材料期刊网

作为含有多金属氧酸Keggin分子构型的固体强酸，杂多酸(HPAs)具有优异的吸水性、质子传导性(cp )、机械、热及化学稳定性。HPA掺杂陶瓷或聚合物质子交换膜(PEMs)可以有效提高复合 PEMs 的亲水性、cp、燃料阻隔性、机械、热及化学稳定性，同时显著降低其cp 及燃料阻隔性的温度与湿度依赖性。当 HPA掺杂陶瓷时，两者之间的氢键作用导致 HPA在基体中的流失率低、分散性强且掺杂量高，此时复合PEMs的cp(10-1 S/cm数量级)较基体 PEMs(10-3~10-2 S/cm)大幅升高；而当 HPA 掺杂磺化聚合物时，两者之间的静电排斥力造成 HPA在基体中的流失率高、分散性差且掺杂量低，此时复合 PEMs 的cp (10-1 S/cm数量级)较基体PEMs(10-2~10-1 S/cm)仅小幅升高。为了有效降低 HPA在聚合物基体中的流失率，可以采用聚合物膜“三明治”状包覆复合PEMs、盐化 HPA、改性基体或通过第三组分负载 HPA以分别在 HPA 与基体或负载之间形成氢键或静电引力等手段；对于 HPA的负载改性，由于陶瓷或聚合物负载在基体中易团簇，相应地 HPA 在基体中的分散性与掺杂量并未提高。有时采用HPA与吸水性较强的磷酸共掺杂陶瓷基体或负载，以协同提高复合 PEMs 的cp ，然而效果并不显著。以上各种结构的 HPA 掺杂PEMs通常由溶液浇铸法、自组装法、溶胶-凝胶法及浸润法等制备；不同方法往往相互关联，即制备过程可能涉及两种或3种方法的耦合使用。改性 HPA或其负载以显著提高 HPA在磺化聚合物基体中的分散性与掺杂量，借此构建全新、高效的质子传输通道形态以实现复合PEMs的超高cp(100 S/cm数量级)，是今后PEMs技术的重点发展方向之一。

As a strong solid-acid with a Keggin molecular-configuration of polyoxometalate,heteropolyacids (HPAs)exhibit superior hygroscopy,proton conductivity (cp ),as well as mechanical,thermal and chemical stabilities.Doping of ceramics or poly-mers with an HPA endows the resulting composite proton-exchange membranes (PEMs)with efficiently improved hydrophily,cp , fuel barrier property,as well as mechanical,thermal and chemical stabilities,and also the considerably decreased dependencies of their cp and fuel barrier property on temperature and humidity.When HPA is doped with ceramics,the hydrogen bonding between the two components results in a low rate of the HPA running-off,high dispersion and high doping capacity of the HPA in the matrix, and the cp of the composite PEMs(10-1 S/cm)is significantly enhanced compared to that of the matrix PEMs(ca.10-3-10-2 S/cm). When HPA is doped with sulfonated polymers,the electrostatic repulsion between the two components leads to more HPA run-off, much lower dispersion and low doping capacity of the HPA in the polymeric matrix,and the cp of the composite PEMs(10-1 S/cm)is only slightly higher than that of the matrix PEMs (ca.10-2-10-1 S/cm).To reduce the running-off rate of an HPA from polymeric matrices,different approaches can be employed,such as use of sandwiching polymer membranes to protect the composite PEMs, salination of the HPA,modification of the matrices or support of the HPA on the third component to form hydrogen bonding/electro-static attractions between the HPA and the matrices or the support.For the modification of the HPA support,the dispersion and do-ping capacity of the HPA are not improved in the matrices because the ceramic or polymeric support tends to form cluster within the matrices.Occasionally,an HPA and hygroscopic phosphoric-acid are jointly employed to dope ceramic matrices or supports to syner-gistically enhance the cp of composite PEMs,which has no obvious effect.The aforementioned HPA-doped PEMs of various struc-tures generally are prepared by solution-casting,self-assembly,sol-gel and infiltration methods,and a preparation process possibly involves two or three types of methods.To modify an HPA or its support for higher dispersion and doping capacity of the HPA with-in sulfonated-polymer matrices,and construct an original,efficient proton-transport channel configurations to accomplish an ultrahigh cp(100 S/cm)for composite PEMs,is one of the key future development directions for the PEMs technology.