Cross-linking of Imidazole-grafted Sulfonated Poly(ether ether ketone) as Proton Exchange Membranes for Direct Methanol Fuel Cells

Sulfonated poly(ether ether ketone)(SPEEK) membrane is considered as a promising candidate to replace the Nafion membrane for the direct methanol fuel cell(DMFC) due to its high proton conductivity and excellent methanol resistance. However, the SPEEK always suffers the poor chemical stability. Herein, a novel imidazole functionalized cross. linked SPEEK membrane was synthesized via covalently cross. linked method. The results show that the modified SPEEK membrane exhibits greatly enhanced proton conductivity(0. 14 S/cm at 25 degrees C) in comparison with the Nafion 115 membrane(0. 086 S/cm) by introducing the imidazole groups. Increasing the cross. linking degree of the membranes leads to a decrease in proton conductivity and a great reduction in methanol permeability due to the more compact network structure. When the cross. linking degree reaches 20%, the proton conductivity and methanol selectivity are 0. 105 S/cm and 4. 57x10(5) S.s/cm(3), respectively, demonstrating a good balance between proton conductor and methanol separator. Importantly, the oxidative and dimensional stabilities of cross. linked SPEEK membrane are significantly im. proved. A passive DMFC incorporated with the optimized Im. C. SPEEK. 20 membrane delivers a peak power density of 29. 7 mW/cm(2) at room temperature, close to that with Nafion 115(31. 8 mW/cm(2)), suggesting a promising application potential in DMFCs.