DFT - experimental IR spectroscopy of lithiated single ion conducting perfluorinated sulfonated ionomers: Ion induced polarization band broadening

Group Vibrational Mode Assignments as a Broadly Applicable Tool for Characterizing Ionomer Membrane Structure as a Function of Degree of Hydration

“…These modes arise from the sulfonate form of the exchange site with a local 3-fold axis of symmetry. Eigenvector animations (refs , , and and SI Video 15) show calculated peaks at 1051* cm –1 , 1059* cm –1 , and 1014* cm –1 (Aquivion, Nafion, and 3 M, respectively) that correlate to observed bands (Figure ) at 1057 cm –1 , 1061 cm –1 , and 1060 cm –1 . Figure shows animation extrema snapshots of the pure modes and side chain modes used to schematically derive the ionomer C 3 V ,HF modes.…”

“…Eigenvector animations (refs and and SI Video 9) of calculated peaks at 1396* cm –1 , 1405* cm –1 , and 1395* cm –1 (Aquivion, Nafion, and 3 M, respectively; wavenumbers superscripted with * are DFT calculated eigenvalues) correspond to observed bands at 1414 cm –1 , 1414 cm –1 , and 1412 cm –1 , respectively (Figure ). Figure are extrema animation snapshots of small molecule pure modes (Col. 1) and side chain group modes (Col. 2) used to schematize derivation of the C 1,HF ionomer group modes (Col. 3).…”

“…Eigenvector animations (refs and and SI Video 13) show C 1,LF group modes at 777* cm –1 , 786* cm –1 , and 791* cm –1 for dehydrated Aquivion, Nafion, and 3M, respectively. The C 1,LF group modes are correlated to bands (Figure ) at 905 cm –1 , 910 cm –1 , and 926 cm –1 for dehydrated Aquivion, Nafion, and 3 M, respectively.…”

“…Infrared (IR) and Raman spectroscopy, correlated to density functional theory (DFT) calculated normal-mode analyses, facilitate characterization of the PFSI exchange site environment versus state of hydration. ,− DFT, a quantum mechanical description of electronic, structural, and vibrational properties of molecular and crystalline systems, is based on the Hohenberg and Kohn theorems. − The total system energy is a functional of electron density. The exact ground state may be obtained if this functional is known.…”

“…Visualization of eigenvector animations (e.g., using Maestro 9.6) enabled assignment of normal modes having internal coordinates of mechanically coupled functional groups . While it is not practical to consider the contribution of every oscillating fragment in a normal mode assignment, single-functional-group assignments, such as the Nafion 1060 cm –1 assignment to the sulfonate group, − have been a source of decades of confusion. − Warren and McQuillan, Cable et al, and Smotkin et al ,,,, noted the importance of considering vibrational contributions from mechanically coupled functional groups.…”