Zwitterion threaded metal–organic framework membranes for direct methanol fuel cells

Selective ion transportation membranes are a crucial component of energy storage and conversion devices. Herein, we report the fabrication of a zwitter-MOF membrane by threading zwitterion sulfobetaine methacrylate (SBMA) through a ZIF-8 membrane. The SBMA were encapsulated into ZIF-8 membranes by a self-confined growing method. The sulfonate and quaternary ammonium (QA) groups on SBMA generate hydrogen-bond networks in MOF channels as ion transporting pathways for cations and anions, respectively. The as-prepared poly-SBMA@ZIF-8 (pSZ) membrane presents both high proton and hydroxide conductivity, respectively. Apart from fast ion transportation, the pSZ membrane exhibits efficient blocking of the methanol crossover for direct methanol fuel cells (DMFCs) due to the well-intergrown morphology and size sieving of the ZIF-8 membranes. It is the first report of a zwitter-MOF membrane with high conductivity of both proton and hydroxide ions. Furthermore, the DMFCs assembled by the pSZ membranes exhibit a good performance in not only an acid system but also in an alkaline system. It shows the enormous potential of MOF-based membranes for application in DMFCs.