Binding and transport of Mo V in perfluorinated ionomers by EPR and EPR imaging

Abstract

EPR spectra of MoV(as MoCl5) in ethanol solutions and in perfluorinated ionomers (PFI) with long pendant chains (Nafion) have been measured as a function of MoCl5 concentration in the solutions (in the range 3.60 × 10–6 to 1.15 × 10–4M) and degree of neutralization of the sulfonic groups in the ionomers. Two MoV sites were characterized in the ethanol solutions, and their relative intensity was found to depend on MoCl5 concentration. Both sites, however, show evidence for chlorine ligands around the paramagnetic cation. The MoV site in PFI swollen by ethanol is identical to the site detected in neat ethanol solutions at higher MoCl5 content, and was assigned to a molybdenum site with five chlorine ligands and an oxygen ligand from the solvent. The diffusion coefficients of this species were determined by 2D spatial–spectral electron paramagnetic resonance imaging (2D EPRI) in Nafion–ethanol, by simulating the concentration profiles along the spatial coordinate measured during the diffusion process. The diffusion coefficients in Nafion–ethanol are 5.0 × 10–7, 7.1 × 10–7, 10.4 × 10–7 and 13.3 × 10–7 cm2 s–1 at 280, 300, 315 and 330 K, respectively. The activation energy for diffusion is 15.4 kJ mol–1.