Multidimensional network of polypyrrole nanotubes loaded with ZIF-67 to construct multiple proton transport channels in composite proton exchange membranes for fuel cells

Due to the designability of their proton transport channels, high-performance long-lasting composite proton exchange membranes (PEMs) are currently the subject of extensive research. However, the compatibility and channel order of the internal components of the composite membranes are still challenging. In this work, hollow polypyrrole (PPy) nanotube structures were obtained to provide a nitrogen source and to act as a skeleton to confine and separate cobalt nanoparticles on the surface of PPy nanotubes. Finally, zeolitic imidazolate framework material-67 (ZIF-67) was attached to the surface. By using this method, PPy@ZIF-67 filler can minimize the particle size and inhibit Co2+ ions from aggregating, thus constructing a reasonably distributed transport channel and improving the proton transport capacity. As a result, the synthesized polymer nanotubes loaded metal-organic framework (MOF) nanofiber network can enhance the physicochemical properties and stability of the membrane by providing a more extensive interfacial interaction. In addition, the composite membrane has excellent ionic conductivity and power density, reaching 233.7 mS cm–1 and 837 mW cm–2 at 80 °C and 100% humidity. It indicates that the nanofibrous MOF structure not only improves the compatibility with the substrate but also provides sufficient leap points for proton transport via the interfacial conduction pathway between the PPy@ZIF-67 filler and the substrate, thus allowing the resulting composite membrane to facilitate proton transfer via the Vehicle and Grotthuss mechanisms synergistically.