posted on 2024-01-26, 06:03authored byJingbo Wang, Jeonghoon Lim, Monong Wang, Baoxia Mi, Daniel J. Miller, Bryan D. McCloskey
Ion-selective membranes are necessary components of many
electrochemical
systems including fuel cells, electrolyzers, redox flow batteries,
and electrodialyzers. Perfluorinated sulfonated membranes (PFSMs)
dominate these applications due to their excellent combination of
fast ion transport, stability, and processability. However, perfluorinated
cation exchange membranes (CEMs) are expensive, and their production
process involves chemistry that generates toxic perfluorinated chemicals.
The development of affordable, nonfluorinated membranes with a competitive
combination of high ion selectivity, transport, and stability could
help enable the widespread use of the technologies listed above while
hastening the development of emerging electrochemical systems, including
aqueous alkaline CO2 sorbent regeneration. To this end,
we pursue the use of thin-film composite polyamide (PA-TFCs) membranesthose
that typically find application in reverse osmosis and nanofiltration
desalinationas cation-selective exchange membranes. Given
their negative surface charge under neutral-to-alkaline conditions,
PA-TFCs can serve as effective CEMs in these pH regimes. We prepared
a series of PA-TFCs from traditional monomers (trimesoyl chloride
and piperazine) and compared their thicknesses, charge densities,
water transport properties, ion transport properties, and long-term
stability in a high pH environment to traditional CEMs (Nafion and
FKE) and commercial nanofiltration and reverse osmosis membranes.
We find that some of the best-performing PA-TFC membranes have similar
resistances and Na+ transference numbers compared to Nafion
117 in Na2SO4 and NaHCO3-containing
solutions. This proof-of-principle study suggests that further optimization
of PA-TFCs could enable cost-effective ion exchange membrane alternatives
to PFSMs.