DESC0023904

There is a national need for a comprehensive energy portfolio to build a sustainable energy economy while addressing the climate crisis. The Department of Energy’s goals to achieve carbon pollution-free electricity by 2035, and further, to achieve net-zero emission by 2050, will rely on the development of electrochemically driven membrane technologies. Among these technologies is anion exchange membrane water electrolysis which does not require expensive platinum group metals like related proton exchange membrane-based systems. However, the hydroxide solution electrolyte in anion exchange membrane water electrolyzers gradually degrades current commercial anion conducting membranes, which were not designed for anion exchange membrane water electrolysis applications. Therefore, new robust anion exchange membranes that demonstrate high hydroxide conductivity and high hydroxide stability and are able to operate at temperatures >60 °C are needed. The objective of this program is to synthesize, develop and manufacture anion exchange membranes with new aromatic backbones that do not contain phenyl-ether bonds, which are susceptible to hydroxide attack. High molecular weight poly(carbazole) copolymers shall be synthesized to include rigid structures-which can increase the operation temperature range, and flexible methylene bridges-which will impart flexibility to avoid brittle membrane behavior. The poly(carbazole) copolymers will be grafted with alkyl ammonium groups to produce hydrophilic, phase separated hydroxide conducting channels. The ionic channels will allow efficient hydroxide conductivity and reduce membrane swelling due to water uptake. The polymer structure and architecture will be manipulated via adjustments in copolymer composition and alkyl ammonium group lengths which will afford tailorable morphology specifically for anion exchange membrane water electrolysis applications. During the program, the company and our national lab partner will systematically polymerize carbazole and a modified carbazole comonomer into high molecular weight copolymers via a facile Friedel Craft polycondensation reaction. The composition of the copolymers shall be characterized to identify structure - property relationships. The influence of the chain length of the alkyl ammonium group will be investigated with regard to membrane morphology, phase separation and ionic channel formation. The poly(carbazole) copolymer composition and structure will be characterized for hydroxide stability, hydroxide anion conductivity, gas (oxygen and hydrogen) diffusion, mechanical strength, and stability. The rigid hydrophobic backbone should serve to block undesirable permeability and diffusion of gas(es) through the bulk structure of the membrane. The membrane properties will be evaluated for mechanical properties, including wet/dry tensile and swelling behaviors. The durable membranes will be converted into membrane electrode assemblies and evaluate for performance and degradation by a national lab. A detailed property - structure relationship study shall be conducted to design better membranes for anion exchange membrane water electrolysis applications, which will afford validation of a Technology Readiness Level 3. TRL 6 shall be reached via membrane incorporation into membrane electrode assemblies and the electrolyzer cells performance characterization. Robust anion conducting membranes for electrochemical devices shall be commercialized primarily for anion exchange membrane water. As described in topic C56-18m, there are “no commercial materials today” that possess sufficient stability at any temperature under the conditions of sustained electrolysis. These anion conducting membranes may be applicable to fuel cells and redox flow batteries, as part of the developing hydrogen infrastructure.