Polyfunctional acid materials possess proton conduction at high temperatures and low relative humidity (RH) making them suitable solutions to the poor performance exhibited by conventional polymer electrolyte membrane fuel cells (PEMFC) under these conditions. The current study explores the synthesis and characterization of 2,4,6-triphosphonic acid-1,3,5-triazine (TPAT) as an additive in poly (arylene ether sulfone) (PAES) copolymers for PEMFC applications. Reaction of 2,4,6-trichloro-1,3,5-triazine and triethylphosphite followed by acid hydrolysis yielded TPAT, confirmed via P-31, H-1 and C-13 NMR. TPAT in various wt.% amounts was added to acidified disulfonated biphenol-based PAES copolymers to obtain BPSH-35/TPAT membranes exhibiting non-linear proton conductivity properties. The 1% TPAT membrane showed highest conductivity under 90% RH and hydrated state (100% RH) at 0.015 S/cm and 0.032 S/cm respectively; the 3 and 5 wt% membranes showed the lowest proton conductivity. Our findings emphasize the value of BSPH-35/1% TPAT membrane for further exploration in PEMFCs.