Novel Sulfonated Poly(ether Ether Ketone Ketone)s For Direct Methanol Fuel Cells Usage: Synthesis, Water Uptake, Methanol Diffusion Coefficient And Proton Conductivity

摘要

A novel series of sulfonated poly(ether ether ketone ketone)s (SPEEKKs) with different degrees of sul-fonation (Ds) were synthesized from 1,3-bis(3-sodiumsulfonate-4-fluorobenzoyl)benzene(1,3-SFBB-Na), 1,3-bis(4-fluorobenzoyl)benzene (1,3-FBB) and 33',5,5'-tetramethyl-4,4'-biphenol (TMBP) by aromatic nucleophilic polycondensation.The chemical structures of SPEEKKs were confirmed by FT-IR spectroscopy and the Ds values of the polymers were calculated by ~1 H MMR and titration methods, respectively. The thermal stabilities of the SPEEKKs in acid and sodium forms were characterized by thermogravimetric analysis (TGA), which showed that SPEEKKs had excellent thermal properties at high temperatures. All the SPEEKK polymers were easily solution cast into tough membranes. Water uptakes, proton conductivities and methanol diffusion coefficients of the SPEEKK membranes were measured. Water uptake increased with Ds and temperature. Compared to Nafion, the SPEEKK-60, -70 and -80 membranes showed higher proton conductivities at 80 ℃, while the other SPEEKK membranes showed relatively lower proton conductivities. This may be due to the different distribution of ion-conducting domains in membrane. However, these membranes showed lower methanol diffusions in the range of 8.32 × 10~(-9) to 1.14 × 10~(-7) cm~2 s~(-1) compared with that of Nafion (2 × 10~(-6) cm~2 s~(-1)) at the same temperature. The membranes also showed excellent mechanical properties (with a Young's modulus >1 GPa and a tensile strength > 40 MPa). These results indicate that the SPEEKK membranes are promising materials for use in direct methanol fuel cell (DMFC) applications.