Preparation and characterization of high conductivity comb polymer anion exchange membranes

Abstract A comb-shaped anion exchange membrane was successfully constructed by simultaneously introducing a hydrophobic aliphatic long-chain bromododecane (BA) and a hydrophilic short-chain bromoethanol (BE) as a quaternizing agent into the side chain of poly-4-vinyl-pyridine (P4VP). The aforementioned membrane chemical structure was investigated by FT-IR, and confirmed that the BA and BE were successfully grafted onto the P4VP backbone. A series of performance test results reveal that the water uptake (WU) and swelling ratio (SR) are effectively controlled with the BA content increased from 0% to 75.0%, which the value was corresponding to the water uptake decreases from 92.3% to 31.8%, and the swelling ratio decreases from 78.4% to 7.8%. Interestingly, the conductivity of synthesized membrane in this paper is much increased with substantially the same ion exchange capacity (IEC) (from 50.0 mS·cm−1 for BE100.0%-BA0%/P4VP to 75.0 mS·cm−1 for BE25.0%- BA75.0%/P4VP at 70 °C), which can be attributed to the microphase-separated structure. On the other hand, the membrane BE25.0%-BA75.0%/P4VP has the best overall performance, which with the conductivity of 75.0 mS·cm−1 at 70 °C, which the temperature closest to the alkaline fuel cell operating temperature. And it also had excellent tensile strength (16.0 MPa) and elongation at break (5.9%), indicating sufficient flexibility and processability, and it has excellent chemical stability immersed it into 3 mol·L−1 KOH for up to 240 h, which was the conductivity can still reach more than 70% of the initial value. And the aforementioned membrane also with the better thermal stability (the thermal decomposition temperatures above 200 °C). The single cell test result reveal that the membrane displayed good cell performance with a power density of 47.52 mW·cm−2 at 70 °C. In summary, the comprehensive performance of BE25.0%-BA75.0%/P4VP is expected to be applied to alkaline polymer fuel cells.