Novel Side-Chain Type Sulfonated Poly(phenylquinoxaline) Proton Exchange Membranes for Direct Methanol Fuel Cells

Side-chain type sulfonated poly(phenylquinoxaline) (SPPQ)-based proton exchange membranes (PEMs) with different ionic exchange capacity (IEC) were successfully synthesized by copolymerization from 4,4'-bis (2-diphenyletherethylenedione) diphenyl ether, 4,4'-bis (2-phenylethylenedione) diphenyl ether and 3,3',4,4'-tetraaminobiphenyl, and post-sulfonation process. The sulfonic acid groups were precisely grafted onto the p-position of phenoxy groups in the side chain of PPQ after the convenient condition of the post-sulfonation process, which was confirmed by ¹H NMR spectra and FTIR. The sulfonic acid groups of side-chain type SPPQ degraded at around 325 °C, and their maximum stress was higher than 47 MPa, indicating great thermal and mechanical stability. The water uptake increased with the increasing IEC and temperature. The size change in their plane direction was shown to be lower than 6%, indicating the stability of membrane electrode assembly. The SPPQ PEMs displayed higher proton conductivity than that of main chain. In the single cell test, the maximum power density of side-chain type SPPQ-5 was 63.8 mW cm^-2 at 20 wt% methanol solution and O₂ at 60 °C, which is largely higher than 18.4 mW cm^-2 of NR212 under the same conditions. The SPPQ PEMs showed high performance (62.8 mW cm^-2) even when the methanol concentration was as high as 30 wt%.

Synthesis and characterization of a novel sulfonated poly (aryl ether ketone sulfone) semi-crosslinked membrane with high proton selectivity through click reaction for direct methanol fuel cells

A novel sulfonated polyvinyl alcohol containing alkynyl groups (SPVA-C≡C) and a new sulfonated poly (aryl ether ketone sulfone) (SPAEKS) are synthesized. Semi-crosslinked membrane (semi-crosslink-SPAEKS-x) was prepared by click reaction of mercapto-alkynes between 1, 5-pentanedithiol and SPVA-C≡C. The chemical structures of SPAEKS, SPVA-C≡C and semi-crosslink-SPAEKS-x are confirmed by 1H-NMR and FTIR spectra. The semi-crosslink-SPAEKS-x membranes show good mechanical properties, excellent dimensional stability and oxidative stability. The proton conductivity of SPAEKS and semi-crosslink-SPAEKS-x membranes is in the range of 25.6–52.5 mS/cm. The methanol permeability of semi-crosslink-SPAEKS-x membranes is in the range of 1.4–1.7 × 10−7 cm−2 s−1, which is much lower than that of Nafion 117 membrane (18.3 × 10−7 cm−2 s−1). Especially, the proton selectivity of semi-crosslink-SPAEKS-15 membrane (24.3 × 104 S s cm−3) is above seven times higher than that of Nafion 117 membrane (3.4 × 104 S s cm−3).

The preparation of novel sulfonated poly(aryl ether ketone sulfone)/TiO2 composite membranes with low methanol permeability for direct methanol fuel cells

A sulfonated poly(aryl ether ketone sulfone) (SPAEKS) with locally dense sulfonic acid groups is synthesized and different amounts of TiO2 is doped into SPAEKS matrix to prepare composite membranes (SPAEKS/TiO2-x). SEM shows that TiO2 in the composite membranes has good dispersibility when TiO2 content is not higher than 3%. The composite membranes show good mechanical properties, dimensional stability and oxidative stability. The proton conductivity of composite membranes is near to that of Nafion 117 membrane and methanol permeability of composite membranes is much lower than that of Nafion 117 membrane. Therefore, the proton selectivity of composite membranes is higher than that of Nafion 117 membrane. In particular, proton selectivity of SPAEKS/TiO2-3% (12.8 × 104 S s cm−3) is four times higher than that of Nafion 117 membrane (3.2 × 104 S s cm−3).