Insight into alkaline stability of N-heteroatom on N-dimethylpiperidinium based anion exchange membranes (AEMs) for alkaline water electrolysis

Abstract

Alkaline stability is the main obstacle for anion exchange membranes (AEMs) for alkaline electrolysers. In order to research the effect of N-heteroatom polymers on the alkaline stability of N-dimethylpiperidinium (DMP) based AEMs, in this work, nine kinds of blend membranes were prepared by blending poly (oxindole biphenylene) (POBP), poly (N-methylisatin biphenylene) (mPOBP) and poly (biphenyl 4-imidazolecarboxaldehyde) (PB4Im) with poly (aryl piperidine) polymers (PTP-85) at the ratio of 1:19, 1:9, and 1:4, respectively. Moreover, in the preliminary investigation of alkaline stability, we broke the limitation of the immiscibility of the blend membranes and performed a comparative investigation by the 1H NMR. Surprisingly, the obtained blend membranes showed a much higher degree of degradation than PTP-85 in terms of ex-situ alkaline stability. The alkali absorption of different N-heteroatom polymers in different concentrations of NaOH at 55 °C and 80 °C showed that the alkaline stability of blend membranes was lower with the increase of alkali absorption. The in-situ stability test also demonstrated that the performance of blend AEMs decreased significantly after in-situ durability test under the galvanostatic mode. These results showed that blending with N-heteroatom polymers could negatively affect the alkaline stability of DMP-based AEMs, providing insight into the relationship between N-heteroatom and stability of DMP-based AEMs.