(6ia) Morphology and Ion Transport in Polymer Electrolyte Membranes

Polymer electrolyte membranes have broad applications in energy storage and conversion, clean-water-related technologies and medicine. Common examples include fuel cells, redox flow cells, electrodialysis, reverse osmosis, hemofiltration and hemodialysis. My current research as a postdoctoral fellow at Lawrence Berkeley National Laboratory is focused on the fundamental investigation of morphology-conductivity relationships in proton-conducting block copolymer electrolyte membranes, comprising ionic and non-ionic blocks.

Membranes currently used for proton transport in fuel cells are nonporous (e.g. Nafion). In this poster, I show that the introduction of pores into block copolymer electrolyte membranes provides fine control over water uptake and conductivity. We start with a membrane comprising a mixture of homopolymer polystyrene (hPS) and a polystyrene-b-polyethylene-b-polystyrene (SES) copolymer. Porous membranes are fabricated by rinsing the hPS/SES mixture membranes in tetrahydrofuran and methanol. The polystyrene domains in the porous SES membranes are then sulfonated to give a porous membrane with hydrophilic and hydrophobic domains. The porosity is controlled by controlling ϕ_v, the volume fraction of hPS in the blended membrane. The morphology of the membranes was studied by scanning transmission electron microscopy (STEM), electron tomography and resonance soft X-ray scattering (RSoXS). The porous structures before and after sulfonation are qualitatively different. Water uptake of the membranes increases with increasing ϕ_v. Proton conductivity is a non-monotonic function of the water content of the membranes.

Using this novel method, we were able to control the water uptake of block copolymer electrolyte membranes without changing the chemistry or chain architectures. We believe that the novel processing method described above has created microscale pores in the block copolymer electrolyte membranes which allows us to tune the water uptake of these membranes to optimize proton conductivity.

As a faculty candidate, my proposed research will be initially focused on ion-containing polymers. I propose to build a program aimed at establishing the design principles of functional ion-containing polymers with a scientific focus on obtaining a fundamental understanding of the structure – property relationships in specific systems.

My proposed research is broadly organized into three interrelated projects:

1. Hybrid ion-containing polymer membranes for clean energy and water;
2. Morphology and transport properties of thin film ion-containing polymers;
3. Ion-containing polymers for endovascular drug filtration.