Terminally-Crosslinked AEM Membranes for Alkaline Stability

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Solution Overview

Problem

Anion exchange membranes (AEMs) face challenges in maintaining stability and conductivity under high alkaline conditions, particularly at elevated temperatures, due to the trade-off between chemical stability and ionic conductivity resulting from crosslinking processes.

Innovation Solution

A terminally-crosslinked methyl morpholinium-functionalized poly(arylene ether sulfone) (xMM-PES) membrane is developed, where crosslinking occurs only at the ends of the polymer chains using an azide compound, maintaining structural integrity and enhancing conductivity through a three-dimensional structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If crosslinking is performed to enhance alkaline stability of AEM polymer backbones, then chemical stability is improved, but ionic conductivity is reduced due to formation of rigid 3D-network and low water uptake

Engineering Contradiction:

Improvealkaline stabilityVSAvoidconductivity loss

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The crosslinking is segmented to occur only at the terminal ends of polymer chains rather than throughout the entire polymer network. This terminal crosslinking approach creates isolated crosslinking points that provide stability without forming a continuous rigid 3D-network, thereby maintaining water uptake and ionic conductivity pathways within the polymer backbone structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The crosslinking density is made non-uniform by concentrating crosslinks specifically at the terminal regions of polymer chains while keeping the central polymer backbone regions uncrosslinked. This local differentiation allows the terminal regions to provide stability while the central regions maintain flexibility and conductivity, resolving the contradiction between stability enhancement and conductivity preservation.

Inventive Principle:

Principle #3Local quality

2Strength

If a rigid 3D-network is formed through crosslinking, then mechanical stability is improved, but water uptake is suppressed and ionic conduction is reduced

Engineering Contradiction:

Improvemechanical stabilityVSAvoidwater uptake

Core Design Contradiction:

StrengthVSQuantity of substance

Solution Approach 1:

The crosslinking network is segmented into isolated terminal crosslinking points rather than a continuous rigid 3D-network. This segmentation allows water to penetrate and be retained within the polymer matrix while still providing mechanical stability at the chain ends, thus maintaining both mechanical strength and adequate water uptake for ionic conduction.

Inventive Principle:

Principle #1Segmentation

3Reliability

If quaternary ammonium cations are introduced to improve alkaline stability, then chemical stability is enhanced, but conductivity may be affected due to steric hindrance from bulky structures

Engineering Contradiction:

Improvealkaline stabilityVSAvoidsteric hindrance to OH- approach

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

Instead of using traditional quaternary ammonium cations with bulky structures that create steric hindrance, the invention inverts the approach by using methyl morpholinium cations with smaller, more compact structures. This inversion reduces steric hindrance to hydroxide ion approach while maintaining alkaline stability, allowing both stability and conductivity to coexist.

Inventive Principle:

Principle #13The other way round (Inversion)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The xMM-PES membrane exhibits excellent thermal, mechanical, and chemical stability with high ionic conductivity, minimizing conductivity loss and water uptake, while maintaining high performance under high temperature and partially hydrated conditions.

Implementation Method 1

crosslinking only occurs at ends of the polymer chains (xMM-PES), thereby minimizing conductivity loss, significantly increasing mechanical and chemical stability

Methodology Applied

Scientific EffectThermal activation of azide crosslinking: Heat Treatment

Data Source

PatentUS10300477B2Terminally-crosslinked methyl morpholinium-functionalized block copolymers, and anion exchange membranes using the same

Publication Date: 2019.05.28 IND ACADEMIC COOPERATION FOUND UNIV OF INCHEON

AI summary

The present disclosure herein relates to a terminally-crosslinked methyl morpholinium-functionalized block copolymer, and an anion exchange membrane using the same, and more particularly, to a terminally-crosslinked block copolymer which has a novel structure, and in which, in a poly(arylene ether sulfone) multiblock copolymer (MM-PES) having methyl morpholinium as a conducting group, an azide compound may be used as a crosslinking agent so that crosslinking only occurs at ends of the polymer chains (xMM-PES), thereby minimizing conductivity loss, significantly increasing mechanical and chemical stability, attaining additional conductivity resulting from the three-dimensional structure of morpholinium, and reducing water uptake while enhancing water retention capacity, uses thereof as an alkaline fuel cell anion exchange membrane (AEM), and a method for conveniently preparing the same through simple heat-treatment.