Miguel Antonio Modestino
Novel ionomer materials for electrochemical energy conversion devices
The large scale deployment of renewable energy technologies relies in our ability to develop practical energy storage solutions. Electrochemical energy conversion devices such as water electrolyzers are promising technologies that can use the intermittent power supplied by renewable sources to produce transportable fuels such as hydrogen. Significant advances have been made in proton-exchange membrane (PEM) water electrolysis, but their large scale implementation has been hindered by multiple technical challenges. Many of these challenges are associated with poor mass and/or charge transfer at electrocatalytic interfaces in membrane-electrode assemblies (MEA). In this presentation, I will describe the self-assembly behavior of state-of-the-art ionomers (i.e. Nafion®) that lead to transport limitations when confined to electrocatalytic interfaces. Using in situ grazing-incidence X-ray scattering (GISAXS), we demonstrate that interfacial interactions can significantly affect the internal morphology and dynamics of Nafion films during water uptake. Furthermore, the results presented here demonstrate that upon thermal annealing of Nafion thin-films, static crystalline domains form near the substrate interface which restricts the swelling of the material. These morphological characteristics translate directly into effects on macroscopic swelling behavior, where the crystallinity of the matrix and parallel orientation of ionomer domains limits the maximum water uptake and conductivity of films. To mitigate these limitations, my group is developing new materials based on acid doped hydrogels and amorphous perflourinated ionomers that can deliver high water uptake, ionic conductivity, and gas permeability. By tuning molecular composition of the polymers and their structural morphology (cross-linking density and film thickness), these engineered materials can be tailored to optimize transport in MEA catalyst layers and improve the performance of PEM water electrolyzers and hydrogen fuel cells.