Transport Properties of 2-FPTf and TFMSA Monohydrate

by Mohammed Wahed Abdullah

Institution: Arizona State University
Department: Physics
Degree: Doctorate Degree
Year: 2015
Keywords: NMR, 2FPTf, TFMSA, PhD Thesis, Mohammed Abdullah
Posted: 04/10/2016
Record ID: 2063520
Full text PDF: https://repository.asu.edu/attachments/164068/content/Abdullah_asu_0010E_15639.pdf


Proton and fluorine diffusivity and ionic conductivity of 2-fluoropyridinium triflate (2-FPTf) and proton and fluorine diffusivity, ionic conductivity, and viscosity of trifluoromethanesulfonic acid (TFMSA) monohydrate have been measured over a wide range of temperatures. Diffusivities were measured using the pulsed-gradient spin-echo (PGSE) technique on a 300 MHz NMR spectrometer. Conductivities were measured using electrochemical impedance spectroscopy (EIS) on standard equipment and viscosities were determined using a Cannon-Ubbelohde viscometer. For 2-FPTF, the diffusivity of mobile protons increased from 1.84+/-0.06 x 10(-11) m2/s at 55 degC to 1.64+/-0.05 x 10(-10) m2/s at 115 degC while the diffusivity of 2-fluoropyridine fluorines increased from 2.22+/-0.07 x 10(-11) m2/s at 70 degC to 9.40+/-0.28 x 10(-11) m2/s at 115 degC. For TFMSA monohydrate, the diffusivity of protons increased from 7.67+/-0.23 x 10(-11) m2/s at 40 degC to 3.92+/-0.12 x 10(-10) m2/s at 110 degC while the diffusivity of fluorines increased from 4.63+/-0.14 x 10(-11) m2/s at 40 degC to 2.79+/-0.08 x 10(-10) m2/s at 110 degC, protons diffusing approximately 1.5 times faster than fluorines over the entire temperature range. NMR spectra indicate that proton diffusion occurs via direct hopping from TFMSA molecule to molecule. The conductivity of 2-FPTf varied from 0.85+/-0.03 mS/cm to 35.9+/-1.08 mS/cm between 25 and 110 degC. The conductivity of TFMSA monohydrate varied from 6.60+/-0.2 mS/cm to 84.6+/-2.5 mS/cm between 23 and 139 degC and its viscosity varied from 27.5+/-1.4 mPa.s to 4.38+/-0.22 mPa.s between 49 and 121.5 degC, in good agreement with literature values. Temperature dependences of the measured properties showed Arrhenius behavior with activation energies for proton diffusion, fluorine diffusion and ionic conduction for 2-FPTf above the melting point of 16.9+/-0.8 kJ/mol, 48.0+/-2.4 kJ/mol and 27.8+/-1.4 kJ/mol respectively. Activation energies for proton diffusion, fluorine diffusion, ionic conduction and viscosity for TFMSA monohydrate were 23.4+/-1.2 kJ/mol, 26.0+/-1.3 kJ/mol, 22.1+/-1.1 kJ/mol, and 26.9+/-1.3 kJ/mol respectively. The degree of dissociation of the charged species, calculated using the Nernst-Einstein relation, varied from 13 to 24% for 2-FPTf and from 25 to 29% for TFMSA monohydrate over the temperature range.