Degree

Doctor of Philosophy (PhD)

Department

chemical engineering

Document Type

Dissertation

Abstract

Water and energy scarcity are two of the main problems the world is facing today. A number of industrial processes like chemical manufacturing plants, energy production, electricity generation are heavily dependent on availability of a reliable source of water. Similarly, every step of water collection, treatment, and distribution, is an energy intensive process. The efficient use of electrochemical devices can help tackle some of these problems. Bipolar membranes (BPMs) have historically been deployed in electrodialysis setups for mineral acid and base production. The need to have disparate pH environments in electrochemical cells, and prevent species crossover, have motivated researchers to examine BPMs as an electrolyte separator. BPMs have the unique capability to split water into protons and hydroxide ions charge carriers in addition to conducting those ions in opposite directions to maintain current flow in the electrochemical setup. Most materials related research for BPMs has focused on water-dissociation catalysts. There are few reports that investigate the importance of high-quality bipolar junction interfaces for improving water-splitting in BPMs. This Dissertation studies how tuning bipolar junction interfaces affect the kinetics for water splitting in addition to ionomer conductivity. In the first part of the work, BPMs with systematically varied interfacial area values were prepared using soft lithography. Polarization experiments with the new, micropatterned interface BPMs reveal a 250 mV reduction in the on-set potential when increasing the interfacial area by 2.2x and a 15% increase in current density at 2 V. This approach was conducive for making BPMs with different chemistries ranging from perfluorinated AEMs and CEMs to alkaline stable, ether-free poly(arylene) hydrocarbon AEMs. These polymer chemistries are more robust for fuel cell and electrolysis applications. Nanopatterned surface ion exchange membranes (IEMs) have also been prepared using block copolymer (BCP) lithography. These membranes were demonstrated to have upto 5% improvement in through-plane conductivity without affecting the permselectivity of the membrane. Finally, modification of bipolar junctions in electrode surfaces was shown to impact the microstructures of anion exchange ionomer (AEI) thin films, leading to enhanced conductivity. Overall, this dissertation demonstrates that improving the properties of IEMs and ionomer-electrode interactions play a crucial role in improving the performance of electrochemical processes used to address problems in the water-energy nexus.

Date

7-13-2021

Committee Chair

Arges, Chris G.

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