Recently, the iChEM researcher, Prof. Tongwen Xu in University of Science and Technology of China, collaborating with Prof. Michael D. Guiver in Tianjin University, made a new progress in development of alkaline anion exchange membranes for fuel cells. The results were published in Adv. Mater., entitled “Alkaline Anion-Exchange Membranes Containing Mobile Ion Shuttles “(DOI: 10.1002/adma.201506199).

Alkaline anion exchange membrane fuel cell (AAEMFC) is now considered as one of the most promising green energy-conversion technologies for stationary and mobile applications, due to the high fuel conversion efficiency at high pH and low cost stemming from their ability to operate in basic conditions using non-precious metal catalysts. One key impediment to commercialization is insufficient hydroxide ion (OH^-) conductivity of the central AAEM component, arising from a polymer architecture defect of conventional AAEMs in view of the OH^- conduction mechanism. AAEMs transport OH^- via the Grotthuss-type mechanism, where continuous interconversion occurs between hydration complexes (inactive OH^-(H₂O)₄, and active OH^-(H₂O)₃), driven by fluctuations in the solvation shell of the hydrated ions. Conventional AAEMs contain cationic groups bound covalently to polymer backbone by a hydrophobic sidechain. For OH^- conduction, the cationic sites enhance these fluctuations through electrostatic interactions with OH^-, but the hydrocarbon residue of the side chain is hydrophobic and less mobile, providing only minor contributions to OH^- transport.

In this study, they prepared an AAEM by threading ionic guests into poly (crown ether) hosts via host-guest molecular recognition. The pH- and thermally-triggered disruption of this interaction allows ion shuttle mobility, which accelerates OH^- transport. Based on this new concept, the mobile shuttle AAEM has among the highest reported OH^- conductivity for polymeric membranes to date, even at the case of a much lower IEC (a parameter that indicates the content of cationic groups). The mobile shuttle architecture provides a novel mode of ion transport for AAEMs, which can be utilized in a number of ion exchange applications, and which have conductivities higher than conventional membranes. Furthermore, this study provides a new vehicle for improving the understanding of OH^- transport through hydrated polymer media, and will catalyze exploration of new applications of this novel class of polymers with a unique mode of ion transport.

This work is supported by the Basic Research Program of China (973 project), the National Natural Science Foundation of China and Collaborative Innovation Center of Chemistry for Energy Materials (2011•iChEM).(Provided by Liang Wu and Xiaolin Ge)

Link: http://onlinelibrary.wiley.com/doi/10.1002/adma.201506199/epdf