Stability of Poly(2,6-dimethyl 1,4-phenylene)Oxide-Based Anion Exchange Membrane Separator and Solubilized Electrode Binder in Solid-State Alkaline Water Electrolyzers

In this work, we investigate the performance and degradation of polyphenylene oxide (PPO) based AEMs in a solid-alkaline water electrolyzer at 50°C using electrochemical testing and 1-D and 2-D NMR spectroscopy. The PPO AEMs were derivatized with trimethylamine (TMA) and quinuclidine (ABCO) to yield AEMs with TMA+ and ABCO+ cations. The AEMs underwent chemical degradation during electrolysis. The cell voltage at 0.2 A/cm2 for BrPPO-ABCO+ and BrPPO-TMA+ increased by 0.4 V and 0.2 V respectively after 5 hours of operation at 0.1 A/cm2. Postmortem analysis of the membrane and AEM binder recovered from the electrodes using 1D and 2D NMR spectroscopy revealed degradation via the backbone hydrolysis mechanism. The degradation occurred preferentially in the vicinity of the oxygen evolution electrode. Backbone hydrolysis resulted in loss of AEM mechanical integrity as well as solubilization and loss of binder in the electrodes. Impedance spectroscopy revealed an increase both in the high frequency resistance (from 0.41 to 0.53 Ohm-cm−2 for BrPPO-TMA+ and from 0.83 to 1.86 Ohm-cm−2 for BrPPO-ABCO+) and in the charge transfer resistance (from 0.26 to 1.47 Ohm-cm−2 for BrPPO-TMA+ and from 0.28 to 6.77 Ohm-cm−2 for BrPPO-ABCO+) over this timeframe, corroborating degradation of the membrane separator and the electrode binder.