Improving Hydrogen Production for the Future: How Does an Ionomer’s Morphology and Chemistry Effect the Ionomer-Catalyst Interface in Water-Electrolysis?
Authors: Sweeney Alana Blaise , Herring Andrew M. , Kuo Mei-Chen 
Published: December 2024

The evidence of the impacts that fossil fuel energy sources have on the environment is inescapable. From poor air quality, warmer temperatures, to contaminated land and water, research thrusts in the use of non-fossil fuel renewable energy sources have greatly increased. There has been a large impact, both economically and environmentally, with the switch to using hydrogen as an energy carrier and reagent for renewable energy. There is still much room for improvement, as the current cost per kilogram of hydrogen produced via renewables is $5-6. The DOE is pushing to decrease that cost to $1 per kilogram in the next decade through its Hydrogen Energy Earth Shots thus, making the process more accessible for wide use of hydrogen [1]. Ionomer-based water electrolysis is a promising avenue to gather hydrogen with little to no carbon emissions. Within water electrolysis there are many moving parts that impact the cost and efficiency of hydrogen production. For our interests, we will be working on the understanding of the ionomer membrane and interfaces in the membrane electrode assembly. Currently, fluoropolymers are widely used as polymer membranes within the energy field, although there is concern about their lifelong byproducts from the production and disposal practices. These byproducts have been found in soil, water, and even blood, as a result of contaminated drinking water [2]. By fully understanding the capabilities of these ionomers, we can move away from the predominant use of fluoropolymers which have dominated other options for polymer membrane materials despite their rising environmental and cost concerns [2].

We aim to improve these macromolecules by altering both the material’s morphology and chemistry. The morphology of the polymer refers to the backbone and the configuration of how each chain aligns. We believe by studying how different configurations align, such as lamellar and cylindrical stacking, and how these regions react to water swelling, we can observe the most ideal sequence for ionomer-catalyst interactions. These studies will be conducted by testing different copolymer configurations, as in random and block sequences of the backbone monomers, adjusting ratios of monomers, altering linkages between copolymer segments, the changing of side groups, and varying hydrophilic and hydrophobic blocks. As for the polymers’ chemistry, by testing varying ion-conducting groups we can adjust the characteristics of the ionomer itself and how the ionomer works with the catalyst. To do so, we will begin with synthesizing a known ionomer, Polyisoprene-ran-poly(vinylbenzyl chloride) (Pip-ran-PVBCl), via nitroxide-mediated polymerization followed by hydrogenation and quaternization reactions with different cationic groups. Specifically, we will be adding groups of varying lengths of carbon chains, including triethylamine (TEA) and trimethylammonium (TMA) as the longer the carbon chain the lower the Ion Exchange Conductivity (IEC). This is due to the decreasing reactivity of long carbon chains [3]. We expect these to give us a strong baseline of ionomers which we can further test the solubility of to better understand how the different cationic side groups can change the amount of water at the ionomer-catalyst interface.

To further test these interactions with the catalysts, working with our colleagues in the Center of Ionomer-based Water Electrolysis (CIWE), through microelectrodes, small-angle x-ray scattering (SAXS), wide-angle x-ray scattering (WAXS), and calorimetry. Through CIWE, we are working with computer scientists who can develop digital twins of this work and therefore bridge the knowledge gap from researcher to consumer. By gathering more data and through machine learning we can improve the ionomers for use in ionomer-based water electrolysis, so that we can aid in the push to harness efficient hydrogen production materials for future hydrogen production.