金属有机框架质子导体及其质子交换膜的研究进展

Recent Progress on Proton-Conductive Metal-Organic Frameworks and Their Proton Exchange Membranes

质子交换膜是新型燃料电池的关键组件之一.以Nafion为代表的商用全氟磺酸质子交换膜成本较高、操作温度较低,限制了宽温度范围下的大规模应用.金属有机框架材料(Metal Organic Framework, MOFs)因其比表面积大、结构规整、可设计性强等优点,在质子交换领域备受关注.作者从三方面综述了MOFs质子导体的相关研究.第一部分主要介绍了MOFs传导质子的作用机理;第二部分从有水/无水条件下工作的两种不同MOFs出发综述了MOFs质子导体的相关发展;第三部分系统回顾了MOFs质子交换膜的相关研究,包括MOFs薄膜与MOFs混合基质膜结构.最后指出了MOFs质子导体及其质子交换膜研究中尚未解决的问题,并展望该领域的未来研究方向.

Proton exchange membranes(PEMs) are important components for novel fuel cells. A significant effort has been made by researchers towards proton conductive materials and membranes, some of which have been successfully commercialized. However, commercial perfluorosulfonic acid membranes like Nafion suffer key issues which limit their large-scale applications in a wide temperature range, including high cost and low operation temperature. Therefore, it is highly desirable to prepare new-type PEMs possessing high proton conductivity, thermal and chemical stability, water uptake and excellent durability. Metal organic frameworks(MOFs) are attractive candidates for proton exchange membranes due to their high porosity, ordering pore structures and excellent designability. This review focuses on the recent progress on proton-conductive MOF structures and their proton exchange membranes. In the first section, the authors briefly introduce the proton conducting mechanism of MOFs and their testing methods. The Grotthuss mechanism refers to the proton transferring process in a continuous and long-range hydrogen network, whereas the Vehicular mechanism involves in the diffusion of proton carrier molecules. Then in the next section, the authors summarize the progress on bulk MOFs proton conductors. According to the work condition, proton-conducting MOFs can be divided into two types, namely working under humid and anhydrous environment. These works show the potential of proton-conductive MOFs to be applied in a wide temperature range, and some of them even have reached a relatively high conductivity larger than 10-2 S·cm-1, comparable with Nafion. In the third section, a review on the MOFs-based proton exchange membranes is shown. Researchers have proven that MOFs thin films have huge potential on proton conduction. Nevertheless, most of the MOFs-based PEMs are still mixed matrix membrane(MMM) structure. In order to boost the performance of MMMs-type MOFs-based PEMs, several strategies can be applied such as modifying MOF with functional groups, using 1 D/2 D MOFs structure and introducing the third phase into membranes. Last, the authors discuss the current issues and perspectives on MOFs proton conductors and their PEMs.