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PreprintCC BYChemRxiv

Resolving Month-Long Nanostructural Evolution in Degrading Anion Exchange Membranes

  • Shakkira Erimban1,2
  • Esteban D. Gadea1,2
  • Ignacio J. Bombau1,2,3,4
  • John J. Karnes5
  • Johanna J. Schwartz5
  • Valeria Molinero1,2
5 affiliations
  1. 1Department of Chemistry
  2. 2University of Utah
  3. 3Facultad de Ciencias Exactas y Naturales
  4. 4Universidad de Buenos Aires
  5. 5Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, California, 94550
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Abstract

Chemical degradation reshapes the hydrated ion-transport channels of anion exchange membranes (AEMs), but conventional aging measurements do not reveal how their nanostructure evolves toward functional failure. Here we resolve this structural evolution using high-resolution kinetic Monte Carlo (kMC) simulations. The simulations are calibrated to reproduce the experimental ion exchange capacity (IEC) and water uptake (WU) over a month degradation of a PPO-TEA membrane. The ionomer-peak position remains essentially unchanged even after 70% cation loss, while the water channels narrow from approximately 0.8 to 0.6 nm and progressively fragment. The hydrated network loses percolation at a critical hydrophilic volume fraction 𝜙!≈ 0.26, close to the threshold (𝜙!≈ 0.25) inferred from experimental conductivity using a percolation power law. Two complementary descriptions, a percolation law and a connected-carrier model, reproduce the normalized conductivity decay without using conductivity to calibrate the degradation kinetics. These results link conductivity failure to the loss of connected transport pathways within a membrane that retains its characteristic phase-separation length scale. The structural predictions are similar for two kinetic models with different dependencies on local hydration. Thus, a persistent ionomer-peak position can conceal substantial deterioration of the ion-transport network. Resolving channel connectivity along the aging trajectory provides a structural measure of membrane durability that complements conventional characterization of phase separation.

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Cite

BibTeXRIS
BibTeX
@misc{erimban2026resolving,
  title = {{Resolving Month-Long Nanostructural Evolution in Degrading Anion Exchange Membranes}},
  author = {Shakkira Erimban and Esteban D. Gadea and Ignacio J. Bombau and John J. Karnes and Johanna J. Schwartz and Valeria Molinero},
  howpublished = {ChemRxiv},
  year = {2026},
  month = oct,
  doi = {10.26434/chemrxiv.15010223/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010223/v1},
  note = {CC BY},
}
RIS
TY  - UNPB
TI  - Resolving Month-Long Nanostructural Evolution in Degrading Anion Exchange Membranes
AU  - Shakkira Erimban
AU  - Esteban D. Gadea
AU  - Ignacio J. Bombau
AU  - John J. Karnes
AU  - Johanna J. Schwartz
AU  - Valeria Molinero
PY  - 2026
DA  - 2026/10/11
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15010223/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010223/v1
AB  - Chemical degradation reshapes the hydrated ion-transport channels of anion exchange membranes (AEMs), but conventional aging measurements do not reveal how their nanostructure evolves toward functional failure. Here we resolve this structural evolution using high-resolution kinetic Monte Carlo (kMC) simulations. The simulations are calibrated to reproduce the experimental ion exchange capacity (IEC) and water uptake (WU) over a month degradation of a PPO-TEA membrane. The ionomer-peak position remains essentially unchanged even after 70% cation loss, while the water channels narrow from approximately 0.8 to 0.6 nm and progressively fragment. The hydrated network loses percolation at a critical hydrophilic volume fraction 𝜙!≈ 0.26, close to the threshold (𝜙!≈ 0.25) inferred from experimental conductivity using a percolation power law. Two complementary descriptions, a percolation law and a connected-carrier model, reproduce the normalized conductivity decay without using conductivity to calibrate the degradation kinetics. These results link conductivity failure to the loss of connected transport pathways within a membrane that retains its characteristic phase-separation length scale. The structural predictions are similar for two kinetic models with different dependencies on local hydration. Thus, a persistent ionomer-peak position can conceal substantial deterioration of the ion-transport network. Resolving channel connectivity along the aging trajectory provides a structural measure of membrane durability that complements conventional characterization of phase separation.
ER  -