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.

A novel anion exchange membrane based on silicone/polyphenylene oxide with excellent ionic conductivity for AEMFC

“…At the same time, the increase of inorganic fillers formed a cross‐linked structure that acted synergistically with the PPO main chain structure. As shown in Figure 6, QPPO‐Si‐5 membrane have a distinct hydrophilic/hydrophobic microphase separation structure, 39 and the QPPO‐Si‐5 membrane had the highest OH − ion conductivity, 78.7 mS/cm at 80°C, which was higher than the QPPO membrane (63.8 mS/cm at 80°C). Lee et al 40 designed a block‐type PPO‐based anion exchange membrane with ionic conductivity up to 32.8 mS/cm.…”

Anion exchange membranes based on poly (styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) grafted poly (2,6‐dimethyl‐1,4‐phenylene oxide)

“…The self‐assembly of SEBS, resulted from the alternating structure of flexible and rigid blocks, leads to the formation of unique microphase‐separated structures in SEBS‐based alkaline AEMs. In the atomic force microscope (AFM) graphs, the bright regions represented the aggregated phase of hydrophilic ion clusters of QA groups, and the dark regions were caused by the hydrophobic phase which was resulted from the polymer backbone 34 …”

“…In the atomic force microscope (AFM) graphs, the bright regions represented the aggregated phase of hydrophilic ion clusters of QA groups, and the dark regions were caused by the hydrophobic phase which was resulted from the polymer backbone. 34 For the AEMs based on SEBS, the functionalized polystyrene and polyethylene segments constitute the hydrophilic and hydrophobic phases of the membrane, respectively. 35 SEBS-CH 2 -QA-0.7 membrane (Figure 8b) had more CDPC side chains, so there were more hydrophilic QA groups, which replace the original hydrophobic structure (benzene ring).…”

Tripartite Cationic Interpenetrating Polymer Network Anion Exchange Membranes for Fuel Cells

“…Nonetheless, a high IEC value means that the membrane will absorb a large amount of water and swell rapidly with the sacrifice of mechanical, dimensional, as well as chemical stability of the membrane. − Normally, the strategy of constructing semi- or fully interpenetrating polymer networks inside the membrane by crosslinking can effectively enhance molecular interactions, which is effective in reducing water molecules from entering the membrane at high IEC values. − Besides the contradiction between high IEC value and high ionic conductivity, another major problem faced by AEMs is insufficient alkali stability. Typical AEMs composed of polysulfone (PSU), poly­(phenylene oxide) (PPO), and polyether ketone (PEK) always suffer from the notorious chain degradation under extreme pH conditions, − in which high concentration of OH – tends to destroy the aryl ether (C–O) bonds within those polymers, damaging the long-term stability of AEMs. − Other polymers without introducing C–O bonds, such as polystyrene (PS), poly­(ethylene- co -octene)- b -polystyrene (SEBS), etc., have been employed as the framework of AEMs to increase their stability at high temperatures and high pH values. , As an example, Sung et al prepared a series of AEMs with SEBS as backbone, among which the AEM with a preferred crosslinking degree exhibited excellent alkaline stability after storage in 1 M KOH solution at a constant temperature of 80 °C for 500 h …”