Zhenghui Zhang

Aromatic polyelectrolytes via polyacylation of pre-quaternized monomers for alkaline fuel cells

To overcome alkali-resistant and synthetic hurdles to alkaline anion-exchange membranes (AAEMs) for alkaline fuel cells, the polyacylation of pre-quaternized monomers as a straightforward and versatile approach has been proposed for the first time. Via this approach, novel aromatic anion-exchange polyelectrolytes featuring a long pendent spacer (i.e., –O–(CH2)4–) instead of a conventional benzyl-type spacer (i.e., –CH2–) are successfully synthesized, and exhibit not only high OH− and CO32− conductivity (91 mS cm−1 and 51 mS cm−1 at 60 °C, respectively) but also outstanding alkaline stability (e.g., no degradation of ammonium groups after aging in 6 mol dm−3 NaOH at 60 °C for 40 days). Using this kind of AAEM, a promising peak power density of 120 mW cm−2 is obtained on a preliminary H2/O2 single cell at 50 °C. This powerful synthetic approach together with exceptional membrane properties should pave the way to the practical application of this kind of AAEMs in alkaline fuel cells.

Novel aromatic proton-exchange polyelectrolytes via polyacylation of pre-sulfonated monomers

Disodium 2,2′-di(sulfopropyloxy)-biphenyl as a novel sulfonated aromatic diarene monomer has been facilely synthesised via one-step etherification in high yield and successfully applied in polyacylation under mild conditions for the first time. Proton-exchange membranes of the resulting side-chain-type sulfonated aromatic polyketones exhibit proton conductivity higher than Nafion® while maintaining a low swelling ratio, which may be ascribed to the microstructure of Nafion-like ionic clusters as observed by atomic force spectrometry. This work demonstrates that polyacylation directly from pre-ionised monomers offers a novel and powerful tool to advanced aromatic proton-exchange polyelectrolytes for fuel cells.

Proton-conductive polyimides consisting of naphthalenediimide and sulfonated units alternately segmented by long aliphatic spacers

Sulfonated polyimides (SPIs) consisting of naphthalenediimide and sulfonated units alternately segmented by long aliphatic spacers have been facilely synthesized. Such an unprecedented molecular design of SPIs avoiding conventional aromatic-type imide units allows the stacking of naphthalenediimide moieties and aggregation of sulfonate groups simultaneously, imparting high conductivity and excellent hydrolytic stability.

Silane Cross-Linked Sulfonted Poly(Ether Ketone/Ether Benzimidazole)s for Fuel Cell Applications

γ-(2,3-epoxypropoxy) propyltrimethoxysilane (KH-560) was incorporated in various proportions into side-chain-type sulfonated poly(ether ketone/ether benzimidazole) (SPEKEBI) as a crosslinker, to make membranes with high ion exchange capacities and excellent performance for direct methanol fuel cells (DMFCs). Systematical measurements including Fourier transform infrared (FT-IR), scanning electron microscopy-energy-dispersive and X-ray photoelectron spectroscopy (XPS) proved the complete disappearance of epoxy groups in KH-560 and the existence of Si in the membranes. The resulting membranes showed increased mechanical strength and thermal stability compared to the unmodified sulfonated poly(ether ketone/ether benzimidazole) membrane in appropriate doping amount. Meanwhile, the methanol permeability has decreased, leading to the increase of relative selectivities of SPEKEBI-x-SiO2 membranes. Furthermore, the H2/O2 cell performance of SPEKEBI-2.5-SiO2 membrane showed a much higher peak power density compared with the pure SPEKEBI memrbrane.