Construction And Performance Of Ion Transfer Channels In High Performance Proton Exchange Membranes

Today’s electro-membrane processes are developing at a high rate,with ion exchange membranes as the core component of which,often considered to be ion exchange resins in membrane form,their main function is to enable selective transport of ions between separated anodic and cathodic reactions by constructing different positively or negatively charged functional groups,and to complete the charge balance between ions and water through membrane transport to connect the complete circuit.In contrast,proton exchange membranes(PEMs)are ion exchange membranes that have negatively charged functional groups(mainly sulphonic acid groups)and are capable of selectively transporting cations.This functionality enables a variety of electrically driven membrane processes such as water treatment,electrodialysis,fuel cells,redox liquid flow cells,reverse electrodialysis and water electrolysis,and shows great potential in the areas of green production,energy conservation and storage,emission reduction and energy conversion.Advancing the development of high-performance PEMs is key to achieving the requirements for high-speed ion transport,and the fact that transport channels are primarily influenced by the molecular micro-and nano-scale in the design of membrane structures brings up the question that researchers in the field have focused on,namely the choice and trade-off between permeation and conduction properties.In this thesis,with the goal of achieving high speed proton transport performance,various strategies are proposed around the construction and coordination of multiple ion channels to achieve further optimisation of the transfer process.The main elements and results of the study are as follows.Firstly,a sulphonated imide polymer(SPI)matrix with a rigid twisted structure was designed and synthesised under the influence of a self-polymerising microporous polymer.The conformational change of the polymer depends on the type of polymer chemical structure and the introduction of this non-planar structure affects the conformational change of the polymer,leading to the formation of nanoscale cavities and ion channels,increasing the free volume,which can be used for fast proton transport.This was demonstrated by microporous porosity tests and proton conductivity tests.Secondly,the microphase separation channels were constructed by block polymerisation,which worked in conjunction with the microporous structure,resulting in the preparation of a block polymer with a self-polymerising microporous structure and a proton exchange membrane with excellent electrochemical properties.Then,based on a sulphonated polyimide proton exchange membrane,a metal-organic backbone containing amino flexible side chains is introduced as a filler,and the amino group on the filler is used to form an acid-base pair interaction with the sulphonic acid group on the polymer backbone to increase the proton transfer channel through hydrogen bonding.The conformational relationships within the composite membrane and the proton transport mechanism in the membrane are further clarified in the discussion of the factors affecting the performance changes of the blended membrane.The unique porous structure of MOF and the synergistic effect of amino modifications facilitate the formation of continuous transport pathways,and the tight acid-base electrostatic interactions can accelerate proton conduction via the Grotthus mechanism.It provides a promising strategy for the design and development of composite proton exchange membranes.In order to further design and optimize the continuity and multiplexing of proton transport channels in the composite proton exchange membrane,hollow polypyrrole nanofiber tubular structure(PPy)is used to provide a nitrogen source and play the role of skeleton.In this work,we fabricate hollow polypyrrole(PPy)nanofibre-like structures to provide a nitrogen source and act as a skeleton to confine and separate cobalt nanoparticles on the surface of PPy nanotubes,finally attaching and anchoring ZIF-67 to the surface.By using this method,PPy@ZIF-67 filler can minimize particle size and inhibit Co nanoparticles from aggregating.,thus constructing a reasonably distributed transport channel and improving the proton transport capacity.As a result,the synthesized polymer@MOF nanofibre network can enhance the physicochemical properties and stability of the membrane by providing a larger size of interfacial interaction.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 synergistically facilitate proton transfer via the Vehicle and Grotthuss mechanisms.