| The regulation and intensification of transfer properties play vital roles in design of high-performance membrane, and the transfer properties are highly dependent on the membrane microstructure. To solve the trade-off relation between methanol barrier property and proton conduction property in proton exchange membrane (PEM), this study centers on two key scientific issues, including the relationship between transfer properties an d m embrane m icrostructure as w ell as t he f ormation m echanism an d control method of membrane microstructure. Based on t he principle of bioadhesion, water retention of plant, and proton channel of cell, we establish and develop the bio-inspired approach to fabrication of PEM. The relevant methods and theories on intensification of methanol barrier and proton conduction are tentatively proposed, in hope of offering some guidance to the materials design & preparation of PEM for practical applications. The details were summarized as follows:Manipulation of membrane microstructure and intensification of methanol barrier property: (i) inspired by the bioadhesion principle, dopamine was utilized to modify the microstructure of membrane surface. By immersing Nafion in dopamine solution under mild conditions, a dense polydopamine nano-layer was formed and adhered tightly t o N afion s urface. It w as found t hat the pol ydopamine l ayer reduced t he hydrophilicity of Nafion surface, m eanwhile blocked the ion channels on N afion surface and decreased the channel size in inner Nafion. Methanol dissolution was thus decreased, yielding a n enhanced methanol ba rrier p roperty; and (i i) according t o hybridization method, inorganic fillers were utilized to manipulate the microstructure of membrane bulk. Hybrid membranes were fabricated by embedding silica-polymer submicrospheres i nto c hitosan ( CS) m atrix, and i t w as found t hat the polymer-inorganic interfacial interaction governed the membrane microstructure: (i) attractive force would generate strong interfacile stress, which remarkably inhibited the mobility of CS chains and led to dense chain packing, in turn reduced free volume cavity size; (ii) repulsive force enhanced the mobility of CS chains, which allowed for a loosened chain packing and increased free volume cavity size. Methanol crossover results r evealed t hat r educing t he free vol ume c haracteristics w ould enhance t he diffusion resistance and thus elevating methanol barrier property.Manipulation of membrane microstructure and intensification of proton conduction property: (i ) a ccording t o h ybridization m ethod, na notubes w ere ut ilized t o c reate proton transport pathway. Phosphorylated titanate nanotubes (PTNTs) were embedded into CS matrix to prepared hybrid membranes. It was found that the PTNTs enriched phosphorylate acid groups and then constructed an uninterrupted pathway for proton migration by Grotthuss mechanism through–POH groups and sorbed water, rendering an elevated proton conduction property; (ii) inspired by the water storage mechanisms in plant cell, PEM with high w ater retention properties was fabricated. Polymeric microcapsules (PMCs) were embedded into CS for fabricating composite membranes. It was found that the PMCs served as versatile water reservoirs and hence increased the w ater u ptake o f m embrane. The P MCs en dowed a water-state s witching and reduced the chemical potential of sorbed water. The water release rate of composite membranes was therefore reduced under low humidity, which in turn conferred better proton c onduction p roperty to composite membranes; and ( iii) i ntrigued b y t he exquisite proton channel in biological systems, proton carriers in PEM were designed. Imidazole mic rocapsules ( IMCs) w ere e mbedded in to S PEEK ma trix to f abricate composite membranes. It was found that the acid-base complex formed by the acidic groups in SPEEK and the basic groups in IMCs, mimicking the Schiff base- aspartic acid complex i n ba cteriorhodopsin, c onstructed t he f acile and e fficient pr oton pathways unde r humidified conditions. Under l ow humidity, the e mbedded IMCs, mimicking the vacuole in plant cell, could release water into SPEEK materix and thus endow stable water environment to the pathway. The latter efficiently improved the proton conduction property of IMC-filled membranes. |
