US-12626944-B2 - Antioxidant substituted sulfonated ion exchange membranes

Abstract

The disclosed technology relates to antioxidant substituted sulfonic acid polymers and ion exchange membranes prepared therefrom. The bonding of the polymer with an antioxidant can minimize the antioxidant from interfering with ion conductivity and prevent the antioxidant from leaching onto other layers or onto catalysts.

Inventors

• Thomas S. Corrigan
• Christopher M. Rasik
• William Storms-Miller
• Bryan Tucker

Assignees

• THE LUBRIZOL CORPORATION

Dates

Publication Date

20260512

Application Date

20211201

Claims (14)

1. 1 . A fuel cell comprising: (a) bipolar plates, (b) an anode, (c) a cathode, (d) diffusion media, and (e) an ion exchange membrane comprising a polymer composition comprising sulfonic acid moieties, wherein the polymer comprises 0.2 to 25 mol % relative to the sulfonic acid moieties of an antioxidant covalently bonded directly, or through a linking group, to the sulfonic acid moieties of the polymer.
2. 2 . The fuel cell of claim 1 , wherein the polymer composition comprises a perfluorosulfonic acid polymer.
3. 3 . The fuel cell of claim 1 , wherein the polymer composition comprises a sulfonated poly (benzimidazole) polymer.
4. 4 . The fuel cell of claim 1 , wherein the polymer composition comprises a sulfonated poly (ether ether ketone) polymer.
5. 5 . The fuel cell of claim 1 , wherein the polymer composition comprises a poly (styrene sulfonate) polymer.
6. 6 . The fuel cell of claim 1 , wherein the polymer composition comprises a sulfonated polyvinyl chloride.
7. 7 . The fuel cell of claim 1 , wherein the polymer composition comprises a 2-acrylamido-2-methylpropane sulfonic acid (AMPS) polymer.
8. 8 . The fuel cell of claim 1 , wherein the linking group comprises, an amine or an aryl ether.
9. 9 . The fuel cell of claim 8 , wherein the amine comprises ammonia.
10. 10 . The fuel cell of claim 8 , wherein the aryl ether comprises phenyl ether.
11. 11 . The fuel cell of claim 1 , wherein the linking group comprises an electrophile.
12. 12 . The fuel cell of claim 11 , wherein the electrophile comprises a carboxyl containing olefin.
13. 13 . The fuel cell of claim 11 , wherein the electrophile comprises a dicarboxylic acid.
14. 14 . The fuel cell of claim 11 , wherein the electrophile comprises maleic acid.

Description

CROSS REFERENCE TO RELATED APPLICATION This application claims priority from PCT Application Serial No. US21/061373 filed on 1 Dec. 2021, which claims the benefit of U.S. Provisional Application No. 63/119,814 filed on 1 Dec. 2020, the entirety of which is hereby incorporated by reference. BACKGROUND OF THE INVENTION The disclosed technology relates to antioxidant substituted sulfonic acid polymers and ion exchange membranes prepared therefrom. Proton exchange membrane fuel cells (PEMFCs) are a promising technology to enable the diversification of drivetrains for heavy duty vehicle applications and provide clean fuel alternatives to traditional combustion engines. Lifetime requirements and high demand placed on heavy duty PEMFCs leads to premature failure of the polymer electrolyte membrane (PEM), a critical PEMFC component. Over time, free radical species produced during normal operation of PEMFCs chemically react with the PEM, compromising system performance by decreasing mechanical integrity and proton conductivity. Current strategies to address this issue utilize some combination of the use of end group fluorination of perfluorosulfonic acid (PFSA) polymers and suspended metallic antioxidants (Ce or Mn). Unfortunately, unbound metallic antioxidants cause an undesirable decrease in proton conductivity as well as leaching into other layers of the membrane electrode assembly (MEA), exposing the membrane to radical degradation and poisoning of catalysts. These same issues can occur in anion exchange membranes. There is a need for a polymer electrolyte membrane that can withstand attack by free radical species without the drawbacks associated with free radical scavengers, such as simple ionically associated metallic antioxidants that may be transported through the membrane. SUMMARY OF THE INVENTION The disclosed technology solves the problem of polymer electrolyte membrane (PEM) degradation from free radical species by covalently bonding an antioxidant to the PEM, either directly, or through a linking group. The bonding of the PEM with antioxidant can also minimize the antioxidant from interfering with ion conductivity and prevent the antioxidant from leaching into other layers or onto catalysts. The disclosed technology therefore provides a polymer composition having sulfonic acid moieties, wherein the polymer comprises 0.2 to 25 mol % relative to the sulfonic acid moieties of an antioxidant covalently bonded directly, or through a linking group, to the polymer. Also provided is an ion exchange membrane prepared from the polymer composition, as well as a membrane electrode assembly, and fuel cell containing the ion exchange membrane. DETAILED DESCRIPTION OF THE INVENTION Various preferred features and embodiments will be described below by way of non-limiting illustration. The technology provides an antioxidant substituted sulfonic acid polymer composition having a certain amount of antioxidant covalently bonded to the polymer directly, or through a linking group, relative to the sulfonic acid moieties of the polymer. Methods of determining the content of sulfonic acid moieties in a sulfonic acid polymer are well-known in the art and include, for example, through monomer composition and measurement of ion exchange capacity (IEC). Sulfonic acid polymers are widely discussed in the literature and are not particularly limited here. Examples of sulfonic acid polymers include any sulfonate ion exchange polymer, which is to say, polymers containing sulfonic acid moieties. Sulfonic acid polymers can include, but are not limited to, perfluorosulfonic acid polymers, sulfonated poly(benzimidazole) polymer, sulfonated poly(ether ether ketone) polymer, sulfonated polyvinyl chloride, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and poly(styrene sulfonate) (block co) polymer, as examples, but the sulfonic acid could be any other sulfonic acid polymer now known or developed in the future. The antioxidants that may be covalently bonded directly, or through a linking group, to the sulfonic acid moieties of the sulfonic acid polymers can be any of the known antioxidants. An antioxidant is a compound which is able to inhibit an oxidative attack of an aggressive chemical species to, for example, the ion exchange material. Under the operation conditions of a fuel cell, peroxides and other free radicals may be such aggressive chemical species. Consequently, radical scavengers or hydrogen peroxide decomposition catalysts are examples of suitable antioxidants. Examples of radical scavenger antioxidants can include, but are not limited to, hindered amines; hydroxylamines; arylamines; poly(arylamines); phenols; polyphenols; butylated hydroxytoluene; phosphites; benzofuranones; salicylic acid; azulenyl nitrones and derivatives thereof; tocopherols; 5,5-dimethyl-1-pyrroline-N-oxide; cyclic and acyclic nitrones; gold-chitosan nanocomposites; ascorbic acid; heteropoly acids, and molybdenum based, such as molybdenum dithicarbamates