Phosphonic Acid Polymer Blends for High-Temperature Fuel Cell Membranes
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Solution Overview
Problem
Commercially available ionomer membranes based on perfluorinated sulfonic acids are not suitable for temperatures above 100°C due to drying and decreased proton conductivity, limiting their use in fuel cells where higher temperatures enhance CO tolerance and electrode kinetics, and existing phosphonated ionomers face issues with low phosphonation degrees, poor solubility, and polymer degradation.
Innovation Solution
Development of polymer mixtures containing 1-hydroxymethylene-1,1-bisphosphonic acid groups with high acid strength and content, incorporated into blends with cation exchange or basic functional groups, and crosslinked to prevent condensation and bleeding, enabling high proton conductivity at elevated temperatures and reduced humidification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phosphonic acid is incorporated into basic polybenzimidazole membranes, then proton conductivity is improved at elevated temperatures, but phosphoric acid bleeds out at temperatures above 100°C
Solution Approach 1:
The patent extracts the problematic basic polybenzimidazole matrix and replaces it with a sulfonated ionomer matrix that is chemically compatible with phosphonic acid groups. This eliminates the bleeding issue while preserving the proton conductivity benefit, as the sulfonated ionomer provides a stable environment for the phosphonic acid groups without causing them to leach out.
Solution Approach 2:
The patent uses a stable, non-degradable sulfonated ionomer matrix that permanently anchors the phosphonic acid groups, replacing the unstable basic polybenzimidazole system. This creates a durable membrane that maintains its properties over time and through repeated thermal cycles, eliminating the bleeding problem inherent in the polybenzimidazole system.
2Reliability
If phosphonic acid esters are hydrolyzed to free phosphonic acid, then acid strength is improved, but polymer degradation occurs
Solution Approach 1:
The patent performs the hydrolysis of phosphonic acid esters to free phosphonic acid during the membrane fabrication process itself, rather than as a post-treatment step. This preliminary action allows the membrane to be formed in its final, highly conductive state, avoiding subsequent handling that could cause degradation. The membrane is cast and processed immediately after hydrolysis, minimizing exposure time to potential degradation conditions.
Solution Approach 2:
The patent carefully controls the hydrolysis conditions by adjusting parameters such as water content, temperature, and processing time during membrane fabrication. This optimized hydrolysis achieves complete conversion to free phosphonic acid for maximum acid strength while limiting exposure conditions that would cause polymer degradation, thereby achieving both high conductivity and polymer 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
The resulting polymer blends achieve high proton conductivity and mechanical stability, preventing phosphonic acid bleeding and maintaining performance in fuel cells at temperatures up to 1800°C with reduced humidification, suitable for various membrane applications including fuel cells and gas separation.
Implementation Method 1
phosphoric acid can act as both a proton donor and a proton acceptor
Implementation Method 2
Cation exchange groups or their nonionic precursors of the type SO2X3
Implementation Method 3
Production of optionally physically, ionically or covalently crosslinked blends and blend membranes of low molecular weight hydroxymethylene oligophosphonic acids
Implementation Method 4
Suppression of the condensation of the phosphonic acid group
Data Source
AI summary
The invention relates to blends and blend membranes from low-molecular hydroxymethylene-oligo-phosphonic acids R-C(PO3H2)x(OH)y and polymers, the group R representing any organic group and the polymers containing the following functional groups: cation exchanger groups or their nonionic precursors of the type SO2X, X = HaI, OH, OMe, NR1R2, OR1 with Me = any metal cation or ammonium cation, R1, R2 = H or any aryl- or alkyl group, POX2, COX and/or basic groups such as primary, secondary or tertiary amino groups, imidazole groups, pyridine groups, pyrazole groups etc. and/or OH groups. Low molecular hydroxymethylene-oligo-phosphonic acids R-C(PO3H2)x(OH)y are preferred in which x = 2 and y = 1. The invention also relates to low-molecular hydroxymethylene-oligo-phosphonic acids R-C(PO3H2)2(OH)1 and polymers, wherein the group R of the hydroxymethylene-oligophosphonic acid contains an aliphatic or aromatic basic group which ionically interacts with the acidic groups of the polymer or of the polymer mixture. The invention further relates to blends and blend membranes from low-molecular hydroxymethylene-oligo-phosphonic acids R-C(PO3H2)2(OH)1 and polymers, wherein the OH groups of the low-molecular hydroxymethylene-1,1-bisphosphonic acid are covalently cross-linked with each other or optionally with OH groups of the polymer. The invention also relates to polymers that are modified with the 1-hydroxymethylene-1,1-bisphosphonic acid group. The polymers are produced by reacting polymers which contain carboxylic acid groups or carboxylic halide groups -COHal (Hal=F, Cl, Br, I) with phosphite compounds or by reacting polymeric aldehydes or polymeric keto compounds with phosphite esters while carrying out an amine catalysis, an oxidation of the intermediary hydroxyphosphonic acid with MnO2 or any other oxidant. The invention finally relates to methods for producing the aforementioned materials and to the use of membranes of the aforementioned materials in membrane processes and especially in fuel cells, even at temperatures of >100°C.