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

[Image: see text] 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) (H(6)NMP) in the presence of sulfate ions. Two families of materials are isolated and structurally characterized, i.e., [Ln(2)(H(4)NMP)(2)(H(2)O)(4)](HSO(4))(2)·nH(2)O (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Er, Yb; n = 4–5, Series I) and [Ln(H(5)NMP)]SO(4)·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 °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 °C and 100% relative humidity and with similar proton conductivity.