Anion exchange membranes (AEMs) with robust alkaline stability and high ionic conductivity are imminently required for the promising electrochemical energy conversion devices – fuel cells.
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.
In recent years, the microphase separation structure of ion-exchange membranes constructed by intermolecular interaction forces, such as hydrogen bond, cation−dipole interaction, and π−π interaction, has received extensive attention. Porphyrins can provide an active self-aggregation driving force through π−π interaction. Herein, a series of TMAP-Zn-PMHQ-X anion-exchange membranes (AEMs) were rationally designed in which the porphyrin was introduced to construct highly efficient ion channels. The as-prepared membranes are composed of functionalized fluorophobic polymers as the main chain and quaternized zinc porphyrin as the hydrophilic side chain. TMAP-Zn-PMHQ-13.5% with an ion-exchange capacity (IEC) of 0.35 meq•g −1 has an OH − conductivity of 152.5 mS•cm −1 and a swelling ratio of 53.3% at 80 °C. Meanwhile, the OH − conductivity of the membrane remains 95.76% after being tested in a 2 M NaOH solution at 80 °C for 500 h. A single cell based on the TMAP-Zn-PMHQ-13.5% AEM can achieve a power density of 631.6 mW•cm −2 at a current density of 998.9 mA•cm −2 at 80 °C. This kind of porphyrin selfassembled strategy provides an effective way to fabricate AEMs with good OH − conductivity and a relatively low IEC.
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