Phosphate anion-quaternary ammonium ion pair coordinated polymer membranes
Ion exchange membranes materials according to the present disclosure exhibit improved conductivity at low and intermediate relative humidity without sacrificing mechanical strength. Polymers are provided that include a backbone with one or more aryl groups, a halocarbyl group, and a halocarbyl side chain attached to the backbone, wherein the halocarbyl side chain includes a halide separated from the backbone by a hydrocarbyl chain, a hydrocarbyl ring, or combinations thereof. The halide is substituted with a tertiary amine and halide anions are then exchanged with hydroxide anions. The polymers are then contacted with phosphoric acid, which is deprotonated by the hydroxide ions, forming anions which enhance interactions with adjacent quaternary ammonium groups and induce excess phosphoric acid molecules to cluster around those quaternary ammonium groups. The membranes exhibit negligible dopant leaching even at high relative humidity.
1. An ion exchange membrane material comprising a polymer comprising a repeating unit according to Formula I:
wherein Ar includes one or more aryl groups, R1 is a saturated or unsaturated hydrocarbon group, a hydrocarbon ring, or a combination thereof,
A is a quaternary ammonium group,
D is an ionic dopant, and R2 is a halocarbon group; and
wherein the ionic dopant includes dihydrogen phosphate anions and phosphoric acid molecules, and wherein the phosphoric acid molecules form a cluster surrounding the quaternary ammonium group, wherein A includes trimethylamine, 1-methylpiperidine, pyridine, 1,2-dimethylimidazole, quinuclidine, pentamethylguanidine, or combinations thereof.
2. The ion exchange membrane material according to claim 1 , wherein the one or more aryl groups include:
or combinations thereof.
3. The ion exchange membrane material according to claim 1 , wherein the number of phosphoric acid molecules per A group is above about 9.
4. The ion exchange membrane material according to claim 3 , wherein the number of phosphoric acid molecules per A group is above about 14.
5. The ion exchange membrane material according to claim 1 , wherein R2 is CF 3 .
6. A method of making an ion exchange membrane material, comprising:
providing one or more polymers, the one or more polymers including a plurality of repeating units, wherein the repeating units include:
a backbone including one or more aryl groups;
a halocarbon group attached to the backbone; and
a halocarbon side chain attached to the backbone, wherein the halocarbon side chain includes a halide separated from the backbone by hydrocarbon chain, a hydrocarbon ring, or combinations thereof;
substituting the halide with a tertiary amine to form an amine-substituted polymer and halide anions;
exchanging halide anions with hydroxide anions; and
contacting the amine-substituted polymer and hydroxide anions with phosphoric acid to provide an ionic dopant to the amine-substituted polymer and form quaternary ammonium groups; and wherein the ionic dopant includes dihydrogen phosphate anions and phosphoric acid molecules, and wherein the phosphoric acid molecules form a cluster surrounding the quaternary ammonium groups, wherein A includes trimethylamine, 1-methylpiperidine, pyridine, 1,2-dimethylimidazole, quinuclidine, pentamethylquanidine, or combinations thereof.
7. The method according to claim 6 , wherein the one or more polymers are provided as a crosslinked polymer network.
8. The method according to claim 6 , wherein the number of phosphoric acid molecules per amine group is above about 9.
9. The method according to claim 8 , wherein the number of phosphoric acid molecules per amine group is above about 14.
10. An electrochemical energy conversion system comprising: an anode; a cathode; and
an ion exchange membrane disposed between the anode and the cathode,
wherein the ion-exchange membrane includes a polymer comprising a repeating unit in accordance to Formula I:
wherein Ar includes one or more aryl groups, R1 is a saturated or unsaturated hydrocarbon group, a hydrocarbon ring, or a combination thereof,
A is a quaternary ammonium group,
D is an ionic dopant, and R2 is a halocarbon group; and
wherein the ionic dopant includes dihydrogen phosphate anions and phosphoric acid molecules, and wherein the phosphoric acid molecules form a cluster surrounding the quaternary ammonium group, wherein A includes trimethylamine, 1-methylpiperidine, pyridine, 1,2-dimethylimidazole, quinuclidine, pentamethylguanidine, or combinations thereof.
11. The system according to claim 10 , wherein the ion exchange membrane is disposed on a reinforcing substrate.
12. The system according to claim 11 , wherein the reinforcing substrate includes a polyethylene mesh.
13. The system according to claim 10 , wherein the number of dopant molecules per A group is above about 9.