A New Class of Intermediate Temperature 1D Anionic Coordination Polymer Proton Electrolytes

Borosulfates and borophosphates are two examples of a recently-discovered new class of intermediate temperature (150 °C-400 °C) solid acid electrolytes that exhibit a 1D anionic coordination polymer structure. We have shown that the borosulfates exhibit extremely high proton conductivities under low humidity environments, while the borophosphates are much more thermally stable, but require significant humidity for proton conduction. We have made significant advances in developing and scaling-up solvothermal synthesis methodologies that can be varied to produce a different solid- state borosulfate and borophosphate structures (verified by SCXRD and PXRD) and exert significant crystallite size control. Examples will be presented of approaches for improving proton conductivities in these materials that include varying mixtures of cations, cation and carrier doping, as well as process optimizations to produce higher quality sintered monoliths.