Porous Proton Exchange Membrane Based Zeolitic Imidazolate Framework-8 (ZIF-8)

Metal-organic frameworks (MOFs) are emerging material class for the past few years due to its tailorability characteristics for various applications. However, the research and development (R&D) of MOFs is still scarce for fuel cell system. This may be due to the several difficulties faced in selecting a good MOFs-based electrolyte, which consequently affects both proton conduction and methanol crossover, especially for direct methanol fuel cell (DMFC) system. Owing to excellent thermal and chemical stability with controllable pore size possessed by zeolitic imidazole framework-8 (ZIF-8) crystal structure has made it most widely investigated. Furthermore, the superhydrophobicity of the ZIF-8 allows high proton conductivity and methanol barrier properties, especially in the DMFC system. In fact, there has been a huge development on fabricating the ZIF-8 membrane, regardless the effects on proton conduction and methanol permeation for fuel cell application. Thus, in this paper, the specialty possessed by MOFs as proton conductors has been discussed; in conjunction with the properties, the synthesis and fabrication of ZIF-8 membrane as alternative proton conductor and methanol barrier for DMFC application have also been highlighted.