Keywords Highlights Abstract Graphical abstract 218 Research Paper Received 2019-10-09 Revised 2019-12-06 Accepted 2019-12-24 Available online 2019-12-24 Bipolar membrane Alkaline hydrolysis Membrane degradation Density functional theory Poly(biphenyl alkylene) Polysulfone • No increase in voltage for polyphenylene-based membranes under operating conditions. • Commercial bipolar membranes showed 3-4 mV/d increases in operating voltage. • DFT calculations and stability tests showed PBPA membrane was most stable. Journal of Membrane Science and Research 6 (2020) 218-225 Alkaline Stability of Novel Aminated Polyphenylene-Based Polymers in Bipolar Membranes Department of Chemical and Environmental Engineering, University of Arizona, 1133 E. James E. Rogers Way, Tucson, AZ 85721 USA Rodrigo J. Martínez, Yingying Chen, Don Gervasio, James C. Baygents, James Farrell * Article info © 2020 MPRL. All rights reserved. * Corresponding author: farrellj@email.arizona.edu (J. Farrell) DOI: 10.22079/JMSR.2019.115517.1298 1. Introduction Bipolar membranes (BPMs) are used to split water into H + and OH - ions in a variety of industrial applications, including: production of mineral acids from salt solutions, recovery of organic acids from fermentation broths, pH control in biochemical processes, recovery and purifcation of pharmaceuticals, deacidifcation of fruit juices, and energy storage and conversion [1,2,3]. Despite their commercial availability since 1977, the use of bipolar membranes has been limited due to the low stability of the strong-base anion exchange membranes under alkaline conditions. Bipolar membranes consist of a strong base anion exchange membrane laminated to a strong acid cation exchange membrane. The interface between the two membranes normally contains a weak base or weak acid catalyst to promote water splitting [4]. When placed in an electrodialysis cell, Journal of Membrane Science & Research journal homepage: www.msrjournal.com This research investigated stability of two novel aminated polyphenylene polymers as anion exchange layers in bipolar membranes. Bipolar membrane stability was tested under operating conditions of 50 mA/cm 2 , and under conditions of soaking in room temperature 1 M NaOH. The stability of the custom made bipolar membranes was compared with those for two commercial membranes. For the polyphenylene-based membranes, there was no measurable increase in operating voltage when run continuously at a current density of 50 mA/cm 2 . For the two commercial membranes, the operating voltages increased by 3.2 to 4.4 mV per day when operated continuously over an 85 day testing period. Commercial membrane degradation in 1 M NaOH was similar to that under real operating conditions, with average rates of voltage increase of 3.2 to 3.5 mV/d. The custom made membrane containing a quaternary ammonium-tethered poly(biphenylalkylene) (PBPA) anion exchange layer did not show any loss in performance in either stability test. Density functional theory (DFT) simulations were used to calculate activation barriers and reaction energies for nucleophilic attack on the polymer backbones and cation functional groups on each of the four anion exchange polymers. Cation loss from all four polymers was thermodynamically favorable, with activation barriers ranging from 64 to 138 kJ/mol. The two commercial polysulfone-based anion exchange membranes were susceptible to cleavage of the ether bonds. However, the polyphenylene-based anion exchange polymers were considerably more stable with respect to backbone cleavage. The DFT calculations showing that the PBPA polymer was the most stable confrmed the results of the stability tests. http://www.msrjournal.com/article_37575.html