High performance polymer electrolyte membrane with efficient proton pathway over a wide humidity range and effective cross-linking network

Abstract

It is vital to constructing long-term proton transfer channels with sufficient conduction sites in proton exchange membranes. The mPBI-TGDDM/ZrSP polymer electrolyte membranes are prepared by covalent cross-linking with tetrafunctional N,N,N′,N′-tetraglycidy-4,4′- diaminodiphenyl-methane (TGDDM) and doping with the zirconium 3-sulfopropyl phosphonate (ZrSP). The new high-temperature proton conductor ZrSP contains sulfonic acid groups and phosphonic acid groups. TGDDM has high functionality which efficiently enhanced the dimensional stability, mechanical properties, and oxidative resistance of the membranes under low cross-linking degrees (5%–10%). The low cross-linking degree and good mechanical stability also allow high doping levels of ZrSP and consequently high proton conductivity. At 100% relative humidity (RH), 50% RH and 0 RH, the proton conductivity of mPBI-TGDDM(5%)/ZrSP(50%) membrane is 0.127, 0.078 and 0.0186 S cm−1 at 180 °C, respectively. A large number of sulfonic and phosphonic acid groups in the membrane can establish an efficient proton pathway over a wide humidity range. High cross-linking will decrease the conductivity, and high doping will increase the conductivity, thus affecting the performance of the fuel cells. The mPBI-TGDDM/ZrSP membranes exhibited good methanol resistance and good membrane selectivity and thus the membranes have great application potential in direct methanol fuel cells (DMFCs).