Tröger’s Base Microporous Anion Exchange Membranes with Hyperbranched Structure for Fuel Cells

Abstract

The application of anion exchange membranes (AEMs) in alkaline fuel cells is profoundly affected by its performance. In this work, Tröger’s base microporous AEMs with hyperbranched structure (QA-BTB-x%) are prepared by superacid catalysis. The introduction of the hyperbranched structure can enhance the free volume of the AEMs, which will improve the water uptake (WU) of the AEMs and thus promote the transport of OH–. By increasing the content of the branching agent from 0% to 8%, the WU of the AEMs gradually increased from 41.7% to 62.6% at 80 °C. The maximum OH– conductivity of the QA-BTB-5% AEMs can reach to 95.2 mS cm–1 in ultrapure water at 80 °C with a low swelling ratio (14.9% at 80 °C). Small angle X-ray scattering (SAXS), atomic force microscopy (AFM) and transmission electron microscopy (TEM) show that the QA-BTB-5% AEMs has a good microphase separation structure that is beneficial for OH– transport. After a long-term alkaline stability test, the QA-BTB-5% still has a high OH– conductivity. The maximum power density of the QA-BTB-5%-based single cell can reach to 548 mW cm–2 in H2/O2. All of the results demonstrate obvious performance enhancements of AEMs upon the introduction of hyperbranched structure into the polymer backbone.

Development of highly conductive anion exchange membranes based on crosslinked PIM-SEBS with high free volume

“…2a). 14,19,20,39,[41][42][43]45,46,[51][52][53][54][55] This conrms that the x-PIM-SEBS membranes developed in the present study exhibit higher WU for their SR values compared to the comparison group. This improvement is attributed to the chemical crosslinking of SEBS, displaying high WU due to its elastic structure, and PIM, a hydrophobic component with a rigid structure, inhibiting the excessive expansion of the membranes and, thereby, ensuring remarkable dimensional stability despite the high WU values.…”

“…2b). 19,20,[39][40][41][42][43]45,46,[56][57][58] The x-PIM-SEBS membranes exhibit l values of 16.44-22.20, higher than those of polyarylene-based membranes but lower compared to those of SEBS-based ones. This implies that it is possible to suitably adjust the amount of water contained in membranes by crosslinking PIM and SEBS, two polymer components with different properties.…”

“…14,[29][30][31][36][37][38] In addition, ongoing research efforts address the use of polymer backbones with high free volume, combined with a rigid structure, to induce microphase separation in AEMs. [39][40][41][42][43][44][45][46][47] Free volume refers to the empty spaces between the polymer backbones due to the polymer components. For example, when applied to AEMs, meta-terphenyl demonstrates enhanced microphase separation compared to para-terphenyl due to the free volume arising from its intrinsic structure; this leads to the formation of continuous ion channels and, thus, improves ionic conductivity.…”

“…12,48,49 In addition, improved phase separation and high ionic conductivity have been conrmed in AEMs based on binaphthyl, xanthene, and Tröger's base-type molecules having a twisted structure and hence a high free volume. 43,45,50 Another strategy for enhancing microphase separation based on free volume includes the use of polymers of intrinsic microporosity (PIMs), which exhibit microporosity due to their rigid-twisted backbone structure. 39,40,43,44 Here, the effective suppression of polymer chain packing results in a high free volume.…”

Tuning and Coupling Irreversible Electroosmotic Water Flow in Ionic Diodes: Methylation of an Intrinsically Microporous Polyamine (PIM-EA-TB)

“…Figure B shows the molecular structure of the methylated PIM-EA-TB. Methylation is readily achieved, for example, with iodomethane or other alkylation reagents. , Once methylated, the intrinsically microporous polymer becomes anion conducting. Figure C shows the experimental configuration for ionic diode measurements.…”