Relative Insignificance of Polyamide Layer Selectivity for Seawater Electrolysis Applications

Low-cost polyamide thin-film composite (TFC) membranes are being explored as alternatives to cation exchange membranes for seawater electrolysis. An optimal membrane should have a low electrical resistance to minimize applied potentials needed for water electrolysis and be able to block chloride ions present in a seawater catholyte from reaching the anode. The largest energy loss associated with a TFC membrane was the Nernstian overpotential of 0.74 V (equivalent to 37 Ω cm² at 20 mA cm^-2), derived from the pH difference between the anolyte and catholyte and not the membrane ohmic overpotential. Based on analysis using electrochemical impedance spectroscopy, the pristine TFC membrane contributed only 5.00 Ω cm² to the ohmic resistance. Removing the polyester support layer reduced the resistance by 79% to only 1.04 Ω cm², without altering the salt ion transport between the electrolytes. Enlarging the pore size (∼5 times) in the polyamide active layer minimally impacted counterion transport across the membrane during electrolysis, but it increased the total concentration of chloride transported by 60%. Overall, this study suggests that TFC membranes with thinner but mechanically strong supporting layers and size-selective active layers should reduce energy consumption and the potential for chlorine generation for seawater electrolyzers.

Citation

Zhou, X., Shi, L., Taylor, R. F., Xie, C., Bian, B., Picioreanu, C., & Logan, B. E. (2023). Relative Insignificance of Polyamide Layer Selectivity for Seawater Electrolysis Applications. Environmental Science & Technology. https://doi.org/10.1021/acs.est.3c04768

Acknowledgements

This research was funded by National Science Foundation grant CBET-2027552 and Penn State University through the Stan and Flora Kappe endowment