Ion-conducting membranes
An ion conducting polymeric composition mixture comprises a copolymer of styrene and vinylbenzyl-R s . R s is selected from the group consisting of imidazoliums, pyridiniums, pyrazoliums, pyrrolidiniums, pyrroliums, pyrimidiums, piperidiniums, indoliums, and triaziniums. The composition contains 10%-90% by weight of vinylbenzyl-R s . The composition can further comprise a polyolefin comprising substituted polyolefins, a polymer comprising cyclic amine groups, a polymer comprising at least one of a phenylene group and a phenyl group, a polyamide, and/or the reaction product of a constituent having two carbon-carbon double bonds. The composition can be in the form of a membrane. In a preferred embodiment, the membrane is a Helper Membrane that increases the faradaic efficiency of an electrochemical cell into which the membrane is incorporated, and also allows product formation at lower voltages than in cells without the Helper Membrane.
1. An anion-conducting polymeric membrane comprising a polymer blend or mixture of a copolymer consisting essentially of styrene and vinylbenzyl-R s with at least one polymeric constituent selected from the group consisting of:
(a) a linear or substituted non-aromatic polyolefin;
(b) a polymer comprising uncharged cyclic amine groups;
(c) a polymer, excluding polystyrene, comprising at least one of a phenylene group and a phenyl group;
(d) a polyamide; and
(e) the reaction product of styrene and vinylbenzyl-R s monomers with a crosslinking monomer having two carbon-carbon double bonds,
wherein R s is a positively charged cyclic amine group and the copolymer contains 10%-90% by weight of vinylbenzyl-Rs based upon the total weight of the copolymer, wherein the total weight of said at least one polymeric constituent in the membrane is less than the weight of the copolymer in the membrane, and wherein said polymeric membrane enables a carbon monoxide selectivity of at least 50%.
2. The polymeric membrane of claim 1 , wherein said membrane has a thickness of 10-300 micrometers.
3. The polymeric membrane of claim 2 , wherein said membrane is a Helper Membrane identifiable by applying a test comprising:
(1) preparing a cathode comprising 6 mg/cm 2 of silver nanoparticles on a carbon fiber paper gas diffusion layer;
(2) preparing an anode comprising 3 mg/cm 2 of RuO 2 on a carbon fiber paper gas diffusion paper;
(3) preparing a polymeric membrane test material;
(4) interposing the membrane test material between the anode and the cathode, the side of the cathode having the silver nanoparticles disposed thereon facing one side of the membrane and the side of the anode having RuO 2 disposed thereon facing the other side of the membrane, thereby forming a membrane electrode assembly;
(5) mounting the membrane electrode assembly in a fuel cell hardware assembly;
(6) directing a stream of CO 2 humidified at 50° C. into the cathode reactant flow channels while the fuel cell hardware assembly is at room temperature and atmospheric pressure, with the anode reactant flow channels left open to the atmosphere at room temperature and pressure;
(7) applying a cell potential of 3.0 V via an electrical connection between the anode and the cathode;
(8) measuring the current across the cell and the concentration of CO and H 2 at the exit of the cathode flow channel;
(9) calculating the CO selectivity as follows:
Selectivity
=
(
CO
production
rate
)
(
CO
production
rate
+
H
2
production
rate
)
;
and
(10) identifying the membrane as a Helper Membrane if the average current density at the membrane is at least 20 mA/cm 2 , where the cm 2 is measured as the area of the cathode gas diffusion layer that is covered by catalyst particles, and CO selectivity is at least 50% at a cell potential of 3.0 V.
4. The polymeric membrane of claim 1 , wherein said positively charged cyclic amine group is imidazolium or a pyridinium.
5. The polymeric membrane of claim 4 , wherein said positively charged cyclic amine group is an alkylpyridinium.
6. The polymeric membrane of claim 1 , wherein:
said polyolefin is polyethylene;
said polymer comprising cyclic amine groups is polybenzimidazole;
said polymer comprising at least one of a phenylene group and a phenyl group is polyphenylene oxide, and
said constituent having two carbon-carbon double bonds is at least one of divinyl benzene and butadiene.
7. The polymeric membrane of claim 1 , wherein the copolymer contains 35%-90% by weight of vinylbenzyl-R s .
8. The polymeric membrane of claim 7 , wherein the copolymer contains 40%-90% by weight of vinylbenzyl-R s .
9. The polymeric membrane of claim 8 , wherein the copolymer contains 50%-80% by weight of vinylbenzyl-R s .
10. The polymeric membrane of claim 1 , wherein said copolymer has a molecular weight between 1,000 and 10,000,000 atomic units (A.U.).
11. The polymeric membrane of claim 10 , wherein said copolymer has a molecular weight between 10,000 and 1,000,000 A.U.
12. The polymeric membrane of claim 1 , wherein said copolymer has a molecular weight between 25,000 and 250,000 A.U.