Crosslinked Anion Exchange Blend Membranes for Stable Alkaline Conductivity
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Solution Overview
Problem
Anion exchange membranes (AEMs) face challenges with lower ionic conductivity and limited chemical stability, particularly in alkaline environments, due to their hydrocarbon backbone and sensitivity to OH- counterions, which affects their performance in electrochemical conversion processes.
Innovation Solution
The development of anion-exchange blend membranes composed of halomethylated polymers quaternized with sterically hindered tertiary nitrogen compounds, embedded in inert matrix polymers, and optionally covalently crosslinked with polyethylene glycol and sulfonated polymers to enhance ionic conductivity, chemical stability, and mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If AEMs use a hydrocarbon backbone to reduce cost, then manufacturing cost is reduced, but ionic conductivity decreases due to lower hydrophobicity and reduced separation between ionic groups and polymer backbone
Solution Approach 1:
The membrane is segmented into distinct hydrophobic backbone regions and hydrophilic ionic channels. The backbone provides structural support while the segregated ionic channels, enriched with water and mobile ions, provide high conductivity pathways, resolving the contradiction between hydrocarbon backbone usage and ionic conductivity requirements.
Solution Approach 2:
The membrane employs a composite structure combining a hydrocarbon-based polymer backbone with grafted or incorporated hydrophilic groups (such as sulfonate, carboxylate, or phosphate groups). This composite approach allows the hydrophobic backbone to provide mechanical strength and low cost, while the hydrophilic components create conductive pathways for ions.
2Adaptability or versatility
If AEMs exchange with OH- ions for use in alkaline processes, then application versatility is improved, but chemical stability decreases due to degradation of the anion exchange group and polymer main chain
Solution Approach 1:
The polymer backbone is designed with local chemical modifications to provide resistance against OH- attack. Specific structural features such as aromatic rings, heteroatoms, or crosslinked regions are strategically placed to protect vulnerable anion exchange groups from nucleophilic attack by hydroxide ions, maintaining chemical stability while enabling alkaline operation.
Solution Approach 2:
The membrane undergoes preliminary crosslinking or stabilization treatments during manufacturing to pre-establish a chemically resistant structure. This preliminary action creates a protective network that prevents degradation when the membrane is subsequently exposed to alkaline conditions, allowing versatile application in alkaline fuel cells and electrolyzers.
3Reliability
If the separation between polymer backbone and ion group phase is increased to improve ionic conductivity, then ionic conductivity is improved, but mechanical stability may be compromised
Solution Approach 1:
The membrane architecture transitions from a two-dimensional planar structure to a three-dimensional phase-separated morphology. Ionic channels are formed as continuous three-dimensional pathways through the membrane, allowing efficient ion transport while the backbone maintains structural integrity in a different spatial dimension, resolving the conflict between conductivity and mechanical stability.
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
These membranes exhibit significantly improved anion conductivity, chemical stability in alkaline solutions, and mechanical stability, with chloride conductivity increasing after treatment and maintaining stability over extended periods in strongly alkaline conditions.
Implementation Method 1
A hydrophilic linear polyethylene glycol bearing functional groups on both chain ends which can undergo nucleophilic substitutions with the basic functional groups of the matrix polymer (examples: epoxide groups, halomethyl groups) and thereby covalently anchored
Implementation Method 2
Conversion of the CH2Hal group (Hal=Cl, Br) to an anion exchange group is achieved by reaction with a tertiary amine such as trimethylamine
Data Source
AI summary
The invention relates to:—anion exchange blend membranes consisting the following blend components:—a halomethylated polymer (a polymer with —(CH2)x—CH2—Hal groups, Hal=F, Cl, Br, I; x=0-12), which is quaternised with a tertiary or a n-alkylated/n-arylated imidazole, an N-alkylated/N-arylated benzimidazole or an N-alkylated/N-arylated pyrazol to form an anion exchanger polymer. - an inert matrix polymer in which the anion exchange polymer is embedded and which is optionally covalently crosslinked with the halomethylated precursor of the anion exchanger polymer,—a polyethyleneglycol with epoxide or halomethyl terminal groups which are anchored by reacting with N—H-groups of the base matrix polymer using convalent cross-linking—optionally an acidic polymer which forms with the anion-exchanger polymer an ionic cross-linking (negative bound ions of the acidic polymer forming ionic cross-linking positions relative to the positive cations of the anion-exchanger polymer)—optionally a sulphonated polymer (polymer with sulphate groups —SO2Me, Me=any cation), which forms with the halomethyl groups of the halomethylated polymer convalent crosslinking bridges with sulfinate S-alkylation. The invention also relates to a method for producing said membranes, to the use of said membranes in electrochemical energy conversion processes (e.g. Redox-flow batteries and other flow batteries, PEM-electrolyses, membrane fuel cells), and in other membrane methods (e.g. electrodialysis, diffusion dialysis).