Yurong Zhang

Silane-cross-linked polybenzimidazole with improved conductivity for high temperature proton exchange membrane fuel cells

Silane-cross-linked polybenzimidazole (PBI) membranes with high proton conductivity and excellent mechanical properties were successfully prepared by using a silane monomer, γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560), as a cross-linker. Fourier transform infrared spectroscopy and solubility tests were used to characterize and confirm the cross-linked structure in the membranes. The silane-cross-linked membranes displayed excellent chemical stability and improved mechanical strength. Especially at high temperature (130 °C), where the tensile strength value was in the range of 68.6 to 99.3 MPa, while that of the pristine PBI was 61.7 MPa. Moreover, the proton conductivity was significantly enhanced because the silane-cross-linked structure in the membranes could absorb more phosphoric acid. Considering the tradeoff of mechanical properties and proton conductivity, 3% KH560 in weight was demonstrated to be the optimum content in the membranes, for instance, the SCPBI-3/7.95 PA (the cross-linker content was 3 wt% and the PA doping level was 7.95) had a proton conductivity of 0.081 S cm−1 and that of the SCPBI-3/9.07 PA was 0.114 S cm−1 at 200 °C, while that of pristine PBI was 0.015 S cm−1 at 200 °C.

Quaternized poly (ether ether ketone)s doped with phosphoric acid for high-temperature polymer electrolyte membrane fuel cells

Quaternized poly(ether ether ketone)s (QPEEKs), which were aminated by trimethylamine (TMeA), triethylamine (TEtA), tripropylamine (TPrA) and 1-methylimidazole (MeIm), were prepared and used as phosphoric acid (PA)-doped high-temperature proton exchange membranes. These QPEEK membranes showed high glass transition temperature (Tg was higher than 483 K) and high thermal stability (T5% was higher than 486 K). The tensile strengths of these QPEEK membranes were higher than 60 MPa. The PA-doped im-QPEEK, which was aminated by MeIm, had the highest Wdoping (159 wt%) and proton conductivity (0.05 S cm−1 at 473 K). For the other three PA-doped QPEEK membranes, the Wdoping and proton conductivity decreased with the increase of the length of trialkyl side chains on quaternary ammonium groups. According to our study, the PA absorbing ability was subjected to the structures of quaternary ammonium groups instead of the basicities of quaternary aminating reagents. All PA-doped membranes had great oxidative stability and could last for more than 5 h in 3 wt% H2O2, 4 ppm Fe2+ Fenton solution at 353 K.

UV irradiation-induced cross-linked bicarbonate anion exchange membranes based on vinylimidazolium-functionalized poly(arylene ether ketone)

A novel cross-linking strategy for imidazolium-functionalized poly(arylene ether ketone) containing tetramethyl groups, used as anion exchange membranes, is presented in this paper. The preparation of anion exchange membranes comprised of converting benzylic methyl to bromomethyl groups by a radical reaction, quaternization of the bromometylated poly(arylene ether ketone) with 1-vinylimidazole and subsequent anion exchange reaction. The photo-crosslinking reaction, induced by UV-light under the activation of a photo-initiator, was simple and controllable compared to the conventional cross-linking process via a multifunctional cross-linking agent. All the vinylimidazolium-founctionalized poly(arylene ether ketone) membranes showed good mechanical and thermal stabilities. Moreover, the cross-linked membranes exhibited better dimensional stabilities. The ionic conductivity of cross-linked membranes was still acceptable although that property decreased with UV irradiation time due to the compact cross-linked structure. For example, the VImPAEK-15 min-HCO3 membrane with irradiation time of 15 min showed a moderate bicarbonate anion conductivity of 0.021 S cm−1 and a low swelling ratio of 10.74% at 70 °C. The alkaline stability test under both high and relatively low alkaline conditions was carried out. Although the vinylimidazolium cation is unstable in strong alkaline solution, the cross-linked vinylimidazolium-based membranes are chemically stable in the bicarbonate anion form under relatively low alkaline conditions. The results showed that the cross-linked membrane induced by UV irradiation could be used for electrochemical devices that were operated at less extreme pHs.

Impacts of Sandification on Ecological Functions and Conservation Measures in Xianghai Wetlands

The present conditions, causes of sandification and its impacts on the ecological functions of Xianghai wetlands have been studied. Results indicate that human irrational exploitation is the key cause of the sandification of the wetland. The ecological functions of the wetlands, for instance, in flood control, pollution filter, water purification, aquatic productivity, and habitat provision for a wide range of animal species, have been seriously affected. To effectively exploit and utilize the river flooding wetland resources, it is necessary to create integrate assessment index system for wetland. It is suggested that positive management strategies and measures for regulation and restoration of wetlands, sustainable exploitation of wetlands and water resource should be taken, so as to control sandification.