The high oxygen reduction reaction due to nitrogen content in modified char enhances columbic efficiency and bacterial activity that eventually improves the MFC performance in terms of high-power density (0.148 Wcm � 2) and 82.2% of COD elimination. The presence of graphitic and pyridinic, pyrrolic, and N groups accompanying carbon structures favor oxygen reduction via the 2e � or 4e � pathway, respectively. Finally, molecular dynamics simulation also confirmed the low oxygen diffusion and reduced fraction-free volume for oxygen diffusion after including modified biochar in SPES. The economic assessment shows a five times lower cost of modified biochar doped membrane than Nafion 117 membrane.