Cross-linked Fluorinated Polymer Membranes for Fuel Cells
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Solution Overview
Problem
Fluorinated polymers with sulfonic acid functional groups used in electrolyte membranes for electrochemical devices face a trade-off between high proton transport capability and mechanical resistance, often resulting in reduced durability due to the need for cross-linking processes that compromise water absorption and ion conductivity.
Innovation Solution
A process involving a fluorinated polymer with a low concentration of sulfonyl fluoride groups, reacted with a cross-linking agent to form covalent bonds, enhancing mechanical resistance while maintaining ion conductivity and hydrophilicity, involving a liquid composition with water and a cross-linking agent that promotes the formation of covalent bonds between sulfonic acid groups and the cross-linking agent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polymers having a high number of sulfonic acid groups are used to provide high proton transport capability, then ion conductivity is improved, but mechanical and physical resistance is reduced
Solution Approach 1:
The patent creates a composite structure by cross-linking multiple polymer chains through covalent bonds formed between sulfonic acid groups and cross-linking agents. This composite network structure combines the ion conductivity benefits of high sulfonic acid group content with the mechanical strength provided by the cross-linked network, resolving the contradiction between these two properties.
Solution Approach 2:
The cross-linking creates localized regions of high mechanical strength at the cross-link points while maintaining the overall polymer structure's ion conductivity pathways. The sulfonic acid groups remain accessible for ion transport while being tethered within a mechanically robust cross-linked framework, allowing different regions to fulfill different functional requirements.
2Strength
If cross-linking is used to improve the physical resistance of membranes, then mechanical strength is improved, but water absorption ability is limited
Solution Approach 1:
The patent optimizes the cross-linking density and the selection of cross-linking agents to achieve a balance where sufficient cross-links provide mechanical strength while leaving adequate spacing and hydrophilic character for water absorption. By controlling parameters such as cross-linking agent concentration and reaction conditions, the patent maintains water absorption ability despite cross-linking.
Solution Approach 2:
The cross-linking agents act as intermediaries that connect polymer chains while preserving the hydrophilic nature of the sulfonic acid groups. These cross-links provide mechanical strength without blocking the water absorption pathways, serving as bridges that maintain both structural integrity and hydrophilicity.
3Strength
If cross-linking involving sulfonyl fluoride functional groups is used, then mechanical resistance is improved, but ion conducting capability is compromised
Solution Approach 1:
The patent performs preliminary conversion of sulfonyl fluoride groups to sulfonic acid groups before cross-linking. This preliminary action ensures that the ion-conducting functional groups are already in their active form, and subsequent cross-linking does not involve the sulfonyl fluoride groups, thereby preventing compromise of ion conducting capability while still achieving mechanical reinforcement.
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 process results in cross-linked fluorinated polymers with improved mechanical and physical resistance without compromising ion conductivity, leading to more stable and durable membranes suitable for fuel cell applications.
Implementation Method 1
reacting said fluorinated polymer (P) with at least one cross-linking agent (XL) of formula R(X) n wherein R is selected from a bond, O, S, N or R is an aromatic or aliphatic group, linear, cyclic, branched, optionally substituted and/or fluorinated, optionally comprising heteroatoms (O, S, N); n is an integer ≥ 2; and wherein X is a functional group selected from the group consisting of -NH 2 , -NHR a (R a = C 1 -C 20 alkyl, -Si(R b ) 3 , R b = C 1 -C 5 alkyl), -OH, -SO 2 W (W= OH, F, Cl, Br, I), said reaction being carried out under conditions that promote the formation of covalent bonds between the at least one functional group -SO 3 M of fluorinated polymer (P) and at least one functional group X in cross-linking agent (XL)
Data Source
AI summary
A process for the preparation of cross-linked fluorinated polymers comprising sulfonic acid functional groups comprising the steps of: a) providing at least one fluorinated polymer (P) comprising at least one -SO3M functional group and less than 2% of -SO2F functional groups with respect to the total amount of -SO3M and -SO2F functional groups, wherein each M is selected from H and alkaline metals; and b) reacting said fluorinated polymer with at least one cross-linking agent of formula R(X)n under conditions that promote the formation of covalent bonds between the at least one functional group -SO3M of fluorinated polymer (P) and at least one functional group X of the cross-linking agent.