The ion exchange membrane holds a central role in electrochemical energy storage systems. Conventional membranes encounter various challenges, such as limited strength, large area resistance, reactant crossover issues, and expensive costs. These challenges of ion exchange membranes have constrained the development of electrochemical energy storage and power generation systems. In my Ph.D. research, I have chosen to use the novel Ultra High Molecular Weight Polyethylene (UHMWPE) membranes invented in our group in energy storage and generation applications to explore their potential to address the critical problems mentioned above. With the unique combination of high mechanical strengths, high porosity, small thickness, and hydrophobicity, the UHMWPE membranes are expected to outperform t...[ Read more ]

The ion exchange membrane holds a central role in electrochemical energy storage systems. Conventional membranes encounter various challenges, such as limited strength, large area resistance, reactant crossover issues, and expensive costs. These challenges of ion exchange membranes have constrained the development of electrochemical energy storage and power generation systems. In my Ph.D. research, I have chosen to use the novel Ultra High Molecular Weight Polyethylene (UHMWPE) membranes invented in our group in energy storage and generation applications to explore their potential to address the critical problems mentioned above. With the unique combination of high mechanical strengths, high porosity, small thickness, and hydrophobicity, the UHMWPE membranes are expected to outperform traditional ion exchange membranes while significantly reducing production costs.

In this thesis, I present two unique UHMWPE-based ion exchange membranes:

Pore-Filling NPE Membrane: By utilizing UHMWPE as the substrate, this high-performance pore-filling NPE membrane surpasses conventional commercial Nafion separators. Its design enhances mechanical strength, shortens the proton transport pathway, thereby decreasing area resistance, confines the water swelling of Nafion material, and reduces the water channel size to decrease ion crossover and reduce overall costs. The pore-filling NPE membrane exhibits a robust mechanical strength of up to 141 MPa, approximately 5.5 times of traditional Nafion membranes. Additionally, the area resistance has been reduced by approximately 40% compared to the thinnest commercial Nafion membranes. As a result, the pore-filling NPE membranes can achieve a high current density of 240 mA·cm^-2 with an 80% energy efficiency in redox flow batteries and reach a peak power density of 1.01 W·cm^-2 at 1.9 A·cm^-2 in fuel cells. The pore-filling NPE membrane holds great promise for applications in aqueous flow batteries, proton exchange membrane fuel cells, and electrolyzers.

Sandwich NPE Membrane: Benefiting from UHMWPE's hydrophobic, porous, and ultra-thin properties, the sandwich NPE membrane introduces an innovative proton transfer mechanism-volatile proton transport with "free water" and achieves theoretical 100% ion selectivity from the non-volatile ions. This newly designed ion exchange membrane effectively tackles the challenging issue of electrolyte cross-contamination in aqueous flow batteries without sacrificing proton conductance, thereby improving the battery efficiencies and capacity retention of aqueous flow batteries. As a result, the all-vanadium flow battery equipped with the NPE membrane demonstrated an energy efficiency of 80% and a stable discharge 100% capacity retention over 500 cycles at a current density of 160 mA·cm^-2. The sandwich NPE membrane shows great potential for enabling the deployment of catholyte/analytes of different chemical species in future acidic or alkaline flow batteries, leading to the development of low-cost, high-energy-density flow batteries.

In summary, this thesis integrated the novel UHMWPE membranes into ion exchange membranes and prepared two innovative ion exchange membranes to provide transformative solutions for electrochemical energy storage and power generation systems. These superior membranes provide the possibility for more efficient and economical energy storage and power generation development, with great potential for industrial and commercial applications.