Fundamental investigation of the transport properties of superacids in aqueous and non-aqueous media.

摘要

In the quest to develop more efficient energy providers one of the main focus of research has been on the improvement of ion transport. In lithium battery research this has led to the incorporation of various lithium salts, ceramics and plasticizers into the poly(ethylene)oxide (PEO) matrix, the polymer most used In Proton Conduction Membrane (PCM) fuel cell research this has led to the development of new membranes, which are designed with to replicate Nafion's (©DuPont) proton transport but also improve upon its deficiency of transporting intact fuel molecules and its dependence upon the presence of solvating water molecules.; To better understand the process of ion transport, NMR was used to investigate dynamic properties such as D (self-diffusion coefficient) and T₁ (spin-lattice relaxation time) of various proton and lithium ion-conducting systems. Ionic conductivity and viscosity measurements were also performed. The systems studied includes aqueous superacid solutions (trifluoromethanesulfonic (TFSA), para-toluenesulfonic (PTSA) and bis(trifluoromethanesulfonyl)imide (TFSI)); nano-porous (NP-) PCM's incorporating various ceramics and 3M fuel/2M H₂SO₄ solutions; and P(EO)₂₀LiBETI (LiN(SO ₂CF₂CF₃)₂ composite incorporating SiO ₂ ceramic nano particles.; The objective of the study of the superacid solutions was to determine the effect of concentration on the transport. It was found that beyond the ionic conductivity maximum, fluctuations in both D and T₁ supports the existence of local ordering in the ionic network, caused by the reduced solvent dielectric coefficient and increasing viscosity. Of the three superacids TFSA was the most conductive and most affected by reduced solvent concentration.; For the P(EO)₂₀LiBETI composite the aim was to determine the effect of the ceramic on the ion transport of the composite in a solvent free environment. Results show that the ceramic causes only modest increase in the lithium transport below 90°C.; The objective in the study of the NP-PCM's was to determine the effect of the ceramic type and concentration on the proton and fuel transport through the polymer/acid system. Results show that the greater the surface area and concentration of the ceramic the greater the proton and fuel diffusion. The results were also shown to be fuel dependent, with dimethyl oxalate giving the lowest fuel diffusion.