Quaternized Branched Polyethyleneimine Modified Nitrogen‐Doped Graphene Quantum Dots/Quaternized Polysulfone Composite Anion Exchange Membranes with Improved Performance

Abstract Anion exchange membrane (AEM) is essential for the development of alkaline anion exchange membrane fuel cells, and its performance largely depends on its internal microstructure. Herein, to improve the performance of AEM, quaternized branched polyethyleneimine modified nitrogen‐doped graphene quantum dots (QBPEI@N‐GQDs) are introduced to quaternized polysulfone (QPSU) polymer matrix to prepare a series of QPSU/QBPEI@N‐GQDs (QQ‐n‐N‐GQDs) composite AEMs. Due to the uniform distribution of hydrophilic QBPEI@N‐GQDs, an obvious hydrophilic/hydrophobic microphase separation structure is formed inside the QQ‐n‐N‐GQDs composite AEMs. Compared with the pristine QPSU AEM, the QQ‐0.7%‐N‐GQDs AEM shows slightly higher water uptake (WU) and swelling ratio (SR), as well as much higher ionic conductivity (76.18 mS cm −1 at 80 °C for QQ‐0.7%‐N‐GQDs AEM versus 46.14 mS cm −1 at 80 °C for pristine QPSU AEM) and better maximum power density of single fuel cell (85.2 mW cm −2 for QQ‐0.7%‐N‐GQDs AEM versus 46.3 mW cm −2 for QPSU AEM). Moreover, the chemical stability of QQ‐n‐N‐GQDs composite AEMs has not been significantly adversely affected by the introduction of QBPEI@N‐GQDs.