Nanoporous proton-transporting media are critical components in fuel cells and other electrochemical devices, yet general molecular design criteria for new materials with enhanced performance remain obscure. Aqueous lyotropic liquid crystals (LLCs) comprise a platform for detailed studies of the molecular-level features governing proton transport in monodisperse, water-filled nanopores lined with well-defined chemical functionalities. We report new alkylsulfonic acid LLCs that exhibit H+ conductivities as high as σ = 380 mS/cm at 80 °C, which rival those of more acidic, perfluorinated polymers, thus demonstrating that the acidity of the pore functionality is not the sole determinant of proton transport. Direct experimental comparisons of LLCs with convex and concave nanopores of similar dimensions indicate that H+ conductivities therein sensitively depend on the hydration state of the acid functionalities and the pore curvature. These experiments suggest that judicious manipulation of pore curvature provides a new means for optimizing the activities of proton-exchange membranes and nanoporous solid acid catalysts.
Bibliographical noteFunding Information:
We thank Marc A. Hillmyer for helpful discussions regarding bulk electrolyte solution conductivities. We gratefully acknowledge financial support for this work from the U.S. Department of Energy (DOE)-Basic Energy Sciences (BES) DESC0010328. Synchrotron SAXS analyses were conducted at Sector 12 of the Advanced Photon Source at Argonne National Laboratory, which is supported through the U.S. DOE Contract DE-AC02-06CH11357 under GUP-37637 and GUP-50116, with respective help from Dr. James Jennings and Carlos Baez-Cotto. This work also utilized University of Wisconsin Madison instrumentation facilities funded in part by NSF CHE-9974839 and CHE-1048642 and materials characterization facilities funded by DMR-0832760 and DMR-1121288. G.L.J. acknowledges a National Defense Science and Engineering Graduate (NDSEG) Fellowship from the U.S. Department of Defense.
© 2017 American Chemical Society.