Curable Ionic Copolymer Membranes With Strength and Hydrolytic Stability
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Solution Overview
Problem
Existing anion exchange membranes suffer from inadequate mechanical strength and hydrolytic stability, making them unsuitable for applications in electrochemical devices such as fuel cells and electrolyzers.
Innovation Solution
Development of ionic copolymers with specific monomer units, including styrene and vinylbenzyl halide, combined with nitrogen-containing bases to form cationic copolymers that are curable and provide improved strength and hydrolytic stability, forming membrane compositions suitable for electrochemical devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional copolymers with cationic nitrogen-containing groups are used to prepare anion exchange membranes, then the membranes can be formed, but they exhibit inadequate mechanical strength and are brittle with low tensile strength
Solution Approach 1:
The patent employs composite materials by combining poly styrene-co-vinylbenzyl chloride copolymer with poly vinylidene fluoride-hexafluoropropylene copolymer in a layered structure. The cation-exchange membrane layer contains the ionic functional groups while the adjacent poly vinylidene fluoride layer provides mechanical strength and structural stability, creating a composite that overcomes the brittleness and low tensile strength of traditional single-layer cationic membranes.
2Reliability
If traditional anion exchange membranes are used, then they can facilitate ion transport, but they are prone to hydrolytic degradation
Solution Approach 1:
The patent introduces an intermediary layer of poly vinylidene fluoride-hexafluoropropylene copolymer between the cation-exchange membrane and the aqueous environment. This intermediary layer acts as a protective barrier that shields the hydrolytically sensitive cationic groups from water, preventing hydrolytic degradation while still allowing the membrane to perform its ion transport function. This mediator approach extends the membrane lifespan without compromising reliability.
3Strength
If crosslinking is performed to improve mechanical strength, then tensile strength increases, but the membrane may become overly rigid and lose flexibility
Solution Approach 1:
The patent applies crosslinking locally and selectively within the poly vinylidene fluoride-hexafluoropropylene copolymer layer rather than throughout the entire membrane structure. This localized crosslinking provides the necessary mechanical strength and dimensional stability in the structural layer while leaving the cation-exchange membrane layer relatively uncrosslinked, maintaining its flexibility and ion transport capabilities. The differential treatment of different layers resolves the contradiction between strength and flexibility.
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 resulting membranes exhibit enhanced mechanical strength and hydrolytic stability, enabling their use in electrochemical devices like fuel cells and electrolyzers without brittleness or degradation issues.
Implementation Method 1
Copolymers according to the present disclosure can be combined with a free-radical initiator to provide a curable membrane precursor composition. The curable membrane precursor compositions can be cured to form membrane compositions.
Data Source
AI summary
A cationic copolymer comprises the divalent monomer units: wherein: each Ar1 independently represents phenylene; each L independently represents a direct bond or wherein each R1 independently represents an alkyl group having 1 to 4 carbon atoms, and each R2 independently represents an alkylene group having from 1 to 6 carbon atoms, and each Z− represents a non-interfering anion; each Ar2 independently represents an optionally substituted divalent aryl ring, with the proviso that if L represents a direct bond, then Ar2 represents an optionally substituted cationic divalent aryl ring accompanied by Z−; each R3 independently represents H or an alkyl group having 1 to 6 carbon atoms; and each D independently represents a direct bond or Ar2, wherein adjacent D and L are not both direct bonds, and wherein if L is a direct bond, then D is Ar2. The cationic copolymer can be free-radially cured and used in a membrane.