Surmounting the sluggish oxygen reduction reaction (ORR) kinetics in developing the metal-free cathode catalyst for fuel cell, carbon nanomaterials with heteroatoms doped intended to focus vigorously. Electronegativity difference between heteroatoms is prone to maximize the C-C bond polarization to generate ORR active sites. The current work emphasizes on synergistic effect of nitrogen, sulfur and fluorine tri-doped porous carbon toward potential ORR catalyst. Pyrolysis of sulfonated-polyaniline supported on Ketjenblack (KB) in presence of NH4F turns into N-S-F tri-doped catalyst. F tri-doping creates more active sites through inducing maximum charge polarization/spin density alterations which are promising for ORR improvement. ORR activity of doped catalysts is examined by rotating ring disk electrode in both acidic and alkaline media with dominant four electron transfer. The Enhanced activity with superior stability, CH3OH sensitivity and CO susceptibility of the developed N-S-F/KB catalyst finds suitable application in polymer electrolyte membrane fuel cell (PEMFC). The peak power densities of 7.3 and 24 mW cm(-2) in alkaline and acidic medium respectively are obtained in the PEMFCs using this catalyst. Demonstration of a tri-doped N, S, F catalyst toward ORR and its fuel cell performance studies in acidic and alkaline media is the first of its kind in the literature. (C) 2019 The Electrochemical Society.