M.Sc Thesis


M.Sc StudentHalabi Manar
SubjectElectrospinning of Ionomer/Metal Nanofibers with Electrical
and Ionic Conductivity
DepartmentDepartment of Chemical Engineering
Supervisors PROF. Gideon Grader
DR. Gennady Shter


Abstract

Electrospinning (ES) is a method which uses a large electric field to destabilize a liquid surface, generating fibers with nanometer dimensions. Due to their large surface area, electrospun nanofibers are being used in many applications such as catalysis, bio-medical, sensing and more. For example, anion conductive nanofibers could serve as a catalyst layer in polymer electrolyte membrane fuel cells (PEMFC) since they have ionic conductivity (OH-) and enable gas transfer. Addition of metal NPs to the electrospun mats can also provide an electron conduction pathway and catalytic activity. A complex mat, which includes metal nanoparticles (NPs) in the ionomeric network, has not been demonstrated before.

In this research, anion conductive nanofiber mats from FAA-3 ionomer were obtained by ES. Nanofibers with different morphologies were prepared, depending on the solvent used in the precursor solution, the ionomer concentration and the relative humidity (RH) during ES process (RHES). The anionic conductivity and water uptake (WU) of the ionomeric nanofiber mats were measured as a function of the RH. To obtain electrical conductivity, Ag nanoparticles (NP) were added in two ways: to the precursor before ES or by impregnation (after ES). Ag NPs were impregnated into nanofiber mats and their effect on WU and electrical conductivity was investigated.

It was found that increasing ionomer concentration in the precursor solution led to a morphological change from beads to fibers. Different morphologies of the ionomer electrospun fibers were obtained when dissolving FAA-3 in propanol or DMF. Flat, ribbon-like fibers obtained with propanol solvent have a higher WU and anionic conductivity. The ionic conductivity of a single fiber (SF) was found to be an order of magnitude higher (27  ) than the electrospun mat’s conductivity (3.4  ).

The effect of RHES on fibers properties was examined. Branching effect was observed when ES took place at 30% RH, an explanation of this effect was proposed.

The ES experiments of FAA-3 and Ag were successful when small Ag NPs (35 nm) and low Ag concentrations were used.

During impregnation, higher Ag concentration in suspension gave rise to electrical conductivity. The WU of impregnated samples showed that longer impregnation time does not change the uptake significantly. Impregnation using higher Ag concentration in suspension, decreased the WU of the loaded fiber mats.

The obtained results increase the understanding of ionomers ES process, toward development and design of new anion conductive ionomer fibers, useful for high performance electrochemical devices.