Phase Transformation Dynamics in Sulfate-Loaded Lanthanide Triphosphonates. Proton Conductivity and Application as Fillers in PEMFCs

Phase transformation dynamics and proton conduction properties are reported for cationic layer-featured coordination polymers derived from the combination of lanthanide ions (Ln(3+)) with nitrilo-tris(methylenephosphonic acid) (H6NMP) in the presence of sulfate ions. Two families of materials are isolated and structurally characterized, i.e., [Ln(2)(H4NMP)(2)(H2O)(4)](HSO4)(2)center dot nH(2)O (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Er, Yb; n = 4-5, Series I) and [Ln(H5NMP)]SO4 center dot 2H(2)O (Ln = Pr, Nd, Eu, Gd, Tb; Series II). Eu/Tb bimetallic solid solutions are also prepared for photoluminescence studies. Members of families I and II display high proton conductivity (10(-3) and 10(-2) S.cm(-1) at 80 degrees C and 95% relative humidity) and are studied as fillers for Nafion-based composite membranes in PEMFCs, under operating conditions. Composite membranes exhibit higher power and current densities than the pristine Nafion membrane working in the range of 70-90 degrees C and 100% relative humidity and with similar proton conductivity.