Constructing Mechanisms And Manipulation Of The Effective Proton Conducting Channels For The Phosphorylated Hybrid Membranes

Optimization of chemical composition and topology is vital for high-performanceproton exchange membranes (PEMs). Compared to-SO3H,-PO3H2are alternativesespecially for high temperature and low humidity conditions. Amphoteric-PO3H2canboth provide protons as donators and stabilize them as acceptors. Thus extensivehydrogen bond networks are formed, water retention property, conducting barrier isenhanced or lowered. However, unlike sulfonation, phosphorylated polymers wereinsufficient for the more complicated chemistry. Phosphorylated PEMs can be madeby doping H3PO4, but leaching is liable under fuel cell condition. Hence,phosphorylated membranes by fixing-PO3H2on inorganic phase are competitive.Through immobilizing-PO3H2in inorganic phase, phosphorylated PEMs can be easilyachieved. Based on above, various phosphorylated PEMs were fabricated. By finelyregulating both the chemical composition and topology of inorganic phase, themicro-phase structure in the mesoscopic scale was tuned, and effective conductinggroups were introduced, efficient conducting channels were constructed, synergisticeffects of conducting groups were strengthened. These approaches can offer effectiveprotocol to develop PEMs.Effective phosphorylation methods for versatile inorganic phases were developed,and phosphorylated PEMs were fabricated. The inorganic surface was firstly activatedby epoxy then phosphorylated by POCl3. Herein:(i) the surface of SiO2weremodified by phosphorylated organic chains with different lengths, and thephosphorylated membranes were prepared by incorporating the phosphorylated SiO2into sulfonated poly(ether ether ketone)(SPEEK) matrices. By altering the modifiedchain lengths, the amounts of-PO3H2were changed, and the synergistic effects of theconducting groups anchored in the organic matrices or in the inorganic phase wereregulated. Compared to the monolayer of the functional groups formed on the SiO2surface introduced by short chains, the long chains could promote SiO2phosphorylation degree, and thus more-PO3H2were introduced into membranes.However, sufficient synergistic interactions in hybrid phases were formed for themembranes doped SiO2with short chains, and more effective conducting groups wereintroduced, resulting in the supreme performances.(ii) Mesoporous SiO2withdifferent phosphorylation forms and topological morphologies in the mesoscopic scale were prepared and incorporated into SPEEK to fabricate hybrid membranes. Formesoporous SiO2, both the amounts and location of-PO3H2were changed, and themesostructures were altered. It was confirmed that, more conducting groups should beintroduced by the inorganic phase, and also the connected conducting channelsfabricated in the inorganic phases could contribute to the high-performance.(3)Hollow mesoporous SiO2with multi-level structure in the mesoscopic scale werephosphorylated via various methods, and chitosan (CS) hybrid membranes werefabricated. By chemical or physical modification methods, both the outer surface andthe inner mesowalls of SiO2were phosphorylated, and meanwhile, molecules with-PO3H2were immobilized in the hollow structures. Intensive hydrogen networks wereformed by-PO3H2with-OH and-NH2in matrices; continuous conducting channelswere fabricated in the mesoporous shells; hollow structures could serve as “acidicreserviors”, as a result, membrane performance was highly enhanced.(4)Furthermore, other conducting pairs, which behave as donors and acceptors, wereutilized in the membranes. The outer surface of mesoporous SiO2was modified by-NH2and the inner walls was phosphorylated, then membranes were fabricated.Tighter donor-acceptor complexes were formed by-NH2than-PO3H2with-SO3H,leading to intensive synergistic effects and the effective conducting channels along theinorganic phase. High-performance PEMs were fabricated.